ML20245H414
| ML20245H414 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 08/10/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20245H407 | List: |
| References | |
| GL-83-28, NUDOCS 8908170078 | |
| Download: ML20245H414 (2) | |
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ENCLOSURE 1
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. SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PORTLAND GEi4ERAL ELECTRIC COMPANY TROJAN NUCLEAR PLANT DOCKET NO. 50-344 GENERIC LETTER 83-28 ITEM 4.5.3 REACTOR TRIP SYSTEM RELIABILITY FOR ALL DOMESTIC OPERAT~ LNG REACTORS 1,. 0 INTRODUCTION On Fet uary 25, 1983, both of the scram circuit breakers at Unit 1 of t.he Salem Nuclear Power Plant failed to open upon an automatic reactor trip signal
_ from the reactor protection system (RPS). This incident was tenninated manally by the operator about 30 seconds after the initiation of the automatic trip signal. The failure of the circuit breakers was determined to be related to the sticking of the underyc1tage trip attachment., Prior to this incident, on February 22, 1983, at Unit 1 of tne Salem Nuclear Power Plant, an automatic trip signal was generated based on steam generator low-low level during plant startup. In this case, the reector was tripped manually by the operator almost .
coincidentally with the automatic trip. .
Following these incidents, on February 28,19S3, the NRC Executive Diracer for Operatiens (EDD), directed the staff to investigate and report on the generic irplicatiens of these occurrences at Unit 1 of the Salem Nuclear Power Plant. The results of the staff's inquiry into the generic implications of the Salem Unit 1 incic'erts are reported in NUREG-1000,
- Generic Implications of f .
the ATW5 Events at the Salem Nuclear Power Plant". As.a result of this i investigation, the Co-dssion (NRC) ree.uested (by Generic Letter 83 28 dated July 8,1.cE3) all licensees of operating reacters, applicants for en operating license, eri holders of construction permits to respond to generic issues raised by the ar.alyses of these two ATWS events.
The licensees were recyired by Generic Letter' 83-28 Item 4.5.3 to confirm that on-lina functional testing of the reactor trip system (RTS), including i independent testing of the diverse trip features, was being perfomed at all 1
plants.
Existing intervals for on-line functional testing required by Technical Specifications were to be reviewed to determine if the test intervals were adequate for achieving high RTS availability when accounting for consit'erations i such as: (1) uncertainties in component failure rates; (2) uncertainties in '
comon mode failure rates; (3) reduced redundancy during testing; (4) operator error during testing; and (5) component " wear-out" caused by the testing.
2.0 DISCUS $10N The NRC's contrector. Idaho Nationai Engineering Laboratory (INEL), reviewed the licensee Owners Group availability analyses and evaluated the adequacy of the existing test intervals, with a consideration of the above five items, for al' plants. The results of this review are reported in detail in EGG-NTA-8341,
, *A Feview of Reactor Trip System Availability Analyses for Generic Letter l 83-28. Item 4.5.3 Eesolution.* dated Msrch 1989 and surcarized in this report.
The results of our evaluatien of Item 4.5.3 and our review of EGG-KTA-8341 are l presented below.
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-2 The Babcocir & Wilcox (B&W), Combustion Engineering (CE), General Electric
- (GE), and Westinghouse (W) Owners Groups have submitted topical reports either l
in response to GL 63-28, Jtem 4.5.3 or to provide a basis for requesting Technical Specification changes to extend RTS sur eillance test intervals l
(STI). The owners groups' analyses addressed the adequacy of the existing l
intervals for on line functional testing of the RTS, with the considerations required by Item 4.5.3, by quantitatively estimating the unavailability of the RTS. These analyses found that the RTS was very reliable and that the unavailability was dominated by common cause failure and human error.
The ability to accurately estimate unavailability for very reliable systems was considered extensively in NUREG-0460,
- Anticipated Transients Without Scram for Light Water Reactors", and the ATWS rulemaking. The uncertainties of such estimates are large, because the systems are highly reliable, very little
. experience exists to support the estimates, and comon cause failure probabilities are difficult to estimate, Therefore, we believe that the RTS unavailability estimates in these studies, while useful for evaluating test intervals, must be used with caution.
NUREG-0460 also states that for systems with low failure probability, such as th"e RTS, comen mode f ailures tend to predominate, and, for a number of reasons, meditional testing will not appreciably lower RTS unavailability.
