Emergency Diesel Generator Diesel Generators as Emergency Power Sources

1. DIESEL GENERATORS AS 3. Why diesel engines are used as the EMERGENCY POWER SOURCES prime movers for emergency power generators instead of alternative Learning Objectives engine designs.

The predominant means of supplying 4. An overview of the regulations, codes, onsite emergency (standby) electrical guides, and standards that establish power for nuclear power plants is the use of the design basis for these emergency emergency diesel generators (EDG's). power systems. Therefore, diesel generator sets are the specific focus of this NRC training course. 5. How the above documents are Upon completing this lesson students will translated into the licensee's understand the fundamental criteria used in application and design for a nuclear selection of emergency diesel generators . for onsite electric power supplies at nuclear power plants (NPP's). That will include an 6. The major components of a diesel overview of the primary applicable federal generator system, as well as some regulations, regulatory guides, codes, and considerations involving site facilities industry standards. that support EDG operation.

In addition, this lesson will conclude with a NOTE: Many participants in this course will summary overview of the EDG and its already be very familiar with the regulatory associated systems and components, as criteria applicable to EDG's. However, the well as remarks on how they interface with NRC requires such documentation to be site facilities. For the EDG to be capable of part of the course because some attendees performing its design basis function, all of may be relatively new on the job. Even its on-skid and off-skid support systems those with considerable experience may and components must also meet their own benefit from a brief review of the underlying design basis functional requirements. documentation. This Chapter provides an overview of the fundamental requirements The primary objective of this lesson is to relevant to EDG's in nuclear service. For set the stage for later Chapters by giving both new and experienced staff it can serve students a fundamental understanding of: as a convenient reference.

1. The basic regulatory requirements 1.1 Regulatory Basis for Redundant, establishing the need for redundant Independent Power Systems power systems (onsite and offsite) for operating nuclear power plants. Federal regulations applicable to nuclear power plants, and hence onsite emergency 2. Three fundamental performance power supplies, originate in Title 10, Part requirements that emergency diesel 50 of the Code of Federal Regulations (10 generators (EDG's) must meet. CFR 50). This document is the successor

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to the Atomic Energy Commission (AEC) one "postulated" accident but regulations General Design Criteria of 10 July 1967, to require much more complex scenarios to which many early Nuclear Power Plants, be considered in selecting EDG systems. meaning those starting construction prior to 1972, were licensed. Supporting regulatory Independence is the absence of shared guides, codes, and industry standards used components that could result in the to implement these federal regulations are simultaneous failure of both units. That briefly described in this Chapter. includes physical and electrical separation, such that a transformer or cable tray fire, One of the most important nuclear power for example, would not impact operation of plant safety requirements is for redundant, the other emergency diesel generator. and independent, power systems. This is contained in 10 CFR 50 Appendix A, Redundancy is required to achieve the General Design Criterion (GDC) 17, which desired operational reliability, and also to specifically requires both off-site and onsite accommodate "down time" for testing and power systems "to permit functioning of maintenance. This means a dual EDG structures, systems, and components installation, where the required power is important to safety." available with either unit out of service.

GDC 17 further states that onsite electric Testability is somewhat self-explanatory. power supplies, including the distribution EDG testing is discussed in a later Chapter. system, shall have sufficient independence, redundancy, and testability to perform their 1.2 Regulatory Guide (RG) 1.9 sets the safety functions assuming a single failure. Three Fundamental Performance This requires emergency power systems to Requirements for EDG's be designed such that failure of one will not adversely impact the other (more about that Regulatory Guide 1.9, Rev 4 (March 2007) later). Each electric power source must be is "Application and Testing of Safety- capable of providing the capacity and Related Diesel Generators in Nuclear capability to assure that: Power Plants" (new title for this edition) and evolved from AEC Safety Guide 9. A copy 1. "Fuel design limits and design conditions of RG 1.9, Rev 4 is included in this Manual of the reactor coolant pressure boundary as Appendix 2. It establishes the three are not exceeded" for any anticipated fundamental performance requirements every occurrences, and EDG must meet to perform its design function. They are as follows: 2. The "core is cooled and containment integrity and other vital functions are 1. The unit must be able to "...start and maintained in the event of postulated accelerate a number of large motor accidents." loads in rapid succession while main- taining voltage and frequency within A Loss of Offsite Power (LOOP) event is acceptable limits...."

