OVER TWENTY YEARS OF EXPERIENCE IN I.T.U. TRIGA MARK-II REACTOR
Hasbi YAVUZ
Istanbul Technical University – Institute For Nuclear Energy Ayazağa Kampusu 80626, Maslak, ISTANBUL – TURKEY
I.T.U. TRIGA MARK-II Training and Research Reactor, rated at 250 KW steady-state and 1200 MW pulsing power is the only research and training reactor owned and operated by a university in Turkey. Reactor has been operating since March 11, 1979; therefore the reactor has been operating successfully for more than twenty years. Over the twenty years of operation: • The tangential beam tube is equipped with a neutron radiography facility, which consists of a divergent collimator and exposure room. • A computerized data acquisition system was designed and installed such that all parameters of the reactor, which are observed from the consol, could be monitored both in normal and pulse operations. • An electrical power calibration system is built for the thermal power calibration of the reactor. • Publications related with I.T.U. TRIGA MARK-II Training and Research Reactor are listed in Appendix. • Two majors undesired shutdown occurred. • The I.T.U. TRIGA MARK-II Training and Research Reactor is still in operation at the moment.
OVER TWENTY YEARS OF EXPERIENCE IN ITU TRIGA MARK-II REACTOR
Hasbi YAVUZ
Istanbul Technical University- Institute for Nuclear Energy Ayazağa Kampüsü 80626, Maslak, ISTANBUL-TURKEY
ABSTRACT
ITU TRIGA Mark-II Training and Research Reactor, rated at 250 kW steady-state and 1200 MW pulsing power is the only research and training reactor owned and operated by a university in Turkey. Reactor has been operating successfully since March 11, 1979.
Over the twenty years of operation:
• The tangential beam tube has been equipped with an neutron radiography facility, which consists of a divergent collimator and exposure room. • Two major undesired shutdowns occurred. • A computerized data acquisition system has been designed and installed such that all parameters of the reactor are observed from the computerized data acquisition system, can be monitored both in normal and pulse operations. • An electrical power calibration system has been built for the thermal power calibration of the reactor. • Studies related with ITU TRIGA Mark-II Training and Research Reactor have been published.
INRODUCTION
The first research reactor of Turkey was the TR-I reactor at Cekmece Nuclear Research and Training Center ( CNRTC-in Istanbul) became critical on May 1962. This swimming pool type reactor operated until May 1977 at a steady-state power level of 1 MW. It provided research, training and irradiation service for a variety of applications. Nuclear medicine groups used more than 90 percent of radioisotopes in hospitals. The second research reactor of Turkey is the TRIGA Mark-II Training and Research Reactor which is owned and operated by the Istanbul Technical University (ITU) Institute for Nuclear Energy. Reactor construction period was from May 1977 to March 1979. Institute for Nuclear Energy is a state institution and has been providing nuclear energy educational, training and research programs at graduate level since 1961.
Among various TRIGA reactor types, ITU TRIGA Mark-II Research and Training Reactor at the Institute for Nuclear Energy, was the first Mark-II with stainless steel clad fuel rods which has a steady state power of 250 kW and a peak power of 1200 MW in pulsing operation. However, the rotary multiple-position specimen rack (Lazy-Susan) has not been purchased by the Institute.
Fig.1 shows the vertical view of the reactor. Cutaway view of the reactor is given in Fig.2.
NEUTRON RADIOGRAPHY FACILITY
The tangential beam tube is equipped with a neutron radiography facility that consists of a divergent collimator and an exposure room. A collimator is placed into the tangential beam tube, which is filled with air. An exposure room is located at the outer face of the collimator next to the reactor shield. The exposure room is sized to accommodate a movable carriage table for the objects, converters, films, and a beam catcher.
An electrically driven concrete rolling door has been designed to provide sufficient area for loading and unloading. It can be rolled away on the rails to a distance of about 3 meters from the exposure room. The wall blocks and the top block of the exposure room are made of heavy concrete. A water tank is placed top of the concrete ceiling block. By moving the objects away from the beam tube along the longitudinal axis of the collimator, it is possible to enlarge the irradiation area compared to the exit cross-section area of the collimator and thus, to vary the neutron flux on the objects Fig.3, [2].
The thermal and total neutron fluxes and gamma exposure rates have been measured inside and exit of the neutron flux beam collimator, and its surroundings. The ratio of neutron fluxes to gamma exposure rate at maximum power has been reported. The results have been compared to those measured in the absence of the collimator. The neutron fluxes have been determined by using the foil activation method with gold foils enclosed in cadmium capsules. The gamma exposure rates have been measured by using LiF7 (TLD700) Thermoluminescent Dosimeters [3].
