ML19289D732

Specifies Three Mods That May Be Necessary to Resolve NRC Concerns Re Atws.Requests Commitment That Plant Design Will Not Preclude These Mods

ML19289D732
Person / Time
Site:	Palo Verde
Issue date:	02/14/1979
From:	Parr O Office of Nuclear Reactor Regulation
To:	Vanbrunt E ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
References
NUDOCS 7903140293
Download: ML19289D732 (3)

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% *.....p rES 11 ;g7a Docket Nos. STN 50-592 and STN 50-593 Mr. E. E. Van Brunt, Jr.

Vice President - Nuclear Project Management Arizona Public Service Company P. O. Box 21666 Phoenix, Arizona 85036

SUBJECT:

ANTICIPATED TRANSIENTS WITHOUT SCRAM (ATWS) - PALO VERDE NUCLEAR GENERATING STATION, UNITS 4 AND 5 Potential modifications to nuclear reactor facilities that may be necessary to resolve staff concerns have been identified in a Staff Report, " Anticipated Transients Without Scram for Light Water Reactors," NUREG-0460, Volume 3, December 1978.

For the Palo Verde 4 and 5 facility, these modifications are:

(1) Provision of diverse actuation circuitry for mitigating systems.

This diversity can be attained by implementation of (as or (b) below:

(a) Provision of a diverse, four-channel supplementary pro-tection system (SPS) described by Combustion Engineering.

It would be diverse and independent from the reactor trip system. The staff would require that such a system meet IEEE-279.

(b) Provision of actuating circuitry for some existing systems (i.e., primary system relief valves, turbine trip, and auxiliary feedwater) that is diverse from the reactor scram system.

(2) Provision of increased pressure relief capacity, through the addition of pressurizer safety valves, sufficient to comply with Service Level C of the ASME code for the ATWS events specified in the next paragraph. Further analysis may show that a larger pressurizer, increased auxiliary feedwater flow rate, or scme combination of these design variables would reduce or substitute for this requirement in future designs.

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I 4 I973 Mr. E. E. Van Brunt, Jr. (3) Demonstration of the functionability of valves needed for long-term cooling following conditions calculated for specified ATWS events. This demonstration would include the postulated initiating events described in Appendix IV of NUREG-0460,Section IV.2, and prescription four in Table 7 of Appendix VII of NUREG-0460 (99 percent MTC and reliability based failure assumptions).

Volume 3 of NUREG-0460, which describes the rationale for specifying these plant modifications, is currently being reviewed by the Advisory Comittee on Reactor Safeguards. We plan to issue requests to all reactor vendors to supply generic analyses of ATWS mitigation capa-bility and anticipate presenting to the Commission in May 1979 our recommendations for its actions to resolve the ATWS issue.

Although deliberations are ongoing, we are concerned that the design of the Palo Verde 4 and 5 facility might proceed over the coming months so as to preclude full implementation of the design modifications to satisfy the recommendations in NUREG-0460, Volume 3, should they eventually be adopted by the Comission, either with or without rule making. As indicated in NUREG-0460, Volume 3, the resolution of this issue for Palo Verde 4 and 5 may require implementing some or all of the plant modifications of Alternative 4 discussed in NUREG-0460, Volume 3, Section 2.2 and summari::ed above.

Therefore, provide a commitment that Palo Verde 4 and 5 will be designed such that implementation of the above three potential requirements will not be compromised by construction.

Provide your response to this request by March 7,1979 or, if you cannot meet that date, advise us of a date by when you can provide a response.

If you need additional clarification of this report, please advise us.

Sincerely, Yb 8 an D. Parr, Chief Light Water Reactors Branch No. 3 Division of Project Management cc: See next page

Mr. E. E. Van Brunt, Jr. cc: Arthur C. Gehr, Esq.

Snell & Wilmer 3100 Valley Center Phoenix, Arizona 85073 Charles S. Pierson, Assistant Attorney General 200 State Capitol 1700 West Washington Phoenix, Arizona 85007 Donald G. Gilbert, Executive Di rector Arizona Atomic Energy Commission 2929 Indian School Road Phoenix, Arizona 85017 George Campbell, Chairman Maricopa County Board of Supervisors 111 South D1ird Avenue Phoenix, Arizona 85003 Mr. Larry Bard P. O. Box 793 Tempe, Arizona 85281 Dr. Stanley L. Colins Assistant Director Energy Programs (OEPAD)

Office of the Governor 1700 West Washington Executive Tower - Rn. 507 Phoenix, Arizona 85007

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