ML20038A811
| ML20038A811 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/31/1981 |
| From: | Bradley G SANDIA NATIONAL LABORATORIES |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-1121 NUREG-CR-2153, SAND81-1129, NUDOCS 8111160489 | |
| Download: ML20038A811 (56) | |
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NUREG/CR-2153 SAND 81-1129 i S/ - 3 d- I L - 362. L San Onofre Nuclear Generating . Statiori, Units 2 and 3, L Auxiliary Fe'edwater System ! l Reliability' Study Evaluation ; ! __ a-- _ i Prepared by G. cl. B'ra ley, Jr.
- Sandia National Laboratories 6 d % /c f
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NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or i assumes any legal liability or responsibility for any third party's [ use, or the resul's of such use, of any information, apparatus l product or process disclosed in this report, or repmsents that its use by such third party would not infringe privately owned rights. i i t i Available from GP0 Sales Progran. Division of Technical Information and Document Control U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Printed copy price: $3.00 , 1 l and National Technical Information Service Springfield, Virginia 22161
NUREG/CR-2153 SAND 81-1129 l San Onofre Nuclear Generating Station, Units 2 and 3, , Auxiliary Feedwater System Reliability Study Evaluation
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Manuscript Completed: April 1981 Date Published: October 1981 Prepared by G. H. Bradley, Jr. Sandia National Laboratories Albuquerque, NM 87185 Prepared for Division of Safety Technology Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 NRC FIN A1121 l l
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Availability of Reference Materials Cited in NRC Publications Most documents cited in NRC puolications will be available from one of the following sources:
- 1. The NRC Public Document Room 1717 H Street., N.W.
Washington, DC 20555
- 2. The NRC/GPO Sales Program, U.S. Nuclear Regulatory Commission, Washington, DC 20555
- 3. The Nationa' Technical information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publications, it is not intended to be exhaustive.
Referenced documents available for inspection and copying for a fee from the NRC Public Document Room include NRC correspondence and internal NRC memoranda; NRC Office of Inspection and Enforce-ment bulletins, circulars, information notices, inspection and investigation notices; Licensee Event Reports; vendor reports and correspondence; Commission papers; and applicant and licensee documents and correspondence. The following documents in the NUREG series are available for purchase from the NRC/GPO Sales Pro-gram; formal NRC staff and contractor reports, NRC-sponsored conference proceedings, and NRC booklets and brochures. Also available are Regulatory Guides, NRC regulations in the Code of Federal Regulations, and Nuclear Regulatory Commission Issuances. Documents available from the National Technical Information Service include NUREG series reports and technical reports prepared by other federal agencies and reports prepared by the Atomic Energy Commis-sion, forerunner agency to the Nuclear Regulatory Commission. Documents available from public and special technical libraries include all open literature items, such as books, journal and periodical articles, transactions, and codes and standards. Federal Register notices. federal and state legislatior', and congressional reports can usually be obtained from these libraries. Documents such as theses, dissertations, foreign reports aid translations, and non-NRC conference pro-ceedings are available for purchase from the organization sponsoring the publication cited. Single copies of NRC draf t reports are available free upon written request to the Division of Technical Infor-mathn and Document Control, U.S. Nuclear Regulatory Commission. Washington, DC 20555.
i 4 ABSTRACT This report presents the results of the review of the Auxiliary Feedwater System Reliability Analysis for the San Onofre Nuclear Cenerating Station Units 2 and 3. The analysis was prepared for Southern California Edison Company by Combustion Engineering. t: e e 111-
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e CONTENTS Page Summary and Conclusions 1
- 1. Introduction 2 1.1 Background 2 1.2 Review Activities 2 1.3 Content and Results of the Reliability Analysis 3 1.4 Scope and Level of. SNL Effort 3
- 2. AFWS Configuration 4 2.1 General Description 4 2.2 . Component Description 4 2.2.1 Motor Driven Pumps 4 2.2.2 Turbine Driven Pump 6 2.2.3 Piping and Valves 7 2.3 System Operations 8 2.3.1 Plant Startup 8 2.3.2 Normal Plant Operation 8 2.3.3 Normal Plant Cooldown 8 2.3.4 Emergency Operation 9 2.3.5 - Blackout Operation 10
- 3. Discussion 11 3.1 Mode.of AFWS Initiation 11 3.2 System Control After Initiation 11 3.3 Test and Maintenance Procedures and Unavailability 13 v-
.m .-
fage 3.4 Adequacy of Emergency Procedures . 13 3.5 Adequacy of Power Sources and Separation of Power 13 Sources 3.6 Availability of Alternate Water Sources 14 l-3.7 Potential Common Mode Failures 14 L 3.7.1 Environmental Causes 14 3.7.2 Component Proximity 15 3.7.3 Human Factors 15 3.7.4 Common Errors in Design, Manufacture, or 17 Installation 3.7.5 Energy Sources 17 3.7.6 Specific Cases 17 3.8 Application of Data Presented in NUREG-0635 20 3.9 Search for Single-Failure Points 20 3.10 Human Factors / Errors 20 3.11 NUREG-0635 Recommendations 20 3.11.1 Short-Term Generic Recommendations 20 3.11.2 Additional Short-Term Recommendations 28 3.11.3 Long-Tera Generic Recommendations 31
- 4. Major Contributors to Unreliability 34 4.1 Case 1 -Loss of Main Feedwater 34 4.2 Case 2 - Loss of Main Feedwater with Loss lof 35 I Offsite Power l 4.3 Case 3 - Loss of Main Feedwater with Loas of. 35 All AC Power 4.4 Numerical Results ~35 vi
Page
- 5. Conclusions 37
- 6. Glossary of Terms 38
- 7. References 39 i
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- ILLUSTRATIONS Figure Page 1 Auxiliary 'Feedwater ' System SONGS 2 and 3 5 2 SONGS 2 and.3 AFAS Logic _ 12
~3 Reliability Characterization for AFWS Designs 36 in Plants Using the C-E NSSS tx
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1 l Summary and Conclusicas The accident at Three Mile Island (TMI) resulted in many studies that outlined events leading to the accident, as well as events thereafter. One of the important safety systems involved in mitigating such accidents, the Auxiliary Feedwater System (AFWS), was studied and analyzed for each plant. .Results for the Combustion. Engineering (CE)-Designed Plants were reported in NUREG-0635.1 Before obtaining an operating license, the licensee of each nonoperating, CE-designed plant was instructed 2 to do a reliability analysis of his AFWS, like the study made 'by NUREG-0635, for three transient conditions involving loss of main feedwater. Southern California Edison Company (SCE), licensee for San Onofre Nuclear Generating Station (SONGS) Units 2 and 3, submitted a reliability report 3 to the US Nuclear Regulatory. Commission (NRC) in October 1980. Sandia National I.aboratories (SNL) reviewed this report and reached the following conclusions:
- 1. SCE has satisfactorily complied with. the requirement to make a reli-ability study of their AFWS.
