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PROCEDURES N i INSTALL ATION, OPERATION & MAINTENANCE
BERTHOLD "M0LD LEVEL" GAUGE MODEL LB 300-2 ML
FOR THE
Q/B0P SLAB CASTING FACILITY STEEL PRODUCING DIVISION
GARY WORKS
GARY WORKS FEBRUARY, 1986
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i - | q -2- . BERTHOLD " MOLD LEVEL" GAUGE
- SECTION I
TYPE OF EQUIPMENT
1.1 GENERAL DESCRIPTION
1.1.1 The Berthold " Mold Level" Gauge is a highly sensitive 4 radiation measuring system consisting of a C0-60 source, which emits gamma rays contained within a heavy lead shielded container and included shutter mechanism. Attached to this system is a radiation scintillation detector, mounted on the opoosite side of the mold, which provides a signal used to control the flow of the liquid steel into the mold.
1.1.2 This device was manufactured by Berthold Systems, Ltd., West Germany.
1.1.3 This device is identified as follows: Mold Level Detection Gauge Model No. LB 300 ML Series
1.1.4 All drawings, relative to materials of construction, , assembly, source information and safety features, have been submitted, by the manufacture, to the Nuclear Regulatory Commission for their review and approval for use. The NRC Registration Number is as follows: NR-186-D-111-S.
1 i 1.2 APPLICATION 1.2.1 The Berthold " Mold Level" Gauge is capable of detecting the presence or absence of the molten steel within the mold and will be used to control the level of the molten steel with a high degree of accuracy and sensitivity. With this device, ( control is established on an " automatic" basis to preclude i dangerous conditions to exist, such as overflows or I breakouts, on the Q-B0P, No. 2, Continuous Slab Casting I ' Facility.
1.3 EQUIPMENT DESIGN ] 1.3.1 The Model LB 300-2 ML operates on the principle of gamma ray | absorption. The Cobalt-60, radioactive material source, emits gamma rays which are collimated by a shutter mechanism in the heavy duty, lead filled, source housing (see Berthold Assy. Dwy. No. 21260 000 000). The heavy duty shield is | mounted on a movable table tray connected to a " Carter" hydraulic system with a 28" stroke. This system permits ] access to the mold, when the source is in the closed position 3 and mold servicing is required. When the source is in the j use cr open position, the gamma rays are aligned with the ; scintillation detector through blind cavity ports on the f mold. When material is in the path of the radiation beam, less radiation reaches the detector than when material is absent. In this regard, the detector produces an output signal proportional to the amount of radiation detected. This signal is used to activate the caster pour control system. ____
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-3- 1.3 EQUIPMENT DESIGN (cont.) 1.3.2 The Model LB 300-2 ML level monitoring system uses a Cobalt-60, radioactive source containing a nominal 260 mci (250-300 mci) of Co-60 wire. The wire is taper coiled on a rod and encapsulated in an outer stainless steel capsule by Argon - Arc Walding. The outer source dimensions are approximately 11.4" x 1". The source drawings were previously submitted to the NRC by Berthold and found acceptable for this use under the Registration No. NR-186-D-111-S. 1.3.3 Each source head or housing acts as a complete storage container for the radioactive source subsequent to installation.
1.3.4 The gauge construction materials will not deteriorate from irradiation, corrosion, vibration, shock or other conditions that may exist at this facility.
1.3.5 C0nPONENTS PER SYSTEM 1.3.5.1 Model No. BL 300-2 ML (NRC) Reg. No. NR-186-D-111-S 1.3.5.2 Detector Assembly , 1.3.5.3 Electronic Modules 1.3.5.4 Indicating Lights (Red-Green) 1.3.5.5 Warning Signs - Symbols 1.3.6 The source housing assembly, which weighs approximately 2000 pounds each, is bolted to its individual table tray and cannot be moved following installation. 1.3.7 Each source head or housing contains an air actuated open and close shutter mechanism. 1.3.8 Each source head or housing contains a mechanical, spring type, closing mechanism for source safety control in the event electrical power or air control is lost. 1.3.9 Each source head or housing is equipped with both red and green warning lights that indicate shutter position; red for the open position and green for the closed position. Both lights are mounted in clear view and all concerned personnel instructed in their use. 1.3.10 Each source head or housing will be properly marked with the proper radiation sign and symbol and bear the manufacurer's label that shows the type of radioactive materials,'the amount, the date of manufacture, device model and other pertinent information. . -4-
- SECTION II INSTALLATION AND RELOCATION PROCEDURES 2.1 INSTALLATION 2.1.1 The word " installation" as used herein is defined specifically as the transfer of the Cobalt-60 source from the shielded shipping and storage containment system, as supplied by the manufacturer, Berthold Systems, Inc. into the Model BL 300-2 HL source head assembly (Berthold Dwy. No. 21260 000 000) previously installed at the molten metal mold face in the Q-80P - No. 2 Slab Casting Facility.
2.1.2 Installation of the specific Cobalt-60 source rod will be carried out by the manufacturer, Berthold Systems, Inc., 611 Park View Drive, Pittsburgh, PA, NRC License No. 37-21226-01, ) their specified and NRC approved representative or other persons specifically licensed to conduct this activity.
2.1.3 Delivery of the source will not be accepted at the Gary Works facility prior to NRC License approval for use. 2.1.4 Before delivery of the Cobalt-60 source rad, the Plant | Radiation Officer shall be contacted for instructions. 2.1.5 The shipping box or container shall be surveyed upon delivery and unloaded only if the radiation level conforms with 10 CFR 49 regulations and label markings.
2.1.6 The box shall be stored in a safe, locked and conspicuously posted location.
2.1.7 Upon removal of the outer cover of the shipping container, the manufacture representative will leak test the unit as well as inspect for damage and again survey for safety.
2.1.8 Prior to source installation, the manufacturer's representative i will inspect the Model No. LB 300-2 ML gauge shutter mechanism and provide assurance that the shutter mechanism is functional.
2.1.9 The manufacturer's representative shall make the initial ' radiation survey with the shutter lens in the open and closed positions, in accordance with an appropriate survey pattern sheet which shall be filed for permanent record.
2.2 RELOCATION
2.2.1 The word " relocation" as used herein is defined as the transfer of the entire nuclear device containing a sealed source, without altering or removing the source material, from the initial site, and placing it in a new position oi DONTROLNO. $0e706 $) storage. 2.2.2 Relocation for any purpose shall be conducted by the manufacturer or other persons specifically trained to conduct this activity.
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. -5- 2.3 LEAK TESTING 2.3.1 A leak test is defined as the conduct of a survey in such a manner that will provide evidence for the proof of the integrity of the source capsule.
2.3.2 Leak tests are generally made by wiping, the source or seams of the device or at those locations where, in the event of source leakage, contamination would most likely appear.
2.3.3 An initial wipe (leak) test shall be made after completion of the installation.
2.3.4 Wipe tests shall be made at least every six months thereafter.
2.3.5 Wipe tests shall be made after any relocation, and whenever damage to the device is suspected.
2.3.6 Following the initial leak test by the manufacturer, all subsequent leak tests shall be made by other individuals specifically licensed by the NRC.
SECTION III OPERATING AND MAINTENANCE PROCEDURES
3.1 OPERATING PROCEDURES ' 3.1.1 Although radiation levels in the device areas are low, unescorted access shall be limited to authorized personnel who have received specific training in the operation of the equipment and informed of the existence and potential of radiation exposure.
; 3.1.2 All persons who will operate these devices or attendant equipment will have received specific training and instruc- ' tions regarding both the technical and radiation safety aspects. 3.1.3 Operation of these devices will be carried out in accordance with the instructions provided by the manufacturer-manual " Mold Level Detection Gauge, Section 10.6", Pages 10.6.10 through 10.6.30. j 3.1.4 Source assembly heads not in use shall be locked in their closed positon and be energized only under the direct supervision of the management personnel trained in radiation safety and operation of the device 3.1.5 The beam window in the shielding container may be opened only shortly before casting commences, or alternately for the i purpose of calibration of the system. It is closed again when the cast is complete. The beam window must also be closed, and remain closed, when any work is carried out inside the mold.
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. 3.2 MAINTENANCE PROCEDURES 3.2.1 Maintenance and repair of the device involving the opening of the device source housing or the removal of the sealed source shall not be performed by the licensee (U. S. Steel Corporation, Gary Works) and shall be done only by the manu- facturer or by other persons specific 611y licensed by the NRC to perform this service. Such work shall be authorized by the Division Radiation Safety Officer.
3.2.2 Maintenance work done in areas which could result in exposure to the radiation beam shall be peformed only with the shutter closed and locked. This includes work done on attendant equipment such as molds, table, platform, piping, wiring, etc., on which the device is mounted.
SECTION IV RADIATION PROTECTION PROCEDURES 4.1 TRAINING
4.1.1 The Plant Radiation Officer and members of the Plant Radiation Committee have been given formal training in the principles of radiation protection by a. member of the U. S. Steel Radiation Committee. A Division Radiation Officer shall be designated for the division in which the nuclear device is to be installed. The latter shall be given proper training and shall report to the Plant Radiation Officer in matters pertaining to nuclear devices. (See U. S. Steel Corporation, Gary Works, Radiation Committee)
4.1.2 Operating and maintenance personnel responsisle for the nuclear level device covered by this procedure shall be given
training in radiation protection. Supplemental training on ; i i both the equipment operation and maintenance shall be provided by the manufacturer, Berthold Systems, Inc. This < will inciude operators, electrical and maintenance personnel. I
4.2 MONITORING
4.2.1 Area monitoring shall be performed on a schedule basis using
, a suitable calibrated survey meter in accordance with an established survey pattern. Such surveys will include opera- tion of the shutter system and visual check of the device to observe chr.mical or physical damage.
4.2.2 Suitable Instrumentation includes the: (a) Manufacturer '- Eberline Inst., Corp. Model R0-2 - ! Type ION Chamber No. Ranges 4 Ranges 0- 5 MR/HR 0- 50 MR/HR 0- 500 MR/HR DONTROL NO. 80768 0 - 5000 MR/HR
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-7- 4.2 MONITORING (cont.) * (b) Manufacturer - Eberline Inst., Corp.
Model E-400 . Type Geiger-Mueller No. Ranges Log Type i Ranges 0- 2 MR/HR 0 - 200 MR/HR !
4.2.3 The results of'the survey will be reviewed by the Division Radiation Safety Officer for assurance that the designed shielding characteristics for operation pursuant to 10 CFR 20, 20.105 have not been violated, and safety integrity ' maintained.
4.3 WIPE (LEAK) TEST METHODS
4.3.1 Wipe tests and other tests required by the NRC shall be | performed at intervals required by the NRC for this particular device. This interval is specified in Section II.
4.3.2 Wipe tests required by the NRC shall be conducted only by persons specifically licensed by the NRC to conduct such l service. j
4.4 RECORDS |
4.4.1 Records shall be maintained as required by NRC Regulations 10 CFR 20, including dates of receipt and installation of the device, date and results of wipe tests, including the name of the licensee conducting the test, records of the calibration of all survey instruments, a log of any sig- nificant maintenance required, transfer or disposition of
the device, and name of the specific licensee conducting i and/or supervising such work.
4.4.2 In the event that a source be transferred to another - specific licensee, a copy of that person's license shall be required (in hand), and it be found valid, prior to shipment. 4.5 SIGNS, SYMBOLS AND LIGHTING SYSTEM
4.5.1 Enameled steel signs shall be placed in appropriate area locations, as follows:
(a) Radiation - Caution sign with radiation symbol marker, in magenta and yellow.
(b) Instruction sign specifying person and phone number to call in the event of physical damage to device.
(c) " Shutter Open - Shutter Closed" signs, used in con- junction with red and green indicating lights which are mounted in a clear and visible location. F }
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4.6 EMERGENCY PROCEDURE
4.6.1 In the event there is any damage or suspected damage to the nuclear device, both the Plant Radiation Officer and Division Radiation Safety Officer shall be immediately notified and a radiation level survey shall be made. Damage may be sus- pected following heavy physical shock or failure of shutter system to open or close as observed by either lighting system or electronic control signal. J 4.6.2 No employee shall attempt to handle the device or any other piece of attendant equipment except to close the shutter to the closed position.
4.6.3 If it is determined that the radiation levels are in excess of those originally specified, he shall proceed as follows: (a) Rope off the entire area including all access walkways where the radiation levels exceed 2.0 mR/ hour. (b) An attempt may be made to shield the unit only under the personal supervision of the Division Radiation Safety Officer. (c) The Plant Radiation Officer shall notify the U. S. Steel Radiation Committee Chairman immediately and the device manufacturer. (d) The unit shall be put back in use only after the approval of the Plant Radiation Officer with the advice and concurrence of a representative of the manufacturer.
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. UNITED STATF.S STEEL CORPORATION
GARY WORKS
RADIATION COMMITTEE
in order to maintain compli4'w:: with policies and standards established by the United States Steel Corporation Radiation Committee and the State and Federal Radiation Regulatory Agencies, the Gary Works Radiation Committee is hereby accepted as the Plant Authority and Regulatory apt governing all usage of radiation devices or radioactive materials in Gary Works.
Members of the Gary Works Radiation Committee are as follows:
1. Plant Radiation Officer - Chairman 7. Division Radiation Officer from each Division which operates one or more radiation devices. 3. Plant Security 4. Plant Safety 5. Medical Department 6. Technical Services 7. Metallurgical
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PLANT RADIATION COMMITTEE j in accordance with the policies and standards established by the United States Steel Corporation Radiation Committee, the Gary Works Radiation Committee shall perform the following functions to insure compliance with Corporation requirements and State and Federal laws:
! 1. Approve tha use, installation. reincetion, aad di::;;cstion of all radiation
; devices and radioactive materials. I 2. Approve the design of all radiation devices, radio-isotope sources and containers for radioactive materials, prior to procurement. i 3. Approve the design of housing, shiciding, and storage facilities for such devices and materials. 4. Approve the methods of handling, transporting, operating, and using such devices and materials.
> 5. Approve the methods of disposal of radioactive wastes and effluents. 6. Approve all applications and renewals for licenses and have the G.W. Radiation Officer submit them to the Chairman of tiie Corporation Radiation - Committee for transmittal to proper source for approval. 7. Approves the methods of conducting initial and periodic radiation surveys for : any given installatic n or use of newly procured radiation devices of ) radioactive materials, r;luding trials, demonstrations and services provided by outside concerns. 8. Approve the installation and operation of radiation devices or uses of rMioactive materials based upon radiation surveys. 9. Notify the Corporation Radiation Committee conceming installation, subsequent changes or removal of such devices and materials. 10. Approves training programs for personnel. 11. Approve emergency procedures in the event of accidents or damage to equipment involving radiation devices or radioactive materials. .
J ' 12. Approve the establishing of all programs of health monitoring, such as film ' badges, radiation dosimeters, blood tests, or air analysis and others, as may be required by the Corporation Radiation Committee. 13. Approve the procedures to notify promptly the Corporation Radiatiori ~ Committee of any emergency situation arising from damage to radiation equipment, excessive exposure of personnel to radiation, or contamination 4 caused by loose radioactive materials.