Tirst, testing more frecuer.tly than weekly is generally impractical, and even so the increased testing coul# at best lower the failure probability by less than a factor of fcur compared to monthly testing. Secondly, increased testing could pessibly increase the probability of a cornen mede failure through increased stress on the system. Eina11y, rct all potential failures are detectable by testing. Jn scrrary, NUREG-0460 provides additional justification to dencostrate that the currently used test intervals (monthly or quarterly) are adequate to maintain high RTS availability.
3.0 CONCLUSION
All four venders' topical reports have shown the currently configured RTS to be highly reliable with_ the currently used test intervals. Our contractor has reviewed these analyses and perforced independent ettimates of their own which conclude that the current test intervals provide high reliability. In addition, the analyses in NUREG-0460 have shown that for a number of reasons, more frequent testing than monthly will not appreciably lower the estimates of failure probability.
Eesed on our review of the Owners Group topical reports, our contractor's inependent analysis a theexistingintervals,ndthefindingsnotedinNUREG-0460,weconcludethat as recorrended in the topical reports, for on-line functional testing are consistent with achining high RTS availability at all operating reactors.
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EGG-WTAeB34 [1CLOSUR Q Marsh 1989
- . ' -~= TECHNICAL EVALUATION REPORT
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- ' O National A REVIEW OF REACTOR TRIP SYSTEM AVAILABIL:TY Analysts roR GENERIC LETTER 83-28. ITEM 4.5.3, Engineering REs0LorIou laboratory i
Managed Dy The U S. David P. Mackowiak Depanmen: John. A. $chroedt? -
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9 EGG-NTA-6341 TECHNICAL EVA'UATION REPORT: A REVIEW OF REACTOR TRIP SYSTEM AVAILABILITY ANALYSES FOR GENERIC LETTER 83-28 ITEM 4.5.3, RESOLUTION I
8 David P. Mackowiak John A. Schroeder i
EG&G Icaho, Inc.
Idaho Falls, Iceho 83415 F
FIN D6001: Evaluation of Conformance to G'eneric Letter E3-28 for ors (Project 2) .
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i SUWARY i
The two anticipated transient without scram (ATW5) events at the
.l Salem Nuclear Power Plant in February of 3983, focused the attention of l
the Nuclear Regulatory Commission (NRC).on the generic implications of
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ATW5 events. The NRC then published Generic Letter 83-28 (GL E3-28) which listed the actions the NRC required of all licensees holding operating licenses and others with respect to assuring the reliability of the Reactor Protection System (RPS). GL 83-28 Item 4.5.3, required licensees to demonstrate by review that the current oneline fanctional testing intervals are consistent with achieving high reactor trip system I l
(RTS) availability. The licensees responded to the GL B3-26 Item 4.5.3, requirements as Owners Groups with reports either_in direct response to Item 4.5.3, or with a technical basis for reauesting extensions to the l surveillarte test intervals (STIs) that generally included the Item 4.5.3 required reviews.
9 The NRC's Instrumentation and Control Systems Branch (ICSB), Office !
of Nuclear Reactor Regulation (NRR), requested the Idaho Nattonal Engineering Laboratory (INEL) to review the licensee availability analyses anc evaluate the over.all adequacy of the existing test I intervals. INEL review resulti showing general compliance with Item 4.5.3 will provide the NRC with a basis to close out Item 4.5.3 without further review.
For the review, the INEL defined three acceptance criteria, reviewed the licensees topical reports, contractor review reports, and NRC safety '
evaluations, and determined the adequacy of the analyses and the RTS availability estimates with regard to the review criteria.
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The INEL review criteria to determine the licensees' Item 4.5.3 compliance were, (I) the five areas of concern of Item 4.5.3, (2) the l
analyses' plant applicability, and (3) the NRC's RTS electrical unavailability base case estimates from the ATW5 Rulemak,ing Paper, KECY-E3-293.
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i ACRONYMS
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ATW5 Anticipated Transient Without Scram j
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B&W Babcock & Wilcox BNL Brookhaven Natica.a1 Laboratory CE Combustion Engineering j GE General Electric HTGR High-Temperature Gas-Cooled Reactor ICSB Instrumentation and Control Systems Branch INEL Idaho National Engineering Laboratory LWR Light Water Reactor NFSC Nuclear Facility Safety Committee 4 NRC Nuclear Regulatory Commission NRR Office of Nuclear Reactor Regulation PORC Plant Operations Review Committee PSC Public Service Company of Colorado FWR Pressurized Water Reactor RSSMAP Reacter Safety Study Methodology Applications Program RPS Reactor Protection System
- RTS Reactor Trip System SER Safety Evaluation Report STI Surveillance Test Interval TER Technical Evaluation Report W Westinghouse v
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. ) TECHNICAL EVALUATION rep 0RT: A REVIEW OF REACTOR TRIP SYSTEM AVAILABILITY ANALYSES FOR GENER!c LETTER 83-28.
