ML18031A608
| ML18031A608 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/21/1986 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | Bernero R Office of Nuclear Reactor Regulation |
| References | |
| TAC-63178, NUDOCS 8607250068 | |
| Download: ML18031A608 (8) | |
Text
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ACCESSIQN NBR: 8607250068 DOC. DATE: 86/07/2i NOTARIZED:
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50-259 Bv'owns Fev v g Nucleav Power Stationi Unit i. Tennessee AUTH. NANE AUTHOR AFFILIATION GRIDLEH> R.
- Tennessee Valleg Authoritg RECIP. NAME RECIPIENT AFFILIATION BERNERO> R. N.
Division oF Boiling Mater Reactor (BMR > Lic ensing DOCKET 05000259
SUBJECT:
Responds to 860617 v equest for formal submittal oP Documentation v e facilitg risk assessment performed bg util.
Studg currentlg in dvaFt stage 5 will be forwarded once updated.
Summav'g v'ept will be provided bg Sept i986.
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TENNESSEE VALLEYAUTHORITY CHATTANOOGA. TENNESSEE 37401 5N 157B Lookout Place Mr. Robert M. Bernero Director of BWR Licensing OEfice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 JUL 2 i $86
Dear Mr. Bernero:
In the Hatter of the Tennessee Valley Authority Docket No. 50-259 This letter is in response to your "letter dated June 17, 1986 to S. A. White requesting formal submittal of documentation related to a risk assessment performed by TVA on its Browns Ferry Nuclear Plant (BFN) unit 1 TVA initiated an effort several years ago to develop a full scope probabilistic risk assessment (PRA).
The study is currently in a draft stage and reflects the plant, circa 1980.
As you recognized in your letter, it, has many shortcomings which TVA is working to overcome.
These shortcomings include the fact that the study is based on design drawings of that date rather than as-constructed
- drawings, does not incorporate modifications made to the plant in recent years, does not completely address operator recovery
- actions, does not have operator and plant review, and conservatively equates core damage with core melt.
Additionally, the draft study does not Eully credit at least one key system for preventing core damage and the potential for core melt, the control rod drive hydraulic system, which your NRC/Oak Ridge National Laboratory (ORNL) Severe Accident Sequence Assessment (SASA) study and the Industry Degraded Core Rulemaking Program (IDCOR) studies have shown to be very beneficial in preventing core melt in BWRs.
Also, an uncertainty analysis is required to put the sequence probabilities in perspective and the study. does not have the benefit of the design baseline program currently underway.
The baseline effort will reestablish the original plant design basis, update the key drawings documenting, plant configuration, and validate the in-place hardware with respect to the design basis.
As a result oE the above and other shortcomings, the present condition of this report is such that no meaningful conclusions can be drawn from it.
The PRA will continue to be updated and eventually will include information from our design baseline effort. I will Eorward you a complete copy of the study once it has been updated.
Unfortunately, the completed report will not be available in the near term due to the extensive nature of the effort required to incorporate the results of the design baseline program and other efforts required to make it meaningful.
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Mr. Robert M. Bernero JUL 21 $86 Accordingly, in the interim I have directed the preparation of a technical summary report describing the draft PRA with appropriate upgrading and corrections.
This report will emphasize the relative contributions of various sequences to plant degradation.
Preparation of the report will require about eight months.
The report will include an executive summary portion as well as the technical details.
This report can address a number of issues and interests within NRC, provided a careful and critical perspective is maintained.
Consequently, the technical insights available to date will be included as well as a brief discussion concerning, how TVA is addressing some of the issues.
It will include a summary of your proposed "competent analysis" of the shortcomings of the 'draft PRA version on which it is based, along with our plans for PRA upgrade so that you may understand fully any reservations I have concerning the submittal of the study.
I believe this document will address our respective needs in the near term in a format that reduces the amount of work required to identify important PRA findings.
This should provide sufficient information for NRC to adequately consider key issues for restart.
If you have any questions concerning this approach, please inform my staff.
The summary report, which includes our summarized "competent analysis" of the PRA shortcomings, is currently being prepared and I will provide you with a firm schedule for submittal of this document by September 1986.
Very truly yours, TENNESSEE VALLEY AUTHORITY R. Gridley, irector Nuclear Safety and Licensing cc:
See page 3
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Mr. Robert M. Bernero JUL 2 1 586 cc:
Mr. James Taylor, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Mr. R. J. Clark U.S. Nuclear Regulatory Commission Browns Ferry Project Manager 7920 Norfolk Avenue
- Bethesda, Maryland 20814 U.S. Nuclear Regulatory Commission Region II ATTN:
Dr. J. Nelson Grace, Regional Administrator 101 Mariet.ta Street.,
NW, Suite 2900 Atlanta, Georgia 30323