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PLANT RADIATION COMMITTEE (continued)
14. Inform immediately the Corporation Radiation Committee of any existing or pending legislation or regulation relative to use of radiation devices or radioacti* materials. 15. Receive new and revised policies, standards, and regulations from the Corporation and from State and Federal agencies; develop new or revised plant procedures as needed for compliance; publish to plant personnel ! involved. ! 16. Approve orocedures and have a program of monthly radiation surveys initiated ar.d maintain appropriate records for inspection agencies. 17. Approves standards of operation, maintenance, and safety for areas with radioactive devices. 18. Develops and approves changes or new prccedures as needed fer corrective action. 19. Review findings of Plant Radiatien Officer's compliance audits; develop or approve corrective measures as needeo to ensure compliance. 20. Committav meet:; quartcr!/ :nd m;nutes of the .v.celing maintained.
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RADIATION OFFICER
Member of the Radiation Cor. rr.it:ae. Plant " Senior Spec)alist" in radiation. Administrator and Compliance Officer for the Plant Radiation Committee.
Functions: ; 1. Member of the Gary Works Plant Radiation Committee (Chairman) 2. Audits compliance of Division Radiation Officer's Operating and Maintenance | personnel with the rules, regulations, and laws of: United States Steel Corporation Radiation Committee r ; a. b. Gary Works Radiation Committee I c. The State of Indiana d. The Federal Govemment 3. Maintains all N. licenses for radiation sources. 4. Maintains the State of Indiana's registre. ion of radiation sources, devices, and
installations. . 5. Retains and maintains plant records of all radiation sources, devices, l ; installations and activities as required by law.
6. Makes all reports required by law or by Corporation policy. : 7. Receives state and federal inspectors and accompanies them on inspections; supplies information to inspectors as required. '
; 8. Schedules and makes arrangements for periodic wipe tests, etc., as required hy law and Corporation policy.
I 9. Makes required inventory of sources report and submits it to the State of Indiana and the Corporation Radiation Committee. Includes reports of , changes in inventory. 10. Is informed by Operating or Division Radiation Officer of any emergencies, accidents, damaged sources, or miscellaneous incidents, and advists them on appropriate procedures; makes required notification to the Corporation Radiation Committee Officer and vendor, if necessary. ,11. Directs and arranges for disposal of radiation sources as required by law. 12. Develops, arranges, and directs procedures to be followed for each vendor's use of radiation source or devices in the plant.
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- 13. Consults and advises Technical Services in;
a. Preparing request to Plant Committee for permission to install new sources. b. In preparation of design and specification for installations. c. Preparing applications for required licenses. d. Preparing requests for any neces:ary variances from state or federal regulations.
*14. Consults and advises Technical Services and Division Officers in: a. Preparing operating proceduces. b. Preparing maintenance procedures. c. Preparing safety rwqirements. (Note: The above is needed at the time an application for a license is made) 15. Advises and consults with Operating Department in their preparation of operating, maintenance, and emergency procedures. 16. Trains and informs Division Radiation Officers in their functions and ' procedures. 17. With Division Radiation Officer, directs and conducts initial determination - phase of personnel monitoring programs. , a. Bawd on standards adopted by Plant Radiation Committee, makes determinat'on of which employees must be included in permanent phase of personal monitoring program. b. Submits determination to Plant Radiation Committee for approval. 18. During permanent phase of personal monitoring program, is informed by Division Radiation Officer of any badge reading results which indicate any dosage above zero. Determines and initiates appropriate course of action. 19. Directs receipt of new sources: a. Receives from Engineering, notice from manufacturer of scheduled shipments. b. With Plant Security, instructs receiving deoartment of Stores in storage security requirements. c. With Plant Security, inspects and approves storage facility provided by ~ receiving department. : a. Widi Nent Securit/, recci'.S a.: nit et plant gaie, iias required tests made; | turns unit and vehicle over to Plant Security fer transport to job site or storage area. . ___ _. ._. . _ . __ - -_ . _ . . . - -_ _ .- . . _ - - .
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RADIATION @FFICER (continued)
i e. Informs receiving department and/or stores personnel of any | requirements for clearing personnel from receiving area, barricades, etc. f. With Plant Security, observes placing of unit in storage and approves radiation safety of storage. , g. With manufacturer and construction engineer and/or receiving i department, observes installetion of unit in its permanent site and approves same for radiation safety. ' i . . . Arrc.::ga= for and/nr observes initia! test:: cf ur.;i including tests. for I preparation of actual iso-dose curves.
20. Informs the Plant Radiation Committee of all new laws, rules, and | regulations from: ) a. USSC Radiation Committee b. The State of Indiana C. AvfriC.AJ.R.C.
| d. l.C.C. e. O.S.H.A. f. Other Regulatory Agencies 21. Sebmits to the Plant Radiation Committee for approval: a. All new plant rules and regulations. ) b. Training progra ne. | c. Educational programs and materials. d. All proposed installations or uses of radiation devices. 22. Arranges for and directs educational programs and training programs. 23. Issues and distributes all rules and regulations, etc., approved by the Plant Radiation Committee.
. j 24. Protects against the use of radiation in such a manner as to be injurious or I dangerous to health, life, or property. 25. Issues rules and regulations for occurrences not covered by Plant Radiation Committee rules or regulations. (Committee may approve or disapprove at a later date.) . 26. Keeps records of calibrations, and inspections of all survey meters. 77. Submits all requests for approval of installations or uses of radiation devices to the U.S.S. Radiation Committee after the Plant Radiation Committee has ' approved the request.
} 28. Conducts quarterly meeting of the Plant Radiatior Committee.
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DIVISION R A08 ATION OFFICER
Meraber of Plant , Radiation Cnremittee and responsible for radiation compliance and safety in his Division.
Functions: 1A. Works with Operating departments in developing procedures for operation, maintenance, and emergencies. , 18. Reports emergencies, accidents, and miscellaneous or unusual incidents to Plant Radiation Officer; assists Plant Radiation Off;cer in setting up and actuating emergency or interim procedures. 2. Trains and instructs department supervisors in radiation safety requirements. 3. Works with Operating department in training and instructing employees. 4. Assists Plant Radiation Officer in conducting initial determination phase of personnel monitoring program. Supervises all functions of the permanent phase of personnel monitoring program, such as: a. Advising Plant Radiation Officer in determining what employees / occupations are to be included. b. Ordering badges from suppliers. c. Issuing badges to employees. d. Instructin] new employees in use of badges. e. Collection of badges at prescribed intervals. f. Shipping badges to supplier for evaluation. g. Reviewing evaluation reports from the supplier and reporting to the Fir.nt P.adiation OfRar ar"/ hit. er u:.usua muits. Delivers copy of evaluation reports to Radiation Officer and Plant Medical department. 5. Makes monthly g hysical inventory of sources and radiation survey v devices. Reports results to Plant Radiation Officer. 6. Accompanies Plant Radiation Officer and State or Federal Inspectors on inspections in his Division; fumishes information to inspectors as required:
- 7. With Plant Radiation Officer, directs procedures and activities involved in vendor's one time uscs of sources in plants.
I 8. Consults and advises with Technical Services (Engineering) in preparing request to Plant Hadiation Committee 'or permission to install new tm %es.
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DIVISION RADIATION OFFICER (continued)
9. Consults and advises with Technical Services (Engineering) in preparation of design and specifications for installation. 10. Directs the clearing and barricading of the installation area as needed. 11. Assists Plant Radiation Officer and Plant Security in unloading procedures at installation date. 12. Inspects and approves installation for personnel safety; required waming signs and permanent barricades, etc.
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| \ ' PLANT SECURITY
I Respor'sible for the physical and radiation security of all radiation sources from receipt t at plant entrance to installation at permanent site, to storage in c:. approved secure storage location, and in cases of radiographic work while on plant property. Representative of Plant Security is a member of Plant Radiation Committee.
! Functions: 1 1. Co ordinates security arrangements with shipping schedules of high curie ! radiation sources and naciographic equipment into the Plant. ! 2. Advises Stores on the requirements of a secure storage area. 3. With Plant Radiation Officer, inspects storage areas provided and approves
! same for physical security, a 4. Determines and specifies travel routes for radiation sources and radiographic equipment in the plant. 5. Upon arrival of radiation sources, holds vehicle at plant gate and notifies
4 Plant Radiation Officer of arrival. | 6. Performs a radiation survey of the vehicle before it enters and when vehicle leaves the plant. Makes out a survey inspection report and sends a copy to j the Plant Radiation Officer. ' 7. Conducts vehicle with high curie sources or radiographic equipment to storage site, installation site, or radiographic work site. { 1 8. For high curie sources widch are to be installed, turns source over to vendor at installation site.
; 9. Fce high curie sources which are to be stored, observes placing of source in ' authorized storage location and approves same for physical security. 10. For sources which are to be used for radiographic work, plant security forces | ; shall remain with 'the equipment to assist in supervision of correct procedures j for radiation protection. ' 11. Assists Plant Radiation Officer, Division Radiation Officer, Engineering, : Operating and Maintenance personnel in developing correct radiographic I procedures. i i ,12. Fumishes monitors who will supervise radiation guards ovridd !/, the ! Division responsible for radiograpnic work. i 13. Act as advisor to the Plant Radiation Officer. * 14. Representative may aisc function as Division Radiation Officer for Personnel j Services. !
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PLANT SAFETY
Representative is a, member of Plant Radiation Corrmittee and responsible for plant safety.
Functions:
1. Auists the Plant Radiation Officer in the investigation of any accidents or unusual incidents involving radiation devices. 2. Conducts periodic audits of all records kept to insure plant compliance to regulatory standards. 3. Conducts periodic physical inspections with Plant Radiation Officer to check warning and monitoring devices. 4. Assists Plant Radiation Officer in development of Emergency Procedure in the event of an incident involving a radiation device. 5. Acts as advisor to the Plant Radiation Officer. 6. Representative may also function as Division Radiation Officer to Personnel Services.
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MEDICAL
Responsible for medical records, histcries, exposure reports, excessive radiation exposure investigati,ons ard medical reports. Representative Doctor is menhe of Radiation Committee.
Functions:
1. Keep medical records of employee which shall include radiation exposures records. 2. Issue radiation histories and exposure reports if requested by an employee. 3. Make medical tests and evaluations in cases of suspected excessive exposure to radiation. 4. To assist in the investigation and reports of incidents of radiation exposure. 5. Representative may also function as Division- Radiation Officer for Personnel Services.
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F TECHNICAL SERVICES - ENGINEERING
Provides engineering services relative to the design, purchases, installation, inspections, and uses of radiatio'n devices. Representative is a member of Radiation Committee
Functions:
1. Advises Radiation Officer of projects which will make use of radiation devices. 2. Advises Radiation Officer of shipping schedu!es of radiation devices and equiomant. 3. With Operating and Maintenance Department representatives and Radiation Officer, develops info mation and data necessary for initial request to Plant Radiation Committee for approval to install or relocate radiation devices. 4. Develops designs, specifications for the purchase and installation of radiation devices. 5. Supervises the installation and initial inspections of radiation devices. 6. Develops specifications and contracts for the purchase of radiation services for Engineering projects. 7. Supervises purchased radiation services in cooperation with Plant Security Forces and the Radiation Officer. 8. Prepares information, data, application forms for any required licenses, for ! the Radiation Officer. 9. Obtains from manufacturer drawings, iso-dose curves, etc. 10. With Radiation Officer, Metallurgical, Operating and Maintenance, and the vendor, conducts initial evaluation test of radiation devices.
* 11. With the Radiation Officer, prepares request for any necessary variance from state or federal regulations. 12. Acts as advisor to the Plant Radiation Officer.
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f METALLURG| CAL
Representative is a member of Plant Radiation Co nmittie.
' Functions:
1 Acts as advisor to the Plant Radiation Officer. 2. Acts as advisor for evaluation test and procedure for radiation devices. 3. Representative may also function as Division Radiation for Metallergical.
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SECTION 10.6 MOLD LEVEL" DETECTION
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SECTION 10.6 MOLD LEVEL DETECTION Table of Contents
Title Page
INTRODUCTION 10.6.1
Description 10.6.2 Measuring Arrangement 10.6.2 Basic Principle and Radiation Sources 10.6.3 Shielding 10.6.4 Scintillation 10.6.4 Terminal Box 10.6.6 Mold Level Gauge LB 300-2 10.6.6 Terminal Box and Cable 10.6.9 Connections 10.6.9
OPERATING INSTRUCTIONS 10 ".10 Operations 10.6.12 Sensitivity Adjustment 10.6.19 Switch Point Adjustment 10.6.19 Radiation Protection 10.6.20
Servicing Instructions for Mold Level Monitor - LB-300-2 10.6.23
RADIATION PROTECTION 10.6.31
Introduction 10.6.31 Physical Basics of Radiation Dangers of Radiation 10.6.32 10.6.48 Radihtion Protection Technique 10.6.55
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Acknowledgement ) | | Portions of this section were provided by: !
e SMS Concast Inc.
e Berthold
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SECTION 10.6 ' MOLD LEVEL DETECTION
Introduction The Berthold Mold Level Gauge is a highly sensitive radiation measuring system. A radioactive source supplies ganas radiation through the mold walls and molten steel with a detector picking up the remaining radiation. Radiation safety will be discussed at the end of this section
When the level of molten steel in a mold is accurately known, danger levels such as high level " overflow" or low level " breakout" can be avoided.
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hMEASURING CHANNEL 1 | hMEASURING CHANNEL 2 | h 3U
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1 . l,b@- ib l .. $.$_khI THRESHOLD UNIT LS 3e42 Adjustable threshede Apr hV6H/LO989 signete
ANALOG JISPLAY La Sees Aneleg risplay anit ,
RATEMETER LB 3031-32 Rotemeter with perentlemeter " FULL "edjectman!
ADAPfioN UNat Le 3ece-2 Input empither with eetere settch "fMPTY " edjustment
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Figu.e 10.6.1 Mold Level Gauge LB 300-2
.i ,( CONTROL No 6 60 P]
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! Description
r The Mold Level Gauge LB 300-2 is essentially a highly sensitive radiation measuring system. The system monitors the level of molten metal in the mold through the sold walls without actual contact with the fluid and provides a suitable proportional output signal.
Measuring Arrangement
The schematic layout of a complete mold level gauging system is shown in Figure 10.6.2 below and comprises the following elements:
No. 1 in Figure 10.6.2: A radioactive rod source in a shielded container with a lockable beam window;
No. 2 in Figure 10.6.2: A scintillation counter acting as a radiation detector, complete with a permanently connected 5 meter cable, with or without water cooling depending on individual requirements;
No. 3 in Figure 10.6.2: A terminal. box;
No. 4 in Figure 10.6.2: A shielded 7-conductor cable to connect the terminal box to the LB-2;
No. 5 in Figure 10.6.2: The mold level gauge LB 300-2 electronic package.
