ML17199T488
| ML17199T488 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, 05000000 |
| Issue date: | 12/22/1987 |
| From: | Silady J COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 4009K-BS, NUDOCS 8801050469 | |
| Download: ML17199T488 (2) | |
Text
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Common.th Edison One First Nati Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 - 0767 December 22, 1987 Mr. Thomas E. Murley, Director Office of Nuclear Reactor 'Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Quad Cities Station Units 1 and 2 Dresden* Station Units 2 and 3 Effect of Postulated DC Power Failure NRC Docket Nos. 50-254, 265, 237, and 249 Reference (a):
December 21, 1987 letter from J. -A. Silady to T. E. Murley (attached)
(b):
December 21, 1987 conference calls between CECo (N. J. Kalivianakis, J. s. Abel, et al.)
NRR (G. Holahan, D. R. Muller, et al.) and RIII (M. Ring)*
Dear Mr. Murley:
In reference (a), which is enclosed as Attachment 1, Commonwealth.
Edison addressed an error in the ECCS analysis report recently submitted and approved in support of the Quad Cities Unit 1 Cycle 10 rel9ad.
This was further discussed with your staff in two conference calls (Reference (b)). lists the participants in these calls.
The reference (a) letter and the reference (b) conference calls also discussed whether assumption of a passive component failure is beyond the approved design basis for early vintage BWRs such as Quad Cities and Dresden.
As a result of these discussions, CECo agreed to provide an evaluation of the probability of a postulated battery failure coincident with LOCA and Loss of O~fsite Power considering the actual remaining ECCs equipment that would then be available.
This is provided in Attachment 3.
The available ECCS subsystems summarized in Attachment 4 for various break locations and failures, was developed after considering the implications of a recent event at another BWR facility with a similar LPCI Loop Select Logic design.
As discussed in Attachment 3, the high reliability of the battery system combined with routine battery surveillances result in very low failure probability.
When the unique combination of-independent events (limiting break LOCA plus Loss of Offsite Power plus simultaneous battery failure) and the extremely narrow time window of the sequence of events are considered; the overall probability is extremely low.
T. December 22, 1987 also discusses compensating factors which further reduce any safety significance of this unlikely event.
In addition to detailing battery monitoring and surveillances, Attachment 3 describes the interim operating procedures which have been implemented to recognize and mitigate the concern even if such a remote accident sequence should occur.
CECo will evaluate the existing Quad Cities and Dresden LPCI injection valve swing bus transfer system relative to the recent design issue identified at a similar plant, regardless of -the ultimate resolution or clarification of the need to include passive failure~ in the design bases for early BWR plants._ Alternatives to eliminate the identified design weakness will be developed and evaluated for feasibility based on the many system design constraints (e.g., separation *requirements, system reliability, Appendix R committments, etc). A plant modification. will be proposed assuming the solution does not result in an overall decrease in plant safety.
Within sixty (60) days of this letter, CECo wii,l provide our proposed solution with a schedule for implementation.
The installation schedule will depend on the complexity of the design and *the availability of material.
As discussed in Attachment 1, CECo will also provide the necessary revision to the Quad Cities Unit 1 ECCS analysis report (NEDC-23785P) as soon as they become available from General Electric.
In view of this scenario's extremely low probability and therefore minimal safety significance, Commonwealth Edison believes that the Dresden and Quad Cities units continue to operate consistent with the health and safety of the general public.
Very truly yours, f}4~
J. A. Silady Nuclear Licensing Administrator Attachments (4) cc:
A. B. Davis - Regional Administrator (RIII)
T. Ross - NRR M. Grotenhuis - NRR M. Ring - Region III G. Holahan - NRR NRC Resident Inspectors - Dresden & Quad Cities 4009K/bs