Information Notice 2005-14, Fire Protection Findings on Loss of Seal Cooling to Westinghouse Reactor Coolant Pumps

Fire Protection Findings on Loss of Seal Cooling to Westinghouse Reactor Coolant Pumps

ML051080499
Person / Time
Issue date:	06/01/2005
From:	Hiland P NRC/NRR/DIPM/IROB
To:
Franovich M, NRR/DSSA/SPSB, 415-3361
References
IN-05-014
Download: ML051080499 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

June 1, 2005

NRC INFORMATION NOTICE 2005-14:

FIRE PROTECTION FINDINGS ON LOSS OF

SEAL COOLING TO WESTINGHOUSE

ADDRESSEES

All holders of operating licenses for pressurized water reactors, except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission is issuing this information notice (IN) to inform

addressees about recent inspection findings on post-fire procedural requirements related to

loss of cooling to reactor coolant pump (RCP) seals. NRC anticipates that recipients will review

the information for applicability to their facilities and consider taking actions, as appropriate, to

avoid similar issues. However, no specific action or written response is required.

BACKGROUND

Assuming a fire results in loss of cooling to the RCP seals, licensees may comply with 10 CFR

Part 50, Appendix R, Fire Protection Program for Nuclear Power Facilities Operating Prior to

January 1, 1979, by protecting the cooling to the seals or by demonstrating that the plant can

cope with RCP seal leakoff flow rates. Many licensees have installed RCP seal packages using

high-temperature O-rings that will not result in uncontrolled leakage from RCP seals for

conditions with loss of all RCP seal cooling. Licensees also ensure adequate makeup

capability to compensate for any RCP seal leakoff and maintain reactor coolant system (RCS)

inventory according to requirements of Appendix R, Sections III.G.2, III.G.3, and III.L.1 and

performance goals of Appendix R,Section III.L.2. Note that a plant licensed before January 1,

1979, must meet the provisions of Appendix R,Section III.G and III.L and a plant licensed after

January 1, 1979, must implement the fire protection provisions of its operating license.

DESCRIPTION OF CIRCUMSTANCES

At Surry, NRC inspectors found that certain postulated fires could result in the loss of cooling to

the RCP seals. The inspectors noted that the RCP seal vendor, Westinghouse, advised that

increased seal leakage, to around 21 gpm, could occur if seal cooling is lost and not restored

before hot RCS fluid reaches the RCP seals. Additionally, the Westinghouse Owners Group

(WOG) revised their generic emergency response guidelines for the station blackout event to

recommend that RCP seal cooling not be restored following a prolonged loss of seal cooling in

which the seal temperature exceeds the RCP seal vendors recommendations. The licensee

incorporated this guidance into its emergency operating procedures for the response to a loss

of all alternating current (AC) power event but not in its procedures for safe shutdown of the

reactor after a fire. Restoration of seal injection after the seals become hot could lead to

increased leakage beyond the RCS makeup capability needed to satisfy the performance goals

in Appendix R,Section III.L.2 (NRC Inspection Reports 50-280/03-07 and 50-281/03-07).

Similar findings were made at other nuclear power plants. At Turkey Point, NRC inspectors

found that the post-fire procedures did not provide timely operator action to restore seal

injection and could result in increased RCP seal leakage beyond the capacity of equipment

dedicated to achieve and maintain post-fire safe shutdown according to Appendix R, Section

III.G.2 (NRC Inspection Reports 50-250/04-07 and 50-251/04-07). At North Anna, NRC

inspectors found, similar to the Surry finding, that certain fires could result in a loss of seal

cooling. Seal cooling could be restored after the seal had heated up, thereby potentially

resulting in increased seal leakage beyond the RCS makeup capability required to satisfy

Appendix R,Section III.L.2 (NRC Inspection Reports 50-338/03-06 and 50-339/03-06). At

Summer, the inspectors were concerned that the licensees fire emergency procedure did not

direct personnel to reestablish seal cooling flow in a timely manner, potentially leading to

increased seal leakage beyond the RCS makeup capability needed to satisfy Appendix R,

Section III.L.2 (NRC Inspection Report 50-395/01-10).