- , ws scintmanon munior ww - t.s 300-2 _ __s z a. o_ ,u . - ____ - g % ~ ' ~ ~ ~ -- 0 $ k ,- W" M F2 M R M > W $ 3 $Z7ide @ B[c.F - - ;- yP ternunai box ITd . /,j " :T_-_ g -: _. ; " -n 4 r- / _-- , , < > .-:9: $ $ . _ . 2_ _ __ &v^ I 52^- $ $?'_'. | GT + , ' * W % 1 A '' ~ '" ~ " * rod source in i.e.-:- 5 c A A g -- ___ snm conaner .. $ - _ _ _ _ _ -- --. . _ - - / _ . ------:$ S -: * LS~-l $ hS~ E ( ) ( em j ( .-S g .. @
Figure 10.6.2 Mold Level Gauging System :
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Basic Principle and Radiation Sources
! The physical measuring principle is based on the fact that ' radioactive radiation is weakened as it passes throagh matter. The weakening of ga3ma radiation follows an i exponential law, a beam of rays with the initial intensity 4 1 being weakened as it passes through an object with the ; tEickness d and the density g. 1=1 xe -n x 5 x d o In the case of gamma radiation, which is of interest in this ; context, the mass weakening coefficient r depends only on the type of radiation source. Consequently the measured count rate is determined purely by the product of the thickness and density (g x d) of the sold content. Owing to
4 the high density of the molten bath, the resulting absorption characteristic will be within the highly curved 1 section even if the measuring path should be relatively small, so that the effect of density changes becomes quite insignificant and assuming normal mold geometries the radiation is completely absorbed, except for a negligible proportion.
! The thickness of the sold walls i.e. has no influence on t'he measured count rate difference the walls only introduce a k constant weakening factor which can be compensated by increasing the source activity accordingly. There is no risk of the sold walls or the molten bath becoming activated by gamma radiation.
The activity of the rod source is chosen so that a 4 sufficiently high dose rate remains available after allowing for the operating conditions and the thickness of the mold ! wall at the scintillation counter end. The length of the rod source is determined by the required span of the | i measuring range and by the geometry of the measuring system, ' | which is dictated by the sold design. In practice, the ! effective measuring range is often between 100 and 120 mm.
Viewed from the detector, an increasing proportion of the rod souce will be masked by the molten bath as the mold |
, level rises, and therefore the radiation intensity received i i by the scintillation counter will be reduced in an inverse I proportion to the mold level. | i All non-linearities introduced by the measuring geometry are | compensated by a corresponding non-linear activity distri-
, buted along the rod source so that the radiation intensity ! at the detector end will always be in linear proportion to
, the actual mold level. No electronic linearization will- / therefore be necessary, which greatly simplifies the setting- ' up and use of the Mold Level Gauge.
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In the case of co-60 rod sources, the radioactive subs'tance
is incorporated in metal wire . This wire is wound around a , core at a varying pitch to produce the required intensity distribution and the complete assembly is sealed into a welded special steel tube. This qualifies the capsule as a , sealed source. The sealed capsule has been examined by the German Federal Institute of Materials Testing and submitted to the PTB Standards Office for approval.
Co-60 sources have a half-life of 5.3 years. Normally the rod source will be designed for a useful life of approxi- mately 5 years. In special cases, however, the user may specify a shorter useful life. At the end of its useful life, the rod source must be replaced. When ordering the replacement source, the serial number of the original source, which consists of three groups of figures, must be ' quoted (e.g. 324-12-80).
j Shielding
4 Rod sources are normally contained in a special shield, ) whose shielding effect, function and design depend on the ! source activity, the required dose rates and the mold j design. The shield normally incorporates a manual lockable beam window so that the radiation beau directed at the detector can be sealed off between casts. I i The exact location of the shielding in the mold and the method of operating the beam window are indicated on the associated mold drawing. l ' Scintillation Counter
The radiation detector consists of a scintillation counter (Refer to Figure 10.6.3 Scintillation Counter) whose special
; features are its high specific sensitivity to gamma ! radiation and the fact that its useful life does not vary I with the amount of radiation exposure. Despite the i relatively low emitter activity, a high count rate is I generated which ensures reliable and meaningful results.
! Scintillation counters consist of an NaJ(TI) crystal in ! which the gamma quanta emitted by the radioactive source induces light flashes, the frequency of which is propor- tional to the radiation intensity. The crystal is optically I coupled to a photomultiplier whose photosensitive layers release electrons per light flashes. A high voltage supply a,ccelerates the electrons towards the anode where they re- lease further electrons as they impinge on a dynode system. . 6 4 r
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', MARNJN6 RING f , O'Y STAL POSITION l |
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. TH A EADED HOSE CONNECTOR 1 4
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q , FLEXISLE METAL, HOSE , '. , ; # r , p i
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! . O n WITHOUT WATER C000HG , WITH WATER C000Nfa
3 LB 6639 L8 6639W .;
; Figure 10.6.3 Scintillation Counter ; i
A preamplifier connected in series then produces output pulses of relatively high amplitude which are subsequently converted into standard pulses of several Volts to ensure
, interference free transmission over extended, cable lengths. | This sytem, including the HV supply for the photomultiplier, ) is installed in a strong cylindrical housing. Il
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. dacigned forThs scintillotics Count . una in 011 dicanoicnb havcontinuousor LB 6639 hoc been specifi e been kept extremelcasting machines. cally on in The o v r. enclosedThe scintillation inpermanentlynter isaconnected widecoufacilitate rangey 5 compact in orderinstallati provide a flexible meter long siliconsupplied complete withof sold designs. metal tube a s additional mechanical prof tthe cable which is The optional version LB o ection. same length to includes a permanentl 6639 W of the j ( IMPORTANT: y fitted cooling watescintillation r jacket. counter errorsmust notand exceed 50 - 55Theat the temperagure tillation /orcounter destroy the crystal shocks as C as this would resultscintillationin detector measuring t$e multiplierotherwise the glassmust also be protectedandThe multiplier.1 may become damaged. assembliesof the against severescin- 1 crystal and \ Terminal Box ' j A terminal box is cablebut easily accessibleinstalled near the . Apart mold in low fromconnects t the terminal bposition.o A 7 conductora protected, voltagevoltages,he standard thispulses,x to shieldedthe Mold Level Monit t cable (approximately 5 V)namely approximatelyplusonly transmitsor. 30 V for the high voltagethe control _u supply. Mold Lev _e_i__G_aute_ LB 3 The standard pulses . 00-2 via an opto- Level Gauge.electronicarriving from the detect a A speci'l circuit encoupler to theor areinputapplied of Gaugeconnecting the cable. rejection to prevent the M count pulsesIn the variousinterference pick-usures high, commonold of from which the solde ya lscaled down and averag d bare furthermodulesp through themode rate amplified, standardizedthee Mold Lev l ratemeter into a , resulting signal ischangesevel signal in is inverse derived pro count rate proportion to the inv As the erted so thatportion to ldthe level, mo. count By selecting a mold level. the , it changes in direct owing to the suitable \ wide e range count rate diverse typesthe Mold, the sysof Lev countl Gauge rateand time with an constant, and accuracy ofof sold design. tem can adjustmentbe offered by The adapted to i 2 to 3 percent of thmold level can be meesurextremely\ e total range. ea \ l
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The various functional elements of the Level Gauge take the i form of European standard plug-in circuit cards which are housed in a 19" module chassis incorporating a power supply unit. One module chassis can house two Mold Level Gauges. The Mold Level Gauge consists of the following function modules:
ADAPTION UNIT The EMPTY (1) from Figure 10.6.1 four-decade digital . encoding switch in the ADAPTION UNIT is used for balancing the Mold Level Gauge when the mold is empty. This is carried out by adapting the count rate of the scintillation counter to the ratemeter range by weighting the count rate with a scaling factor between 0.0000 and 0.9999. The adaption unit includes the PLATEAU CONTROL (2) from Figure 10.6.1 trimmer potentiometer for adjusting the high voltage supply in the scintillation counter.
RATEMETER
Count pulses are averaged at the ratemeter. The TIME CONSTANT (3) from Figure 10.6.1 sliding switch allows three different ratemeter time constants to be selected, depending os the requirements of the individual application. An automatic electronic change-over circuit RESPONSE ADJUST reduces the time constant by a factor c f approximately 0.2 when the reading moves outside the tolerance range selected with the RESPONSE LEVEL (4) from Figure 10.6.1 trimaer potentiometer. As soon as the reading has settled within the new range, the system automatically reverts to the longer time constant. This ensures, on the one hand, that when casting proceeds normally, a relatively long time outputconstant signal is active remains and small. the statistical fluctuation of the On the other hand, the system is capable in the event of any disturbance to respond quickly to changees in actual mold level. This feature is of particular advantage when starting under automatic control.
, The full (5) from Figure 10.6.1 potentiometer is provided for balancing the system at 100% mold level if full absorption cannot be reached when working with very small mold cross-sections. The resulting, slightly low reading can be spread over the full scale length with this potentiometer, without affecting the zero setting which has previously been determined with the empty sold.
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. t The rotscotor cloo forca tho 0 L Tho curront outputoubcord gonorcteo en cdditiocol 0/4-20 cA- 10 volt cutput oignol. rocciming circuit. 10 cutput current. A * olo;trically isolated from the ANALOG DISPLAY
! [ coil instrument.The sold level tt anys given time i output voltage. The scale divisions correspond tindicated by a moving- o the
* indicating.instrumentFor accurate calibration of the di (6) is connected to the femalsplay a separate RATEMETER UNIT:from Figure 10.6.1 providede connectors for thi 0 - 10 volt and 1 volt G 20 mas purpose in the THRESHOLD UNIT . HIGH and LOW signa relay and one openls are generated by two thresholds with one thresholdsettings canstatus be adjusted over theu f llcollectorThe threshold output each. Diodes). is indicated by LEDs range, and the (Light Emitting STROKE COMPENSATION
e source are solidly mounted on the watersold, aJacket relative acvement of theIf the scintillation counter and th soldbetween oscillation the sold level andasuring the mesystem, stroke of the osc,illation,will result. Depending on frequency andcaused by : time constant of the system ascan well as on the length of the affect the output signal. COMPENSATION LB 3826 this inflBy means of applying a special positioner at rack with built-in STROKE the sold sust supply a signal of 0/4uenceThe can be com.,ensated. INSTALLATION - 20 mA. The physical arrangement of the Figure 10.6.2,and the scintillation counter will nsource with its shielding although the exact in the sold drawings for each sy t ormally be as shown in s em.location will be indicated The scintillation removed easily and quicklymanner when that thecounterit can be should be mounted in such a a replacement counter must be installe. dmold is changed or when
Page 10.6.8 1
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NOTE: It should be remembered that scintillation counters must not be subjected to severe shocks or temperatures in excess of 50 - 55 c. The inherently high reliability and long useful life of scintillation counters will only be achieved with careful handling, especially during installa- tion and removal. Depending on the mold design and casting process it may be advisable to protect the scintillation counter and, where necessary, also the connecting cable with , a suitable guard against splashing steel and slag. '
When the scintillation counter is installed against the , cooling water Jacket of the sold, the mold cooling water ' will normally also provide adequate cooling of the counter, only if the cooling water return temperature stays below 50 - 55 C. If the scintillation counter is installed outside the mold cooling system, the counter version LB 6639 W with | integral cooling water jacket will normally be required, ' unless other precautions are taken to ensure that the ambient temperatuS* ** th* ""t'r 1 *ti " **"" t ri'* t more than 50 - 55 C by radiant heat or convection.
In either case it must be ensured that the cooling water continues to circulate after the completion of a cast until all parts of the mold have cooled down sufficiently.
- # Terminal Box and Cable The terminal box should be installed in a readily accessible place near the mold, where it is easily reached by the 5 meter long cable. This cable is permanently connected to ' the scintillation counter in order to facilitate connection and disconnection to and from the terminals. The terminal box is connected through a permanently installed cable to the Mold Level Gauge LB 300-2. Any standard commercial 7 conductor shielded cable may be used. The normal voltage level will be approximately 30 volts.
Connections
All connections should be made in accordante with the wiring diagram supplied. It is important that the incoming voltage is the same as that indicated on the nameplate of the Mold Level Gauge LB 300-2. The negative pole of the 0 - 10 volt voltage output is grounded, and the current output is electrically isolated from the remaining circuit.
It is recommended to operate the relays used for HIGH/ LOW signaling at low voltage levels and to check that the uni.ts driven by the relays have been interference suppressed where g necessary.
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. Operamting I n s t r u c t i o n es | Brief Instructions:
The beam window in the shielding containing the radioactive i source is only opened shortly before casting commences, or I alternately for the purpose of checking the system. It is closed again when the cast is completed. The beam window in the shielding must also remain closed when any work is
carried out inside the sold, such as cleaning the sold or i sealing the dummy bar. Figure 10.6.1 shown again on the next page as a convenient reference. , 1. Switch on the gauge and open the beam window in the shielding.
2. With the mold empty and the sold cooling water supply circulating, adjust the scaling factor with the empty decade switch on the ADAPTION UNIT to produce an output signal of 0 V.
3. Now insert a dummy bar into the sold in such a way that the full measuring range is covered. If the reading does not reach 10 V, the full potentiometer on the RATEMETER UNIT must be adjusted until this level is |
reached. i
i 4. Select the maximum acceptable TIME CONSTANT on the j RATEMETER UNIT. For billet casters this will generally ' be position 1, and for slab casters position 2. 5. Set the HIGH/ LOW thresholds on the THRESHOLD UNIT as required.
NOTE: The EMPTY adjustment must be checked periodically, ,
especially after mold changes, and corrected when necessary . as described in Step 2. I
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FMEusVRING CHANNEL | |hMEASUR'NS CHANNEL 3 | h SJ
. THaESHOLD UNIT LO 8882 ,,i ,. ,. ,..... M. ~ ,,,w a .i. ,.
ANALDS DISPLAY a ,., a,,,n, ,L,S 348 8
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ADAPfl0N UNIT LO 3004 3 /s,u, .m.,th.r et,. ..d. .w,, h "f M PTT * .4/v.,m.n,
Figure 10.6.1 Mold Level Gauge LB 300-2
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Operation I The beam window in the shielding should only be opened to I release the radiation beam immediately before casting commences. Similarly, the shielding must be sealed when a cast is finished.
GENERAL NOTES: It is recommended to record all settings, especially the EMPTY and FULL adjustments as well as the preset time constant and the RESPONSE LEVEL, in a log to provide a record for future reference.
START-UP The Mold Level Gauge is switched on with the MAINS (7) from Figure 10.6.1 toggle switch on the front panel of the PONER SUPPLY LB 3897. A status LED indicates that the system has been switched on. The Mold Level Gauge may remain switched on between casts, although the power supply should be switched off whenever the scintillation counter is replaced. EMPTY ADJUSTMENT Before the EMPTY adjustment is carried out, the mold cooling water supply must be switched on. The EMPTY adjustment should be regularly checked and corrected if necessary, especially after each sold change. The EMPTY /. -decade switch in the ADAPTION UNIT can be set to a scaling factor ; between 0.0000 and 0.9999 (the decade switch only shows the decimals) which scales the count pulses arriving from the scintillation counter in such a way that the output signal can be adjusted to zero when the mold is empty. This matches the unit to the exact source intensity and to any fixed absorption between source and scintillation counter and also adapts it to the measuring range of the ratemeter. NOTE: Due to the statistical decay of all radioactive substances, the reading will always fluctuate around a mean value even if the conditions remain unchanged. The ampli- tude of the statistical fluctuations depends on the count- rate recorded by the scintillation counter and on the time constant of the ratemeter which has been selected with the TIME CONSTANT (3) from Figure 10.6.1 switch. If the reading is below 0 volts, the scaling factor should be reduced in coarse steps with the decade switch until the output signal reaches a value between 0 and approximately 5 volts.