- 2. Comparison of the reliability of San Onofre's AFWS to those of CE designed operating plants shows that San Onofre's reliability is at.
the high end of the range for operating plants. Sandia agrees with this assessment. l I i
1.0- Introduction . I 1.1 -Background , 1 The results .of many studies of the TMI nuclear power plant accident conclude that a proper functioning AFWS is of prime importance in mitigating such accidents. Therefore, a letter dated March 10, 19802 stating NRCs requirements for the AFWS was sent to all operating license applicants with a Nuclear Steam Supply System (NSSS) designed by Westinghouse or CE. SCE of Rosemead, California, the applicant for an operating license for SONGS Units 2 and 3 that has a CE-designed NSSS, responded in the form of a reliability analysis 3, prepared for them by CE. The analysis was supported by documented calculations 4 prepared by CE. 1.2 Review Activities This project reviews of those portions of the design review and reliability analysis that satisfy requirement (b) of the letter, which states, " perform a reliability evaluation similar in method to that described in Enclosure 1 (NUREG-0635) . I that was - performed for operating plants and submit it for staff l review." Also reviewed were the responses 5 to the short and long-term recommendations of NUREG-0635 in answer to requirement (c) in the letter. The review was done according to Schedule 1896 submitted by SNL to NRC. 1
2: . 1.3 Content and Results of the Reliability Analysis The reliability analysis 3 was submitted to.NRC in October 1980 and was received by SNL December 1,1980. This analysis studies the failure of the AFWS to provide sufficient Auxiliary Feedwater (AFW) ilow to one of the two steam generators and
-compares results with those obtained for operating plants studied in NUREG-0635. The analysis places SONGS among operating plants with high AFWS reliability.
- 1. 4 Scope and Level of S? 'ffort SNL reviewed the reliability analysis submitted by SCF-Particular attention was directed toward determining that the analysis addressed in depth the reliability of the AFWS when subjected to three transient cas?s (1) LMFW, Loss of Main Feedwater, (2) LMFW/ LOOP, Loss of Main l'eedwater/ Loss of Offsite Power, and (3) LMFW/ LAC, Loss of Main Feedwater/ Loss of All AC Power. The methods used in the analysis were also compared to those used in NUREC-0635. Specific findings are presented in Sections 3 and 4.
Comments and questions were recorded during the review and submitted to NRC January 15, 1981; these questions were forwarded to SCE by NRC on January 19. SCE-and its contractor met with representatives frcm NRC and SNL on February 16 and March 3 at-NRC Headquarters in Bethesda, Maryland. At these meetings the AFWS reliability analysis was reviewed and questions were answered. SCE forwarded The official responses 7 to the questions
m: , x t-to 'NRC February 18. No exact verification' of numerical results
.were made; however, checks were made to assure that the numbers
-reported were satisfactory. I
- 2.0 AFWS Configuration 2.1 ' General Description Figure 1 is'a flow diagram of the AFWS. Major components of the AFWS include. three 100% capacity AFW pumps (two motor-driven and one driven by steam turbine) and associated piping, valves, and instrumentation.-
2.2 Component-Description I 1 2.2.1 Motor-Driven Pumps. Two of the three AFW pumps are driven by electric motors, each supplied with power from a separate preferred power source. The horizontal centrifugal pumps each'has a capacity of 860 gpm at a total developed head of 2842 ft. This figure includes a recirculated flow of 100 gpm and a wear margin of 60 s gpm. The pumps take suction from condensate storage
. tank T-121 through independent suction lines. Each
- l. pump's discharge piping connects to one of the two main feedwater lines between the isolation valves and the steam generator nozzle, providing system separation.
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p. I; . 2.2.2~ Turbine-Driven Pump. A turbine-driven- AFW pump, identical to the motor-driven pumps, provides overall system redundancy of AFW supply and diversity of motive pumping h
. power. .The pump is a horizontal, centrifugal unit with
- a capacity of 860 gpm at a total developed head of 2842 ft. The pump takes suction from the condensate storage tank T-121 through a separate suction line, and its discharge is interconnected through isolation valves and reverse flow check valves to the same piping used by the motor-driven AFW pumps. Steam-supply piping to the turbine driver is taken from each of the two main steam lines between the containment penetrations and the main steam isolation valves. Each of the steam supply lines to the turbine driver is equipped with a check valve and a pneumatic-actuated valve supplied with power from the emergency de power source. The pneumatic-actuated valves are designed to fail open upon loss of 1
air. The turbine driver can operate with steam inlet pressures ranging f rom 1210 to 65 psia. Exhaust steam from the turbine driver is vented to the atmosphere above the tank building roof. The AFW pumps are located in separate areas of the AFW pump room at elevation 28 f t in the' tank building close to the condensate storage' tanks. f
_-_--___--__..r- _-_- 2.2.3 Piping and valves. Welded joints are used throughout most of the system. = Flanged connections are provided at the enction and dischargi of each pump, at the flow-limiting venturis, and at the two tees where the turbine-driven pump ties into the two AFW lines, each line dedicated to one steam generator. Each pump is equipped with manually operated isolation valves at the pump suction and discharge. These valves are used only for maintenance and are locked open during normal operation. The status of these valves (and that of others locked open) is checked at 30 day intervals and is continually monitored through an administrative tagging procedure. Check valves are located close to each pump discharge to prevent backflow through a shut-down pump in event of a loss-of-pump failure. The AFW lines are equipped with ac motor-operated and ac electrohydraulic control valves in the motor-driven pump feed trains, and de motor-operated valves in the turbine-driven pump feed train. The lines that supply water to the AFW pumps from the condensate storage tank are equipped with manually operated gate valves-at the storage tanks, which are normally locked open. Paralled isolation valves are provided in the AFW line to each steam generator outside the containment; one of each valve in parallel is ac-powered, the other de-powered.
