L-91-327, Forwards Evaluation for Generic Issue 94,addl Low Temp Overpressure Protection,To Suppl 901220 Response to Generic Ltr 90-06 Re Generic Issues 70 & 94
| ML17223B368 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 12/06/1991 |
| From: | Sager D FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| REF-GTECI-070, REF-GTECI-094, REF-GTECI-NI, TASK-070, TASK-094, TASK-70, TASK-94, TASK-OR GL-90-06, GL-90-6, L-91-327, TAC-M77457, NUDOCS 9112130075 | |
| Download: ML17223B368 (5) | |
Text
ACCELERATED DIS UTION DEMONST TION SYSTEM e
REGULATORY INFORMATXON DISTRXBUTXON SYSTEM (RIDS)
DOC.DATE: 91/12/06 NOTARIZED: NO ACCESSION NBR:9%12130075 FACIL: M-995 AUTH.NAME SAGER,D.A.
RECIP.NAME AUTHOR AFFILIATION Florida Power 6 Light Co.
RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
DOCKET ¹
SUBJECT:
Forwards evaluation for Generic Issue 94 addi low temp overpressure protection to suppl 901220 response to Generic I
Ltr 90-06 re Generic Issues 70
& 94.
D DISTRIBUTION CODE:
A019D COPIES RECEIVED:LTR ENCL SIZE:
TITLE: Generic Ltr 90-06 Resolution of GE 70N94 PORVs 6 Block Va ve Relzabil NOTES:
RECXPIENT ID CODE/NAME LA PM XNTERNAL: KIRKWOOD,R. NLS3 RXB REG 01 DS R/RPSIB EXTERNAL NRC PDR COPIES LTTR ENCL 1
1 1
1 1
1 1
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1 1
1 1
1 RECIPIENT ID CODE/NAME PD NRR/EMEB PICKETT,D 13H15 RES/DSXR/EIB NUDOCS-ABSTRACT COPIES LTTR ENCL 1
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1 A
D D
D NOTE TO ALL"RIDS" RECIPIENTS:
D D
PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!
TOTAL NUMBER OF COPIES REQUIRED:
LTTR 12 ENCL 12
P.O. Box 128, Ft. Pierce, FL 34954-0128 December 6,
1991 L-91-327 10 CFR 50.4 U.
S. Nuclear Regulatory Commission Attn: Document Control Desk Washington',
D.
C.
20555 Gentlemen:
RE:
St. Lucie Unit 1 Docket No. 50-335 Supplemental Response to Generic Letter 90-06 TAC No.
77457 By Florida Power and Light Company (FPL) letter (L-90-435) dated December 20,
- 1990, FPL committed to provide the results of its evaluation of the potential risk reduction of an LTOP event which is engendered by limiting the allowed outage time for the PORVs as recommended in Enclosure B of GL 90-06.
FPL has completed the
'plant specific evaluation for Unit 1.
The plant specific core damage frequency (CDF) estimate due to LTOP transients is less than the 1E-6/Rx-YR screening value assumed by the NRC and thus the recommended actions would not be cost beneficial.
A summary of the evaluation is attached for your information.
By Generic Letter 90-06, the NRC provided the proposed resolution of Generic Issue 70 "Power-operated Relief Valve and Block Valve Reliability," and Generic Issue 94, "Additional Low-Temperature Overpressure Protection for Light-Water Reactors,"
and required a
response pursuant to 10 CFR 50.54 (f).
The FPL response was submitted by FPL letter L'-90-435 dated December 20, 1990.
Please contact us if there are any questions about this submittal.
Very truly yours, D. A.
Vice St.
L ger esident ie Plant DAS/GRM/kw cc:
Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant DAS/PSL g574-91 9112130075 911206
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ST.
LUCIE UNIT 1 PLANT SPECIFIC EVALUATION FOR GENERIC ISSUE 94 ADDITIONALLTOP PROTECTION Generic Letter (GL) 90-06 concluded that LTOP.(Low,Temperature Overpressure Protection) system unavailability is the dominant contributor to risk from LTOP transients and thus improvement in LTOP system availability when the potential for an overpressure transient is the highest should be achieved through improved administrative restrictions on the LTOP system unavailability.
GL 90-06 proposes that this be accomplished by Technical Specification revisions restricting the maximum allowable out-of-service time for a single LTOP channel in Modes 4
and 5 or Mode 6 with the head installed and the RCS not vented.
The NRC states that the contribution to the total core damage
., frequency (CDF) from LTOP events should be less than 1E-6 'per reactor-year
(/Rx-Yr).
Based on industry data, an estimated CDF of 3.04E-6/Rx-Yr was calculated by the NRC (NUREG-1326). 'his calculation takes into account the LTOP challenge frequency, LTOP system unavailability, and the probability of reactor vessel failure due to the LTOP transient.
Since St. Lucie Unit 1 has had zero LTOP events within the NRC data window (1980-1990), it was necessary to perform a
Bayesian estimation calculation in order to obtain a plant specific LTOP challenge frequency.
A Bayesian estimation updates past data (i.e., generic industry wide data) with plant specific experience and thus has the effect of "specializing" the prior data to a
specific plant.
The Bayesian estimated St.
Lucie Unit 1
LTOP challenge frequency was calculated to be.008/Rx-Yr in lieu of the
.094/RX-Yr "generic frequency calculated by the NRC.
The plant specific LTOP unavailability was found to be slightly larger than the "generic" value calculated by the NRC
(.1-plant specific compared to.087-NRC value).
The plant specific unavailability is based on a review of the operating logs, equipment out-of-service
- logs, and NPRDS reports.
The PORV flow path unavailability considers the number of hours one or both PORV flow paths were out-of-service during Modes 4 or 5 for the data window of 1986-1990.
A plant specific failure-to-open probability was also considered.
The plant specific unavailability is dominated by both flow paths being out-of-service (the probability equals 0.1 based on 407 hours0.00471 days <br />0.113 hours <br />6.729497e-4 weeks <br />1.548635e-4 months <br /> out-of-service and 4002 hours0.0463 days <br />1.112 hours <br />0.00662 weeks <br />0.00152 months <br /> in Modes 4 and 5).
The generic data in NUREG 1326 for reactor failure probability was utilized in the FPL analysis.
A calculation based on the use of plant specific LTOP challenge frequency and PORV flow path unavailability data yielded a St.
Lucie Unit 1 CDF estimate due to LTOP transients of 3.01E-7/Rx-Yr compared to the 3.04E-6/Rx-Yr frequency calculated by the NRC. The plant specific CDF is below the 1E-6/Rx-Yr screening value assumed by the NRC and thus the recommended Technical Specification change would not be cost beneficial.
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