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For accurate zero calibration the scaling factor is now increased as required. As a guideline, the correct zero adjustment (f can be calculated from the current reading (A) and the aEs)ociated setting (f) of the decade switch by using the following equation:
10 V fx = f ------; 10 V-A ' The FULL potentiometer in the RATEMETER UNIT must be set to ZERO during this procedure. ,
EXAMPLE: The current reading A - 5.4 volts, rnd the associated setting of the decade switch f = 0.0356.
The correct se~tting f f r zer adjustment can be calculated as: x
, 10 V
fx = 0.0356 ------= 0.0774 j 10 V - 5.4 V i
FULL ADJUSTMENT
;i With very small mold afzes, a small residual dose rate may reach the scintillation counter even when the mold is completely filled. This results in the output signal uot quite reaching 10 volts at a mold level of 100 percent.
| With the help of the FULL potentiometer the reading can in | ! these cases be adjusted up to a 10 volt output. This ! adjustment produces no feedback reaction, i.e. the zero setting found during the preceding EMPTY adjustment will not | be affected. 1
In order to calibrate the 100 percent point, a prepared dummy bar must be inserted into the sold. Its length must be slightly greater than the actual measuring range to ensure that the range is fully covered by the dummy bar. The setting of the FULL potentiometer is now increased until the output signal has reached 10 volts. The potentiometer setting obtained by this method will be the same for all molds of the same cross-section and design.
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PLOTTING THE CHARACTERISTIC CURVE
After the correct- EMPTY and FULL settings have been found, # the characteristic curve of the system can be plotted to obtain accurate information on the location and response of the measuring range covered inside the mold. For this purpose a dummy bar is inserted into the mold and moved over the full measuring range in steps of a.g. 5 millimeters. The resulting output signal is plotted against the measured mold level to produce a characteristic curve. Figure 10.6.4 shows a typical example of the characteristic curve of a continuous casting machine. For improved accuracy it is recommended to set the TIME CONSTANT switch to position 3 during this measurement.
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Figure 10.6.4 Typical Characteristic Curve of a Continuous Caster Machine
It is important that the suspension bracket of the duasy bar - is designed so that it does not cross the radiation beam, I which could falsify the result. ' '
COWROLtio, bgg O ?
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TIME CONSTANT
Due to the random sequence (based on laws of physics and #
following statistical laws) in which the radiation quanta | arrive at the detector, the output signal fluctuates around a ' mean value even if the mold level should remain constant. These statistical fluctuations become smaller as the time constant of the system increases. The TIME CONSTANT sliding switch can be set to the following ratemeter time constants: , 1 Position 1 0.2 or 1 s- | Position 2 0.5 or 2 s | ' Position 3 1 or 5 s The two different time constants which are provided in each switch position are electronically selected as follows: | e When the output signal is constant, the greater of the two time constants will be effective, but
e When the output signal rises beyond the preset RESPONSE LEVEL then the shorter time constant will become active. The most favorable time constant setting depends on the maximum casting rate and in some cases also on constraints imposed by the automatic control system, although as a matter of principle the longest acceptable time constant should always be selected. , Prior to initial start-up and for correcting any settings, such as the EMPTY and FULL adjustments, as well as for plotting characteristic curves, the shortest time constant , will speed up coarse adjustment while the final precise adjustment should be made with the longest setting.
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RESPONSE LEVEL
The time constant selected with the TIME CONSTANT switch in 1 ( the RATEMETER UNIT changes automatically by a factor 0.2 whenever the output signal moves outside the RESPONSE LEVEL (4) from Figure 10.6.1 nelected with the associated potentiometer. This has the advantage that when casting l proceeds evenly and normally, the longer of the two time ' constants is active and the statistical fluctuations of the output signal remain small. If, however, the mold level should change rapidly then the output signal will approach the new level much faster with the shorter time constant. The RESPONSE LEVEL should be adjusted so that it is slightly higher than the statistical fluctuations plus the typical mold level fluctuations during normal casting. To determine
the initial coarse adjustment, it is recommended to connect I a direct-reading instrument (0 - 10 volts) to the test I r.ockets marked RESPONSE LEVEL and to adjust the associated potentiometer to produce a reading of approximately 2 volts with an empty mold and an output signal of 0 volta. During normal, undisturbed casting the reading should only occasionally exceed the RESPONSE LEVEL setting. If in practice it is found that much smaller fluctuations occur during normal casting, the RESPONSE LEVEL settil.g should be reduced accordingly. In practice the optimal
adjustment can be determined during the actual casting . ! procedure by taking all factors into account.
For systematic determination of the optimal adjustment, the RESPONSE LEVEL tria-potentiometer is turned to the left and adjusted to the smallest value. Thus, practically always the smallest time constant is effective. Then the output signal (as far as possible in the range 2 to 5 volts will be typed by a recorder and the width of fluctuation read off in Volt when the sold level is constant. By means of the tria- potentiometer this voltage value, including a small addition as a safety factor, is then to be adjusted at the measuring sockets RESPONSE LEVEL. |
THRESHOLD SETTING
The THRESHOLD UNIT includes two relays with one changeover i contact each for initiating HIGH and LOW signals. In I addition, one open-collector output is provided for each threshold.
The signal thresholds are fully adjustchle over the entire level measuring range by turning tl.c **Lociated slotted potentiometers as required. The scale divisions are proportional to the output signal and to the sold level.
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. 1 It io rocccsondad to cdjust tho exact throchold cotting by , connecting a separate direct-reading instrument (0 to 10 I volts) to the sockets (8) from Figure 10.6.1 provided on the | THWESHOLD UNIT for this purpose. p | Threshold system A provides the HIGH signal, 5 the LOW signal. When the output signal lies between the two preset thresholds (i.e. normal operating conditiona), both relays are energized (normally closed circuit). If the signal exceeds thrashold A or drops be' 4 threshold B the associated relay drops out and tue appropriate LWD indicates the fault condition.
HV ADJUSTMENT The HV supply for the photomultiplier, which is generated in the scintillation counter, can be adjusted with the HIGH VOLTAGE (2) from Figure 10.6.1. potentiometer in the ADAPTION UNIT. This is preset by the manufacturer to the optimum setting, with a reference voltage of 4 volts and no resdjustment is normally required even when a scintillation counter is replaced.
In order to check the performance of the scintillation
counter when the system is initially commissioned, it is , recommended that the HV plateau is also checked (cf. Servicing Instruction 2.2.5 Faults in Scintillation Counter). For this purpose the HV supply can be adjusted with the potentiometer within certain limits, and the corresponding reference voltage can be checked across the associated sockets.
STROKE COMPFNSATION
. If the sold level ganging system is operating with a stroke compensation, all the basic adjustments such as EMPTY and ' FULL calibration etc., must be carried out when the STROKE COMPENSATION slide switch is set to the OFF position. For | adjustment of the stroke compensation a cold plate is | Placed into the mold until a mold level of approximately 50 percent is simulated. The POSITION potentiometer is preset in its middle position of 5.00. The mold oscillation is started with the STROKE COMPENSATION slide switch set to the | ON position via the STROKE potentiometer. The compensation | factor is adjusted until the sold oscillation no longer influences the output signal.
By means of the POSITION potentiometer, the compensation signal can be rendered symmetrical, if necessary.
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SYSTEM FOR SLAG DETECTION . If the continuous casting system is additonally being operated with a slag detection unit, this system is incorporated in the same rack as the 2nd measuring channel. The Model LB 3821-21 is used as the RATEMETER UNIT. All i other modules correspond to the versions of the sold level gauging system.
In contrast to the general operation manual, the equipment for slag determination must be frequently adjusted at different points in order to guarantee sufficient differentiation between steel or slag in the radiation path.
Deviating from the operation manual, the equipment for slag determination must be adjusted as follows:
Sensitivity Adjustment
The presence of slag in the radiation path must be simulated in the sold. This can be done by filling the mold's irradiation plane with one or more aluginium plates if the slag density is approximately 2.7 g/cm . Sensitivity suffers phen slab sold sizes are less than 300 x 300 mm.
When the indicator reaches approximately 50 percent of full scale, the sensitivity adjustment of the equipment is complete.
Switch Point Adjustment
Instead of the aluminium plate, a steel piece with about the same dimensions is placed in the radiation path. A reading of 90 to 100 percent must now be reached on the indicator. This reading will vary according to mold size. The switch
| point is then adjusted between indication slag and ! indication steel, i.e. approximately 70 to 80 percent.
It must be recognized that the adjustment of the r nsitivity | is only valid for a certain mold size. The sensitteity must be readjusted whenever the sold size changes.
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> Radiation Protection When the human body is exposed to radioactive radiation then, depending on the intensity, energy and duration of r exposure to radiation, chemical and biological reactions may under certain conditions take place which can change, damage or even destroy body cells. In order to prevent such health hazards, limits have been internationally agreed for the maximum permissible radiation exposure of operating personnel. By taking appropriate measures at the design stage and selecting a suitable system geometry it has been ensured that the radiation exposure will in every instance lie below the maximum permissible limit of 5 mSv (500 aren) per annum, provided the correct procedures are observed. Nevertheless, every operator should endeavour to minimize radiation exposure even within the permitted limits by careful and responsible action and by observing the radiaton safety procedures described below. Operators must be aware that the sum total and consequently the effectiveness of the radiation dose absorbed by a body is determined by three factors:
e Distance between source and human body. The radiation intensity decreases .in the same way as light in propor-
tion to the square of the distance, in other words, l doubling the distance to the source reduces the radiation intensity to one quarter. ' CONCLUSION: When handling radioactve substances, maximum distance to the emitter should be maintained.
e Time during which the body is exposed to raditation. This effect is cumulative and increases therefore with the duration of the radiation exposure. CONCLUSION: Operators should not work longer than abso- lutely necessary in the direct vicinity of the source. - e The thickness and density of the shielding material surrounding the source. The shielding effect depends, following an exponential function, on the product of the thickness multiplied by the density, and therefore materials with a Sigh specific weight, such as lead, will normally be used for shielding purposes. CONCLUSION: The source must never be handled without protection and aust not be removed from its normal shielding.
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By procooding corofully cod aboorving tho cbovo procautions, it is possible to reduce the radiation exposure of casting Q machine operators even below the detection capability of film | dosimeters. In particular, it is essential that the radiation beam | should always be sealed off by closing the beam window | immediately after a cast has been completed. Closing the | window eliminates any risk of exposure when routine work is being done in the sold area such as cleaning the sold or sealing the dummy bar. In the event of any major work being carried out on the sold, or when the mold is changed, the sealed shielding shoald be removed from the sold and stored in a secure place on the casting platform.
After any serious disturbance, such as a mold overflow or break-out, it is imperative to check the integrity of the shielding, and to notify the radiological safety officer when any damage is suspected. The safety officer will then assess any damage and contact the manufacturer if there is any likelihood of a fault condition which may Jeopardize the safety or performance of the system. It is recommended to summarize these safeguards and any special precautions which are applicable to a particular casting plant environment in formal procedural instructions.
The provisions in the Radiation Protection Regulations must ( also be observed in every detail. It should be remembered that radioactive sources which are no longer needed or have decayed beyond their useful life must be returned to the National Radioactive Waste Disposal Center or to the manufacturer.
______Technicul Data
MOLD LgVEL GAUGE LB 300-2
______Module chassis Reight 3 U/ width 84 U can accomodate 2 Mold Level Gauging systems ! | Power supply AC, +110/-15 percent 50/60 Hz Power Supply Unit LB 3897-1 220 V LB 3897-2 110 V LB 3897-3 24 V Power consumption Maximum 20 W ,
BONTROLNo. 8 0 7 6 8
t
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Count rate Minimum 500 cps
Time constant Automatic, ! Without change- j electronic over change-over ! Setting 1: 0.2 : 0.2 s 2 or 1 m : Setting 2: 0.4 : 0.4 s or 2 s ! Setting 3: 0.8 : 0.8 s or 4 s ! Long-term stability Better than il percent of radiation intensity
Accuracy Approximately 12 - 3 percent of level measuring range Ambient temperature range '273 K - 323 K (0 to +50'C)
Outputs e 0-10 V maximum 10 mA with change-over e 0-10 V maximum 10 mA without change-over e 0/4-20 mA maximum 500, ohn isolated e HIGH/ LOW relays: 1 change-o over contact each maximum 250 V/2 A, non-inductive e Open collector +30 V, maximum 0.1 A Weight Maximum 6 kg
______hCINTILLATION COUNTER LB 6639 ______With permanently connected 5 meter silicon cable Sensitivity 13,5u Gy/h (1.35 mrd/h) for Co-60 and 1500 cps Ambient temperature range 253 K to 323 K (-20 to +50 C)
gnclosure IP 65
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Page 10.6.22 .
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Weight Approximately 5 kg
( Dimensions LB 6639 without cooling Jacket diameter 50 mm x 346 mm LB 6639 W with cooling Jacket diameter 60 mm x 346 mm
Servicing Instructions for Mold Level Monitor LB 300-2 Maintenance The Mold Level Gauge LB 300-2 has no wearing parts and includes no mechanically moving parts that are. subject to wear. For this reason the monitor requires no maintenance. The radiation beam window in the lead shielding, however, must be checked at regular intervals. Exact maintenance procedure depends on the window type and design.- The Radiation Protection Regulations must, of course, be com- plied with, and it is advisable to discuss the maintenance procedure with the radiological safety officer.
, Troubleshooting
i
CHECKING FOR OPERATOR ERRORS The following settings should be checked and compared against the commissioning record:
e EMPTY adjustment e FULL adjustment e HIGH VOLTAGE (reference voltage) - e TIME CONSTANT When readjustments are necessary refer to theoperating Instructions. Section III.
' CHECKING SOURCE AND SHIELDING
Check the general condition of the source shieldius. The radiation window must be set to OPEN. Any damage to the shielding or signs of chemical reaction must be immediately reported to the radiological safety officer.
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Page 10.6.23 ,, I
( Check the manufacturing date of the source. The date is , indicated by the serial number on the name plate, e.g. 1335-12-79 / The second group of digits identifies the manufacturing month (in this case December), and the third group the year (in this case 1979). Co-60 sources are normally rated for a useful life of approximately 5 years, Cs-137 sources for approximately 10 to 15 years. When they have t eached that age, a new source should be ordered as soon as possible. The order must state the complete reference number of the original-source. If the nominal useful life of the emitter is greatly exceeded , . the statistical fluctuations of the output signal will increase, or the sensitivity of the system may no longer be sufficient for carrying out the EMPTY adjustment.
. CHECKING THE CONNECTIONS Check the cable connections to the scintillation counter and at the rear of the unit. The entire cable must be free from any signs of damage. Fault Tracing
NO READING, In the case of total failure (the green " POWER ON" LED fails to light up) check the main supply and then the fuse in the Power Supply Unit. The Power Supply Unit LB 3897 must be removed if faulty. Check the operating potentials on the front panel of the Power Supply Unit.