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2. The unit must also be able to "...provide power source to be “ready to accept loads” power promptly to engineered safety following loss of offsite power. So, two features if a loss of offsite power and an fundamental questions asked in the accident occur during the same time selection of the emergency onsite power period...." source are:

3. The unit must "...supply power 1. Based on the plant-specific accident continuously to the equipment needed analysis, how fast must electrical power to maintain the plant in a safe be restored to support Emergency Core condition...." Cooling System (ECCS) operation to prevent core damage (i.e., to keep from A later chapter will cover the challenge of exceeding peak fuel clad temperature)? complying with the first of these three Stated another way, how soon must the performance requirements (EDG loading). emergency electrical source be running Item (2) immediately above introduces the with breaker closed, ready to accept the requirement to cope with two events required step loads? By analysis, many (failures / accidents) that occur either of the reactor designs required power to simultaneously or with one following the be available within 15 to 30 seconds other. Finally, please note Item (3) has no after receiving a start signal. Although endurance time. "Continuously" is open- this time included the inherent delay for ended and effectively means "until normal protective circuits to sense the loss of power is restored" (however long it takes). power and initiate a start signal to the emergency power source, the bulk of it 1.3 Why DIESEL Generators? represented the start-up time necessary to spin up the generator, energize its There is no requirement that emergency field, and get it switched on line. diesel generators must be used for onsite electric power supplies at nuclear power To assure an acceptable margin of safety, plants. Hence, a natural question could be, the accident analysis for many reactor why have diesel generators been selected designs assumed emergency generator as the predominant means of supplying this power would be available within 10 power? Some other potential sources that seconds. NOTE: In some plants where could have been selected are: nuclear fuel upgrades have been implemented and new core damage • Gas Engine Generators accident analysis calculations performed, • Generators they have frequently supported a • Steam Turbine generators corresponding increase in the delay time • Hydro Generators for emergency generator availability. However, it was not unusual to have the The answer to “why diesel generators” can containment integrity support systems (e.g. usually be found by looking at the time Containment Spray System) become the requirement set for the onsite emergency new limiting consideration.

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2. Once the accident analysis has set the Criterion 38: Reliability and Testability time limitations on restoration of power of Engineered Safety Features. All to vital safety equipment, the only engineered safety features shall be remaining question is what power designed to provide high functional supplies are readily available that could reliability and ready testability. In reliably supply the needed power within determining the suitability of a facility for those time limitations? proposed site, the degree of reliance upon the acceptance of the inherent and With the exception of large gas engines, engineered safety afforded by the system, which have other onsite energy availability including the engineered safety features, and safety concerns, none of the sources will be influenced by the known and the listed above could reliably match the demonstrated performance capability and required response time and output power reliability of the systems, and by the extent as well as diesel generators could. To use to which the operability of such systems a football analogy, they have the muscle to can be tested and inspected where do the job and the speed to get there in appropriate during the life of the plant. time. Furthermore, diesel generators were readily available and their proven reliability Criterion 39: Emergency Power for had already gained them acceptance as Engineered Safety Features. Alternate emergency power supplies under the Naval power systems shall be provided and Reactors program. designed with adequate independency (independence), redundancy, capacity, and Therefore, although other factors such as testability to permit the functioning required site location and engine type familiarity had of the engineered safety features. As a some influence, the answers to the two minimum, the onsite power system and the questions above ultimately decided the offsite power system shall each, question of what type of generators to use independently, provide this capacity for NPP applications. Fundamentally, the assuming a failure of a single active decision became “what diesel generators component in each power system. will best fill our emergency power needs?" Criterion 48: Testing of Operational 1.4 An Overview of EDG Regulations, Sequence of Emergency Core Cooling Guides, Codes, and Standards Systems. A capability shall be provided to test under conditions as close to design as 1.4.1 Early Plants Licensed under AEC practical the full operational sequence that General Design Criteria (i.e., those would bring the emergency core cooling starting construction before 1972) systems into action, including the transfer to alternate power sources. The primary design criteria applicable from early AEC regulatory requirements...those Even the casual reader will note the close still being the GDC of record at many older similarity between Criterions 38, 39, 48 and nuclear power plants…are as follows: parts of 10 CFR 50 Appendix A, GDC 17.

