ML16342D747
| ML16342D747 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/23/1997 |
| From: | Steven Bloom NRC (Affiliation Not Assigned) |
| To: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| References | |
| TAC-M98829, TAC-M98830, NUDOCS 9707250117 | |
| Download: ML16342D747 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&0001 Ou1y 23, 1997 Mr. Gregory M. Rueger Pacific Gas and Electric Company NPG - Hail Code A10D P. 0.
Box 770000 San Francisco, Cali fornia 94177
SUBJECT:
INSTALLATION OF THE COMPONENT COOLING WATER SURGE TANK PRESSURIZATION SYSTEM - DIABLO CANYON POWER PLANT. UNIT NOS.
1 AND 2 (TAC NOS.
M98829 AND H98830)
Dear Hr. Rueger:
As reported in LER 96-005 dated April 26,
- 1996, Paci tie Gas and Electric Company (PGBE) determined that localized boiling could occur in the Diablo Canyon component cooling water (CCW) systems in the vicinity of the containment fan coolers during a limiting design basis accident.
To ensure equipment operability and containment integrity, PG&E modified the CCW systems for Diablo Canyon so that they were pressurized with nitrogen instead of being vented to atmosphere.
Following the installation of the modification, PG8E submitted License Amendment Request 97-05 by letter dated May 22, 1997.
The NRC staff, following your submittal, requested that you submit your 10 CFR 50.59 safety evaluation associated with this modification.
You submitted the evaluation by letter dated June 12, 1997.
We have reviewed your 10 CFR 50.59 evaluation and we find that your evaluation did not adequately assess the modification.
Pressurizing the CCW system with nitrogen can lead to vapor binding of the CCW pumps.
can affect the heat transfer assumptions and containment analysis that were previously performed, and can affect system leak rate and water inventory considerations (among other things).
While you recognize in your safety evaluation that a rapid depressurization of the CCW system could affect heat transfer and CCW pump operation, you concluded that the increased dissolved gas in the CCW system wi 11 not "significantly impact" CCW thermal conductivity or CCW pump net positive suction pressure.
Your conclusion is apparently dependent on the specific system design and operational parameters that have been established and on the administrative controls that you plan to put in place.
none of which have been reviewed and approved previously by the NRC staff.
Additional factors that we consider important and relevant from a 10 CFR 50.59 perspective but not addressed in your evaluation, include specific equipment malfunction and single fai lure considerations, gradual buildup of nitrogen in the CCW system over time.
and the potential for nitrogen gas release during design-basis accident conditions.
You also concluded in your evaluation that during implementation of the modification, when the integrity of the surge tank vent line was temporarily breached.
there could have been a period of time when the automatic isolation valve for the surge tank vent line may not have been able to perform its automatic isolation function.
It would stand to reason that during this period of time. there would be an increase in the possibility of an equipment 0
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Mr. Gregory M. Rueger Ouly 23, 1997 maltunction as well as a possible increase in accident consequences since the automatic isolation function would not be available.
While we understand that compensatory measures were established to take the place of this automatic isolation function, these measures were not submitted for staff review and approval.
Changing the CCW system from being normally vented to normally pressurized with nitrogen is a substantial modification that introduces vulnerabi lities that were not considered previously.
In order for the NRC to evaluate your license amendment
- request, we request that you respond to the staff's concerns as expressed in this letter, and describe any actions. that you plan to take to remedy this situation.
Because we consider this to be an important issue that deserves prompt action, you are requested to provide your response within 30 days of receipt of this letter.
If you have any questions, please contact Steven D. Bloom, Project Manager, at (301) 415-1313.
Sincerely, Original Signed By Steven D. Bloom Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation
=
Docket Nos.
50-275 and 50-323 cc:
See next page DISTRIBUTION:
I'Docket File PUBLIC PDIV-2 Reading JRoe EAdensam WBateman SBloom EPeyton ACRS
- OGC, 015B18
- KPerkins, RIV/WCFO
- PGwynn, RIV
- LTatum, SPLB
- GHubbard, SPLB
- TMarsh, SPLB DOCUMENT NAME:
DC98829.LTR OFC PDIV-2 NAME SB o:ye DATE 7/>3/97 PDIV-2 EPeyt n
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I'
Mr. Gregory M. Rueger Ouly 23, 1997 CC:
NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission P. 0.
Box 369 Avila Beach, California 93424 Dr. Richard Ferguson, Energy Chair Sierra Club California 1100 11th Street.
Suite 311 Sacramento.
Cali fornia 95814 Ms. Nancy Culver San Luis Obispo Mothers for Peace P. 0.
Box 164 Pismo Beach. California 93448 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo. California 93408 Mr. Truman Burns Mr. Robert Kinosian California Public Utilities Commission 505 Van Ness.
Room 4102 San Francisco.
Cali fornia 94102 Mr. Steve Hsu Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento.
California 94232 Diablo Canyon Independent Safety Committee ATTN:
Robert R. Wellington, Esq.
Legal Counsel 857 Cass Street.
Suite D
Monterey, California 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower 8 Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington. Texas 76011-8064 Christopher J.
Warner.
Esq.
Pacific Gas 8 Electric Company Post Office Box 7442 San Francisco.
California 94120 Mr. Robert P.
Powers Vice President and Plant Manager Diablo Canyon Nuclear Power Plant P. 0.
Box 56 Avila Beach, California 93424 Telegram-Tribune ATTN:
Managing Editor 1321 Johnson Avenue P.O.
Box 112 San Luis Obispo, California 93406
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