ML18033A689

Forwards Request for Addl Info Based Upon NRC Audit of Plant Pra,Section III.11.0 Re Core Melt Frequency for Plant When Compared to Similar Plants of Similar Vintage.Potential Single Failure Vulnerability Noted

ML18033A689
Person / Time
Site:	Browns Ferry
Issue date:	03/29/1989
From:	Black S Office of Nuclear Reactor Regulation
To:	Kingsley O TENNESSEE VALLEY AUTHORITY
References
TAC-63178, NUDOCS 8904030293
Download: ML18033A689 (7)

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. Docket No. 50-260 t

UNITED STATES t

NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 March 29, 1989 Mr. Oliver D. Kingsley, Jr.

Senior Vice President, Nuclear Power Tennessee Valley Authority 6N 38A Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801

SUBJECT:

VOLUME 3$

SECTION III.11.0 (PROBABILISTIC RISK ASSESSMENT)

OF THE NUCLEAR PERFORMANCE PLAN -

BROMNS FERRY NUCLEAR PLANT, UNIT 2 (TAC 63178)

On May 18, 1988, the staff met with the Tennessee Valley Authority (TVA or the licensee) to discussSection III.11.0 of Volume 3 (Nuclear Performance Plan-Browns Ferry) and TVA's approach to resolving the staff's concerns of whether the Browns Ferry plant is an outlier in terms of core melt frequency when compared to similar plants of similar vintage.

The staff's concerns were based upon a limited scope review of a Probabilistic Risk Assessment (PRA) study provided to NRC in November 1986.

This PRA was identified by the licensee as the January 1986 draft PRA.

During this meeting, the licensee committed (NRC Meeting Summary dated May 27, 1988) to provide a sumary of changes made between the January 1986 draft PRA and a newer September 1987 version.

This summary report was submitted to the staff by letter dated August 25, 1988.

The staff used this report as guidance for its review of selected sections of the September 1987 PRA.

The staff reviewed these sections as part of an audit of the September 1987 PRA in Knoxville, Tennessee (November 1 and 2, 1988).

As a result of this audit, a potential signal failure vulnerability was noted.

This issue is discussed in the enclosure.

In order for us to proceed with our review of this Volume 3 issue, we will need your response to this item, including plans for resolution, within 60 days of receipt of this letter.

Since this issue must be resolved prior to restart, we strongly suggest a meeting in April. If you have any questions, please contact the Browns Ferry Project Manager, G. Gears, at 301-492-0767.

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Nr Oliver D. Kingsley, Jr. The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OhlB clearance is not required under P.L.96-511.

Sincerely,

Enclosure:

Request for Additional Information cc w/enclosure:

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I Mr. Oliver D. Kingsley, Jr.

- Browns Ferry Nuclear Plant CC:

General Counsel Tennessee Valley Authority 400 West Summit Hill Drive Ell B33 Knoxville, Tennessee 37902 Mr. R. L. Gridley Tennessee Valley Authority 5N 157B Lookout Place Chattanooga, Tennessee 37402-2801 Mr.

C.

Mason Tennessee Valley Authority Browns Ferry Nuclear Plant P.O.

Box 2000

Decatur, Alabama 35602 Mr. P. Carier Tennessee Valley Authority Browns Ferry Nuclear Plant P.O.

Box 2000

Decatur, Alabama 35602 Mr. D. L. Williams Tennessee Valley Authority 400 West Summit Hill Drive W10 B85 Knoxville, Tennessee 37902

Chairman, Limestone County Commission P.O.

Box 188

Athens, Alabama 35611 Regional Administrator, Region II U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W.

Atlanta, Georgia 30323 Resident Inspector/Browns Ferry NP U.S. Nuclear Regulatory Commission Route 12, Box 637

Athens, Alabama 35611 Dr. Henry Myers, Science Advisor Committee on Interior and Insular Affairs U. S.

House of Representatives Washington, D.C.

20515 Tennessee Valley Authority Rockville Office 11921 Rockville Pike Suite 402 Rockville, Maryland 20852 Claude Earl Fox, M.D.

State Health Officer State Department of Public Health State Office Building Montgomery, Alabama 36130

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ENCLOSURE RE UEST FOR ADDITIONAL INFORMATION BASED RRY PRA The following is an audit finding on dominant sequence 5 of the revised Browns Ferry PRA (September 1987 version):

Sequence 5:

A loss of offsite power event followed by failure of the high pressure coolant

'akeup

systems, and failure of the low pressure injection system and the core spray system to provide coolant inventory makeup to the reactor and required pool cooling.

Finding:

The frequency estimate seems somewhat conservative.

However, during the audit review, the licensee indicated that failure of a single shutdown board 1A following a loss of offsite power event will result in failure of two RHR pumps which are required for successful pool cooling.

There is a possibility that this situation may result in a violation of General Design Criteria (GDC) 17 and 34 of 10 CFR Part 50, Appendix A.

GDC 17 and 34 generally require that the licensed nuclear facility be provided a decay heat removal design that is single failure proof.

Therefore, we recommend that the adequacy of the existing decay heat removal design and the significance of the loss of two RHR pumps resulting from a single failure of shutdown board 1A be carefully considered.

This issue must be resolved prior to Unit 2 restart.

Remarks:

The modeling of the recovery of the 480 V shutdown board 1A during a

period of five to six hours could reduce the sequence frequency.

The Browns Ferry plant-specific procedures should be reviewed carefully for the feasibility estimate is also based on a success criterion that one RHR pump is needed for vessel injection and two RHR pumps are simultaneously needed for pool cooling (referred to as the RC event in the PRA).

This criterion may be overly stringent, assuming that RHR pumps could be re-started manually; and considering an availability of a recovery time of at least two to three hours for the RHR system prior to a substantial pool heat-up.

The future revisions to the PRA should explore a realistic success criterion for a combination of the vessel injection and pool cooling functions.

The failure of a single shutdown board 1A following a transient such as loss of offsite power should result in a potential loss of two RHR pumps needed for pool cooling function.