ML20196B389
| ML20196B389 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/18/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20196B377 | List: |
| References | |
| TAC-66541, NUDOCS 8802110203 | |
| Download: ML20196B389 (5) | |
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[pm UNITED STATES 8"
NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR RE,GULATION RELATED TO AMENDMENT NO. 23 TO FACILITY OPERATING LICENSE NO. OPR-80 AND AMENDMENT N0. 22 TO FACitITY OPERATING LICENSE NO. OPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNIT NOS. 1 AND 2 DOCKET N05. 50-275 AND 50-323
1.0 INTRODUCTION
By letter dated Noverrber 8,1987, Pacific Gas and Electric Company (PG&E or the licensee) rec:uested an anendment to the Technical Specifications appended to Facility Operating license No. E4 R-80 for the Diablo Canyon Nuclear Power Plant, Unit No. 1.
The propost.d an.endment would allow PG6E to defer, on a one-tin,e basis, exercising the turbine valves until seven days fullowing the return of Unit 2 to full pcwer operation. An arrenoment responsive to this request was issued on November 9,1987, under the Cormission's procedure for emergency technical specification changes.
2.0 DISCl:SSION AND EVAltfATION The turbines at Diablo Canycn Unit I corsist of one high-pressure and three low-pressure turbines on a corrmon shaf t.
Stearr it acmittec to the high-pressure turbine via fcur stop valves and four governor salves which are in series (paired) and therefore redundant with respect to stopping steam flow.
Steam is admitted to the low-pressure turbines via twc reheat stcp and intercept valves for each turbine and are similarly redundant for stopping steam ficw. All 20 salves are closeo wnen the turbine overspeed control system ottects turbine overspeed. The valves are held open during operation by hydraulic fluid pressurc. When overspeed is detected, the hyoraulic fluid pressure is "durrped" and the valves are then closed by large springs.
Technical Specification 4.3.4.1.Pa and b. require that these valves be cycled weekly and directly observed durino the cycling creration cr a monthly betis.
The purpose of the cycling is tc assure that the valves are f ree to move in the event they are needed to cicse to prevent turbine overspeed.
Diablo Canyon Unit 2 was shut down on November 7, 1987 due to a rralfunction of a riotor-operated disconrect link on the Unit 2 main generator.
Repairs may tale as little as two weeks if a replacenent unit can be found, and as much as two trenths if the unit should need to be rebuilt.
The expectatior. is that a sirilar unit located at at other nuclear plant can be adapted to Diablo Canyon anc that repairs can be 6ccomplished in a few weeks.
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PDR Diablo Canyon Unit 1 experienced a cortputer failure on November 5th such that the turbine is currently rurning on manual control. The computer is normally used for conducting the valve exercising.
To do so tranually would run the risk of a turbine trip; to repair the cortputer would require the unit to be shut down.
PGEE desires to keep Unit 1 in full pcher operation and postpone the valve exercising until Unit 2 can be returned to power. Overspeed protection is not affected by the manual mode of operation.
PGAE has'had fully successful operating experience with all the valves on both units. The valve cycling has been perfonned 125 tires on Unit 1 and 85 tirres on Unit 2 with no identifica valve sticking or other preblems.
In addition, fcur valves (one of each type) were disassembled during the refuelinc cutage on Unit 1 in 190f; all eight high-pressure turbine valves were inspected on Unit 2 in 1987.
No unfavorable observations were made with respect to closing function.
In further suprcrt of this c.re-tirre recuest for exter'sion, PGIE cites KCAP-11525, "Probabilistic Evaluation of P. eduction ir. Turbine Vahe Test f requercy" (proprietary), which was prepared by Westinghouse for an owners group of plints with Westinghouse turbine-generators.
Ti.e group rembers currently have requirernents for weekly or monthly turbine valve testing. Tte report has been submitttd to the f;PC by Northern States Power Corpany in support of a recuest to substanticily reduce the turbine valve tesi frecuency for the Prairic Island plant.
PCEE's Diable Canyon facility is ar alyzed in this report as 6: ell.
