ML20137D570

Forwards Comments on Allen to M Bender Re micro-earthquake Clusters

ML20137D570
Person / Time
Site:	North Anna, 05000000
Issue date:	01/23/1978
From:	Baum E VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Muller R Advisory Committee on Reactor Safeguards
Shared Package
ML20136A555	List: IA-85-363, Submits Topics for Discussion at Commission 830708 Meeting W/Acrs.Topics Include Seismic Design Margins ML20136A550 ML20136E176 ML20136E418 ML20136E423 ML20136E621 ML20136E929 ML20136F618 ML20137D336 ML20137D440 ML20137D455 ML20137D472 ML20137D477 ML20137D494 ML20137D511 ML20137D540 ML20137D551 ML20137D557 ML20137D562 ML20137D570 ML20137D576 ML20137D583 ML20137D588 ML20137D598 ML20137D601 ML20137D609 ML20137D616 ML20137D621 ML20137D627 ML20137D635 ML20137D641 ML20137D646 ML20137D652 ML20137D659 ML20137D665 ML20137D670 ML20137D849 ML20137D867 ML20137D881 ML20137D911 ML20137D924 ML20137D951 ML20137D978 ML20137E016 ML20137E026 ML20137E044 ML20137E056 ML20137E075 ML20137E098 ML20137E113 ... further results
References
FOIA-85-363 NUDOCS 8508220516
Download: ML20137D570 (3)

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A l VzuoixxA Ex.acraic Ann Powsu CourAxy Rzenxoxn.VrmorwrA sonst January 23, 1978 Mr. Ragnwald Muller, Serial No. 035 Senior Staff Assistant LOA /RMN:kbo Advisory committee for Docket Nos. 50-338 Reactor Safeguards U. S. Nuclear Regulatory Commission 50-339 Washington, D. C. 20555

Dear Mr. Muller:

Attached are our comments on Mrs. Allen's letter of January 4, 1978 to Mr. Myer Bender.

Very truly yours, S

- ~

E. A. Baum, Executive Manager Licensing & Quality Assurance Attachments 9

8508220516 850722 PDR FOIA DELLB5-363 PDR w;

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Question: 1. Can an " unexplained" cluster of 46 micro-earthquakes northwest of the North Anna dam be accurately said not to present some measure of seismic risk to the site?

(Please note attached map and correlation of the cluster with a postulated major regional fault--Spotsylvania or Neuschel's Lineament.)

ANSWER: Yes. The cluster effect was discussed in the Vepco letter of transmittal (Vepco Serial 463, October 25, 1977), a copy of which is attached. Briefly, the microscismic network can detect events.within the system far more efficiently than more distant events.

This issue has been thoroughly discussed before the ACRS Subcommittee on North Anna Unit 1 and 2 and be- ,

fore the full ACRS. The Staff has extensively reviewed both microseismic monitoring results and the Spotsyl-vania or'Neuschel's Lineament. Findings are reported in Section 2.5 of the Safety Evaluation Report and Supplements 2 and 5. The Staff reported that the micro-earthquakes in no way pose a hazard and that no evidence of faulting.along.the lineament exists. This issue was addressed in a letter from Dr. G. A. Bollinger to Vepco of June 10, 1977 and in the report "A Seismic Monitoring Program at the North Anna Site in Central Virginia - January 21, 1974, Through August 1, 1977."

The letter of transmittal (Vepco Serial 398, September 13, 1977) is Attachment 3. Dr. Bollinger's letter is Attachment 4 and the summary from the report is Attach-

. ment 5.

Question: 2. How do USGS seismologists interpret the sig-nificance_of the micro-earthquake cluster?

ANSWER: Vepco is not aware of the USGS position, if any, on this matter. However, the Staff reports in SER supple-ment 2 section 2.5 that the USGS found no evidence of faulting when mapping the Spotsylvania or Neuchel's Lineament. It would not appear necessary for the USGS to duplicate the Staff's review of micro-earthquakes.

Question: 3. Why is the ACRS willing to approve a 40%

design deficiency at North Anna? If the ACRS stipulates that any new reactors constructed in the East must have a minimum safe shutdown earthquake design of .20g, what is the ration-alo for approving North Anna's design of .12g?

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ANSWER: The ACRS did not approve a 40% design deficiency at North Anna. While the ACRS has recommended a 0.20g criteria for new construction cast of the Rocky Mountains, it concluded that the 0.18 (II)g and 0.12 (v)g values were ade-quate for the' North Anna site.

Question: 4. What are the results of the SEISMIC RE-EVALUA-3 TION OF NORTH ANNA requested on April 22, 1977 by NRC's J. P. Knight, Assistant Director for Engineering, DDS?-

ANSWER: No seismic reevaluation,.as such, is being done by the

' Staff. What the Staff has been requested to do is to examine certain safety components to determine what would be required to increase their design margins as now calculated. For example, Vepco, in Amendment 63 to the FSAR, indicated in Table S3.74-2 that the Con-trol and Relay Room A/C coil assembly support had a design margin of 1.05. Since the failure mode could 4

be assumed to be the combination of shear and tension on drilled-in anchor bolts, the idea would be to-determine how many additional bolts would be required

. to improve the margin of 1.05, The Staff review is understood to be still underway.

This review is really a generic matter using North Anna design data for test-bed purposes. This is a point that the Coalition continually and purposely '

ignores.

1 Question: 5. Have those results been made known to the

- Atomic Safety and Licensing Board considering an operating license for North Ann'a?

ANSWER: It is understood that when the Staff review'is completed, the results of that review would be available for inspection by the ASLB and other interested parties.

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