ML20215K778

Forwards Response to NRC Transmitting Safety Evaluation Re Seismic Capability of Component Cooling Water Sys at Facility.Criteria Used Not Original Licensing Criteria & Not Uniformly Applied to Other Plants

ML20215K778
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	05/06/1987
From:	Cockfield D PORTLAND GENERAL ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
TAC-65350, NUDOCS 8705110352
Download: ML20215K778 (6)

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M e Portland General Electric Coiripeny David W. Cockfield Vice President, Nuclear May 6, 1987 Trojan Nuclear Plant Docket 50-344 License NPF-1 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555

Dear Sir:

Failure Modo of Nonseismic CateRory I PipinR at Trojan This letter provides Portland Conoral Electric Company's (PCE) response to the Nuc1 car Regulatory Commission's (NRC) April 2, 1987 letter which transmitted a Safety Evaluation regarding the soismic capability of the Component Cooling Water System (CCWS) at Trojan.

The conclusion of the NRC's review is that ". . . the present CCW system capability at Trojan doca not meet the original licensing critorion, namely, that the isolation valves at the interface of the seismic and nonseismic portions of the system should be capable of isolating at 1 cast one CCW oystem train, given a completo rupture of the nonsoismic portion of the system, coupled with a single active failure." However, in arriving at this conclusion, it does not appear that all available information was considered. It is PCE's view that consideration of a complete doublo-ended guillotino rupture of a Soismic Category II pipe in the CCWS for system operability was not on original Trojan licensing critorion, is not a critorion uniformly applied to other plants, and is not a critorion supported by current licensing guidelines in the Standard Review Plans. The detailed basis of our position is provided in Attachment 1.

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We request that the NRC thoughtfully reconsider the conclusions of the subject Safety Evaluation in light of the detailed explanation provided in Attachment 1. A meeting is requested to discuss and clarify any details of our position in order to resolve this concern.

1 Sincerely, i

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j Attachments et Mr. John B. Martin Regional Administrator, Region V U.S. Nuclear Regulatory Conunission Mr. David Kish, Director State of Oregon Department of Energy Mr. R. C. Barr l NRC Resident Inspector i Trojan Nuclear Plant i

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Trojan Nuclear Plant Document Control Desk Docket 50-344 May 6, 1987 License NPF-1 Attachment 1 Page 1 of 4 PORTLAND GENERAL ELECTRIC COMPANY'S (PGE) POSITION ON NUCLEAR REGULATORY COMMISSION'S (NRC) APRIL 2, 1987 SAFETY EVALUATION ON THE COMPONENT COOLING WATER SYSTEM The subject Safety Evaluation summarizes a potential safety concern associated with the Component Cooling Water System (CCWS) raised during the August 1986 Safety System Functional Inspection by the Region V inspection team. The concern relates to a major break in the Nonseismic Category I (Seismic Category II) portion of the CCWS resulting in both safety trains blowing down, rendering them inoperable. Although auto-matic isolation valves are provided at the seismic /nonseismic interface, the isolation valves do not close rapidly enough to prevent the blowdown of both trains.

The Safety Evaluation correctly iterates PGE's position, provided during the inspection, that only a moderate energy leakage crack need be postu-lated, which would give the interface isolation valves sufficient time to close. However, the conclusion in the Safety Evaluation is that the capability of the present CCWS does not meet the original and current licensing criterion and that PGE should take whatever actions are neces-sary to assure the CCWS meets the original licensing criterion; 10, can withstand a seismic event that results in a complete double-ended guillotine rupture of a Seismic Category II pipe.

PGE reiterates its original position, provided during the August 1986 Safety System Functional Inspection, that only a moderate energy leakage crack need be postulated in the CCWS, both in seismic and nonseismic portions of the system, for system operability determinations. The basis for this position, and detailed responses to specific statements in the Safety Evaluation, is provided in the following.

1. Current NRC Regulatory Guidance There are several statements made in the Safety Evaluation which seem to be inconsistent with current NRC regulatory guidance for nonseismic piping failures.

The Safety Evaluation states that, "The staff disagrees with PGE's position since moderate energy leakage cracks are only postulated in Seismic Category I systems." This statement is contrary to the wording of Branch Technical Position (BTP) Mechanical Engineering Branch (MEB) 3-1, Section B.2.c.(2), which states that, "Through-wall leakage cracks should be postulated in fluid system piping designed to nonseismic standards as necessary to satisfy B.3.d of BTP ASB 3-1."