2.3 System Operation 2.3.1:-Plant Startup. During startup, the AFW pumps are used-under manual ccatrol to supply feedwater from the con-densate storage tank to the steam generators until enough steam is available to start the turbine-driven [ main feedwater pumps. i I 2.3.2 Normal Plant Operation. The AFWS is not required during normal power. generation. The pumps are placed in the automatic mode, lined up with the condensate storage tank, and are available if needed. For the hot standby mode of normal plant operation, 1 it is assumed that four reactor coolant pumps will be in operation, and that a main feedwater pump will be used for the hour following departure from power. The AFW pumps will b<. manually started within 10 min. after shutdown. The capacity of the AFW pumps exceeds that required. j 2.3.3 Normal Plant Cooldown. During cooldown, the AFW pumps are used under manual control to supply water from the condensate storage tank to the steam generators AFW flow to each steam generator is manually regulated by the remote-operated control valves or by locally operated bypass valves. Steam generated during this mode of operation is bypassed to the main condenser. i t 5 .. .. . . . . . . . . . . , . . . . . . . . .
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- The AFW pumps are used_until reactor _ coolant temperature-drops to 3500F, at which point the shutdown cooling.
system is activated _to further cool the reactor'coolantL s ys tem. To' minimize thermal-shock to the steam generators, the condensate storage tanks T-120 and T-121 are normally maintained above 700F. The minimum required pump -
. capacity, 700 gpm, is based on a 750F/ hour cooldown'
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rate and always exceeds that required for this : situation. 2.3.4 ' Emergency Operation. The auxiliary feedwater actuation signal (AFAS) automatically actuates he AFWS by fully opening the isolation and control-valves to deliver a minimum feedwater flowrate of 100 gpm to the intact 7 steam generator (s). The primary source of auxiliary E feedwater is the 150;000-gal, Seismic Category-I, condensate storage tanks, T-121, which is used exclusively for the AFWS. A 500,000-gal, Seismic Category II, l I condensate storage tank, T-120, serves as the primary backup supply of water.- Two hundred thousand gallons of the 500,000-gal' supply is reserved for the AFWS. This is augmented by the fire-protection system in-l case the demand exceeds the water supplied by the other two tanks. R 6 l' Heat is removed from the reactor by boiling the feedwater in the steam generators and1 venting steam to ?. f p. D- s
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the atmosphere 'through. the main steam saf ety relief valves until the operator actuates the atmospheric dump valves. If the main condenser _is available, the steam may be relieved by means of a turbine-bypass _ system. Controlled cooldown can be provided through the atmos-pheric dump valves if the main turbine-bypass system is not available. When the reactor coolant temperature drops to 3500F, cooldown is shifted to the shutdown-cooling system. A signal is required to automatically initiate the minimum AFW flowrate, 700 gpm. Cavitating venturis at each pump discharge limit the discharge flow and thus prevent pump runout. 2.3.5 Blackout Operation. When needed, AFAS automatically actuates the AFWS turbine, turbine controls, and turbine-driven pump (including the de-operated isolation and control valves) to ensure an adequate 700 gpm feedwater supply to the steam generators during a blackout. The de-operated control valves, wnich may be positioned by the operator, are provided for each AFW line af ter overriding the AFAS to control the AFW flow to each steam generator. r
4 3.0 Discussion 3.1 'tiode of AFWS Initiation
- An AFAS as shown in Figure 2 automatically actuates the '
AFWS by starting the AFW pumps,' determining which steam generator i. r (SG) is-intact, and fully opening-the isolation and control . ' valves to_the unaffected.SG. The system generating the AFAS is part of the Engineered Safety Feature Actuation System 1 (ESFAS). An AFAS is generated by one of the following condi-tions by means of 's two-out-of-four logic. 1
- 1. A low SG level coincident with no low pressure trip present for that SG.