THE UNDESIRED SHUTDOWNS
During the twenty-years operations two major undesired shutdowns occurred.
A. Bacterially Infected Tank Water and the Reactor Purification System The reactor was operated at power of 250 kW in July1994. Although the dose rate over the reactor tank should be normally 10-15 mR/h for operating at this power level, it was measured as 150 mR/h. The reactor was shutdown immediately. The existence of any fission products was searched.
According to the results of the analysis made by the use of a multi-channel analyzer, there was no any fission product in the tank water. Because of the failure of conductivity meter at the makeup water purification system, high-conductivity water was added mistakenly into the tank water.
For this reason, the conductivity of the tank water rose to 12.5 µS/cm and the tank water became turbid. Bacteriological analysis showed that the tank water infested with bacteria. A suitable method for the sterilization of the tank water by means of the irradiation and the chemical materials was searched. Hydrogen- Peroxide (H2O2) has been chosen as the most suitable material for the chemical sterilization.
The makeup water purification was modified permanently for this purpose. As a result, conductivity of the tank water was decreased to 0.2 µS/cm by using this modified system. We have gaind some experience about the purification and protection of the tank water from the bacteria during these operations [4].
B. Failures of the Scream Circuits
On 23 March 1999, Reactor gave scram and shut down. Then, unfortunately, people with no electronic experience tried to fix up scream circuits. After the experts in electronic field attacked to resolve scram circuit failures, many of the failures in the scram circuits were found.
All failures written in the reports and the others have been removed from the reactor. Reactor has been operated on February 9, 2000. This reactor failure caused the longest shut down period in twenty-year operation.
COMPUTERIZATION OF ITU TRIGA MARK-II CONSOLE
In 1993, a computerized data acquisition system was installed to the TRIGA Mark-II research reactor. The system was designed such that various parameters of the reactor could be monitored in both pulse and normal operation modes.
The time variations of all quantities on reactor console (such as percent powers, logarithmic and linear powers, fuel and tank water temperatures, period, positions of control rods, pulse power and pulse energy ) can be monitored and data relating to them can also be acquired by this new system.
Furthermore, some additional devices used for the power calibration of the reactor, such as resistance thermometers (RTD), grid voltage and current measurement devices are also included in this system. The block diagram of the data acquisition system is given in Fig.4. On the reactor console, the analog driver cards for various quantities produce output signal in the range of 0-10 V.
These output signals are routed to the meters as well as to several ports to which external devices can be connected. In a built new system, the analog signals from these ports were supplied to a high-level voltage panel (Analog Devices, STB-HL02). STB-HL02 has the sample-and-hold circuitry and produces 0-5 V output signals for 0-10 V input signals for up to 16 channels.
The output of STB-HL02 has been fed to an analog-to-digital (A/D) converter/multiplexes card (Analog Devices, RTI-820). The digital output of RTI-820 card represents an analog input of 0-5 V by 12-bit data, corresponding to numbers between 0 and 4096. RTI-820 was placed in a PC.
A computer program has been written in C-language to drive the hardware described above. The program enables the operator to monitor the signals coming from various channels in real time as well as to record data on the fixed disk.
Consequently, by virtue of this data acquisition system, it has been possible to monitor and record accurately all the reactor parameters during a long operation. One immediate outcome of this capability was the recalibration of the reactor power within 7% uncertainty, which could not be attained before.
Furthermore, this new system has some improvements in reducing the error during an irradiation experiment. In a short irradiation, the extraneous irradiation during the power-up of the reactor can now be calculated accurately and consequent corrections can be made in the irradiation data [5].
POWER CALIBRATION OF REACTOR BY DATA ACQUISITION SYSTEM
Before using the new data acquisition system, total heat capacity at constant pressure of other similar reactor was used for the power calibration of ITU TRIGA Mark-II reactor. This new system allows us to measure the total heat capacity at constant pressure of ITU TRIGA Mark- II reactor within the ±5 % uncertainty.
To measure the total heat capacity at constant pressure, eight electrical heaters each having 5 kW are used. These heaters have been designed in the geometrical norms of fuel elements. During the experiment, eight fuel elements have been withdrawn from the core and placed to the rack in the tank. Then, the heaters have been placed into these empty fuel channels. At the same time, eight resistive thermometers (RTD’s) have been located to different depth from the tank surface.