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Trojan Nuclear Plant Document Control Desk i Docket 50-344 May 6, 1987

. License NPF-1 Attachment 1 Page 2 of 4 i

l PGE does not agree with the NRC position.that moderate energy leakage criteria were developed only for the purpose of analyzing the effects of flooding and spray on surrounding equipment, not on the capability:

of the system itself to withstand a passive failure.' This position

' is in conflict with Section B.3.d of BTP Auxiliary Systems Branch

(ASB) 3-1, referenced in Section B.2.c.(2) ofLMEB 3-1.(above) for

[ application of moderate energy. cracks._Section B.3.d states that, "The functional capability of essentia1' systems and components should be maintained after a failure;of piping not designed to Seismic Category I standards, assuming a concurrent single' active failure."

i The Safety Evaluation also says there is no basis.to' support the contention that a seismic Category II pipe will not catastrophically fail during a seismic event. However, numerous studies (many by the NRC) of piping in commercial buildings subjected to severe earth-quakes demonstrate that direct failure of seismic Category _II piping due to an earthquake is not credible. Generic Letter 87-02,_which exempts all piping from the seismic verification review for operating reactors, reflects this general conclusion.

. Finally, we could not locate any explicit regulatory basis for the-

Safety Evaluation assertion that " Flooding analyses and system failure modes and effects analyses that are performed by the staff are based on the assumption that a seismic event can cause a complete j double-ended guillotine rupture of any seismic Category II piping system." For flooding analyses of piping ruptures, Standard Review Plan (SRP) 3.4.1, " Flood Protection", refers to SRP 3.6.1, " Plant

, Design for Protection Against Postulated Piping Failures in Fluid

. Systems Outside Containment". For failure modes and effects analyses, SRP 9.2.2, " Reactor Auxiliary Cooling Water Systems",

requires that the CCWS be designed for a moderate energy leakage crack or an accident that is initiated from a failure in the CCWS piping. Moderate energy leakage cracks are to be determined in accordance with BTP ASB 3-1. A " failure in the CCWS piping" is not j explicitly defined and sust be interpreted to be a moderate energy i leakage crack in the context of the SRP wording.

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In conclusion, the NRC's current licensing guidance supports the use 4

of moderate energy leakage cracks for postulated failures-in nonsels-j mic piping, and application of this criterion in evaluating the

functional capability of safety systems.

2. Trojan Licensing Basis '

The above regulatory guidance was not in place at the time that

} nonseismic line breaks were considered for Trojan (ie, in 1972) and l are not mandatory for Trojan. There was very little NRC guidance for nonseismic pipe failures available at that time.

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-Trojan Nuclear $ Plant Document Control Desk Docket 50-344- May 6, 1987 License NPF-l' Attachment 1 .;

Page 3 of 4 The Safety Evaluation asserts as the staff's position'at the time of the original Final Safety Analysis Report (FSAR) review thatia Seismic; Category II piping failure should.be based on a double-ended rupture, and that the isolation valves'should be. protecting the CCWS

-against the blowdown of both. trains.(assuming a single' failure). As evidence for this position,' the Safety-Evaluation excerpts a portion aof FSAR Table 9.2-15,~ " Component' Cooling Water System Single Failure Analysis".: The complete text-from FSAR Table 9.2-15.regarding Seismic Category II pressure boundary. failures, is as follows:

"The Seismic Category II parts are closed off of system by SIS so that any failure in Seismic Category II pressure.

boundary will not. affect the Seismic Category I parts of the system. The Seismic. Category II parts of the system can be closed off the system by operator action during other-plant 1 operating conditions."

Two situations are presented in this table; the isolation valves are-shut-by_a safety injection signal (SIS), and the isolation valves are shut by operator action. Neither of these situations supports the position that a double-ended guillotine ruptureLwas assumed in the Trojan'FSAR as an. initiating event requiring: automatic operation to protect against loss of system operability.

The only NRC position applicable to Trojan that PGE is aware of

-pertaining to nonseismic piping failures was promulgated in a ,

September 26, 1972 letter from the Atomic Energy Commission (AEC).

