NRC Generic Letter 1991-07

NRC Generic Letter 1991-007: GI-23, Reactor Coolant Pump Seal Failures and Its Possible Effect on Station Blackout

ML031140509
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Washington Public Power Supply System, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Clinch River
Issue date:	05/02/1991
From:	Partlow J Office of Nuclear Reactor Regulation
To:
References
GL-91-007, NUDOCS 9104290113
Download: ML031140509 (3)

63 'A

• o UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON. D.C. 20555 May 2, 1991 TO: ALL POWER REACTOR LICENSEES AND HOLDERS OF CONSTRUCTION PERMITS

SUBJECT: GI-23, "REACTOR COOLANT PUMP SEAL FAILURES" AND ITS POSSIBLE EFFECT

ON STATION BLACKOUT (GENERIC LETTER 91-07)

The staff published a notice in the Federal Register (56 FR 16130) on April 19,

1991, soliciting public comments on Generic Issue (GI)-23, "Reactor Coolant Pump Seal Failures." This letter informs licensees of the possible effect of GI-23 on their responses to the station blackout (SBO) rule (Section 50.63 of Title 10 of the Code of Federal Regulations [10 CFR 50.63]).

Reactor coolant pump (RCP) seals and their supporting systems have experienced degradations and failures, some of which have been of sufficient severity to be classified as small break loss of coolant accidents (SBLOCAs). Preliminary analyses by the NRC indicated that the RCP seal failures could dominate the overall probability of a core melt caused by SBLOCA. As a result, the staff established GI-23 to provide for the evaluation of the adequacy of current licensing requirements relating to RCP seal integrity and to determine if the U. S. Nuclear Regulatory Commission (NRC) should take any further action.

In resolving the SBO issue (USI A-44), the NRC staff considered the relationship of this issue with other NRC generic issues, including GI--23. In determining estimates of core damage frequency for SBO events in NUREG/CR-3226, "Station Blackout Accident Analyses," the staff assumed that the RCP seals would leak at a rate of 20 gallons per minute (gpm) per pump. During the final resolution of the station blackout issue and the development of the Nuclear Management and Resources Council (NUMARC) Report 87-00, "Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors," NUMARC

and the staff agreed to assume that RCP seal leakage during an SBO would be no greater than 25 gpm per pump. Further, NUMARC and the staff agreed that if the final resolution of GI-23 results in higher RCP leakage rates, then the SBO

analyses would have to be reevaluated.

The SBO rule became effective on July 21, 1988, and the NRC received responses from all licensees addressing the SBO rule by April 21, 1989. Licensees may have analyzed their reactor coolant inventories for the SBO conditions using the specific guidance provided in NUMARC Report 87-00 of 25 gpm for RCP seal leakage for pressurized water reactors (PWRs) and 18 gpm for boiling water reactors (BWRs). These leak rates could be greater if the seals failed during the SBO event.

The preliminary results of the staff's studies for GI-23 indicate that the pump seal leak rates could be substantially higher than those assumed for the resolution of the SBO issue. The staff determined that RCP seal leakage could exceed 25 gpm and lead to core uncovery during an SBO in any of the PWRs and in any of the four BWRs (Millstone Unit 1, Oyster Creek, Nine Mile Point Unit 1,

9104290113 sPD POcK OSOObOOZ P ¶OSO 2 GA

- 2 - May 2, 1991 Generic Letter 91-07 makeup capability.

and Big Rock Point) that do not have an AC-independent public comments on its Having made these findings, the staff is soliciting may be that seal current understanding of GI-23. One possible outcome system during off-normal plant cooling be provided by an independz.it cooling such as could occur during conditions involving the loss of all seal cooling, apply to all PWRs and might an SBO. This recommendation, if adopted, would have AC-independent makeup apply to the above-mentioned BWRs, which do not Therefore, utilities should Lapabilities for their reactor coolant systems. analyses and actions recoanize that such a recommendation could affect their addressing conformance to the SBO rule.

does not require specific Thiis generic letter consists of information only and of Management and Budget action or written response. Therefore, an Office have any questions about this you

(0MB) clearance number is not necessary. Ifcontacts one of the technical listed below or the matter, please :3ntact office.

Regional Administrator of the appropriate regional Sincerely, Ja es G. Partlow As ociate Director for Projects Office of Nuclear Reactor Regulation Technical Contacts: Chu-Yu Liang, NRR

(301) 492-0878 Paul Gill. NRR

(30t) 492-3265

Generic Letter 91-07 - 2 - May 2, 1991 and Big Rock Point) that do not have an AC-independent makeup capability.

HaVins radL thLSte firdinrs, the staff is sClicitil.9 public conmnents on its curry.,t ui.eur t4Laedo., a. -L'-L.. Bla.Loeitle outccme may be that seal C.LLi i.y LL pYUviddc! by an independent cocliiiq SYS L. (Iting off-nUrnial pialmt courciticrs involving the loss of all seal cooling, such as could occur during an SBO. This recommendation, if adopted, would apply to all PWRs and might apply to the above-mentioned BWRs, which do not have AC-independent makeup capabilities for their reactor coolant systems. Therefore, utilities should recognize that such a recommendatiun could affect their analyses and actiouns addressing conforaLrcE to the SEC, rule.

This ger.eric letur corsists of infonnation only and does not require specific action or written response. Therefore, an Office of Management and Budget (ONE) clearance number is not necessary. If you have any questions about 'Ihis matter, please contact one of the technical contacts listed below: or the Regional Administrator of the appropriate regional office.

Sincerely, original signed by James G. Partlow James G. Partlow Associate Director for Projects Office of Nuclear Reactor Regulation Technical Contacts: Chu-Yu Liang, NRR

(301) 492-0878 Paul Gill, NRR

(301) 492-3265 DISTRIBUTION

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See memo Minners to Jordon (CRGR) Dated 2/5/91.

OFFICIAL RECORD COPY Document Name: GL LTR