ITEM 4.5.3 RESOLUTION
- 1. INTRODUCTION 1.1 Historical Backcround In February of 1983, two events occurred at the Salem Nuclear Generating Station that focused Nuclear Regulatory Commission (NRC) attention on the generic implications of anticipated transient without scram (ATWS) events.
First, on February 22,.during startup of Unit'l an automatic trip signal generated as a result of a steam generator low-low level failed to cause a reactor scram. The reactor was tripped manually by an operator
, almost coincidentally with the automatic trip signal, so the fact that the automatic trip had failed to cause a scram went unnoticed.
Three days later on February 25, both of the scram break'ers at Unit .1 failed to open on an automatic reactor protection system (RPS) scram sigral. The operators took action to centrol this second ATW5 and succeeded in terminating the incident in a' bout 30 seconds. Subsequent investigation relsted the failure of the Unit 1 RPS to cause a scram to sticking of the undervoltage trip attachment in the scram circuit breakers.
As a result of these events the NRC Executive Director for Operations directed the staff to undertake three related activities: (1) an
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evaluation of when and under what conditions the Salem plants would be allowed to restart; (2) a fact' finding report of the events at Salem 1 and the circumstances leading to them; and (3) a repo'rt on the generic implications of these events. -
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To address (3) above an interoffice, interdisciplinary group was !
formed including members from the Office of Nuclear' Reactor Regulation's !
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The Babcock & Wilcox (B&W), Combustion Engineering (CE), General Electric (GE), and Westinghouse (W) Owners Groups have submitted topical reports either in response to GL B3-28, Item 4.5.3'3'# or to provide a i basis fer requesting RTS surveillance test interval (5TI) l extensions.5,6,7,8,9,10,11 In general, the owners groups' analyses were not done on a plant specific basis. Instead, the analyses addressed a l particular class of reactor trip system and then discussed the i applicability of the analysis to specific product lines. The NRC reviewed these reports for, among other things, their applicability to GL 63-28 Item 4.5.3 and summarized their findings in Safety Evaluation Reports 32'I3 (SERs).
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1.2 Review Purpose I
1 This report documents a review of the Owners Groups' topical reports, the NRC SERs, and other analyses done at the Idaho National Engineering Laboratery (INEL) by personnel in the NRC Risk Analysis Unit of EG&G Idaho, j Inc. The INEL conducted the review at the request of the U.S. Nuclear
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Regulatory Commission, Office of Nuclear Reactor Regulation, ,
Instrumentation and Control Systems Branch (ICSB). The review was performed to determine if the Owners Groups analyses demonstrated high RTS availability for the current t?st intervals, if the analyses included the I
five areas of concern from GL E3-28, and if all of the plants were covered l
, by the analyses. The results of the review, if all plants are' shown to be
, covered by an adequate analysis, would provide the NRC with a basis for closing out GL B3-28, Item 4.5.3, for all U.S. commercial nuclear reactors without further review.
The body of this report presents the review and its findings with regard to the stated objectives. Section 2 describes the criteria used in
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the review to determine the adequacy of the analyses. The review methodology is discussed in Section 3. Section 4 presents the review results. The review conclusions are given in Section 5. !
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- l The estimates from the NRC ATW5 analysis provide a framework with which to consider the topical report analyses estimates. The numerical i estimates in the SECY-83-293 for the four vendors combined with the five areas of concern from GL 83-28, Item 4.F.3, form the criteria used for this review to determine if the venders' analyses and estimates met the requirements of Item 4.5.3, i
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REV!Ett RESULTS This section summarizes the results of the INEL review of the vendors' analyses with regard to the five areas of concern and plant applicability.
The vendors' estimates of RTS availability are compared to the review availability criteria. Also, some insights concerning RTS availability, i s
gained from an e a mination of RTS importance measures from selected PRAs, are examined.
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4.1 B&W Plants The issues of GL B3-28 Item 4.5.3, were addressed by the B&W Owners i Group and the results were submitted to the NRC by the individual utilities in their responses to GL B3-28. Topical Report BAW-10167 (Reference 5) was .