DISCUSSION

The NRC uses deterministic information to determine the existence of performance

deficiencies. The risk significance of an identified performance deficiency is evaluated using

probabilistic risk assessment (PRA) models.

In each case cited above, the NRC inspectors attributed the performance deficiency to

inconsistent recovery procedures. They observed that the plant emergency procedures for a

loss of all AC power did not agree with the plant procedures for mitigating the effects of a

postulated fire. The post-fire procedures failed to direct plant personnel to restore RCP seal

cooling before the seal temperature exceeds the vendor-specified limit. The inspection findings

from Turkey Point also indicate that the fire mitigation procedures fail to consider that

restoration of seal cooling is a time-critical operator action. For seal packages in general, the makeup capability must exceed the seal leakoff to ensure

that a hot standby condition can be achieved (according to the requirements in Appendix R,

Section III. L.1. (c) and that the pressurizer level is maintained in the indicating range

(according to the performance goals in Appendix R,Section III L.2.b). Furthermore, protecting

seal integrity would be assisted if procedures for operating equipment needed for post-fire

shutdown are consistent with vendor recommendations. For the Westinghouse RCP seals, as

discussed in a recently submitted document on RCP seal performance (Reference 3), a

leakage rate of 21 gpm per RCP may be assumed in the licensees safe shutdown assessment

following the loss of all RCP seal cooling. Assumed leakage rates greater than 21 gpm are

only warranted if increased seal leakage is postulated as a result of deviations from seal vendor

recommendations. Test or operating experience may be used to justify other RCP seal leakage

rates.

Licensees with Westinghouse RCP seals have developed fire emergency procedures to cope

with a loss of all RCP seal cooling by either reestablishing seal cooling to the RCPs before

increased seal leakage occurs (to prevent increased leakage) or by providing sufficient RCS

makeup to achieve and maintain post-fire safe shutdown.

Performance deficiencies and violations of regulatory requirements can result from all of the

following: (1) procedural deviations from the manufacturers recommendations without a

documented basis, (2) inadequate procedures, and (3) inadequate documented analysis to

show that Appendix R,Section III.L requirements are met.

If a performance deficiency exists, it is evaluated in the significance determination process

(SDP) using PRA models. The loss of RCP seal cooling has been extensively modeled in PRA

applications. In particular, the NRC used PRA information from its closure of a generic safety

issue involving RCP seal failure (Reference 1) and from its safety evaluation of an industry

model of RCP seal leakage (Reference 2) as the SDP framework to evaluate the risk

significance of certain fire protection inspection findings. In the Surry case, the NRC estimated

that the increase in the core damage frequency was between 1E-6 and 1E-5 per year (a white

inspection finding). This finding is highly dependent on the plant-specific electrical switchgear

room arrangement and the fire mitigation strategy.

In the recently submitted document on RCP seal performance (Reference 3), the NRC has not

found sufficient new information to improve PRA models from previously issued industry models

(Reference 4) or safety evaluation reports (Reference 2).

The PRA modeling considers two cases. In case 1 (plants with Westinghouse high- temperature O-rings and seals), Westinghouse, the RCP seal vendor, states that after loss of

seal cooling, the seals with high-temperature O-rings will leak at about 21 gpm per pump. If the

licensee implements vendor guidelines, this condition is not expected to proceed to failures

resulting in leak rates greater than 21 gpm per pump. Even if seal cooling is not reestablished, degradation of the seals for leakage rate to significantly increase is not expected for an indefinite period of time if the RCPs are secured before the seal temperature exceeds 235 degrees F. Restoration of seal cooling may result in cold thermal shock of the seal and

possibly cause increased seal leakage. If seal cooling is restored using component cooling

water (CCW) to the thermal barrier cooler, water hammer may occur and possibly compromise

the integrity of the CCW system. As discussed in the recently submitted document on RCP

seal performance (Reference 3), if the CCW system is damaged, then plant shutdown after a

fire accident may not be possible in all scenarios.