Nominal voltages:
+15 V 1 0.05 V -15 V 1 0.05 V +10 V 1 0.01 V If an overload condition is suspected, each module must be removed in turn until the cause has been located. NOTE: Before withdrawing a module, the locking screws must be opened. Due to the heavy duty connectors used it may i sometimes be difficult to withdraw the Power Supply Unit by pulling on the open locking screws. In that case the module to the left of the unit should be removed and the Power Supply Unit carefully levered out with a screw driver.
Page 10.6.24
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Using an oscilloscope, check that the scintillation counter produces count pulses. These can be checked at the ( following points: e Test socket _Jl_ 0UT (ADAPTION UNIT) Output pulses to the RATEMETER , e Test socket J"L IN (ADAPTION UNIT) Input pulses into ADAPTION UNIT, coming from optocoupler (on. rear of module chassis) 1 e Terminal 1 (rear of unit) count pulses from scintillation counter to optocoupler input
The connecting terminals for the scintillation counter (PROBE) must have the following potentials to ground: Terminal 1: positive pulses width approximately 2 us ( amplitude.approximately 7.5 Volts ( Terminal 2: poaltive pulses width approximately 2 us amplitude approximately 2.5 Volts Terminal 3: reference potential for HIGH VOLTAGE adjustment, approximately 4.0 Volts (depending on setting of trimmer potentiometer on ADAPTION UNIT) i k Terminal 5: +15 Volts (load approximately 100 mA)
' Terminal 6: -15 Volts e If no pulses are detected although the supply voltages are correct, the complete scintillation counter must be replaced. NOTE: When the scintillation counter has been replaced, check the plateau and the EMPTY adjustment at the sarliest 5 opportunity.
NO OUTPUT SIGNAL The voltage signal can be checked at the test sockets on the front panel of the RATEMETER. The voltage. output is also applied to the direct-reading instrument in the ANALOG DISPLAY. When no voltage can be measured, the RATEMETER anst be replaced. - The current output is looped through a resistor (50 ohms) parallel to the test socket (1 V 9 20 mA). If the current measured does not correspond to the reading then the circuit either has a continuity fault or too much resistance. ;
Page 10.6.25 g y 4 ______-
. . Percicoible Locd: 500 ohoo The current amplifier is located on a sub-card on the printed circuit card of the RATEMETER and is easily i replaceable.
FAULT IN THE THRESH 0LD UNIT , _ The voltage which corresponds to the preset thresholds can be checked at the test sockets on the front panel. It must l be approximately equivalent to the scale on the rotary control. When the setting of the rotary control and the instrument reading coincide a relay should operate with a clear audible click, and the LED should light up when the relay has dropped out. ,0THER FAULTS IN THE MAIN AMPLIFIER
It is essential to keep a set of spare cards so that the measuring system can be quickly rostored in the event of a fault. This is particularly important where the ADAPTION , UNIT and RATEMETER are concerned as these must be systemati- cally replaced whenever a fault occurs. Once the faulty unit has been located, it should be " double- checked" that the fault has actually been caused by that particular module.
' | Faulty modules must be returned to the manufacturer for' ' repair.
1 FAULT IN THE SCINTILLATION COUNTER
_ The scintillation counter can be damaged by excessive vibration or by ambient temperatures above 60 C. In practice this can mean that although pulses are still being generated, the sensitivity may have decreased and the reading may become unstable. The complete scintillation counter probe can be checked out by testing the voltage plateau.
Preparations for Plateau Check: e The radiation level at the scintillation counter must be sufficient to produce an output signal between approximately 3 and 7 volts. If the normal operating source is not available for this purpose a low activity reference source should be used.
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Page 10.6.26 l - _ _ ......
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. e Turn the FULL potentiometer fully counterclockwise (record the potentiometer position so that the correct i voltage can be restored afterwards) to insure that the . plateau does not become distorted by any spreading that may have previously been selected. e Connect an 0 - 10 volt voltmeter to the test sockets for the 4 V i 21U on the front panel of the ADAPTION UNIT to 3 check the HV reference voltage. Quick Check: . e The HV reference potential is adjusted with a trimmer ' potentiometer by +0.2 volt and -0.2 volt (e.g. to 3.8 volts and 4.2 volts respectively). e When this is done, the reading must remain practically unchanged, i.e. the change should not exceed the statistical fluctuations which will always be present in any case.
e If, however, the potentiometer adjustment results in a clear change of instrument reading, the operating point has shifted or the crystal of the multiplier assembly has j become faulty. In any case it will be necessary to plot the plateau curve.
I Plateau Plotting:
e The HIGH VOLTAGE trimmer potentiometer is gradually turned through its full range in small increments (e.g. by 0.2 volts at a time), and the instrument reading is plotted on graph paper as a function of the HV reference voltage. should be set to positionThe TIME 3 in CONSTANT order to minimize selector switch the statistical error of the reading. After each potentiometer adjustment approximately 1 minute should elapse before the reading is taken and recorded. e The trace on the graph paper must show a clear plateau (kefer to Figure 10.6.5 Plateau Curve), i.e. must be equivalent to at least 0.5 volta referenceits width voltage (equavalent to 150 volts high voltage), and within this range the reading must not change by more than approximately 0.2 - 0.3 volts. The correct operating point should be adjusted roughly to mid- plateau. e If the plateau is found to be too short or too steep then the crystal / multiplier assembly or the complete scintillation counter must be replaced.
Page 10.6.27 fil- r
NOTE: After o ocintillction counter hoc bacn replaccd, the plateau and the EMPTY adjustment should be checked at the first possible opportunity. ;
i-TA ===r. -W = ;& - ~ C L:_-- ='-Q==-. - . =c-i= =i=i& ':==~ 2"W m . - - - - :. =.q.;===yf. - _z_r- _ t==.5ps=-- --____=+==75===. =gn==g;rg-- um!=J W umluel5, --;== = ''==5-_- L~? '==~ ==E=~Tr__- - ^ - = u== - . ~;~E=E't =Et ~~ =+s== c = . - = = r - -
------gs c.;;r_=_ =r m - ==?==-;#c==sa=igva5=itc-iE=Pz=g-:icr =wr-=- 3-:, ==--^E ~ ~ = =~~ j - li .' = = = ==K=~ - =~ ~l==:252 :-- ::=~ :Er -~: ~ = . : V- . .W W - l= ^~~a= " vil -it=:-::- =w q- u:=w --;;-mmre= =v=.2+s 2=v- 7;4====p;- =7=w .-7:zyaw~- --m- .aq L=y : : ;*=~-w = == =- : ======:-.=;== 2== ?t=G=;L= .-PlMSEClfW =c==-res= ^=x=i=y- = = ' =aa- ; ====T2-E E#=~~~M=m==m =1 Yi - =3Kr :=r:1=- =# ~=3=eil = ; -G===- i'i+ = = =& ------~?iis -= . - s-- .. _ =- - = --- - ns =c F- .== - = . . =L- .= -;s~ - :~ 245=z=ct = =rw=p=i :-T. '. ^ . . ' =W.y-Li= = = h='55= ~ = =--- q==ES-E'=rQE-T--|4.~ :.L'i -- & ~Q ~C -' GTT.5~5-li ^=^ . E m := \======: ~-: - ... ' - =1 - =- ~*'.r: 2 . Q'ar-:==m== %' -~ _ -= .--\T==. ; . :Z=Fr== k==.~=- . = =f8==11 = =:~'=-r=_=n=2 :=:= ==:= . -2=:==::-=Lv =- - 5 :; 1 E t=l=- -5Ei3=.z r_ \ EEML=1 4-J=-t=L"=VE- f MEF"ifr= h Cri ~ =< E m ,EMc r_- ===-==r:ws. N -===rc::1-_yj;strAFF;J - =._a;> -+I2c"EM l = k===sar'=+5 E+===- ! --. Mt .2=. zE= = r= =- EJEi- -'-'i"5-E=~Mr- '==&~15t-:E=3MIMl : L -Is t at .a, -- - .g ; _-7 --- --"I {=-55a._%7 'r===.fN= =-#s g_ __ , __x ;x_ gag 55_=._g g 3_(=j=...._g --. .'7s.-..- ~~ '
- ~V:c- -t=t 1_=C _~ L ^ ~ , _ EfqT:r- _~[ f}==i=G~=- EQ 5=== 1 ===i ~''i- t==#?' u= = . - = = == := + =>3 - - - -== .- = = == -== w== 1 == .n== =. ^ '- h ht2=t= . :.~. ~^1===-_T - z -' ==-- ===-r-iw .a . +a N29EK-5= = ~ . h ==~= ~:2;=k-s: - - - - - K@Et'2 =_ -CT_ - 2&nF==~=E" :=9t=; =- 'E~==:MT. :~'' -iL.uB-' W1 : =';- -2 25-:: C.--~ g T._-~= ==1 1]11-g4:T_ =r.f i - :. .6 .-M _ _T - ~ ~ _ ==4ya=gE=g.==j=g=, j=_=E= P=i==Ie 2E Z-~- -zT--- =-1_ =MR=.==2 sa3=i-;3=a=RI- _=_1===U=I: =- F= - iw=14:": c:=t= =--c :-; m-4::T; = -;-1 =M' ==-1 =' :=me= = E== :-f 4;= -q . -.=-s---z .= . _.2c=h '*=5=;i=P =k=hE--4 =; .JL=M=L=l'-;= ~-? . Mr'=i4.4 i&frr= =--M:+ ;1 - C=ic' :d? M=1== M=z i ="E:25~E- 12-+&Z=i^=% C+N;D @-tu G. N-22*L- w := ~ - z= , - F - T=-rr- = c -s- -u* . 2:Z .= 1 =~ M 12ZEL-' lizI'E rr1 =+:= ME=Zu . = , ~:= = + - - -- T. Z-tit 5?-iy= =gg--' t 5s. r-- 1 . - L .I L=Qi' set := 1i p =gMty-Q '._ _g- :$. EQ =T=-[--- = 5 - - =_: =_ii==_=g_ =._ jE .in ~ =EZ. =--Os= V. L ' " ~ ~[g i. 1. f+: u r=-_r== ter r ==== : W =E'REIJ-M= W1= : 3-f-_: =.c ;<2 -! . F i - !- = yve=9 =.====L=-E =w.uk,1= n- ==#+ wL_J-ma =- t = -6, =L =+ = . . + t-- [ REPLACING THE CRYSTAL MULTIPLIER COMBINATTON Switch off the scintillation counter, open the casing and carefully withdraw the electronic module horizontally. The crystal multiplier conbination is then replaced and the casing closed to ensure that the multiplier is protected from incident light; otherwise the photocathode is destroyed immediately. Using a high-resistance measuring device (Ri = 10 k ohm /V) with a measuring range up to 2 kV, the high voltage is measured alongside the high voltage reference. Record a plateau as described under " Preparation for the Plateau Test" and " Recording the Plateau"; the actual measured high voltage is recorded at the semestime. As ' described above, the recording should show a distinct plateau. The correct operating point is the high voltage value which lies approximately 100 volts into the plateau, starting from where the plateau begins. , ; Page 10.6.28 .. . - . - _ . . . To enable the scintillation counter to be replaced without d. having to reset the high voltage, it is advisable to set all probes to the same plateau position; this is the procedure used at the factory. To do this, set the high voltage reference on the ADAPTION UNIT to 4 volts and the High Voltage to the chosen operating point using trimmer R 63 on , the circuit board in the scintillation counter. I To do this, proceed as follows: 1. Record plateait by plotting the output voltage against the reference voltage (Vref). 2. The operating point is chosen at approximately 100 volts = 0.33 volta Vref starting from where the plateau begins. The set point voltage is then determined. (In the example it is approximately 3.65 volts). 3. Switch off the unit, open the casing and withdraw the : crystal multiplier combination. Switch the unit on f 'again and measure the high voltage (point 28 on circuit board 19190.090-000 circuit diagram 19190.901/2). 4. Set the high voltage reference at the front panel of LB 3806-2 to 4 volts. * i 5. Using R 63 in the scintillation counter, set the high , voltage to the value determined in accordance with Step 3. ' 6. Switch off the unit, re-insert the crystal multiplier combination and make sure the casing is properly closed. CRYSTAL / MULTIPLIER ASSEMBLY Faults in the crystal / multiplier assembly may result in the plateau becoming too small or too steep. Faults in either the crystal or the multiplier can in some instances be , detected by a visual check. For this pupose the assembly is I ! , withdrawn from its mounting, but the checks described below i must not be carried out in direct sunlight owing to the high light sensitivity of the photomultiplier, even when i deenergized. After the au metal screen has been removed, | the crystal is detached from the multiplier window by gently | sliding the crystal sideways. Finally, remove any traces of ! oil from the mating surfaces of the crystal and multiplier by gently wiping them with a soft cloth. The crystal must be perfectly clear inside and not show any cracks or dull areas. The normal coloring is slightly greenish. Yellowish to brownish coloring is a sign of . ;[ thermal overloading and indicates that the crystal must be replaced. Donmol.NO. 8 0 7 6 8 Page 10.6.29 . .- - , , , .,-._-,,,.----._,,.,----,,,,,...,--.,,-,...-,,-,,,----.y -- - - ,,._,,m-.-,,...... -,.,,,,.m..._...... ,-,--,.- - , . - - - - , - - - , , , - - , , , . , , r . The cultiplier window io coated with a vapor-deposited layer i acting as photocathode. This layer gives the window a ' brownish tint similar to smoked glass. If the window is either completely cler:r or stained then the photocathode has ' been destroyed (e.g. by incident light or glass breakage). Faults caused by damage to the dynode system (e.g. by excessive vibration) cannot be identified by visual inspection. Before reassembly, apply a drop of clean oil to the mating faces of cyrstal and multiplier and distribute it evenly by gently rubbing to en'urea a sound optical connection between the two components. Finally replace the au metal screen, making sure that it is only under light tension. ' . . . Page 10.6.30 . . 1 'l l R a ci i a t i o n Protection Introduction A great number of radiometric measuring systems are being used today in industrial applications for very different tasks, | especially for measuring, monitoring and control purposes. 1 Radiometric measuring techniques can often still be used when |' conventional measuring methods are no longer applicable, due to technical and physical reasons. In addition, radiometric | measurements offer a high degree of operational safety, since ! they are not affected by any chemical or most of the physical ; characteristics of the product that is to be measured. | Fidiometric measuring systems use radioactive substances of 1;fferent types and activities, which are best suited for each , respective measuring task. | Handling of these radioactive materials is regulated by law to prevent improper handling and thus radiation exposure of the personnel. Properly trained radiation protection officials must make sure that these regulations are enforced. ( For people who occasionally come in contact with radioactive substances, it is advisable that they be acquainted with the technical aspects of radiation protection. The objectives of this dissertation of radiation are as i follows: ' e Inform the reader about the basic principles of radiation protection, e Offer the possibility of minimizing radiation exposure, and e Carry-out simple radiation protection calculations. Based on this knowledge gained, some basic laws for radiation protection and the ponnibility of practical application can be attained. For practical calculations, the frequently used gamma sources find application in level gauging and density measuring systems. ( r Page 10.6.31 ( psi . . .. . - _ _ _ _ _ . _ . - _ _ . _ _ . . . - _ _ . . _ . . . - . . - . - _ . _ - ___. . . . . | f 1 * : | | BASIC SCIENTIFIC PRINCIPLES , ) Physical Basics of Radiation An atos comprises a nucleus which is surrounded by electron | shells. This atomic nucleus consists of the positively charged protons and the neutrons, which have no charge. Depending on the position in the periodic system of the elements, the nucleus contains a t'.ifferent number of protons and an equivalent number of neutrons. In an electronically neutral atom the number of positive , protons must be equal to the number of negative electrons which move in different shells around the atomic nucleus. If the number of protons and electrons is not equivalent, an ion which is not neutral will result. An atom is characterized by its atomic number (Z) which , specifies the numb'er of protons in the nucleus as well as | the number of electrons in the shell. ' Protons and neutrons, the nuclear components, together are called nucleons, and they collectively determine the mass number (L) of the atom. Usually, the stonic number is written to the lower left of each element and the mass : number to the upper left. The element cobolt (Co) is given ' as an example: 60 Co 27 Since the atomic number is already specified by the symbol of the element, it is redundant and often one just writes 60 Co or Co-60 respectively. The same element with the same number of protone may poesess a different number of neutrons; these elements are called isotopes. Different isot' opes are instable, i.e. they decay spontaneously without any external impact and emit nuclear radiation. Radiation involves either particle radiation consisting of protons, neutrons or electrons, or electromagnetic waves radiation, such as light or radio-waves. The spectrum of electromagnetic waves may range from long-wave radio- radiation to visible light and short-wave X-radiation to gamma and cosmic radiation. (See Figure 10.6.6.) . Page 10.6.32 -- _ . . _ ------_ _ . .