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The AEC had other GDC's which formed to test periodically (1) the operability and the basis for those currently appearing in functional performance of the components 10 CFR 50 Appendix A. Likewise, AEC of the systems, such as onsite power Safety Guides that were used to interpret sources, relays, switches, and buses, and and implement those early design criteria (2) the operability of the systems as a became the foundation for current NRC whole and, under conditions as close to Regulatory Guides. Some early NPP's design as practical, the full operation have voluntarily adopted portions of current sequence that brings the systems into requirements applicable to EDG's, such as operation, including operation of applicable IEEE 387 (discussed later). Therefore, no portions of the protection system, and the further time will be spent on early criteria. transfer of power among the nuclear power unit, the offsite power system, and the 1.4.2 Plants Licensed by NRC using the onsite power system. GDC of 10 CFR 50 Appendix A (construction began 1972 or later) Criterion 33, 34, 35, 38, 41, and 44: Establish the criteria for specific safety As explained in Section 1.1, the 10 CFR 50 systems to be able to perform their required Appendix A General Design Criteria are functions even assuming a Loss of Offsite the successor documents to AEC GDC's. Power (LOOP) and a single failure of a Those listed below provide primary design source of onsite power (e.g. one EDG Train criteria for EDG's. Some others that have or Division). relevant secondary criteria such as for the physical plant design will not be described 1.4.3 "Top Level" NRC Regulations that (e.g., GDC 2, 4, 5, and 50). Pertain to NPP Licensing, Construction, Commissioning, and Operation: Criterion 17: "Electrical Power Systems" To recap the previous discussions on page • 10 CFR 50.10 − License required. 1-2, GDC 17 states the fundamental safety mission for on-site (and off-site) electrical • 10 CFR 50.23 − Construction permits. systems, as well as the key attributes of A permit for the construction of a independence, redundancy, and testability. production or utilization facility will be issued prior to the issuance of a license Criterion 18: "Inspection and Testing of if the application is otherwise Electrical Power Systems" Electric acceptable, and will be converted upon power systems important to safety shall be due completion of the facility and designed to permit appropriate periodic Commission action into a license as inspection and testing of important areas provided in 50.56 of this part. and features, such as wiring, insulation, connections, and switchboards, to assess • 10 CFR 50.34 – Details the contents of the continuity of the systems and the applications; technical information. For condition of their components. The purposes of this course, the following systems shall be designed with a capability excerpts from this document are of

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particular significance to EDG selection: • 10 CFR 50.36 – This document covers technical specifications intended to "(a) Preliminary safety analysis report. define safety system limiting conditions Each application for a construction for operation that may prevent design permit shall include a preliminary safety and license safety function. More about analysis report. …(3) The preliminary this topic appears later in the Chapter, design of the facility including: under Regulatory Guides 1.93, 1.156. (i) The principal design criteria for the facility. Appendix A, General Design • 10 CFR 50.54 − Conditions of licenses. Criteria for Nuclear Power Plants, establishes minimum requirements for • 10 CFR 50.55a − Codes and standards. the principal design criteria for water- "Each operating license for a boiling or cooled nuclear power plants similar in pressurized water-cooled nuclear power design and location to plants for which facility is subject to the conditions in construction permits have previously paragraphs (f)* and (g)* of this section been issued by the Commission and and each construction permit for a provides guidance to applicants for utilization facility is subject to the construction permits in establishing following conditions in addition to those principal design criteria for other types specified in §50.55: of nuclear power units; "(a)(1) Structures, systems, and (ii) The design bases and the relation of components must be designed, the design bases to the principal design fabricated, erected, constructed, tested, criteria; and inspected to quality standards (iii) Information relative to materials of commensurate with the importance of construction, general arrangement, and the safety function to be performed…." approximate dimensions, sufficient to

provide reasonable assurance that the final design will conform to the design * NOTE: Items (f) and (g) above refer to bases with adequate margin for In-service inspection requirements. safety..." • 10 CFR 50.56 − Conversion of "(b) Final safety analysis report. Each construction permit to license; or application for a license to operate a amendment of license. Upon facility shall include a final safety completion of the construction or analysis report. The final safety analysis alteration of a facility, in compliance with report shall include information that the terms and conditions of the describes the facility, presents the construction permit and subject to any design bases and the limits on its necessary testing of the facility for operation, and presents a safety health or safety purposes, the analysis of the structures, systems, and Commission will, in the absence of good components and of the facility as a cause shown to the contrary issue a whole…" license of the class for which the