To be consistent with 10 CFR Part 50, Appendix B, Quality Assurance Criteria for Nuclear

Power Plants and Fuel Reprocessing Plants, protection of seal integrity depends on fire

protection and RCP recovery procedures being consistent with the manufacturers

recommendations and that the associated instrumentation, alarms, and recovery procedures

are available after a fire.

In case 1 (plants with Westinghouse high-temperature O-rings and seals), the NRC PRA

modeling accounts for two failure scenarios, given a loss of seal cooling with no RCPs

operating. In failure scenario 1 (hot shock), during initial heating of the seals, hydraulic

instability caused by fluid flashing can potentially open (pop) the second-stage seal faces

(Reference 2). For this scenario, the NRC PRA model assumes that the popping failure of the

second-stage seal occurs at 13 minutes after loss of RCP seal cooling.

In case 1, failure scenario 2 (cold shock), if RCP seal cooling is restored after the seal

temperature exceeds the vendor-specified limit, given survival from the initial hot shock of the

seals, the NRC uses seal failure probabilities and consequential seal leakage sizes similar to

those used in failure scenario 1.

In case 2 of the NRC PRA model (Westinghouse plants with old, pre-high-temperature RCP

seals), Westinghouse, the RCP seal vendor, states that after loss of seal cooling, the old

seals could fail after about 30 minutes. Therefore, protection of seal integrity requires the

restoration of seal cooling within the appropriate time limit. However, this time limit is

approximate. Plant-specific vendor guidance may differ based on (1) commitments made with

respect to the station blackout analysis and (2) licensee-specific vendor recommendations.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contact(s) listed below or the appropriate NRR

project manager.

/RA/

Patrick L. Hiland, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts:

Phil Qualls, NRR

Michael Franovich, NRR

301-415-1849

301-415-3361 E-mail: pmq@nrc.gov

E-mail: mxf1@nrc.gov

Albert Wong, NMSS

301-415-7843 E-mail: axw2@nrc.gov

Attachment: References

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contact(s) listed below or the appropriate NRR

project manager.

/RA/

Patrick L. Hiland, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts:

Phil Qualls, NRR

Michael Franovich, NRR

301-415-1849

301-415-3361 E-mail: pmq@nrc.gov

E-mail: mxf1@nrc.gov

Albert Wong, NMSS

301-415-7843 E-mail: axw2@nrc.gov

Attachment: References

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

DISTRIBUTION:

ADAMS

IN File

ADAMS ACCESSION #: ML051080499 DOCUMENT NAME: E:\\Filenet\\ML051080499.wpd

OFFICE

DSSA:SPLB

Tech Editor

DSSA:SPLB

ADPT:DLPM

ADPT:DLPM

NAME

CVHodge

PKleene

SWeerakkody

CGratton

EABrown

DATE

05/12/2005

04/06/2005

04/08/2005

05/12/2005

05/16/2005 OFFICE

ADPT:DIPM

ADPT:DIPM

ADPT:DIPM

A:SC:OES:IROB:DIPM

C:IROB:DIPM

NAME

SRMonarque

KRCotton

GSShukla

EJBenner

PLHiland

DATE

05/12/2005

05/12/2005

05/12/2005

05/16/2005

06/01/2005

OFFICIAL RECORD COPY Attachment

REFERENCES

1.

NRC Regulatory Information Summary 2000-002, Closure of Generic Safety Issue 23, Reactor Coolant Pump Seal Failure, February 15, 2000 (ADAMS ML003680402)

2.

NRC Office of Nuclear Reactor Regulation, Safety Evaluation of WCAP-15603, Revision 1, WOG 2000 Reactor Coolant Pump Seal Leakage Model for Westinghouse

PWRs, Westinghouse Owners Group Project No. 694, May 2003 (ADAMS

ML0314003760)

3.

Westinghouse Owners Group, Reactor Coolant Pump Seal Performance for Appendix R

Assessments, WCAP-16396-NP, Revision 0, January 2005 (ADAMS ML050320187)

4.

Westinghouse Electric Company, LLC, WOG 2000 Reactor Coolant Pump Seal Leakage

Model for Westinghouse PWRs, WCAP-15603, Revision 1, May 2002 (ADAMS

ML021500485)