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submitted to the NRC to provide a technical basis for increasing the l on-line STIs and allowed outage times (A0Ts) for B&W RTS instrument
. strings. The analysis presented in BAW-10167 was built upon the previous i
analysis done to address the GL B3-28, Item 4.5.3 issues. However, some information that ass resolved in the generic letter analysis was not repeated in the subsequent Topical Report because it,was not relevant to '
the proposed Technical Specification changes. To make BAW-10167 applicable to both GL B3-28, Item 4.5.3 arid STI/ADT issues, the Owners Group submitted BAW-10167, Supplement 1 (Reference 6), to the NRC. Supplement I completed j ,
the B&W analysis by addressing all remaining Item 4.5.3 issues'. The I BAW -10367 and Supplement I analyses included the impleme,ntation of the automatic shunt trip on the reactor trip circuit breakers as required by GL !
. 83-28, Item t. 3.
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~ The INEL has previously reviewed the BAW-10167 and Supplement 1 analyses and documented the review in a TER, EGG-REQ-7728 (Reference 15).
For the TER, sensitivity studies which incitard aT1 of the Item 4.5.3 areas of concern were conducted on the RTS mocels. The sensitivity study results showed the models tn be insensitive to variations in the failure rates associated with the Item 4.5.3 areas of concern.
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" failure rates. The insensitivity to increased compenent failure rates along with the CE analysis results showing trip circuit breaker common cause failures to be the major contributor to RTS unavailability provides a a basis for this review to conclude that RTS test-induced component wear-cut is not an issue at CE reactors.
The INEL reviewed CEN-327 and the TER and determined that the CE analyses have adequately covered all five areas of concern or they have been shown not to contribute to RTS unavailability and that all currently operating CE reactors are included.
4.3 GE plants i
Licensees with GE reactors responded to the GL 83-28, Item 4.5.3 '
requirements as the BWR Owners' Group by submitting NECD-30844 (Reference 4) to the NRC. The RTS availability analysis specifically included the five areas of concern and covered both generic relay and solid state RTS designs which includes all currently operating BWRs. GE !
stated that the relay RPS configurations for BWR p1' ants have.the same primary design features. Therefore, the generic relay RTS models used in ;
NECD-30844 do net differ significantly from the specific BWR plants. GE
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used the Clinton I drawings fok the solid-state RTS models. Since Clinton i 2 is currently the only GE plant with a solid state RTS, no plant unique analysis is necessary.
The EWR Cwners' Group also submitted NECD-30851P (Reference 8) to the NRC. The analysis in this second repert used the base case results from NECD-30844 to establish a basis for requesting revisions to the current
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Technical Specifications for.the RTS. The INEL had previously reviewed NECD-30644 and NECD-30851P with regard to both Item 4.5.3 and STI extension acceptability and documented the review in a TER, EGG-EA-7105 (Reference 17). Due to insufficient information, the INEL review could not '
complete the solid-state RTS review and accepted only the relay RTS analysis results. The NRC reviewed the topical reports and the TER and 9 .
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- 3. Unavailability of components due to unscheduled maintenance
- 4. Unavailability of components due to human error
- 5. Unavailability of components due to commen cause failure. l While the y analysis did not directly include any sensitivity studies concerning these five areas, the component unavailabilities were increased I as the test interval length increased. The STI analysis results showed a l factor of 3 to 5 increase in the RTS unavailability estimates for the longer test interval. Two conservatism exist in the models that are ;
relevant: first, no credit was taken for early failures that would be ;
detected and, second, no credit was trken for the diversity inherent in the y RTS design. 'These two conservatism, had they been included in the l model, would cause the increase in the RTS unavailability estimates to be smaller than the observed factors.
Test-induced component wear-cut was not addressed in any manner in the y RTS analysis. However, the RTS analyses done by the other venders, References 3, 4 and 6, specifically investigated the effects of this issue <
en RTS unavailability. Despite the differences among the other vendors' FT5 designs, they all found thi effects of test induced component wear-out on RTS unavailability to be insignificant. Based on the other venders'
, analyses, the INEL concluded that the effects of test-induced' component wear cut on y RTS unavailability would also be insignificant. Therefore, the IhEL considers all y plants to be covered by adequate analyses.
4.5 Quantitative Review of Venders' RTS Availabilities
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So far, only the adequacy of the vendors' analyses has been discussed. No determination has'been made of the acceptability of the numerical estimates from the various RTS availability analyses. In this section, the INEL review considers the four Owners Groups' RTS availability l
estimates to determine if they are indeed indicative of "high availability."
