ML19340B110

Submits Response to Item 3 in IE Bulletin 79-26, Boron Loss from BWR Control Blades. Shutdown Margin Testing Conducted Prior to Initial Startup Verified That Withdrawal of Control Rods Did Not Result in Criticality

ML19340B110
Person / Time
Site:	Brunswick
Issue date:	09/25/1980
From:	Furr B CAROLINA POWER & LIGHT CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
IEB-79-26, NO-80-1397, NUDOCS 8010210270
Download: ML19340B110 (3)

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Carolina Power & Light Company ' '

.,~Z September 25, 1980

'F m nII: 93 FILE: NG-3513 (B)

SERIAL: NO-80-1397 Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, GA 30303 BRUNSWICK STEAM ELECTRIC PLANT, UNIT NO. 2 LICENSE NO. DPb 62 ~

DOCKET N0 Q50-324j SUPPLEMENTAL RESPONSE TO IE BULLETIN 79-26

Dear Mr. O'Reilly:

'1 In accordance with our response to IE Bulletin 79-26 dated January 3, 1980, Carolina Power & Light Company (CP&L) provides '.;-

I following supplemental response addressing Item 3 of the subject bulletin for the Brunswick Plant.

Item 3 of the subject bulletin requested that at the next cold shutdown.or refueling outage, CP&L conduct shutdown margin tests t'o l

verify that full withdrawal of any control blades from the cold xenon-free core would not result in criticality. Also, it was requested that we verify complfance with the shutdown margin require-ment in a manner that accommod tes the boron. loss phenomenon.

In a'ccordance with the Technical Specifications and Item 3 of i

the bulletin, shutdown margin (SDM) testing was conducted prior to the initial startup of the Unit 2 reactor which verified that the full withdrawal of any control rod did not result in criticality.

In order to verify compliance with the SDM Technical Specification, l

j two control rods were withdrawn from the cold, xenon-free core to insert the required amount of reactivity. The two rods chosen for this test are listed in General Electric's Cycle Management Report for Brunswick 2, Cycle 4.

Rod 26-27 was analytically determined to be the control rod with the highest reactivity worth at the beginning of cycle, and rod 22-31 was diagonally adjacent to 26-27.

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,Mr. J:mes P. O'Reilly Saptembar 25, 1980 a

The calculation of the required shutdown margin for the SDM demonstration was as follows:

Required SDM = 0.0038 + R - [(T - 68) y TC).

Where: 0.0038 = Ak required by Technical Specifications R = Difference between maximum ~k,ff during the cycle and k at the beginning of cycle.

ff T = Primary coolant temperature ( F)

TC = Temperature coefficient (Ak/k F)

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From the GE cycle management report:

R = 0.00

-5 TC = -4.0 x 10 Ak/k F At the time of the shutdown margin test:

T = 124 F Based on these parameters, the required shutdown margin was calculated l

to be 0.00604.

In order to insert this amount of reactivity, rod 26-27 was withdrawn fully, and rod 22-31 was withdrawn to position

48. The nuclear instrumentation was monitored after this withdrawal, and it was verified that the reactor did not go critical.

i At the completion of the previous operating cycle, both of the control rods used in the SDM demonstration, as well as all other rods in the Unit.2 core had very little exposure. The control rod with the 3reatest exposure had a B-10 depletion corresponding to

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13.17 percent and the control rod used for the SDM test had a B-10 depletion of less than 11.0 percent.

_l Section 12 of General Electric's Topical Report NEDO-24232,

" Control Blade Lifetime Evaluation Accounting for Potential Loss of B C," recommends that additional SDM be demonstrated if any control g

blade in the core has' a-B-10 depletion of 34 percent, or is expected to have this depletion prior to the next refueling outage.. All of

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the control rods in Unit No. 2 have very low exposures and are not anticipated ~to-exceed 34 percent B-10 depletion prior to the end of L

'this operating cycle.

For this reason, we feel that there is no reason to include the boron Icss phenomenon _into the shutdown demonstration at this time.

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Mr. Jrmes P.'0'Railly- '

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If'you have any questions regarding th'is information, please contact my. staff.

Very truly yours, i

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B. J. Furr Vice President Nuclear Operations DCS:kbb*

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. cc:

Mr. Norman C. Moseley 1

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