ML19207B242

Responds to NRC 790531 Ltr Requesting Info Re IE Bulletin 79-12.Mods Will Be Performed to Rod Withdrawal Sequence to Assure Against Reccurence of Fast Period Scrams

ML19207B242
Person / Time
Site:	Hatch
Issue date:	07/26/1979
From:	Widner W GEORGIA POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 7908230669
Download: ML19207B242 (3)

Text

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Georg.a Power Company 230 Peo: Wee SPeet 6

) ~3 P:e O't.ce Box 4545 /

A' a~a Georg.a 30302 i . c , . _.

TW:ne 404 522 6060 .'Cf.NCE~

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m Power Generation Department ,/ 3 d l'l 3 ' Georgia Power

1. i9' 03 July 26, 1979 United States Nuclear Regulatory Commission

REFERENCE:

Of fice of Inspection and Enforcement RII: JPO Region II - Suite 3100 50-321 101 Marietta Street 50-366 Atlanta, Georgia 30303 ATTENTION: Mr. James P. O'Reilly The Georgia Power Company offers the following information in response to your letter of May 31, 1979, requesting information concerning I&E Bulletin 79-12.

Georgia Power Company has reviewed the items of concern identified by Bulletin 79-12 and we agree that the items, while not a safety concern, represent a potential unpact on operating capacity factors, and therefore are undesirable anu should be minimized to the extent practical. Therefore, the responses listed below to each item of the Bulletin represent actions which will be taken by September 1, 1979, in order to preclude the operationally undesirable occurence of short period scrams by high notch worth.

1. Georgia Power Company believes that it is not currently possible to obtain a computer program which would have sufficient accuracy to not inadvertently mislead the reactor operators. The large number of variables and the time dependent nature of Xenon transients preclude the effective modelling of the large, loosely coupled BWR core. The resources which would be expended in the effort to obtain useful predictions can be channeled into the more productive efforts describe below.

2&3. To avoid reoccurences of fast period scrams we will modify the start-up rod withdrawal sequences to reduce the possibility of high notch worth. We will begin use of a banked withdrawal sequence in RSCS groups 3 and 4 using position 4, 8, 12, and 48 with the constraint that these rods must be notched between positions 4 and

12. This banking of all rods within the group flattens the flux distributions and precludes pulling of high worth rods from high flux regions. In RWM groups 5 and 6, rods in the groups are banked as above to cover cases when a high xenon inventory might cause criticality to occur in this region. Also peripheral rods are av;ided in these groups because of the tendency for high notch worth to occur there during peak xenon conditions. p a= - = _ :.

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We will provide cautions in the rod withdrawal precedures warning the operator that:

a. Notch withdrawal should always be used when instrumentation indicates that the reactor is close to criticality.

b. Normally the first rod in groups 3 and 4 have a potential for higher rod worth.

High xenon concentration can alter normal rod worth configurations, especially in the peripheral c.

regions,

d. The operator should monitor all SRMs closely during the approach to criticality so as to have the best possible data at his disposal.

The above modified withdrawal sequence will be used for all start-ups on Units 1 and 2 except the initial critical for this cycle on Unit 1.

The initial critical for Unit 1 in this cycle is used to calculate shutdown margin and must be performed using the classical BWR-4 withdrawal sequence. This cold critical will be closely monitored.

4. The " emergency rod in" switch is typical of many used in the Hatch control room and to date none of these type switches have experienced any problems.

5. We will incorporate the events and their causes described in the bulletin as well as the above actions into our training program to reemphasize the problems associated with high notch worth during approaches to criticality.

Should you have any questions, please contact my office.

Yours very truly, Y'

W. A. Widner Manager of Nuclear Operations SFC/ JAB /mt 7870G6

xc: United States Nuclear Regulatory Commission Office of Inspection and Enforcement Division of Reactor Operations Inspection Washington, D.C. 20555 ATTN: Director bxc:J. H. Miller, Jr. C. E. Belflower W. E. Ehrensperger J. T. Beckham, Jr.

F. G. Mitchell, Jr. V. C. Valekis G. H. Burson, Jr.

C. F. Whitmer R. J. Kelly R. A. Glasby J. H. Boykin D. L. McCrary C. R. Thrasher R. A. Thomas R. W. Staffa R. F. Rogers (NRC)

M. Manry Route to SRB Members

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