- 2. A low SG level coincident with a pre-set-differential
?- pressure present between the two SGs with.the. higher l pressure associated'with the SG to be fed. The AFWS is initiated manually when used during -plant I startup and cooldown. I
; 3.2 . System' Control After Initiation
! After initiation, when the SG water level returns to a level above the low level setpoint, the AFW pump-discharge valves will shut, automatically. Manual control of the AFWS-pumps and valves is also possible.from the-control room. [ If the control room becomes uninhabitable,-sufficient AFWS instrumentation and controls are provided outside the control l:
" room on a Seismic Category I evacuation shutdown panel and at l:
other locations for operating of the AFWS.- Controls are availab1
50 figs 2 & 3 AFAS LOGIC Press j- Press i SG-1 SG-2 SG S)G-' - , , , I l SG-1 Psg-1 Level Level Psg-2 SG-2 Low SG SG Low Press Psg-2 Psg-l Press SG-1 SG-2 Low Low f!0T Level Level fl0T _- m j D D l 1 1 Afl0 Afl0 N) %) re:'o t e Renote M.moa l fianual AFAS-1 AFAS-2 j Figure 2 _m________._______._.._____.._
at the pump.for the' turbine-driven pump and at the switchgear for.the motor-driven pump. The feedwater control valves can be operated by handwheels. If;the reactor trips and the control room is evacuated, the AFW pumps can atill . supply feedwater to. the steam generators for the removing reactor-decay heat and for plant cooldown. 3.3 Test and Maintenance Procedures and Unavailability The test and maintenance procedures are being prepared and reviewed in accordance with the overall plant operations and licensing schedule. They were not reviewed as part of the study; however, events were considered _ based on the technical specifications and data from NUREG-0635. 3.4 Adequacy of Emergency Procedures Emergency procedures are being reviewed by the licensee. The licensee states that they will be completed and available for NRC review and audit 6 months before fuel loading. Any-deficiencies identified during the NRC review and audit will be corrected and implemented before full power operation. 3.5 Adequacy of Power Sources and Separation of Povar Sources All . safety-related power sources, supplies, etc meet the requirements for separation and redundancy in accordance with' the design criteria, regulatory guides, and Institute of Electrical and Electronics Engineers (IEEE) standards. h A
3.6 Availability of Alternate' Water Sources The primary alternste source of feedwater is the 500,000-gal,' Seismic Category II, condensate storage tank, T-120. . Two hundred thousand gallons is always available for the ! AFWS. The alternate source must be valved in manually. The i fault tree did not consider the backup source to increase system reliability, nor did it consider the failure of the l primary source, which was considered negligible with respect to the failure of other system components. 3.7 Potential-Common-Mode Failures The San Onofre AFWS susceptibility to common-mode failure environment, component proximity, human error, common errors in design manufacture or installation, and common energy sources is discussed in this section. 3.7.1 Environmental Causes. AFWS components, except for two check valves, are located outside containment and are qualified for service in the anticipated adverse environments. Specifically, the effects of high and moderate energy line breaks near AFWS components have been examined in detail and the results reported in Section 3.6 of the Final Safety Analysis Report (FSAR). The worst case vulnerability of the AFWS occurs in the pump room, where all three pumps are located. In this case all components'are being qualified based on a 30-min blowdown of the main steam line, resulting in peak l
temperatures to 3020F and pressure peaks to 2.76 psig. In accordance with NUREG-0588, a detailed review was made of the environmental qualifications for SONGS, which specifically included the AFWS components. The review was submitted to the NRC in SCE letter dated February 15, 1981. 3.7.2 Component Proximity. The AFWS consists of separated trains to prevent. system f ailures caused by the physical proximity of redundant trains. Physical-separation barriers are provided in areas of close proximity. A detailed analysis of protection of the AFWS from the effects of pipe whip, jet impingement, and missiles is contained in Sections 3.5 and 3.6 of the FSAR. 3.7.3 Human Factors. The AFW actuation system is part of SONGS Engineered Safety Features Actuation System and is designed to initiate AFW to an intact steam generator automatically upon loss of Main Feedwater (MFW). This system provides a four-channel, 2-of-4-coincidence logic to minimize the dependence on operator actions that has existed in earlier CE plant AFWSs.- Virtually all system components are controlled remotely from the plant control room. The control room has been the subject of extensive design review effort. The review effort included the following: \ m
Panel--labeling and equipment terminology
-Panel. grouping Types of instrumer.iation and accuracy Display and/or device testing capabilitica Direct vs inferred readings Differences between Units 2 and 3
, a l All of;these were considered in the context of man / machine -systems and operability analysis, human-factors data, and principles for minimizing operator error 'and effectively mitigating the consequences of such
, errors and accidents caused by equipment malfunction.
Human-factors considerations played the major role in this review. A representative sample of emergency operating instructions was also reviewed and confirmed by operator walkthrough as part. of a detailed NRC lluman Factors Engineering Branch (HFEB) Audit of the San Onofre Units 2 and 3 Control Room on August 4-8, 1980. As a result of a detailed review by the applicant and of the NRC Audit, the control panels are being modified. These modifications, which were approved 'I by the 11FEB of the NRC, include relocation of feedwater controls and indications.
L y t ' 3.7.4 Common Errors in Design, Manufacture, or Installation. The AFWS meets'the requirements of the Auxiliary Systems Branch's Technical Position regarding system diversity by using a variety of components. Both motor- and
~
turbine-driven feed pumps are used in conjunction with ac and de motor-operated and electrohydraulic valve operators. SCE has a Quality Assurance Program to monitor the design, manufacture, and installation of all equipment. 3.7.5 Energy Sources. The AFWS consists of-three trains. 'One, which is totally independent of the plant ac power system, relies on a steam turbine-driven pump and de-powered valves. The remaining two trains are each-powered from one of the two emergency onsite power - supply systems. These systems are completely independent. 3.7.6 Specific Cases.- In addition to the generic review of common mode failure categorizations above, a DOE sponsored study, Common Cause Failure Experience in Nuclear Plant Auxiliary-Feedwater Systems for Reliability Analysis (WARD-SR-3045-4) was reviewed. This study listed a specific common-mode-tailures experienced during AFWS operation.. This listing was compared to the SONGS AFWS design as outlined below to determine the potential for these failures. h i- i ..= . .
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-1.:-Operator failed to open the valve from the condensate-storage tank to the two AFWS pumps. The two AFWS
. pump loops failed to be available on demand as.
required by technical specifications. Docket 50-317-516.. . l The SONGS AFWS has three. lines from the condensate storage tank to the pumps. Valves in these lines are locked open, do not have remote operators, and are not required to be operated during system operatior, and testing.- Surveillance of these valves is conducted at 30-day intervals.
- 2. Filters (in parallel) on suction side of three pumps plugged up with foreign material that restricted flow. Docket 50-305-354.
The SONGS AFWS contains temporary suction 4 strainers for use during system startup.. These strainers will be removed for normal operation.
- 3. Condensate storage . tank water level was intentionally.
drawn down below technical specification limits to maintain maximum steam generator blowdown. Failure to maintain water supply to multiple AFWS pumps within specifications. Docket 50-315-340. Condensate storage tank water level was intentionally drawn down below technical specification limits because makeup water supply was dirty '(high oxygen content). Failure to maintain water supply to ., multiple AFWS pumps within specifications. Docket
- j. 40-247-449.