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- TABLE 1. COMPARISON OF VENDOR AND NRC RTS UNAVAILABILITY ESTIMATES 8
Unavailability Estimates Unavailability Estimates I Vender ( Failure s/Dema nd) (Failures / Demand) !
. BW l Davis Bessie Model C d IE-10 3E-5 d
Oconee Class Model IE-6 C 3E-5 ,
1 CE
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Plant Class 1 2F-7' 2E-5 Plant Class 2 3E-6' 2E-5 Plant Class 3 3E-6' . 2E-5 '
Plant Class 4 2E-6' 2E-5 GE Relay Plants 3E-6 f
2E-5 Solid-state Plants 3E-6 2E-5 y .
Solid-state Plants i SE-59 SE-5 d
- a. All estimates are rounded off to one significant digit.
- b. From Reference 24, Table A-3, base case RTS electrical unavailability estimates
- c. From Reference 5, base case.
- d. Includes automatic shunt trip on the reactor trip circuit breakers.
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- e. From Reference 7 Tables 4.1-1, 4.2-2, 4.1-3, and 4.1-4, respectively; base case test interval, high pressurizer pressur,e unavailability estimate.
- f. From Reference 4. .
- g. From Reference 19, solid state RTS base case. Applied to relay-plants '
based on similarity of design (see Reference 11, Section 3.2.2 and 3.2.3).
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, From.these responses, the INEL concluded that Fort St. Vrain has conducted the review required by ail 83-28, item 4.5.3, and thst the NRC. t considers the PSC and NRC rei:vews adequate to meet the Item 4.5.3 requirements. )
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- 6. REFERENCES
- 1. U.S. Nuclear Regulatory Commission, Generic Ieplicatiens of ATWS Events at the Salem Nuclear Power Plant, NUREG-1000, April 1983.
- 2. U.S. Nuclear Regulatory Commission Letter, D. G. Eisenhut to All Licensees et al., Recuired Actions Based on Generic Implications of 1
Salem ATWS Events, Generic Letter 83-28, July 8,1983.
- 3. Combustion Engineering, Reacter Protection System Test Interval Evaluation, Task 486, CE NPSD-277, December 1984.
4 S. Visweswaran et al., BWR Owners' Group Response to NRC Generic Letter 83-28. Item 4.5.3, NECD-30844, January 1985.
- 5. R. S. Enzinna et al., Justification for Increasine the Reacter Trio System On-line Test Interval, SAW-10167, May 1986.
- 6. R. S. Enzinna et al., Justification for Intressine the React'er Trio System On-line Test Interva l . Supelement Number 1, 8AW-10167, Supplement Nummer 1, February 1968.
- 7. Cembustion Engineering, RPS/ESFAS Extended Test Interval Evaluation,
. CEN-327, May 1986.
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- 8. W. P. Sullivan et al., Technical Specification Imerevement Analyses for SWR Reacter Protection System, NECD-308519 May 1985.
- 9. R. L. Jansen et al., Evaluation of Surveillance Frequencies and Out of Service Tires for the Reacter Protection Instrumentation System, WCA?-20271, January 1983.%
- 10. R. L. Jansen et al., Evaluation of Surveillance Frequencies and Out of Service Times for the Reacter Pretectien Instrumentation System.
Sucolement 1. W';AF-10271 Supplement 1, July 1983,
- 11. R. L. Jansen et al., Evaluation of Surveillance Frequencies and Out of Service Times fer the Reacter Protection Instrumentation System.
Sueciement 1-P-A, wCAP-10271, Supplement 1-P-A, May 1986.
- 12. U.S. Nuclear Regulatory Commission Memorandum, G. C. Lainas to E. J.
Butcher, Actectance for Refe encine of General Electric Comeany (GE)
Tepical Reports hECD-30Eco. "EWR Owners' Group Rescense to NRC Generic Letter 83-28." anc NECD-30551P. " Technical Specification Improvement Analyses for EWR Reactor Pretection System." April 28, 1986.
- 13. U.S. Nac'sar Rego11 tory Commission Letter, C. O Thomas to J. J.
Sheppard, Acceptance for Referencing of Licensino Topical Report WCAP-10271. " Evaluation of Surveillance Frequencies ane Out of Service Tiees for tr.s Reactor Factectiun Instrumentation Systems." February 21, 1985.
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