- - _ _ . -- _ _ - - . _ - _,_ -_-..-_,-.- - T i i ! i 2 ! .I, _?, , ...... e,...... n a ; ; 4 : H: unr .a , une.. n , r.su.wa son.a.u was | , ,, ,, .. , i | w.n.amage temi i io ' ie- 104 se' to - 10- * it- - - - , , ; ,- ; an.,s ievi to. to ' i io- ir so- io- so- . Figure 10.6.6 , Spectrum of Magnetic Waves The emitted nuclear radiation shows different energy levels, which are specified in electron-volt (eV). The energy of particle radiation depends primarily on the kinetic energy :( of the particles, and in the case of electromagnetic waves radiation on the wave-length (frequency) which can be equated with a corresponding energy in eV. Types and Characteristics of Nuclear Radiation 1 Alpha-radiation involves particle radiation, i.e. electrically charged particles of an atom. These particles are relatively large, so that the interaction with other atoms is high; alpha-radiation, therefore, has only a short reach (e.g. in air approximately 5 - 6 cm). The pentetrating capacity of this type of radiation is so low that it can be completely shielded by a sheet of paper less than 0.1 mm thick. |, The human body is sufficiently protected.against external ' radiation by the skin. Alpha-radiation, however, will become dangerous if it gets into the body through breathing, eating or open wounds. If it comes into close contact with sensitive tissues in the human body, it may cause a great deal of damage. Therefore, incorporation of alpha-radiation should absolutely be avoided. It hi|; Page 10.6.33 m _ _ - _ .- . . _ . .-_ _. . , _ _ _ - = -_- - _- - . . . _. . _ _ _ . l . Beta-radiation also involves particle radiation, in this case consisting of electrons which have a relatively small , mass and therefore a better penetration capacity than, alpha-radiation. The penetration capacity depends on the energy and is roughly inversely proportional to the density of the substance. Maximum reach in air can be up to approximately 10 m. In paper it is 10 mm and in aluminium approximately 4 mm. Important: If beta-radiation is suddenly retarded as a result of its impact on a heavy element, secondary radiation will result. This " retarded radiation" is one type of X-radiation referred to as soft gemaa- radiation. Its penetration capacity is significantly higher than that of the original beta-radiation. Aluminium or plexi-glass are especially suitable for shielding beta-radiation. The damaging effect of beta- radiation to human tissues can be caused by external radiation as well as by internal radiation through incorporation. Gamma-radiation does not involve particle radiation, but , I consists of high-energy photons, i.e. electromagnetic waves radiation of very high frequency. Like the radio- and X- radiation it is therefore similar to light and has the same dissemination velocity as light. In contrast to particle radiation no maximum reach can be given. Since the photons have no charge and no rest mass, they have no pronounced interaction with other materials; therefore, they have a | relatively high penetration capacity. i The higher the mass of the aton, the higher the intere.ction with other materials, so that substances with a high specific weight are particularly suitable as shielding material. For gamma-radiation lead is therefore the preferred shielding material. Neutron-radiation, like alpha- and beta-radiation, involves particle radiation. The particles are electrically neutral ) nucleus components. Thus, the interaction with other I materials is very slight, and consequently their penetration , capacity is very good and therefore they are hard to shield. ' The interaction with setter primarily depends on the energy (corresponding to the velocity) and is based on the scattering of the atomic cores and absorption (intake). With fast neutrons scattering processes predominate which develop according to the laws of the elastic shock known in mechanics. Page 10.6.34 I i , - - - _ _ , - . - _ _ _ _ _ . - ...... -. , - - _ - - . --. , -__ _ __ l . Since the neutron has roughly the same mass as a hydrogen .( nucleus, it is substantially scattered on heavy elements without suffering a major loss of energy. I However, neutrons colliding with hydrogen cores lose roughly fifty percent of their energy, so that after a very brief period (approx. 18 shocks) it is moderated to a slow (thermal) velocity corresponding with the Braun molecular movement. Neutron radiation becomes dangerous only in high concentration and has to be shielded. For shielding purposes substances with a high hydrogen content are necessary, e.g. water, paraffin cr plastics, together with substances with a high absorption cross-section, e.g. boron or lithium. .t . I I ( ht+0Rotna, S 0 7 6 8 Page 10.6.35 w .- - - . -- - . - - . - , . - - _ . _ - . . I . . I | L* s., .. , ' '' 4 Alpha- particles # i k (nuclear component) . ' . '. - a 's $ Beta-particles ,' : ',.' (electron . I 1, .. e, '. . ' ' .'s T Gamma-radiatioon - 3 , OM (waves radiation) 8 1. 5 .. , ' = o Neutron (nuclear component) Figure 10.6.7 Types of Radioactive Decay (Schematic Configuration) Page 10.6.36 .. - .- . . Activity i Radioactive sources are cubstances which decay as a result of nuclear reactions, emitting ionized radiation. The number of emitted radiation quantums per time is referred to as activity, and the unit of measurement is the reciprocal second (1/s = a y) or the new unit Becquerel (Bq), one Bq being equal to 1 decay per second. The older unit curie (Ci) is also still being used as unit of. measurement, one Curie being equal to the activity of 1 g radium with 3.7 x E10 decays per second. Conversions can be made as follows: ' 1 Ci = 3.7 x E 10 Bq or 37 GBq l sci = 3.7 x E 06 Bq or 37 MBq * $$*'i45al gc. iti n.: E,ca e . t. .a s' w holI, a s.27 el ' g g \E. .a31 wev , M* ' "7N \ E .).17 haw .E .O.M2uev ,6 3 m2,6 T E,.t.LS w E g.1.t73 pw ' cri.s m.: w h ye, ae,.t3n w 5 ( CO */.1 E' Figure 10.6.8 Decay Scheme of Co-60 and Cs-137 Half-Life Period ! Due to the radioactive decay the activity of a source decreases according to specific physical laws. The time in which a source loses half of its original activity (Ao) is . referred to as half-life period (HWZ). The current activity (A) after a certain time perriod (t) is calculated as follows: A = Ao x EXP ( .693 x t/T) i ~ Page 10.6.37 "PS[ . . -- -- - _ - - , - .-._. . - - . - _ _ - - -. . . _ _ - - _ _ - - - - _ _ - - - - _ _ _ - . . For some of the more important sources the following HWZ can be given: j co-60 - 5.3 years Cs-137 - 30.1 years An-241 - 458 years ! Examples of Calculations: How high is the activity in percent after 10 years with the following sources? a) for Co-60 l A =Ao x 100% x EXP( .693 x 10/5.3) = 274 b) for Cs-137 A = Ao x 100* x EXP( .693 x 10/30.1) = 79% Radiation Dose The effectiveness of radiation hitting a certain spot is referred to as dose. It depends on the source activity, the distance from the source, the time of exposure, and the efficiency of the shielding. Different types of doses can be distinguished: Ion Dose The effectiveness of radiation can be determined directly via its ionization effect (e.g. in air). This ion dose is measured in Coulomb per kg (C/kg). Up to now, the standard unit of measurement has been the Roentgen (R). Roentgen is converted into Coulomb per kg as follows: 1 R = 2.58 x E -4 C/kg Page 10.6.38 . , . . . Energy Dose Nuclear radiation colliding with matter loses different types of energy as a result of processes of interactions. The energy dose specifies how much energy is imparted to the radiated body. Unit of measurement is the Gray (Gy), one Gray being equivalent to the energy dose corresponding to the energy of 1 Joule per kg (J/kg). In addition, the older unit Rad (rd) is vtill being used; it is converted as j follows: I rd = E -2 J/kg = E -2 Gy For certain substances the energy dose can be calculated from the ion dose by means of conversion factors. In belly l tissue the following conversion is valid for beta- and j gamma-radiation: ) i I 1R = 1 rd 1 1 C/kg = 38.8 Gy \ Dose Equivalent Even with the energy dose being the same, ionizing rays may have varying degrees of biological effectiveness (ionization effect) in body tissue. To assess this varying biological effectiveness for different kinds of radiation, a so-called RBW-factor (relative biological effectiveness factor) is used. The energy dose multiplied by the RBW-factor gives the dose equivalent, which like the energy dose is nowadays indicated in Joule per kg (must not be indicated in Gy, since this term should exclusively apply to the energy dose). The dose equivalent 1 Joule /kg may also be expressed by 1 Sievert (Sv). In addition, the term ren is still being used which expresses the following relationship: I rea = E -2 J/kg = E-2 Sv 1 area = 0.01 mJ/kg = 10 sySv ( s DNf4 Page 10.6.39 sas - , _ . - - - -- . _ - - . - - - - .. , - . . . ~ . . ______._ . . To convert different types of radiation from energy dose to dose equivalent, the following RBW-factors have to be taken r into consideration: , Alpha-radiation - RBW-factor = 20 Beta- and gamma-radiation - RBW-factor = 1 Neutrons, depending on energy - RBW-factor = 3 to 10*) *) Note: If the energy is not known, invariably use a RBW- factor of 10 to provide maximum cafety. Dose Rate While the dose specifies the effectiveness of a radiation field on a body, the dose rate indicates how fast the effectiveness is achieved. Unit of measurement for the intensity of a radiation field is the radiation dose per time unit (T) expressed in dose rate: dose rate = dose / time The dose rate is normally given in hours (h), so that nowadays it is expressed in J/kg per hour or better in Sievert per hour (Sv/h). Up to now the usual term was rea/h. The dose rate (D1) generated by an unsealed source at a given distance (a) can easily be calculated from the activity (A) provided the specific gamma-radiation constant (k) for the corresponding source is known. Dose rate and dose can be calculated according to the following formulas: Axk Dose rate D1 = -- g-- a AxkxT Dose D = --- g----- a Page 10.6.40 _ 7 . . If a shielding is used, dose rate and dose are reduced by 'l the reduction factor (S) and the formula for calculating the dose is extended as follows: AxkxT D = -- g------a xS The following specific gamma-radiation constants (k) apply j to the sources must frequently used in industrial ' application: | | , Nuclide k (old) k (new) arem x m 2 uSv x m 2 ! for co-60 1,35 ------0,365 ------| h x sci h x MBq ' - - aren x n' uSv X m' for Cs-137 0,35 ------0,095 ------h x aCi h x MBq - - .t aren x m' uSv x m' for An-241 0,075 ------0,002 ------h x aCi h x MBq ExamplesHof calculations: The dose rate of a Co-60 source with an activity of 5 aCi or 185 MBq respectively in a distance of 50 cm is to be calculated: 5 aci x 1,35 aren x m2 , ------= 27 ares /h D1 = ------(0,5 m) g---hx x aci | ; or 185 MBq x 0,365 x uSv x m 2 D1 = ------= 270 uSv/h (0,5 m) g------BqxhxM ( 1 r. Page 10.6.41 hU3i m _ - _ _ , ______, . . . ______, . ______. - . ______. _ . _ . _ . . _ _ . . _ . , _ _ _ . _ _ . _ , _- _. _. - _ - -- .__ __ - . . The dose rates calculated with the above formulas are valid for unshielded sources. If a shielding is used, the dose , rate is reduced by the corresponding shielding factor. If the activity of a source is unknown, it can be calculated by means of the corresponding gamma-radiation constant from the dose rate measured in~a given distance from the source. Apart from the dose equivalent described above, several other dose terms are used in the radiation protection praxis. The person dose, for example, is the dose equivalent for belly tissue, indicated by a doseneter (film doseneter, pocket doseneter) which is worn at an appropriate place on the body surface. The tern local dose means the dose equivalent for belly tissue, which can be measured at a certain spot. The whole-body dose, on the other hand, is the average value of the dose equivalent measured at different parts of the body. In case the whole body is exposed to radiation, head, trunk, upper arm and thigh, for example, are taken into consideration as well, provided the whole body is exposed to an evenly distributed dose of radiation. Body dose and measured person dose, therefore, must not necessarily be equivalent. Therefore, an accurate assessment of the body dose has to be carried out by means of a calculation based on the measured data taking into account the radiation conditions. | . Page 10.6.42 \ . . Shielding of Sources , | Shielding of Alpha- and Beta-Radiation Due to their low penetration capacity, shielding of alpha- and beta-radiation is easy. As mentioned above, alpha- radiation can be shielded by a thin sheet of paper and beta- radiation by a thin metal sheet. Shielding of Gamma-Radiation The shielding efficiency for gamma-radiation depends primarily on the specific weight of the absorber. The nuclear radiation decreases layer by layer by an equal amount. The layer thickness in which the original dose rate is reduced by half is referred to as half-value thickness (HWD). The corresponding weakening factor (s) for a certain material thickness (d) can be calculated as follows: Please note, that the sine of the half-value layer depends on the extent of the radiation field and therefore it is valid only for a specific measuring geometry. For Co-60, Cs-137 and An-241 the following half-value thicknesses can be specified for the most important shielding materials: . ( naterial HWS for: Co-60 Cs-137 An-241 1 Water 157 mm 110 mm 40 mm Concrete - 68 mm 47 mm 15 mm Steel 20 mm 14 mm 0.8 mm | | Lead 14 mm 9 mm 0.13 mm | Tungsten 9 mm 6 mm - The above values are average values for measuring fields common in the praxis of industrial application. | Based on the known formulas, a calculation of the radiation dose to be expected can now be carried out. i \ .- 50tHROLNo* O U 68s i Page 10.6.43 pPSi, s. - , . . Example 1: / A source with 10 mci Co-60 is installed in a lead-shielding . ' of 67 mm thickness. Operations, which may last for about 30 min, have to be carried out in a distance of 50 ca. d 67 0,69 ----- 0,69 -- Weakening factor: s =e HWD =e 14 = 27,6 AxkxT 10 x 1,35 x 0,5 Radiation dose: D = -- g----- = ---- g------= 0,98 mrem Example 2: A Co-60 source in a shielding generates a dose rate of 0.75 mres/h in a distance of 1.5 m (limit of control crea). For safety reasons the control area is to be reduced to a distance of 0.5 m. Which additional lead shielding will have to be used? a 1,5 Required weakening factor: a = 1 = --- =9 | d 0,69 --- a = e HWD Additional shielding thickness: In s x HWD in 9 x 14 d = ------= ------= 44.6 mm Pb 0,69 0,69 | . | i | i ; Page 10.6.44 ______- _ _. . _ , _ ._ _ -- - . - _ _ . -_. _- . ._ _ _- __ . . 9 Shielding qf Neutron-Radiation a Neutron-radiation is shielded by means of substances with high hydrogen content, e.g. water, paraffin or polyethylene; the fast neutrons are retarded down to thermal energy by the hydrogen. The thermal neutrons then have to be shielded by means of thin sheets of cadmium, which has a high absorption cross- section for thermal neutrons. 100 mm paraffin being roughly equivalent to a "l/10 value ' layer" can be given as approximate value. I Calculation of the Maximum Neutron Dose Rate l Based on the neutron emission Ne the neutron flow density FD ! can be calculated for the distance r: N * F = --- D --- n/cm2 x see 4 Tr48 r )! If we assume that all neutrons emitted by the Am-Be-241 - source have an energy of 10 MeV and thus the highest relative biological efficiency (RBW), the neutron flow i density FD, generating a dose rate of I arem/h will be x sec j Fd/1 = 6,8 n/cm t 4 Thus the maximum possible dose rate D of an An-Be-241 source will be I l D= - E- ares /h F d/1 ; i ' a I - .. , I ' i .": Page 10.6.45 (psi'ae 1 ------~ , ------,--,-e.