The SONGS condensata storage tank T-121 is dedicated to the AFWS. Normal secondary makeup for SG blowdown, etc is from Tank T-120. All tank
+
penetrations other than AFWP suctions are located -t e
at an elevation greater than that corresponding to the Technical Specification limit. Additionally, Tank T-121 hc4 redundant low level indications in the control roms to alert the operator to' a condition j of less than technical specification capacity. 4
- 4. Two AFWS pumps failed'to start because of defective control switches that failed to close cont' acts.
^
Docket 50-305-350. I At SONGS, the controI_'ewitches for the steam valves to the turbine' driven AFWP are 'different - f rom the start-stop switches for the taotor driven pumps.
- 5. A breaker accidentally opened and interrupted ' power to the turbine overspeed protection (which tripped the-reactor), and also interrupted power to an AFWS lube-oil pump, preventing start of the relate 4 AFWS pump.
Docket 50-305-361. All auxiliary features of the turbine driven AFWP at SONGS are independent of ac power.
- 6. Two AFWS valves were upgraded during licens'ing and were not seismically qualified because of over-sight. Docket 50-289-491.
The entire SONGS AFWS is seismically qualified. s The post-TM1 modification has been completed by using the same design requirements and quality-assurance procedures as for the original AFWS design. s il
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,i Data ~from Table III-3 of NUREG-0635 along with data from
.. f. % 1/ T CEs mliabillty: data ba,se .were used for the basic ' events described .
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,i9 i., l, ; ~ operating plants for Case 3 too high (see paragraph'4.4). J < .,
- f. +3;91 Search for single Failure Points k -
, 'No single failure point!s were identified by the licensee.
In the meetings the Condensata Storage Tank T-121 was discussed y 7 48 a' potential single failure point. It was discounted because
.its f ailure probability was so small that including it in the 4
_ fault tree would not change the result.. i , I
, 3.10 Human Factors / Errors Human Factors are discussed above in the Common-Mode I-Failure section. No~ human-error failure events were considered in the' fault tree analysis prepared by CE because of the i
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- automatic operation of the AFWS.
3. Y e . 4 3.11 NUREG-0635 Recommendations a 5 3.11.1 Short-Term Generic Recommendations. ] ' 7 ,
- 1. Technical Specification Time Limit on AFWS Train Outage.
- 4. ,
Recommendation GS-1. The licensee-should propose reodifications to the Technical Specifications to
. limit the time that one AFWS pump and its c
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associated flow train.and essential instrumentation [ % ' can . be -inoperable. - The outage time. limit and 4.,.
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~21- l subsequent action time should be as required in current Technical Specifications; i.e., 72 and 12 hours, respectively.
Response - The existing SONCS Units 2 and 3 Technical ' Specification complica with the recommendation. This specification limics operation with cne AFW train out of service :o 72 hours and the subsequent action ti.e to 12 hours.
- 2. Technical Specification Administrative Controls on Manual Valves - Lock and Verif y Position Recommendation CS The licensee should lock Open single valves or multiple valves in series in the AFWS pump suction piping and lock open other single valves or multiple valves in series that could interrupt all AFW flow. Monthly inspections should be made to verif y that these valves are locked o pen. These inspections should be proposed f or
' incorporation into the surveillance requirements of the plan Technical Specifications. The long term resolution cf this concern is discussed in Recommendacion GL-2.
Response - The SONGS Units 2 and 3 AFWS design incorporates individual suction lines f rom the primary AFW supply tank (condensate storage tank T-i 121) to each \FW pump. Each suction line contains
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3 a" two manual valves in series, which will be locked ) open in accordance with the system diagram. There I r 4, . . , are no alternate water supply lines to the AFW YwN<
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pumps. Manual valves in the pump discharge ; *
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lines will also be locked open. No single valve in >
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the pump discharge lines can terminate all AFWS [~ e, [ s-- em flow. The Technical Specification surveillance h gr I
.ja-requirements will include a requirement to verify A[g[4 u,% .
the position of all locked-open manual valves during
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- 3. AFWS Flow Throttling - Water Hammer g j;] -
Recommendation GS The licensee has stated that $$n. ;. i. / it throttles AFWS flow to avoid water hammer. l.( bay $h The licensee should reexamine the practice of i throttling AFWS flow to avoid water hammer. The licensee should verify that the AFWS will supply on demand enough initial flow to the necessary steam generators to assure adequate decay-heat removal after loss of main feedwater flow and a reactor trip from 100% power. In cases where this reevaluation results in an increase in initial AFWS flow, the licensee should provide enought infor-mation to demonstrate that the required initial AFWS flow will not result in plant damage because of water hammer. Response - SONGS Unit 2 and 3 design maete these _ _ _ _ . . . l
requirements. Tests will be done to verif y the adequacy of operating procedures for refilling the steam generator to prevent unacceptable water hammer upon refill. These teste will be accomplished on both units before reaching 100% power. The steam generator spargers have been modified by including "J" tubes that discharge from the top of the feedring. The feedwater piping has been designed to minimize the drainable volume of the feed pipe.
- 4. Emergency Procedures for Initiating Backup Water Supplies Recommendation CS Emergency procedures for transferring to alternate sources of AFW supply should be available to the plant operators. These procedures should include criteria to inform the operator when, and in what order, the transfer to alternate water sources should take place. The following cases shoild be covered by the procedures.