Moreover, a pipe having lots of holes on its surface has been placed to central thimble. Tank water has been pumped the perforated pipe from the tank surface through. Hence, tank water has been well stirred to supply the homogenization of tank water temperature during the experiment. The grid voltage and current consumed by electrical heater have been measured and recorded by data acquisition system.
By using, acquired data has been used to calculate the original total heat capacity at constant pressure has been found as 69.81 MJ/oC ±5 % . The power calibration has been made by using this constant, resistive thermometers and water stirrer. It is achieved to ±7 % uncertainty for power calibration, which could not be attained before. The uncertainty of ±2 % comes from the temperature measurement during the power calibration [6].
RESEARCH ACTIVITES
If the research activities have been reviewed, the ITU TRIGA Mark-II serves many researchers who not only from our Institute and our University (ITU) but also other institutions. Some of the papers have been published in the Science Citation Index. Fig.5 shows the researchers graphically. Researchers are from eleven different universities, two different divisions of a ministry, Research Centers of Turkish Atomic Energy Authority. All the academic staffs of ITU Institute for Nuclear Energy have publications related with ITU TRIGA Mark-II Reactor. Main publisher group is from the varies faculties and institutes of ITU.
Except for the papers covered by the Science Citation Index, many papers, Ph.D. and M.Sc. thesis and a number of B.Sc. thesis related with ITU TRIGA Mark-II Reactor have been written. Fig.6 shows the distribution of the publications.
CONCLUSION
The TRIGA Mark-II reactor has been used for education, training and research for over the twenty-one years. All demands came from researchers and all educational activities to use reactor have been met in accordance with the regulations. There has not been any demand so far for using Lazy Susan.
Over 20 years, the ITU TRIGA Mark-II Reactor has been operated and maintained by the academic staff of the Institute for Nuclear Energy besides their academic activities. The reactor has been operated for all researchers. ITU TRIGA Mark-II Reactor is the only reactor in Turkey, which is operated continuously over twenty years.
The pneumatic transfer system terminal ends in a closed metal box with a window and it is equipped with ventilation exhaust system is provided to prevent the uptake of Ar-41 by the operator.
The cooling insufficiency problem appeared in summer time is related to the Istanbul’s climate and not a particular problem of the ITU TRIGA Mark-II Reactor . A similar problem has been experienced in TR-2 Reactor in CNRTC. Important changes need to be done in design in order to overcome these problems. Taking all demands came from researchers regarding reactor operation into consideration, it can be concluded that such a change is not needed.
REFERENCES
[1] Safety Analysis Report for the TRIGA Mark-II Reactor, for the Institute for Nuclear Energy of Istanbul Technical University, August 1978. Turkey
[2] Yavuz, H., Durmayaz, A., Sarı, E., “The Neutron Radiography Facility Designed for ITU TRIGA Mark-II Reactor”. Eleventh European TRIGA Users Conference, September 11-13, 1990. Heidelberg, W. Germany.
[3] Yavuz, H., Durmayaz, A., “Post-Installation Evaluation of the Neutron Radiography Facility of ITU TRIGA Mark-II Reactor”. Twelfth European TRIGA Users Conference, September 28-October 1, 1992. Pitesti, Romania.
[4] Büke, T., Şişman, A., Durmayaz, A., Yavuz, H., “An Experience on the Purification of Bacterially Infested ITU TRIGA MARK-II Reactor ”, Fourteenth European TRIGA Users Conference, September 22-25, 1996. Mainz, Germany.
[5] Yavuz, H., et. al., “Computerization of ITU TRIGA Mark-II Console”. Twelfth Eleventh European TRIGA Users Conference, September 28-October 1, 1992. Pitesti, Romania.
[6] Yavuz, H., et. al., “Applied Research and Development Project at ITU MARK-II Reactor”, ITU Research Fund Project No: 280, September, 1993.
Fig. 1 Vertical view of I.T.U. TRIGA Mark II Reactor
Fig.2 Cutaway view of I.T.U. TRIGA Mark II Reactor
reactor MARK-II TRIGA ITU the of Facility Radiography Neutron Fig.3
of the data acquisition system Diagram Block Fig.4
60.00
40.00
(%) Researchers 20.00
0.00
ITU Other Univ. TAEA Ministries
Fig.5 Researchers profile
60.00
40.00
Publications(%) 20.00
0.00
Articles Papers Ph.D. M.Sc. Reports Fig.6 Distribution of the publications