---w -. - - - - , , m - . --v---. ~-,,.,w 7- v-- r----- ! . . Example: Neutron source Am-Be-241, 300 sci i Neutron emission 7.5 x E 5 n/s Dome rate in 1 m distance 7.5 x 10 5 75 2 ------= ----- = 5,97 n/cm x sec Fd= 4n x (100)* 12,56 5,97 D = ---- = 0.88 ares /h 6,8 Radiation Exposure of Human Beings ! It is irrelevant whether the human body is exposed to radiation externally or internally through radioactive substances which have been assimilated. The damage of a - tissue depends on type, strength and duration of the radiation dose. The following types of radiation exposure may occur: | External hsdiation Exposure External radiation exposure can be expected when handling sealed radioactive substances in technical facilities. Protection against this type of exposure is possible if the equipments are handled properly and the radiation protection regulations are followed. In exceptional cases external exposure is also possible if skin or clothing are contaminated, but only if the source is leaky as a result of trouble, or when handling open radioactive substances. In these cases special precautions have to be taken. Page 10.6.46 . . Internal Radiation Protection e This type of exposure occurs if radioactive substances are -incorporated into the body, e.g. through the lungs or open wounds. When handling sealed radioactive substances this type of exposure is not to be expected. This danger arises only when handling open sources. Since this kind of exposure may be very dangerous, special precautions have to be taken. ! Environmental Radiation Exposure The list below shows the average radiation exposure of the | population of he Federal Republic of Germany, expressed in mSv (area) per fear: Natural Radiation Exposure cosmic radiation exposure 0.33 (33) Terrestrial radiation 0.67 (67) Internal radiation exposure 0.20 (20) Civilizing Radiation Exposure I Medical radiation exposure 0.50 (50) ' Industrial and artificial radiation exposure 0.10 (10) ' ______| t Total radiation exposure 1.80 mSv (180 ares) ______ | In other parts of the world the natural radiation exposure may be 10 times as high as the average radiation exposure | given above. j Depending on the degree of occupational radiation exposure we distinguish between different categories of personnel. These dose rate values, recommended by international agencies, are the basis of the Radiation Protection ; Regulations. ! i \ O Page 10.6.47 dhh/ 1 _ . , _ . , . . _ _ , . _ -- ___,- ,, , ,,,,,,,,,.,c , _ _ _ . _ -- ---7 . ., , . - - ---,,-__y .,,,,,_y , , - _ f . Occupationally not Exposed Persons i Persons and, more particularly, members of the plant which are not occupationally exposed to radiation must not be exposed to an annual dose exceeding 5 mJ/kg = 5 mSv (0.5 rea) if they work in a monitoring area adjacent to the control area. Occupationally Exposed Persons in the Category B Personnel whose annual dose is higher than 5 mJ/kg = 5 mSv (0.5 rem) but less than 15 mJ/kg = 15 mSv (1.5 rem) belong to the occupationally exposed persons in category B. The body doses are to be recorded but medical examination is only required when handling open radioactive sources. Please note that during a quarter the body dose must not exceed fifty percent of the annual dose. Occupationally Exposed Persons in the Category A Persons whose annual dose exceeds 15 mJ/kg = 15 mSv (1.5 ren) must be classified in category A. The maximum permissible radiation dose for these persons is 50 mJ/kg = 50 mSv (5 rea) per annum. The person doses are to be determined by means of officially evaluated doseneters. A medical examination once a year is mandatory. In this case, too, the body dose per quarter must not exceed fifty percent I of the annual dose. BIOLOGICAL BASICS OF RADIATION Dangers of Radiation If life-tissue is exposed to radiatior., chemical and biological processes occur in the individual cells which may change, damage or destroy ',he cells. Alpha, beta and gamma-radiation interact with the electrons of the atom shell and neutrons are retarded by the cores. Thus, electrons may be separated and as a result the atoms will become ionized. These ions are unstable and therefore react with adjacent atoms. Thus, undesired combinations may result, which can be harmful or even toxic. Since these cells are especially sensitive to radiation during the phase of cell division, tissues with a high rate of cell division, e.g. marrow and skin, are especially endangered by radiation, while other cells which are divided less | frequently, e.g. connective tissue and muscles, are less sensitive. Page 10.6.48 ______, ______. _ . _ . . L One has to distinguish between damages occuring at the # radiated organism (somatic radiation damages) and damages in the gera-cells, which only affect the descendants (genetic radiation damages). Somatic _ Radiation Damages can occur as a result of short- term as well as long-term radiation exposure. Short-term exposure of the whole body will cause the following damages: s radiation hang-over e retardation of the blood formation i e sterility , e inflammatory diseases of the skin Depending on the dose the following effects may result when the whole body is exposed to radiation for a short ters: : Dose : Effect 1 ______, up to 0.2 Sv (20 rem) :no effect evident 1 : ' up to 1 Sv (100 ren) | alight changes of the blood-picture, but no serious damages are likely to : occur | | ! up to 2 Sv (200 ren) | radiation hang-over, vomiting. : serious illness possible, good chance of recuperation : 2 - 6 SV (200-600 ren) | increase in mortality : . more than 6 Sv (600 ren):no chance of survival : : Permanent exposure to radiation with even distribution will cause much less damage, due to the regeneration capacity of I living organisms, but may nevertheless lead to chronic illnesses, such as leukemia or cancer. This is also the case if the body is exposed only once to a high dose of radiation. I c l O1WROL No. g g) . , y. 3 Page 10.6.49 f5I-m _ _ , . . _ . , , _ _ _. - ______. . _ _ _ _ . . _ _ _ . ______. ______- _ _ _ _ _ - ______ . Genetic Radiation Dam, ages. are caused by changes in the gern- . cells and will lead to mutations. A lower limit for the ) probability of mutations cannot be specified. In assessing this limit, however, it is necessary to take into consideration the natural radiation (cosmic and terrestrial radiation) to which human beings are exposed in any case, and which may be quite high in certain areas. The acceptable dose rate for handling radioactive sources has been specified in the Radiation Protection Regulations, so that the probability of somatic damages or additional changes of the genetic material is low. MEASURING SYSTEMS FOR DOSE RATE MEASUREMENTS The human body is not equipped for registering nuclear radiation. In order to detect this radiation it is therefore necessary to use suitable measuring instruments with appropriate detectors for the different types of radiation. The most common detectors are ionization chambers, counter tubes (Geiger-Muller counter tubes or halogen counter tubes respectively) and scintillation counters. IONIZATION CHAMBER Basically a gas-filled plate capacitor in which the radiation received triggers positive and negative charge particles (ions and electrons) which generate an electric current directly proportional to the dose rate. Since these currents are very small, it is necessary to amplify these currents substantially.- ! nA ionizing particle current meter l ||: | I Figure 10.6.9 Ionization Chaber | | Page 10.6.50 | __ - . . . . . _ . . COUNTER TUBES Counter tubes are built in such a way that the radiation received triggers a flow of electrons by means of ionization of the special filler gas (gas amplification effect). Thus, strong pulses are generated which can then be counted by simple means. The number of pulses per time unit is a measure for the dose rate. Although the temporal resolution capacity and the energy independence are not very high, l counter tubes are well suited for application in certain ranges of the photon energy and are also preferred because they are econom> priced (this is also true for the corresponding electronics). \ .h a - thin metal housing < .- b - counting wire C~ {'! . l h c - isolator c b' Y l' i. ----4: \ Figure 10.6.10 Counter Tibes ( Scintillation Counter , With this detector flashes of light are generated in a crystal by the radiation received; these flashes are registered at the photo cathode of a photo multiplier and transformed into electrical pulses. The temporal average of these pulses is formed and serves as a measure of the dose rate. Scintillation counters have a high detection efficiency for radiation, but the technical expenses are also quite high. a - scintillation crystal b f . " b - light-proof cover \ I c - radiation quantum * ,' 4 d d - flash of light 8 SU!' y . x y" e photo cathode , , - L, j , ,, ,, f - dynode system ,A i i Figure 10.S.11 Scintillation Cmmter Construction and arrangement of the detectors for nuclear ( radiati9n have to be suited for the detection of different types of radiation with their individual characteristics. Page 10.6.51 h Ep . Since the penetration capacity of alpha and beta-radiation is low, the radiation windows of the detectors have to be accordingly thin. With alpha and beta-radiation detector i evidence is produced directly by means of their ability to ionize the filler gas in the ionization chamber or the counter tube, or to stimulate a scintillator to emit light. With gamma-radiation evidence is produced by secondary electrons being directly released across the detector walls, or by stimulating a scintillator. Neutron-radiation, too, can only be detected indirectly. Fast neutrons are retarded down to thermal energy by means of so-called moderators (hydrogen cores as e.g. in water, paraffin or plastics) before being measured by detectors containing a strongly neutron-absorbing element, such as bt,ron or lithium. Person Dose Measurement In person dosimetry instruments have to be used which measure not only the intensity of a radiation field (dose rate), but also accumulate the resulting radiation dose while taking into consideration the duration of the reaction. The measuring results of these dosemeters have to be evaluated in more or less long intervals. I In film dosimetry the blackening of photographic emulsion is utilized to determine the radiation dose. Film dosemeters contain a film in a cartridge protected from the light; this cartridge has a number of metal filters. From the blackening generated behind the various filters the exposure dose and the " radiation grade" can be told. The special advantage of film dosemeters is their sturdiness as well as their small dimensions. Glass dosemeters contain a silver-activated phosphate glass enclosed in a capsule. Depending on the degree of radiation more or less strong fluorescent centers are generated which, upon evaluation, are stimulated by UV-light. The intensity of the fluorescent light is proportional to the dose received by the glass. Glass doseneters are sensitive to dirt and therefore have to be protected properly. Pocket dosemeters provide direct reading of the dose received. They consist of a small electrometer whose cross- wire is made visible on a scale through a magnifying glass. Pocket doseneters are charged by a brief connection to a voltage supply and discharged according to the radiation dose to which they are exposed. To prevent error caused by self-discharge, which cannot be avoided, we recommend a daily reading of the pocket dosemeters. Page 10.6.52 | _ _ _ . . . g Depending on the prevailing working conditions, the supervisory authority can specify the manner in which the body dose is to be determined: e by assessment or calculation o by measuring the local dose or local dose rate a by measuring the person dose. If the supervisory authority has not specified the manner in which the body dose is to be determined, the person dose has to be measured with doseneters which have to be obtained from the supervisory authority in each country. After evaluating the doseneters, the control office specifies the person dose rate and notifies the company which supplied these data in writing. I 1 Page 10.6.53 C{f!v - . . Table 10.6.1 j Measurement, Evaluation, and Features Measurement Evaluation Characteristic Features Translucency Evaluation only by Universally applicable; of film offical authority yields a lot of informa- and only in fixed tion when evaluated pro- intervals. perly. / Measuring value is Disadvantage: primarily used for Subject to many uncon- 5 - C subsequent dose trollable error influences; , balancing; useless limited measuring range; l- for immediate cannot be stored. i ' - measures since info is available to user only after a long time (weeks). Discharge of Read-out immediately Fast, accurate information. capacitory and at any time by Disadvantage: chamber the user. short measuring range; Automatic evaluation regular charging required c , g g systems with computer connection to the O data evaluation system are being - developed. Fluorescence Evaluation any time Ideal long-term dosemeter intensity in and, due to storage with high reproducibility, case of UV- of measuring values, due to storage of measuring stimulation as often as desired values. m by the user and the Disadvantage: $ / offical authority too inaccurate in the low e energy range (roentgen). - Attempts to improve the ;;; measuring sensitivity and ' ; ', the energy dependence are ||| 6200 A being made. __:.' ,', *[,' . Page 10.6.54 L . . The results of all measurements and calculations have to be I recorded and kept in file for 30 years, and have to be submitted to inspection by the supervisory authority on request. | Occupationally exposed persons in the category A must be ' examined by an authorized physician; occupationally exposed persons of category B only if they handle open radioactive substances. This examination has to be repeated once a year. Further employment in the control area is only permissible after a certificate of non-objection has been granted. Radiation Prot'ection Technique BASIC PRINCIPLES OF RADIATION PROTECTION To avoid damages to the human body with almost absolute certainty, an annual dose for the persons in the different categories has been fixed internationally. The aim of radiation protection is to adhere strictly to the specified permissible dose values and furthermore to avoid unnecessary radiation exposure as far as possible in order to keep the radiation dose for the personnel as low as ' possible. ' I The formula for calculation of the radiation dose shows what kind of radiation protections can be carried out. The radiation dose (D) depends on the activity (A) of the source, its specific gamma radiation constant (k), the distance (a) from the source, the radiation time (T), and the weakening factor (s) of an available shielding. AxkxT D = -- g------a xs The activity of a source and the corresponding specific gamma radiation constant are pre-determined by the measuring task. However, when designing a specific measuring system, one should try to keep the required source activity as low as possible by selecting particularly suitable detectors and electronic circuits. . t , Page 10.6.55 )iI, ...... ______- ______- _ _ _ _. __ . . . Based on the above formula, the following radiation protections measures, which illustrate some important basic j principles of radiation protection, can be obtained: e Increasing the Distance (a) to the radiation source, i.e. the distance between the source and the body. Since the : dose rate (just as the light) follows the square law, ' doubling the distance means reduction in radiation intensity to one quarter. This is the most efficient as well as the most reasonable method of radiation protection. Consequence: ; Always keep the largest distance possible when operating i in the proximity of radioactive substances, especially persons who are not immediately concerned with that operation. Since, on the other hand, even weak sources generate a substantial dose rate if the distance is short, test sources with low activities must not be touched by hand, but only with pliers or tweezers, if they are not equipped with an extension handle. e Shortening the Duration of Exposure (T) The time as a linear effect, i.e. doubling the period of exposure means ; twice the radiation dose. . Consequence: Operations close to the source should be well planned, so that the time of exposure in the immediate proximity of the source is kept as short as possible. e Use of Shielding with a high weakening factor (s) which has an exponential dependence on the product of thickness and density of the shielding material. Apart from a few exceptioons, radioactive substances applied in the - industry are already installed in a suitable shielding on delivery. Consequence: , The designed shielding effect is ensured only when the shielding functions peoperly and is handled adequately. With these measures it is possible to avoid, under normal i operating conditions, that the operating personnel is exposed to a dose which exceeds the limits specified by law. A careful approach, reducing the exposure times to a minimum and keeping a maximum possible distance from the source can , help, in practically all cases, to reduce the exposure to below the detection limit of a film doseneter. ' ; Page 10.6.56 ____ _- . _ _ _. _ . _ _ _ . . _ . ______. . _ . . _ _ _ _ . ; . . T RADIATION PROTECTION AREAS Barred Areas Areas with a dose rate higher than 3 mSv/h (300 aren/h) must be secured, so that nobody can enter them unchecked, not even with parts of the body. Access is only permitted under ; specific conditions and if there is an absolute need for it. ' The body dose has to be calculated and the person dose measured. NOTE: These areas are restricted to the active radiation bundle. If it in possible to reach into the area, the area must be guarded accordingly. Control Areas These are areas with dose rates of equivalent to or larger than 7.5 uSv (0.75 mres/h). Control areas must be marked off and provided with a radiation warning symbol and the addition " Control Area". Entry to the control areas is only allowed for persons carrying out specific operations. The body doses must be determined or the person dose measured. The authority concerned may grant exceptions if it can be proved that the whole body doses will not exceed 15 mSv/ year g (1.5 ren/ year). NOTE: DIN 54 115, sheet 1 point 5.3.6 stipulates that in small areas in which whole body radiation is practically impossible, the regulations for control | areas, such as marking off and identification, may be j dispensed with. 1 1 Monitoring Areas Plant Monitoring The plant monitoring area starts at the control area with a dose limit of 15 mSv per annum (1.5 ren/ year), if a person , stays in the area for 40 hours per week (which is equivalent to a dose rate of 7.5 uSv/h or 0.75 ares /h respectively), and reaches to a dose rate of 5 mSv per annum for a theoretical stay of 24 hours per day, i.e. 8760 per annum. * This will result in a dose rate of 0.57 uSv/h (57 uren/h). 