The case in which the primary water supp1v is not initially available. Procedures for this case should include any operator actions required to project the AFWS pumps against self-damage before water flow is initiated. The case in which the primary water supply is being depleted. The procedure for this case whould provide for transfer to the alternate E i _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _
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J_ water sources before draining the primary water supply. i . Response - The primary supply source fo the SONGS Units 2 and 3 AFWS is the 150,000-gal condensate i storage tank T-121. The alternate water supply, assuming depletion of the water in T-121, is the 500,000-gal condensate storage tank T-120. Emergency procedures will be available to plant 2 operators for transferring to and from alternate sources. , 5. Emergency Procedures for Initiating AFW Flow 1 Following a Complete Loss of AC Power. --; Recommendation GS The as-built plant should be - capable of providing the required AFW flow for at 5-least 2 hours from one AFW pump train, independent IN of any ac power source. If manual AFWS initiation _ or flow control is required following a complete loss of ac, emergency procedures should be esta-blished for manually initiating and controlling ' the system undar these conditions. Because the water for cooling the lube oil for the turbine-driven pump bearings may depend on ac power, design - or procedural changes shall be nade to eliminate this dependency as soon as practicable. Until this is done, the emergency procedures should 1 provide for an individual to be stationed at the L k 7 2
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turbine-driven pump in case of loss of all ac power to monitor pump bearing and/or lube oil tem pe ra ture s. If necessary, this operator would operate the turbine-driicn pump in a manual on-off mode until ac power is restored. Adequate lighting 1 powered by de power sources and communications at local stations should atao be provided if manual initiation and control of the AFWS are needed. (See Recommendation GL-3 for the longer term resolution of this concern.) Response - The SONGS 2 and 3 AFWS design incorporates automatic actuation of the AFWS turbine-driven pump and de-operated isolation and control valves on loss of all ac power. The turbine driven pump has no ac dependencies. The SONGS Units 2 and 3 AFWS design can be automatically initated and operated for 2 hours independent of any power source.
- 6. AFWS Flowpath Verification Recommendation GS The licensee should confirm floupath availability of an AFWS flowtrain that has been out of service to perform periodic testing or maintenance as follows:
Procedures should be implemented to require an operator to determine that the AFWS valves are properly aligned, and a second operator to independently verif y proper alignment.
The licensee should propose Technical Specifications to assure that, before plant startup following an extended cold shutdown, a flowtest would be done to verify the normal flowpath from the - primary AFWS water source to the steam generators. The flowtest should be conducted with AFWS valves in their normal alignment. Response - Procedures will require that, after an AFWS outag because of maintenance or periodic test, an operator shall determine that the AFWS valves are properly aligned, with verification by a second operator. Technical Specification sur-veillance requirements will include a flowtest of the AFWS to verif y normal flowpath from the primary water source to the steam generators with AFWS valves in their normal alignment following an extended cold shutdown. .-
- 7. Non-Safety Grade, Nonredundant AFWS Automatic Initiation Signals Recommendation GS The licensee should verify -
that the automatic start AFWS signals and associated
- circuitry are safety grade. If this cannot be verified, the AFWS automatic-initiation system should be modified in the short term to meet the functional requirements listed below. For the longer term, the automatic-initiation signals and
circuits should be upgraded to meet safety-grade requirements as indicated in Recommendation GL-5. (1) The design should provide for the automatic initiation of the AFWS flow. (2) The automatic initiation signals and circuits should be designed so that a single failure will not result in the loss of AFWS function. (3) Capability for testing the initiation signal and circuits shall be a design feature. (4) The initiation signals and circuits should be powered f rom the emergency buses. (5) Mantial capability to initiate the AFWS from the control room should be retained and imple-mented so that a single failure in the manual circuits will not result in the loss of system functicn. (6) The ac motor-driven pumps and valves in the AFWS should be included in the automatic actuation (simultaneous and/or sequential) of the loads to the emergency buses. (7) The automatic-initiation signals and circuits shall be designed so that their failure will not result in the loss of manual capability to initiate the AFWS from the control room. Response - The SONGS design meets Recommendation GL-5 (safety grade).
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- 8. Automatic Initiation of AFWS Recommendation GS The licensee shall install a system to automatically initiate AFWS flow. This system need not be safety grade; however, in the short term, it should meet criteria similar to Item 2.1.7.a of NUREG-0578. For the longer term, the automatic initiation signals and circuits should be upgraded to meet safety-grade requirements.
Response - The SONGS Units 2 and 3 design incorporates a safety-grade automatic AFWS start system. 3.11.2 Additional Short-Term Recommendations
- 1. Primary AFW Water-Source Low-Level Alarm Recommendation - The licensee should provide redundant level indication and low-level alarms in the control room for the AFWS primary water supply, to allow the operator to anticipate the need for making up water or transferring to an alternate water supply and prevent low-pump suction pressure. The low-level alarm setpoint should allow at least 20 min for operator action, assuming that the largest capacity AFW pump is operating.
Response - Redundant AFW primary water-level indication and low-level alarms are in the control room. The low-level setpoint will allow at least 20 min for operator action.
- 2. AFW Pump Endurance Test Recommendation . The licensee should do a 48-hour
-)
endurance test on all AFWS pumps, if such a test or continuous period of operation has not yet been done. Following the 48-hour pump run, the pumps should be shut down, cooled, and then restarted and run for 1 hour. Test acceptance criteria should include demonstrating that the pumps remain within design limits with respect to bearing / bearing oil temperatures and vibration, and that pump-room ambient conditions (temperature, humidity) do not exceed environmental qualification limits for safety-related equipment in the room. 4 The licensee should summarize the conditions and results of the tests. This summary should include (1) A brief description of the ' test method (including flow schematic diagram) and how the test was instrumented (i.e., where and how bearing ten-peratures were measured), (2) A discussion of-how the test conditions _(pump flow.. head, speed and steam temperature) compare to design operating conditions,-(3) Plots of bearing / bearing oil tem-- [ perature vs time for each bearing of each AFW pump / driver demonstrating that temperature' design limits'
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-were not exceeded,-(4) A plot of pump-room ambient
temperature and humidity vs time demonstrating that pump-room ambient conditions do not exceed environ-mental qualification limits for safety-related equipment in the room, (5) A statement confirming that pump vibration did not exceed allowable limits during tests. Response - A 48-hour endurance test will be run on all AFW pumps before full power operation.
- 3. Indication of AFW Flow to the Steam Generator Recommendation - The licensee should implement the following requirements as specified by Item 2.1.7.b ,
on page A-32 of NUREG-0578: Safety-grade indication of AFW flow to each steam generator shall be provided in the control room. AFW flow instrument channels shall be powered from the emergency buses consistent with satisf ying
. the emergency power diversity requirements for the 9
AFWS set forth in Auxiliary Systems Branch Technical . Position 10-1 of the Standard Review Plan, Section 10.4.9. Response - SONGS Units 2 and 3 design meets this - recommendation.
