ML20236E182

Ro:On 890305,moderator Temp Coefficient Determined to Be More Positive than Allowed by Tech Spec 3.1.1.3.a & Limiting Condition for Operation Entered.Control Rods Maintained within New Withdrawal Limits Until Core Burnup Reached

ML20236E182
Person / Time
Site:	Byron
Issue date:	03/10/1989
From:	Pleniewicz R COMMONWEALTH EDISON CO.
To:	Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
89-0238, 89-238, NUDOCS 8903230497
Download: ML20236E182 (2)

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March 10, 1989 filQha.,

i LTR: 89-0238 FILE: 1.02.1052  :

Mr. A..Bert Davis  !

Regional Administrator l Region III }

U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137

Dear Sir:

This report is submitted in accordance with Dyron Station Unit 2 Operating License NPF-66, Technical Specification 3.1.1.3, Action Statement a.3, reporting of Moderator Temperature Coefficient (MTC) more positive than allowed by Technical Specification 3.1.1.3.a.

On 03-05-89, at 0446 hours0.00516 days <br />0.124 hours <br />7.374339e-4 weeks <br />1.69703e-4 months <br />, during startup physics testing analysis after the first refueling outage for Byron Station Unit 2, the moderator temperature coefficient was determined to be more positive than 0 Ak/k/0F for all rods withdrawn, beginning of cycle life, hot zero' thermal power conditions.

Limiting Condition for Operation Action Requirement.(LCOAR) 2BOS 1.1.3-la was subsequently entered.

Withdrawal limits were provided to the Shift Engineer and Shift Control Room Engineer on 03-05-89 at 1332 hours0.0154 days <br />0.37 hours <br />0.0022 weeks <br />5.06826e-4 months <br />, in~accordance with Action a of Technical Specification 3.1.1.3. Control Bank D withdrawal limits may be determined based on a known boron concentration and moderator temperature which will ensure a negative MTC is maintained. Mode 2 Physics Testing was declared complete on 03-06-89, at 0312 hours0.00361 days <br />0.0867 hours <br />5.15873e-4 weeks <br />1.18716e-4 months <br />, when Special Test Exception 3.10.3 was exited. At this time Byron Station Unit 2 was in compliance with the withdrawal limits.

As designated in Action a.2 of Technical Specification 3.1.1.3, the control rods are to be maintained within the new withdrawal limits until a core average burnup of 1000 MWD /MTU is reached. This value is the result of a calculation performed by CECO Corporate Nuclear Fuels Services based on hot -

zero power (HZP), all rods out (ARO), no xenon (noXE) conditions, which is the  !

most limiting case to oltain a negative MTC.

m 8903230497s{0g55 ADOCK 0 PDR PNU T MAR 151989 s

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.i BYRON 89-0238 l

. Paga 2 i The Unit 1 Cycle 3 core average burnup value which was the most limiting case to obtain a negative MTC has been revised from 250 MWD /MTU to 1000 MWD /MTU.

The original value was referenced in the November 14, 1988 letter. At no time were rod withdrawal limits exceeded during Unit 1 Cycle 3. Also, it should be ~j noted that in the letter reporting the Unit 1 positive MTC, Action Statement i 3.1.1.3.a.2 was referred to as 3.1.1.3.b and Action Statement 3.1.1.3.a.3 was referred to as 3.1.1.3.c.

The fo11 ewing data is being submitted per the requirements of Action a.3. MTC was determined to be +0.0435 percent millitho (pcm)/0 F by averaging the values obtained from two cooldown and 2 heatup iterations. The MTC l methodology is described below.

Isothermal Temperature Coefficient (ITC) = Ap/ATave-1 I Corrected ITC = ITC + A m (Tave-557) - AITC(Cb-CbO) + ALTC (% Din)

ATave ACb A% Din where AITC , AITC , AIIC are design constants ATave ACb A% Din j

Cb = BOL, HZP, ARO critical boron concentration

% Din a percent of Control Bank D insertion Tave = (Tave initial + Tave final) /2 MTC = corrected ITC - Doppler Correction + 0.5 conservatism factor The inequality that must be satisfied to maintain a non-positive MTC for Dyron Unit 2 Cycle 2 is given below.

O > ao + 0.01140(Cb-1279) - 0.04163(Tave-557.0F) - 0.00438(% Din) where no = HZP, BOL, ARO MTC in pcm/0 F + 0.5 pcm/0 F conservatism factor.

The above equation was used to determine interim control rod withdrawal g limits. Three unknowns exist in the equation; boron concentration, moderator temperature, and control bank position. Solving the equation for Tave and j{

inputing selected boron concentrations, a family of control bank D position l curves maybe plotted on a boron concentration vs moderator temperature curve. '

Technical Specification 3/4.1.1.3 is being met by maintaining withdrawal limits for the control banks and complying with LCOAR 2BOS 1.1.3-la. a i

Sincerely, Y pm l R. Plenlewicz l

Station Manager '/

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Byron Nuclear Power Station i

CC: P. Brochman, NRC Senior Resident Inspector U.S. NRC Document Control Desk, Washington D.C.

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