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construction permit was issued or an • Regulatory Guide 1.6 – "Independence appropriate amendment of the license, Between Redundant Standby (Onsite) as the case may be. Power Sources and Between Their Distribution Systems," (Formerly Safety • 10 CFR 50.57 − Issuance of operating Guide 6). Each power supply (e.g. license. EDG) shall have the "...capability of performing as a redundant unit of a • 10 CFR 50.63 − Loss of All Alternating standby power supply." Therefore, Current Power (Station Blackout). This mechanically and electrically, the is an additional source of functional Emergency Diesel Generator must be regulatory requirements involving able to operate during and after any Emergency Diesel Generators. Target design basis event without support from EDG reliability is used to determine a preferred power source. station blackout coping capability. • Regulatory Guide 1.9 – "Selection, • 10 CFR 50 Appendix A, General Design, Qualification, and Testing of Design Criteria. – Previously discussed Emergency Diesel Generator Units in this Chapter. See Section 1.1, etc. Used as Class 1E Onsite Electric Power Systems at Nuclear Power Plants," 1.5 Implementation of these Criteria (formerly AEC Safety Guide 9). RG 1.9, into Site-Specific System Design Rev 4 (March, 2007) was introduced in 1.2 of this Chapter and gave three 1.5.1 Overview of Primary Regulatory fundamental performance requirements Guides and Referenced Standards for EDG's. It incorporates portions of Used to Implement Design Criteria GDC 17 − Electric Power Systems, and GDC 18 − Inspection and Testing of For early nuclear plants licensed under Electrical Power Systems. RG 1.9 also AEC General Design Criteria the applicable invokes the following IEEE documents: design requirements were implemented via the AEC's Safety Guides. With transition of • IEEE 308 – "Standard Criteria for Class the criteria to 10 CFR 50, Appendix A, the 1E Power Systems for Nuclear Power NRC's Regulatory Guides (RG's) became Generating Stations." In practice, the means to implement requirements into Section 6.2.4, "Standby Power NPP design. Supplies," of the IEEE 308 standard is implemented through IEEE 387. Under both of these regimes, codes and standards developed by industry groups or • IEEE 387 (1972, 1977, 1984, 1995) – national organizations (e.g., ANSI, IEEE, "IEEE Standard Criteria for Diesel- NFPA, etc.) were incorporated into the Generator Units Applied as Standby regulations. This training course provides Power Supplies for Nuclear Power just an overview of the more important Generating Stations." The parent documents relevant to EDG's. standard to IEEE 387-1995 (and 1984)

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is IEEE Standard 308-1980. IEEE 387 • Regulatory Guide 1.32 – "Criteria for expands on IEEE 308, Section 6.2.4, Safety-Related Electric Power Systems "Standby Power Supplies" with respect for Nuclear Power Plants." RG 1.32 to application of diesel generator units. seeks to implement compliance with portions of the following document: This standard provides many amplifying and supplemental details, in conjunction • GDC 17 – Electric Power Systems. with Regulatory Guide 1.9, regarding the design, testing, and qualification of • IEEE 308 – "Standard Criteria for Class Emergency Diesel Generators used in 1E Power Systems for Nuclear Power nuclear applications. Not all plants are Generating Stations." Invoked by RG committed to use IEEE 387, especially 1.32, this Standard specifies capabilities those licensed prior to 1972. IEEE 387 of a Standby Power Supply (e.g. EDG) also endorses several other codes and to serve as an independent / redundant standards including the unit (or Train or Division) of power. Manufacturers Association (DEMA) guide “Standard Practices for Low and • Regulatory Guide 1.75 – "Physical Medium Speed Stationary Diesel and Independence of Electric Systems." Gas Engines,” last revised in 1972. Deals more with the physical than DEMA is no longer an active association functional independence or separation but its guidelines are still relevant to the between classes and Trains or design criteria applied to EDGs installed Divisions. The criteria are intended to at most US nuclear power plants. Post- ensure adequate independence through 1977 versions of the IEEE 387 standard physical separation and barriers to also outline criteria for initial EDG “first assure continued function under all unit” qualification tests for NPP service. postulated plant events. RG 1.75 also These will be discussed in Chapter 11. invokes the following Standards:

NOTE: IEEE 387-1995 gives the design • IEEE 384 – "Standard Criteria for basis for nuclear service EDG's as 4000 Independence of Class 1E Equipment starts and 6000 operating hours, over a and Circuits.” specified service life of 40 years. Such intermittent duty is very different from y Regulatory Guide 1.93 – "Availability typical commercial service! This course of Electric Power Sources." RG 1.93 will point out the profound impact that provides guidance for the application of has on EDG maintenance and testing, 10 CFR 50.36 (above), particularly as well as some design implications. A section 50.36(c)(2), "Limiting Conditions copy of IEEE 387-1995 is Appendix 3. for Operation," (LCO) when less than the number of power supplies required • IEEE 323 – "Standard for Qualifying by GDC 17 are available. Class 1E Equipment for Nuclear Power Generating Stations." y Regulatory Guide 1.108 – "Periodic

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Testing of Diesel Generator Units Used 1.5.2 Licensee's Implementation of as Onsite Electric Power Systems at EDG System Design Criteria Nuclear Power Plants." (Withdrawn. See 58 FR 41813, 5 August 1993. It should be evident the criteria for design Superseded by Regulatory Guide 1.9, have evolved and what is applicable to a Revision 3). specific plant depends to a large extent on the time frame in which it was constructed NOTE: Some of the early design plants and licensed. Licensees take whatever previously committed to Regulatory documents are applicable at the time their Guide 1.108 only adopted portions of project moves forward, including the proper Regulatory Guide 1.9. revision dates, and implement them into their plant-specific design and operations. y Regulatory Guide 1.137 – "Fuel-Oil The resulting EDG documents include: Systems for Standby Diesel Generators." RG 1.137 also seeks to y System drawings and isometrics implement compliance with portions of y System specifications GDC 17, Electric Power Systems y Equipment specification (above), and it endorses the following y Purchase specifications standard for regulatory compliance. y Installation and Test Criteria y ANSI N195 / ANS 59.51 – "Fuel Oil The design criteria which were applied to Systems for Emergency Diesel the plant are typically listed or referenced in Generators." the licensee design and equipment specifications and the Final safety Analysis y Regulatory Guide 1.155 – "Station Report / Updated Final Safety Analysis Blackout." This Guide seeks to Report (FSAR / UFSAR). implement compliance with all of: Highlights of Licensee FSAR / UFSAR: y 10 CFR 50.63, "Loss of all Alternating Current Power."…The specified station y FSAR / UFSAR Chapter 1, Plant blackout duration shall be based on the (Design) Description: Typically following factors: outlines the design criteria applicable to the plant design, construction, and "(i) The redundancy of the onsite operation. NOTE: Subsequent updates emergency ac power sources; of regulatory criteria may be difficult, or (ii) The reliability of the onsite impractical, for a licensee to back-fit. emergency ac power sources;…" The licensee’s Final Safety Analysis RG 1.155 also invokes NUMARC 8700: Report or Updated Final Safety Analysis Guidlines and Technical Bases for Report (FSAR/ UFSAR) will document NUMARC Initiatives Addressing Station the regulatory requirements followed in Blackout at Light Water Reactors. their licensing process.