- 4. AFWS Availability During Periodic Surveillance Testing Recommendation - Licensees with plants requiring local manual realignment of valves to conduct periodig tests on one AFWS train, and there is only one i
( remaining AFW train available for operation, should propose Technical Specifications to provide for stationing a dedicated individual in communication with the control room at the manual valves. Upon instruction from the control room, this operator would realign the valves in the AFWS train from the test mode to their operational alignment. Response - The SONGS Unit 2 and 3 AFWS incorporates three trains. Those valves that must be repositioned for periodic testing can be operated from the control TOom. 3.11.3 Long-Term Ceneric Recommendations
- 1. Automatic Initiation of AFWS Recommendation CL For plants with a manual starting AFWS, the licensee should install a system to automatically initiate the AFWS flow. This system and associated automatic initiation signals should be designed and installed to meet safety-grade requirements. Manual AFWS start and control capabi-lity should be retained, with manual start backup to automatic AFWS initiation.
Response - The SONGS Units 2 and 3 design incorporates automatic AFWS start.
- 2. Single Valves in the AFWS Flow Path Recommendation CL Licensees with plant designs in which all (primary and alternate) water supplies
to the AFUSs pass through valves in a single flowpath should install redundant parallel flow paths (piping and valves). Licensees with plant designs in which the primary AFWS water supply passes through valves in a single flowpath, but the alternate AFWS water supplies connect to the AFWS pump suction piping downstream of the above valve (s), should install redundant valves parallel to the above valve (s) or provide automatic opening of the valve (s) from the alternate water supply upon low pump-suction pressure. The licensee should propose Technical Specifications to incorporate appropriate periodic inspections to verif y the valve positions into the surveillance requirements. Response - The SONGS Unit 2 and 3 AFWS design incorporates individual suction lines from the condensate storage tank to each AFW pump. Each line contains two locked open manual valves in series. As noted in the reponse to Recommendation GS-2, the Technical Specification will include requirements for verif ying locked-open AFWS manual valve positions.
- 3. Elimination of AFWS Dependency on AC Power Following a Complete Loss of AC Power
4 Recommendation GL At least one AFWS pump and its associated flowpath and essential instrumentation
,should automatically initiate AFWS flow and be -
capable of being operated independently of any ac power source for at least 2 hours. Conversion of de power to ac power is acceptable. Response - As noted in the response to Recommeadation GS-5, the turbine-driven auxiliary feedwater pump will be automatically initiated and capable of operating for 2 hours independent of any existing ac power-supply sources.
- 4. Prevention of Multiple Pump Damage Caused by Loss of Suction Resulting from Natural Phenomena Recommendation GL Licensees having plants with unprotected normal AP'WS water supplies should evaluate the design of their AtWSs to determine if automatic protection of the pumps is needed after a seismic event or tornado. The time available to the control-room operator, and the time needed to assess the problem and take action, should be considered in determining whether operator action can be relied on to prevent pump damage. Consideration should be given to providing pump protection by means such as ,
automatic switchover of the pump suctions to the alternate safety' grade source of water, automatic pump trips on-low suction pressure, or upgrading
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the normal source of water to meet seismic Category I and tornado-protection requirements. Response - The primary AFWS supply is provided by 150,000-gal seismic Category I, tornado / missile-protected condensate storage tank (T-121). This supply is backed up by a 500,000 gal condensate storage tank (T-120), which is non-safety grade but is surrounded by a seismic Category 1 wall. Applicants have demonstrated that these sources will provide 24 hours of assured water supply even in the event of the Safe Shutdown Earthquake (SSE).
- 5. Non-Safety Grade, Nonredundant AFWS Automatic-Initiation Signals Recommendation GL The licensee shculd upgrade the AFWS automatic-initiation signals and circuits to meet safety grade requirements.
Response - SONGS AFWS automatic initiation signals and circuits meet safety grade requirements. 4.0 Major Contributors to Unreliability SCE lists the following contributors for each case: 4.1 Cace 1 - Loss of Main Feedwater The dominant failure mode for a total loss of AFW would be the result of a combination of three separate failures, each asso-ciated with a different AFW pump or suction path. Loss of both AFASs would also result in AFWS failure, but each of these signals comes from a completely separate channel which makes them redundant.
4.2 Case 2 - Loss of Main Feedwater with Loss of Offsite Power The AFWS is automatically transferred to cnsite ac power wita a loss of of fsite power. Therefore the dominant cause of system failure is identical to that for Case 1 with offsite power available. 4.3 Case 3 - Loss of Main Feedwater and Loss of All AC Power In this case the steam turbine pump and those single-channel valves in the turbine pump train become the dominant failure contributors. Each failure mode associated with these components become first order events. 4.4 Numerical Results Numerical results are given below and in Reference 4. Results of Case 1 and 2 are plotted in Figure 3 to show how SONGS compares to operating plants. Case 1 2.2 x 10-5 Case 2 3.8 x 10-5 Case 3 2.0 x 10-2 In Case 3 the numerical result is too high because of the use of CEs data base. The SONGS AFWS has incorporated all of the recommen-dation of NUREG-0635, which was the basic criterion for the high-reliability category. In addition, the system is (with minor ] exceptions) the same as that for Arkansas Nuclear #2, which was l-( rated in the high-reliability category in NUREG-0635. Therefore, the comparative result with Arkansas Nuclear #2 should be used for s Case 3. This result is-plotted in Figure 3. I
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Transient Events Lf1FW Lt1Fil/ LOOP LftFW/ Loss of All AC Plants low f *e d . High Low Med. High Lcw Med. High Corbustion Enar. Calvert Cliffs e
- O Palisades e e o
*1aine Yankee e e o 'tillstone e e o St. Lucie e e o , .
Ark. Nuc. #2 e e a O cn Ft. Calhoun e e e i . SONGS d2 & 3 e e e FIGURE 3 Reliability Characterizations for AFWS Designs in Plants Using the C-E NSSS
This places SONGS in the high category for all three cases. SNL agrees with these assessments.