PGAf states that the report justifies a test frequercy of once per six montFs in order te satisfy the NRC acceptance criteria for acccitably low prchabilities cf damagine turbine overspeed. The t!PC staff's r(view of this report is only beginning, so the request and related report is enly c proposal at this point in time. Nevertheless, the informatier, supplied is substantial at:d does appear to suppot t less frequent testing for turbine valver. The hRC staff will report the results of its resitw of this report in a later safety evaluation.
Based on the foregoing, the hRC staff has concludcd that PGLE has provide sufficient infonnation to support the requested one-tine delay in exercising the turbine valves. Therefore, we find the licensee's proposed change acccptable.
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The hkC staff has rade two changes to the arendtrent cs proposed by l
PG&E. First, PGAE proposed that the valve excrcising fcr Unit 1 be resurred wit hin seven days following Ur.it 2 to full power. Sinte it is possible that Unit 2 might not exactly reach f uTT(ICOT) power when repairs are corpleted, the hPC staff rnodified the proposal to require the seven day perioc to tegin upon Unit 2 reaching power operation (dtiined as Mode 1 or greater than Si pcwer in the technical
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specifications). Second, the FC&f prnposal was conditioried totall 3 cn the return of Ur.it 2 to povier, and theref ore the reouest for e>. tension of titie had ne absolute end. The NRC steff addeo that in any case the
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~ extension will expire by Jar.uary 26, 1988. This was calculated based on PG&E's longest estineted tire for repair (2 n.onths), factored by 25%
which is the usual extension of a surveillance test interval allowed by technical specification 4.0.2.
The changes were discussed with and agreed to by PG&E.
3.0 BASIS FOR EMERGENCY TREATEENT Under the Connission's regulations in 10 CFR 50.92, an errergency situation is deerred to exist when, as here, failure to act in a tirrely way would result in derating or shutdown of a nuclear pcwer plant.
Licensees are also required to explain why the situation occurrea end why it could not be avoidec.
Absent the extensf or, of time granted by the ar enoment, corrpliance with the turbine exercise requirement was due prior to 11:59 p.m. or, Nevenber 9.
Past this tine, FCLE would have to had to declare the turbine overspeed protection system inoperable and isolate the turbire from the steart, supply within si) Locrs.
This, of ccurse, wot'Ic require a shutdown.
A Lovember 7, 1987, Unit 2 was shut dcyn, and PG&E discovered that the valve exercisc could not be performec in the norTral canner due to the computer failure discussed earlier. pG&E r.ade a tirely applicatfor for an amer.cr ent and provided an acequate explar,ation as to why the situation cculc not be avoided.
Fe concloce that PGAE satisficc the requircrrents for er..ergency consideratich cf its recuest.
4.0 FINAL h0 SIGNIFICANT HAZARDS CONSIDEF.ATION OFTERMINATION The Conrission may make a final determination, pursuant tc the prucedures in (10 CFR 50.91), that a proposed anendnent te an crerating license for a facility licensed under paragraph 50.21(b) or paragraph 50.22 or a testing facility involves ne significant hazards consideration, if cperation of the facility in accordar.ce with the propcsed amendnent would not:
(1)
Involve a significant increast in the probability cr consecuences of ar accident pr(viously evaluated; or j
(?) Create the pessibility of a new or different kind cf accider.t frcm any accident pres icusly evaluatea; cv (3)
Involve a significant reduction in a rrargin of saf ety.
FGlf has provided the foll a ing evaluation:
(1) Does the changt involve a significant increase in tFe probability or consequences of an cccident previously evaluated?
.4-1 As discussed in Section B.4, the DCPP turbine overspeed protection system has been demonstreted by testf rig to have a proven reliability of valve operability.
WCAP-ll525 provides an evaluation of the probability of turbine missile generation for the purpose of justifying a reduction in the frequency of turbine valve testing, in a letter to Westinghouse Electric Corporation dated February 2, 1967 (C.E. Rossi, U5hRC to J.A. Martin, Westinghouse), the NRC established acceptable criteria for the prcbability of generating a turbine missile. The evaluation in WCAP-11E25 shows that the probability of a DCPP reissile cjection event for turbine valve test intervals up tc six months is less than the established acceptance criteria.