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y FSAR / UFSAR Chapter 8, Section Additional limiting requirements for the 8.3(4), Onsite Emergency (AC) Power availability of Emergency Power supplies Systems: The bulk of the plant-specific are contained within the Technical design criteria applied by the licensee to Specifications for the supported safety the EDGs is typically included here. systems. These Technical Specifications typically identify the plant mode and y FSAR / UFSAR Chapter 9, Plant required number of available Trains or Auxiliary Systems: Typically includes Divisions of that safety system. Regulatory design criteria for many of the major Guide 1.93 (see previous) should be EDG support systems such as Fuel Oil, referenced to assist with determining Jacket Water, Lube oil, and Starting Air. implementation and compliance with Electric Power Technical Specification All licensees were required to develop plant LCO’s, including Emergency Diesel Technical Specifications that prescribe Generators. plant Limiting Conditions of Operation (LCO’s) for required safety systems. As y FSAR/USFAR Chapter 14, Accident outlined in 10 CFR 50.36, "…The technical (Safety) Analysis: The following specifications will be derived from the constitute a few of the generic plant analyses and evaluation included in the design basis events or accidents where safety analysis report, and amendments Emergency Diesel generators are thereto, submitted pursuant to 50.34…. (c) required to mitigate the resulting effects: Technical specifications will include items in the following categories: Loss of Coolant Accident (LOCA) with LOOP: Safety Injection Actuation (SIAS) (1) Safety limits, limiting safety system due to large or small break Loss of settings, and limiting control settings. Coolant Accident, with a concurrent or (i)(A) Safety limits for nuclear reactors are subsequent Loss of Offsite (preferred) limits upon important process variables that Power (LOCA / LOOP or SI / LOOP). are found to be necessary to reasonably protect the integrity of certain of the NOTE: Many plants were originally physical barriers that guard against the designed for a LOCA with a concurrent uncontrolled release of radioactivity. If any LOOP in such a manner that other safety limit is exceeded, the reactor scenarios may not have been must be shut down…." adequately addressed. Be aware of associated issues contained within IN The following are key typical Technical 93-17 and TI 2515/176 regarding LOCA Specifications which apply to EDGs: with a subsequent LOOP, and LOOP with subsequent LOCA. 3/4.8: Electrical Power Systems 3 / 4.8.1: AC Sources - Operating Loss of Offsite Power (LOOP): Loss of 3 / 4 .8.2: AC Sources - Shutdown normal and preferred electric power to station auxiliaries.

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NOTE: Issues have previously been emergency systems involves evaluation of identified where actual monitoring for the following major components, support loss of offsite power was not being systems, and circuits: performed at the 4KV class 1E buses. This presents scenarios where the 4KV Generator: Serving as the interconnected bus may become disconnected from the emergency electrical source, the generator offsite (preferred) source (i.e. loss follows (responds to) the electrical load power), with no automatic initiation of demands placed on the ESF bus. Major the EDG to restore. components of generators are:

High Energy Line Break (HELB): Steam • Generator housing and stator or feedwater system piping failure with • Generator rotor and exciter Loss of Offsite Power (LOOP). • Voltage Regulator • EDG emergency trip controls and relays NOTE: Issues have been identified where at least one of the Emergency Diesel Engine: Most of the diesel engines Diesel Generators could be adversely installed at current nuclear power plants impacted by the postulated HELB and were selected using guidance of the Diesel was not previously protected against. Engine Manufacturers Association (DEMA). Their "Standard Practices for Low and The preferred plant power source is always Medium Speed Diesel and Gas Engines, the normal offsite power supply, as defined DEMA-1972, was the 6th edition of this in Regulatory Guide 1.9 and associated standard, which has not been actively standards, including IEEE 308-1980, updated since. "Criteria for Class 1E Power Systems for Nuclear Power Generating Stations." As the prime mover, the diesel engine follows (responds to) both the steady state 1.5.3 EDG Component Selection and transient load demands applied to the generator. Its major components and Each emergency diesel generator is one of systems are: the most unique and complex "support systems" found within a nuclear power • plant. The EDG is itself an independent • Starting System (air or electric) miniature power plant serving critical safety • Fuel Oil Delivery System equipment within the much larger facility. • Combustion Air Intake

• Exhaust System Figure 1-1 "Diesel Generator Systems" • on the following page is from RG 1.9 and Lubrication System • illustrates an EDG system, including most Cooling (Jacket Water) System • of its support systems. The selection of Crankcase Ventilation • EDG's to serve as independent, redundant, EDG start logic controls and relays power sources for nuclear power plant • Emergency run controls and Relays

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Figure 1-1 Diesel Generator Systems Systems Generator Diesel 1-1 Figure

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