ML20213G489

Responds to Forwarding Constituent E Southard Ltr Raising Concern Re Safety Implications from Seismic Activity in Northern California Since 1975 & Requesting New Field Studies Prior to Restart.Improvement Program Ongoing

ML20213G489
Person / Time
Site:	Rancho Seco
Issue date:	11/12/1986
From:	Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:	Cranston A SENATE
Shared Package
ML20213G491	List: ML20213G489 ML20213G499
References
NUDOCS 8611180153
Download: ML20213G489 (6)

Text

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, N0Y 12 SBS The Honorable Alan Cranston United States Senate ak Washington, D.C. 20510 J

Dear Senator Cranston:

This is in response to your letter to the Nuclear Regulatory Commission (NRC) dated October 17, 1986, which forwarded concerns expressed by one of your constituents, Ms. Elaine Southard, over the safety of the Rancho Seco Nuclear Generating Station. She was particularly concerned about the safety impli-cations from the seismic activity experienced in Northern California since 1975 and requested that new field seismic studies be completed before plant restart.

Ms. Southard cited two seismic events; the magnitude 5.7 earthquake that occurred in Lake Oroville, California on August 1,1975 and the magnitude 6.0 earthquake that occurred near Bishop, California on July 21, 1976. I have enclosed a summary of the NRC staff's evaluation of these events with respect to the Rancho Seco plant. The effects of these earthquakes were well within the design basis for the plant. ;However, the Lake Oroville i earthquake, in particular, was of interest because it occurred in an area (the Foothills Fault Zone) which was not considered active. Following the Lake Oroville earthquake, subsequent studies indicated active faults in the Foothills Fault System in the Oroville/ Auburn area. The NRC staff assessed the seismic hazard of active faults in the Foothills Fault System to the Rancho Seco facility and concluded that the faults posed no imediate hazard to the plant. This conclusion is based on information which indicates that D- Rancho Seco could withstand an earthquake of magnitude 6.0 to 6.5 in the Foothills Fault Zone even if it occurred at the closest point to the plant which is approximately 13 miles from the plant site. No earthquake of this size or larger has occurred anywhere along the entire Foothills Fault Zone

[- during historical time, nor is there a deep reservoir in the vicinity of the

, site that could serve to increase the chance of this or any other size earthquake occurring. Notwithstanding our conclusion of no imediate seismic hazard at the Rancho Seco site, we requested the licensee to assess the fault movement potential'in the Foothills Fault System to further support our determination of non-capability of the Foothills Fault System for generation of an earthquake of sufficient magnitude to adversely impact safe plant operation. As part of the subsequent follow-up effort, SPUD is currently undertaking additional field work in the Rancho Seco area and expects to issue a report on its findings by mid-1987.

As you are aware, the Sacramento Municipal Utility District is undertaking a substantive management and performance improvement program for the currently shutdown Rancho Seco facility which involves extensive repairs, modifications and testing of plant systems and retraining of plant operators.

8611100153 861112 PDR ADOCK 05000312 H PDR

2-The NRC-is closely monitoring the progress of the management and perfomance improvement program at Rancho Seco and will r.ot permit the facility to resume operations until there is reasonable assurance that the facility can generate electrical power reliably and without endangering the health and safety of the general public.

Sincerely, (3,s s} T. A.B"

'b ijbetorStello,Jr.

Executive Director for Operations

Enclosure:

As stated l

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EDO PRINCIPAL CORRESPONDENCE CONTROL IS FROM: DUE: 11/ EDO CONTROL: 002246 DOC DT: 10/17/86 SEN. ALAN CRANSTON FINAL REPLY:

TO:

OCA FOR SIGNATURE OF: ** GREEN ** SECY NO: 86-1122 EXECUTIVE DIRECTOR DESC: ROUTING:

ENCLOSES' POSTCARD FROM ELAINE SOUTHARD CONCERNING JMARTIN SEISMIC ACTIVITY AT RANCHO SECO NUCl. EAR PLANT GCUNNINGHAM DATE: 10/22/86 ASSIGNED TO: NRR CONTACT: DENTON SPECIAL INSTRUCTIONS OR RFMARKS:

RETURN INCOMING WITH REPLY.

MARK ENVFLOPE ATTN: JIM KOHLENBERGER.

NRR RECElVED: OCT.,23,.1986 _

ACTION: gLB MlltAGLI A';;

NRR ROUTING: DENTON/VOLLMER PPAS MOSSBURG

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m j OFFICE OF THE SECRETARY CORRESPONDENCE CONTROL TICKET PAPER NUMBER: CRC-86-1122 LOGGING DATE: Oct 21 86 ACTION OFFICE: EDO AUTHOR: A. Cranston--Const Ref AFFILIATION: U.S. SENATE LETTER DATE: Oct 17 86 FILE CODE: ID&R-5 Rancho Seco

SUBJECT:

Seismic activity at the Rancho Seco power plant ACTION: Direct Reply DISTRIBUTION: OCA to Ack SPECIAL HANDLING: None NOTES: Elaine Southard DATE DUE: Nov 5 86 SIGNATURE: . DATE SIGNED:

AFFILIATION:

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