Based on the results of WCAP-ll525 the suspension of the Urnt I turbine valve testir.g until Unit 2 returns to full power f ron. the ec.uiptrent outage which started on Noverrber 7, 3907, coes not represent a significant increase in the prob 6tility of turbine missile event. Susper.sion of the Unit 1 turbine valve testing has no effect en the consequences of a turbine missile event.
Therefore, based upon the dcmonstrated reliability of the turbire valve system and the results of WCAP-11525, the proposed one time relief Unit 1 ttrbine valve testing license amerdt"ent does not represer.t a significent increase in the probability er ccr. sequences of an accidert previously esaluated.
(2) Does the change crecte the possibility cr a new or different kind of accident from any accident previousl/ evaluated?
lhe proposed arrendntnt does not change the Fina, number or type of overspeed protection corrponents available. Fased on the results of WCAP-11525, suspension of the Unit 1 turbine valve testing until Unit 2 returns to full power frorn the equipment outage which started cn November 7, 1967 does not result in a significant charige in the failure rate or change f ailure modes for the it.rbine valves. Therefore, the proposed one time relief Unit 1 turbine valve testinc license arrendr ent does not creat( the possibility of a rev or differcr.t kind of accident fron any accicent previously evaluated.
(3) Does the change invelse a significant reduction in a rarain c'
' cit:ty ?
As discussed in Section B.4, the DCPP turbine cverspeed protection system ha: been derronstrated by testing to have proven reliability.
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5-The hRC has established acceptance criteria for the probability of generating a turbine missile. WCAP-115?5 demonstrates that significant relaxation of the existing test interval can l'e obtained without increasing turbine missilt gereration prctabilities above those previously acceptec by the NRC. Based on the results in KCAF-11525, suspension ci ttc l' nit 1 turbine valve-testing until l! nit 2 returns to full power frct the equipment outage which started on November 7, 1987 does not represent a significant increase in the ptcbability of a turbine r.issile event. Remaining within the establisheo acceptance criteria ensures that the prcbability of damaging safety-related conpcnents, ceuipment, or structures as a result of generation of a turbine missile does not exceed the limits reported in the safety analysis.
Thereferc, based upen the high reliability of the turbire valve systera anc the results of WCAP-115' 5, the proposed one c
time relief l' nit 1 turbine valve testing licerse amenanent cces not invche a significant reduction in a margin of safet).
The AFC staf f has reviewed the licensee's analyses presented above end finds that it acceptably addresses the three criteria.
Tie State of Cclifornia was censulted in this natter and had nc comen ts. Thereforc, the hRC sta" has rade a final deterr inatiori that the amendn4rt involves oc significar.t hazards consideratier.
E.C ThTIROM'ENTAt CONSIDFW T10N This at:endtent involves changes in the installation cr use of a facility correnent located within thc restrictM area as defined in 10 CfR Part 20.
We havc dctermined that the an+rcn.ent involves no significant increase in the amounts, and no significant change in the types, of any ef fluents that i
rey be released offsite, ar.c that there is no significant increase in individual or cumulative occupatienal radiation exposure. The Coninission i
has determined above that the amerdaent invcihes no significant hazards consideration. Acccrdingly, the anendment meets the elic for categorical exclusion set forth ir,10 CFR 51.2P(c)(9)ibility criteria t
Pursuant to 10 CFR 51.2P(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
6.0 CONCLUSIOF We have cor cluded, based cn the consicerations discussed at'cVe, that: ( there is reasonable ost.orance that the health ard safety of the public will not be endangered by operation in the proposed manner, end (2) such activities will be conducted in ccepliar.co with the Cornission's regulations and (3) the issuance of this amendment wili not be inimical to the commcn defense and security on tc tN bealth ar.d safety of tLe public. Frincipal Centributer: Charles M. Trarrell Dated: Novernber 16, ISE7}}