- 5. Conclusions Based on this review, we conclude that SONGS Units 2 and 3 should have a high reliability as reported in SCE's evaluation. SCE has, in our judgment, completed requirement (b) of the March 10, 1980 letter.2 i
l
- 6. Clossary of Terms ac alternating current APAS Auxiliary Feedwater Actuation Signal AFW Auxiliary Feedwater AFWP Auxiliary Feedwater Pump AFWS Auxiliary Feedwater System CE Combustion Engineering Inc.
de direct current DOE Department of Energy ESFAS Engineered Safety Festure Actuation System FSAR Final Safety Analysis Report gpm gallons per minute HFEB Human Factors Engineering Branch IEEE Institute esf Electrical and Electronic Engineers LAC Loss of All AC power LMFW Loss of Main Feedwater LOOP Loss of Offsite Power MFW Main Feedwater NRC Nuclear Regulatory Commission NSSS Nuclear Steam Supply System psia pounds per square inch absolute SCE Southern California Edison Company SG Steam Generator SNL Sandia National Laboratories SONGS San Onofre Nuclear Generating Station SSE Safe Shutdown Farthquake THI Three Mile Island l
- 7. References
- 1. NUREG-0635 " Generic Evaluation of Feedwater Transients and Small Break Loss-of-Coolar.c Accidents in Combustion Engineering Designed Operating Plants," January 1980.
- 2. Letter to All Pending Operating License Applicants of Nuclear Steam Supply Systems Designed by Westinghouse and Combustion Engineering from D. F. Ross Jr., Acting Director, Division of Project Management, Office of Nuclear Reactor Regulation,
Subject:
" Actions Required from Operating License Applicants of Nuclear Supply Systems Designed by Westinghouse and Combustion Engineering Resulting from the NRC Bulletins and Orders Task Force Review Regarding the Three Mile Island Unit 2 Accident," March 10, 1980.
- 3. Auxiliary Feedwater System Design Review and Reliabf.lity Evaluation for San Onofre Nuclear Generating Station Units 2 and 3, October 1980.
. 4. CE Power Systems, Combustion Engineering Inc., Calculation Number S-PEC-246
Title:
San Onofre Nuclear Generating Station Units 2 and 3 Simplified AFW Reliability Fault Tree Analysis by C. A. Whitaker Jr., November 21, 1980.
- 5. Memorandum Docket Nos: 50-361/362 from Paul S. Check, Assistant Director for Plant Systems, DSI, to Robert H. Tedesco, Assistant Director for Licensing, DOL,
Subject:
San Onofre Nuclear Generating Station (SONGS) 2 and 3 - Safety Evaluation Report - Input on the Implementation of Recommendations for the Auxiliary Feedwater Systems, February 18, 1981.
- 6. Schedule 189 No. A1121-0
Title:
Review of Auxiliary Feedwater System Reliability Evaluation Studies for Diablo Canyon 1, McGuire 1, Summer 1, San Onofre 2, and Palo Verde, August 6, 1980.
- 7. Memorandum, K. P. Baskin, Manager of Nuclear Engineering, Safety, and Licensing, Southern Edison Company to Frank Miraglia, Branch Chief, Licensing Branch No. 3, USNRC,
Subject:
" Docket Nos. 50-361 and 50-362, San Onofre Nuclear Generating Station Units 2 and 3," February 18, 1981.
Distribution: U.S. Nuclear Regr*atory Commission (130 Copies for AN) Distribution Cont: 4ctor (CDSI) 7300 Pearl Street Bethesda, MD 20014 Armand Lakner U.S. Nuclear Regulatory Commission Washington, DC 20555 1222 C. H. Bradley 3141 L. J. Erickson (5) 3151 W. L. Carner (3) (for DOE / TIC) 3154-3 C. H. Dalin (25) (for NRC distribution to NTIS) 4400 A. W. Snyder 4414 J. W. Hickman 8?14 M. A. Pound a l l l I l r
U S. NUCLE AR REGULATORY COMMIS$10N " " ' NUREG/CR-2153 BIBLIOGRAPHIC DATA SHEET SAND 81-1129 4 ilTLE AND SUBTIT LE (Add Vorurne No. #1warensel 2. (Leave elesk/ San Onofre Nuclear Generating Station, Units 2 and 3, Auxiliary Feedwater System Reliability Study Evaluation 3. RECIPIENT'S ACCESSION NO. 7, AUTHOH tS) 5. DATE REPORT COMPLE TED G.H. Bradley, J r. l vg gig 9 PE HF OHMING ORGANilATION NAME AND MAILING ADDRESS (include I,a Codel DATE REPORT ISSUED
* * * *^"
Sandia National Laboratories October l*1981 Albuquerque, NM 87185 6 (Leave blank) -
- 8. (Leave Nank) -
- 12. SPONSOHING OHGANIZATION N AME AND MAILING ADDRESS (laciudr les Codel
- 10. PROJE CT/T ASK/ WORK UNIT iv0.
Division of Safety Technology Office of Nuclear Reactor Regulation R CONTRACT NO U.S. Nuclear Regulatory Commission FIN A1121 Washington, DC 20555 13 TYPE OF HEPOHT PE RioO Covt 'tEo I/nclus,re dates / 15 LUPPLE ME N T ARY NOTES 14 (Leave Wasal
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- 16. ABST R ACT (200 words or less) -j
+ a 34 "
This report oresents the results of the review of the Auxiliary Feedwater System Reliability Analysis for the San Onofre Nuclear Generating Station, Units 2 and 3.
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t_ E m 17 AE) WOHDS AND DOCUME NT AN ALYSIS 17a DESCRIPTOHS 17h IDENTIF tE RS OPE N ENDE D TE RMS 18 AV AIL ABILITY ST ATE ME NT 19 SE CURITY CLASS (Th,s reporff 21 NO OF PAGES Unclassified Unlimited 20 SbCuliTv ctaSS Ira,s omi
- 22. Price s
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NUREG/CR-2153 SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 A , lARY FEEDWATER OCTOBER 1981 SYSTEM RELIABILITY STUDY EVALUATION I l L J
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