-This letter, which requested an evaluation of-the failure of non-Category I equipment, only required consideration of flooding effects on safety-related equipment and not a determination of system ,

operability. A catastrophic double-ended guillotine failure of Seis- >

mic Category II piping was not required.to be considered for'CCWS l safety-system operability. Rather, failures in both the seismic and

[- nonseismic portions of the CCWS were used as a conservative basis to evaluate flooding effects to other safety-related equipment. Although l the surge tank level switches were installed'following the AEC letter i

in 1972, it was done to provide added conservatism by protecting l against loss of makeup water source with no credit assumed for opera-l tor action. The double-ended pipe break scenario was only discussed in relation to flooding and not considered in establishing system; design.

The -original Trojan design appears to have been based on Westinghouse's generic CCWS design criteria which referred to a " passive failure (a loss of system integrity resulting~in abnormal-leakage)" when it dis-cusses requirements for the CCWS surge tanks and makeup capability as providing a continuous component cooling water supply until a leaking cooling line can be isolated. The Westinghouse Nuclear Steam Supply

Trojan Nuclear Plant Docket 50-344 License NPF-1 Document May 6, 1987 Control Desk Attachment 1 Page 4 of 4 System Layout Cuideline component cooling wat s (dated October leakage", 19, 1971) these criteriawhich ". . er pumps be protected rom f f

makeup pump wer,e sized tothe design.. will .

due tobe less than 50 gpm accommodatecapacity of the Category IConsistent with designed for anAlthough FSAR

. Section relatively small9 2leakagessurge tanks and of the system, the y passive failure in the Sei2.3 and Table 9.2-15 state th operability consideration only passive failure defin smic di category II portionsat the CCWS is e

defines the failures pipos", as 50 gpm for 30 e to b s is found in Section This . n.

the31 FSAR for aoriginal Westinghouseminutes. desi assumed, in terms ofsection " limit critical leakage gn These flow ed cracks in criteria and are rates are based on the In summary, flooding an lcrack otine or double-ended guill much lower than either rupture.

operability considerationyses were treated independ

\ process, and sometimesa s during the original de s gni ently from guillotine failure basis for Trojan oftheSeimaximize conservatively on Plant.

assumed the andflood doubl licensingimpact A catastrophic double e de-ended breaks to minimal impact onoperability. systemassumed s not a designlimited passive failsa

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\ 3. operability.ures, which entail much lRather, s the design basi ess flow and designed forAn industry survey was CCWS.

3 plants, it isAlthough thea guillotineperformed to surveyrupture includes in the nonseismicascertain if other plants a portion are applied in the industryevident that this licensirelatively

. small numberof their In conclusion ng criterion was of in the Trojan,CCWS de ithe Safety Evaluation not uniformly has s gn is not been criterion was uniformly app, lied in cthe nu lapparently not a generic NRCnot originally app ear industry. position, and

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l Trojan Nuclear Plant Document Control Desk - l Docket 50-344 May 6,.1987 License NPF-1 Attachment 1 Page 4 of 4 i

System Layout Guidelines (dated October'19,~1971) required that the component. cooling water pumps be protected from flooding. . . due.to leakage", which ". . . will be less than'50 gpm". Consistent with these criteria, the-design capacity of the Category I surge tanks and makeup pump were sized to accommodate relatively small leakages.

Although FSAR Section 9.2.2.3 and Table 9.2-15 state that the CCWS is designed for any passive failure in the Seismic Category II portions of the system. the only passive failure defined in the FSAR for.

operability considerations is found in Section 3.1. This section defines the failures to be assumed, in terms of~" limited cracks in.

pipes",,as 50 gpm for 30 minutes. 'These flow rates are based on the original Westinghouse design criteria and.are'much lower than either a critical leakage crack or double-ended guillotine rupture.

In summary, flooding analyses were treated independently from operability considerations during the original design and licensing process, and sometimes conservatively assumed double-ended. breaks to maximize the flood impact on the Plant. A catastrophic double-ended guillotine failure =of Seismic Category II piping was not a design basis- for Trojan safety-system operability. Rather, the design basis.

assumed limited passive failures, which entail much less flow and minimal impact on system operability.

3. Licensing Basis for Other Plants An industry survey was performed to ascertain if other plants are designed for a guillotine rupture in the nonseismic portion of.their CCWS. Although the survey includes a relatively small number of plants, it is evident that this licensing criterion was not uniformly applied in the industry.

In conclusion, the Safety Evaluation criterion was not originally applied in the Trojan CCWS design, is apparently not a generic NRC position, and has not been uniformly applied in.the nuclear industry.

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