4 Measures must be taken to ensure that persons will not be j exposed to a higher dose than 5 mSv per annum (0.5 ren/ year) considering the actual visits in this area. . t " R01-No. g 9 7 68 r. Page 10.6.57 Qi . O --. - - . , - - - , , , - . , - . -..,r--..__v------.--_---m%,%.,-,..-,---,,,.-w.-.-,,, c-----,-,.----.-----,,,.-,.e-.c,---..-e,-,.- ______._ -. _ _- . ; . . t External. Plant Monitoring , The external plant monitoring area follows the plant monitoring area and ranges to a dose limit of 0.3 mSv per ! annum (30 arem per annum). Measures must be taken to insure that persons in the external plant monitoring area will not . be exposed to a higher annual dose than 1.5 mSv (150 area). , GENERAL RULES OF BEHAVIOR Basically the Radiation Protection Regulations have to be followed, which stipulate that unnecessary exposure to radiation has to be avoided. Based on the field of application, the configuration of the measuring equipment, type and cover of the source used, as'well as construction and shielding, some rules of behavior can be obtained which ensure safe operation and maintenance of the equipment. When writing up service instructions, which should incorporate the necessary rules of behavior, the following situation should be taken into consideration: e Assembly and disassembly (the radiation path of the shielding must remain locked) - ' e Measures for opertions in the immediate proximity of the ' shielding ; e Ensure that the shutter of the shielding is locked in |. case the container has to be entered ! e Responsibility for the key to open and close the lock of - the operating shielding i 1 Seal Test i If a container in which radioactive substances have been ' installed or the cover of these substances are damaged or corroded, which would adversely affect the sealing of the container or the cover, it is necessary to check the sealing. This test is carried out by an office appointed by the supervisory authority. | For this purpose a wiping test is carried out and the sample is evaluated with highly sensitive measuring instruments. The supervisory authority can stipulate that these tests are to be repeated at fixed intervals. Certificates of these tests have to be filed and submitted to the authority on request. , i Page 10.6.58 - , . _- _ _ .__- - - - . . - - - _ - , - - _ - _ . _ - . - . - . - . - - . . . . Waste Disposal * ' 'l , Radioacive waste has to be disposed of properly, i.e. it has i to be deposited at a collection site for nuclear waste specified by each country. | This obligation must not be circumvented, e.g. by diluting or ! reducing the concentration of radioactive substances, so ' that the radiation falls below the permissible limits, and the regulations would therefore no longer apply. | If the sealed radioactive substances are no longer tight, the supervisory authority has to be notified immediately and measures have to be taken to make sure that the contamination cannot be dispersed. Proper handling and disposal of possibly leaking sources or contaminated parts of the equipment have to be coordinated with the supervisory | authority. NOTE: Radioactive substances which are no longer used are not necessarily radioactive waste. These substances must be properly disposed of as well, e.g. by depositing them at the governmental collection site or by returning them to the manufacturer. In the latter case the manufacturer will fill out a certificate acknowledging the receipt, which will :( also serve as proof to the supervisory authority that the substances have been disposed of properly. Pecking and Transportation Transportation of radioactive substances on public traffic i routes is only permitted if approval has been granted by the ! supervisory authority. The transportation approval stipultes that delivery can only be affected if the following points have been considered: o Packing type A Marking of package . e i e Marking of the shipping documents e Observe maximum permissible activity According to the regulations for transportation of dangerous , commodities the following declarations, depending on type and quantity, are possible: ; | * if - | Page 10.6.59 Df};g [ . .-- - - . . - - _ _ ._ ' . . Radioactive Substances in Transportation and Operation Shieldings ) Delivery of radioactive substances is almost always carried out in packings of the type A. The transportation shielding can also be part of this packing. Construction and stability of the packing have to meet certain requirements (according to Rn 3600 ff), in order to guarantee that under normal transportation conditions leakage or dispersal of the radioactive content and thus an increase of the dose rate is not possible. These requirements are: e Supporting device with weights between 10 - 50 kg e Seal as protection against unauthorized opening i e Solidity according to Rn 1635, viz i Water test: I hour water quantity equals a j precipitation of 5 cm per hour Free fall test: on surface from a height of I 1.2 m on edges from a height of 0.3 m with pieces 50 kg Pressure test: 24 hours 5 times the weight of , the delivered package Puncture test: Rod 3.2 mm diameter with semi- spherical ends with a weight of 6 kg from a fall height of 1 m | Each piece to be delivered must be marked as follows: e weight when gross weight is above 50 kg e tag type A - packing i e danger tag according to Rn 1652 on the sides of the piece ' to be delivered: . : i I Page 10.6.60 , , _ , _ _ . _ _ , _ _ _ . . _ . - - , _ . , . . _ _ _ _ , _ _ _ . , - _ _ _ , - . _ . _ _ . - , , . _ . . _ _ . _ , _ _ . , _ _ _ , . ,- . _ _ _ _ - , _ _ . _ . - - . . . . . , . , _ _ , . , . . I - WHITE. with max. 0.5 arem/h on the outside of the I. packing or II - YELLOW with a maximum of 50 aren/h on the outside and a maximum of 1 aren/h in a distance of 1 : a from the surface of the packing (i.e. transportation identification number max. 1.0) l or III - YELLOW with a maximum of 200 aren/h on the outside and a maximum of 10 aren/h in a distance of 1 m from the surface'of the packing (i.e. transportation identification number max. 10.0) Specifications on the danger tag: Content: The nuclide, e.g. Co-60 or, with a mixed content, the nuclide which would be most dangerous in case of damage t Activity: The total activity is generally specified in Ci or millicurie, if the prefix is written out. With containers the sum of the transportation identification numbers has to be specified and the danger tags have to be attached to 4 pages. The dose rate of 10 aren/h must not be exceeded in a distance of 2 m from the outer surface. The maximum dose rate at the surface of the container is 200 mres/h, but the dose rate of the individual packages in the container must not exceed a maximum of 100 aren/h. The shipping documents (e.g. bill of lading) must include the following s pecifications: - e Radioactive substances (in packages of type A), 7, sheet 8, ...+) , ...+) GGVE for national delivery on road and railway RID for international railway transportation ++ ADR for international truck transportation ! Page 10.6.61 ff 1 __ - . . , | e Condition of the commodity and the packing according to the regulations of the ...+) j e Nuclide: (e.g. Co-60) e Physical and chemical condition: e.g. firm, as Co-60 wire or firm, as Cs-135 silicate ' e Activity: (in Curie) e Category: (I-WHITE, II-YELLOW, or III-YELLOW) e Transportation identification number: (only for II or III YELLOW) e No additional measures have to be taken for loading (The transportation identification number is the dose rate in ures/h measured in a distance of 1 a from the surface of the packing. The value has to be rounded off to the 1. decimal.) ++) For international shipment a) has to be marked red. The activity per package must not. exceed the values Al or A2 according to Rn 3690. Al - Substances in special forms A2 - Substances in other forms Al A2 ------|------3--f-3------: : An-241 : 8 | - Cf-249 | 2 | - Co-60 : 7 : - Cs-137 : 30 : 20 Cr-90 10 0.4 Radioactive Substances in Electronic Instruments e The packing must be according to A1. e The package has to be marked with the tern RADIOACTIVE. | . Page 10.6.62 , _ __ .._ _. _ _ - . ._. . _ _ [ , |. . e The shipping documents have to include the following ( specifications: Radioactive substances (instruments), 7, sheet 4 ! ...+) ! I e The dose rate at the surface of the packing must not exceed 0.5 mrea/h and the activity per unit must not be higher than E-2-times the Al or A2-values according to Rn 3690. That is, e.g.: : E-2 Al' : E-2 A2 ! | ______|______ An-241 : 80 sci ! - Sr-90 : 100 sci : 4 aci Cs-137 : 300 sci 200 aci Co-60 : 70 sci : 70 sci | Radioactive Substances in Small Quantities | e The packing must be according to A1. e The package has to be marked with the tern RADIOACTIVE. e The shipping documents have to include the following ( specifications: Radioactive substances (small quantities, 7, sheet 3, ...+) (marked red) e The dose rate at the surface of the packing must not exceed 0.5 arem/h and activity must not be higher than E- 3-times the Al or A2-values according to Rn 3690. | That is, e.g. E-3 Al E-3 A2 : : : : An-241 : 8 mci : - Sr-90 : 10 sci : 0.4 aci Cs-137 : 30 sci : 20 sci Co-60 | 7 mci 7 mci Empty Packings for Radioactive Substances e No indications concerning radioactivity should be visible on the packing e The shipping documents have to include the following specifications: Radioactive substances (empty packing, 7, sheet 1 ...+) ! Page 10.6.63 gg. w _ _ _ _ . - . _ _ _ . - ___..._ _ _ .___., . . _ _ _ -. _ - ______o - Radiation Protection Safety . Safety Measures When designing the application of radiometric measuring systems, constructional measures have to be included, if necessary, which ensure preventive measures against fire. No easily inflammable substances should be stored in the proximity of radioactive substances, or they should be . covered and protected properly, so that a possible spreading of the fire to the radioactive substances can be prevented. It is mandatory to coordinate all preventive measures against fire with the local authorities, primarily with the , fire department, which must be informed about type, scope and place of application of the radioactive substances used, in order to be prepared in case of fire. When designing alarm plans possible special features of the radiometric measuring system have to be mentioned; the radiation safety officer to be notified in case of emergency has to be included in those plans as well, and also the address and phone number of the supervisory authority. , Malfunctions and Accidents The Radiation Protection Regulations define malfunction as an event which for safety reasons prohibits continuation of 1 the operation of the facility. Malfunctioning means, that a device necessary to guarantee safe operation of the facility, e.g. the seal of the active radiation bundle of the shielding, no longer functions properly. An accident is an event during which persons could be exposed to a radiation dose which exceeds the permissible limits, or during which even contaminations and incorporations of radioactive substances could occur. In terms of safety, malfunctioning and accidents are very serious events and appropriate steps should be taken immediately, in order to prevent dangers for persons as well as for facilities, or to reduce them as much as possible. It is therefore important that the personnel are aware of preventive measures and are prepared for possible malfunctions of the facilities or accidents, so that dangerous consequences can be avoided as for as possible by a proper reaction of the personnel. . s Page 10.6.64 e _ . . - o In any case, the radiation safety officer, who checks the ( situation at site and takes all necessary steps to prevent unnecessary radiation exposure of the personnel, has to be notified immediately. The radiation safety officer will inform the official authority concerned, and, if necessary, get further information from the manufacturer. The necessary steps should be taken in the following order: e Locate the source e Measure the dose rate e Guard and mark the control area e Secure the source and shielding e Check the function and efficiency of the shielding e Record the event and assess possible radiation exposure of the personnel concerned In case the source capsule is damaged, the following points have to be considered ( e Avoid contamination e Handle source with tools (e.g. tweezers) and put both in a plastic bag e Stay behind an auxiliary shielding (e.g. concrete, steel, or lead plate) e Check if vicinity is free of contamination e Secure the radioactive waste properly (deposit at governmental collection site or return to manufacturer) In case the source is leaking and the dose rate might possibly be exceeded, the supervicory authority has to be notified immediately. In case of an accident or malfunctioning or any other event which is importent in terms of safety, the supervisory authority has to be informed and also, if necessary, the authority in charge of public safety. These considerations should be an integral part of the mandatory regular instructions. UNOL No, y 0 '66 /p Page 10.6.65 h,[ fj i w / _ __ - _. . . _. . o - Protection Against Theft Radioactive substances or facilities containing radioactive substances have to be secured against unauthorized use. Firmly installed facilities containing radioactive substances are ordinarily protected against unauthorized use by the fact that these installations are fixed. Portable sensuring systems, on the other hand, have to be protected by keeping them under constant supervision, or, if they are not in operation, by keeping them locked in a room or a container which can be guarded against unauthorized use. This is especially true for test sources of low activities which are used, e.g., to check the function of dose rate measuring instruments. In case radioactive substances are missing, the radiation safety supervisor and the supervisory authority have to be notified immediately. In case of theft the police have to be informed as well. , , Page 10.6.66 | t __ _ | | - . - . . . . . . ; OVERSIZE ~ . DOCUMENT : PAGE PULLED - SEE APERTURE ! CARDS NUMBER OF PAGES: ACCESSION NUMBER (S): ' BGoVaFos6o S w o'/c V6 s%7 , 9&O 9'W/0M / i _ , __- ' ' | | APERTURE CARD /HARD COPY AVAILABLE FROM RECORD SERVICES BRANCH,TIDC FTS 492 = 3959 ) ._ . _ _ . _ _ . . _ _ . . - - _ _ _ _ . _ . - _ ._ __. _ _ . _ .._.D