ML20210C806

Safety Evaluation Supporting Amends 85 & 72 to Licenses NPF-4 & NPF-7,respectively

ML20210C806
Person / Time
Site:	North Anna
Issue date:	09/08/1986
From:	Office of Nuclear Reactor Regulation
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ML20210C781	List: ML20210C778 ML20210C806
References
NUDOCS 8609180433
Download: ML20210C806 (3)

Text

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UNITED STATES h

NUCLEAR REGULATORY COMMISSION 5

j WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS. 85 AND 72 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWEP STATION, UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339

==

Introduction:==

By letter dated January 3,1986, the Virginia Electric and Power Company (the licensee), requested a change to the Technical Specifications (TS) for the North Anna Power Station, Units No. I and No. 2 (NA-182). Specifically, the proposed changes would revise the negative end-of-cycle (EOC) modegator temperature coefficient (QC) limit from a current value of -4.0 x 10~

delta k/k/*F to -4.4 x 10 delta k/k/'F, and would also revise the corresponding 300partpermillion(ppm)equijibriumboronconcentrationvaluefrom-3.1x 10-4 delta k/k/*F to -3.3 x 10 delta k/k/*F.

In addition, the proposed changes would update the EOC MTC limits to reflect current plant operating conditions. The above changes have been proposed in order to provide greater flexibility during the reload design process. The staff's discussion and evaluation of the proposed changes are provided below.

Discussion:

The current NA-182 TS require that the MTC be confimed as the fuel cycle approaches the O ppm boron concentration end ggint of EOC conditions. The negative EOC MTC limit is currently -4.0 x 10 delta k/k/*F in the NA-1A?

TS Gection 3.1.1.4.b).

The value of the EOC MTC is measured upon reaching anequilibriumboronconcentrationo{deltak/k/'F(Section4.1.1.4.b).

300 ppm. The current TS value for this measurement point is -3.1 x 10' If the measured MTC is within this value, no further checks of MTC against the EOC negative MTC limit are necessary.

If the measured MTC at the 300 ppm boron check point violates the NA-1 A2 TS value, operation of the unit may continueifMTCmeasurementsaretakenatjeastevery14effectivefullpower days and found to be within the -4.0 x 10' delta k/k/*F EOC limit.

Bases Section 3/4.1.1.4 of the TS identifies the source for the MTC limit and the conversions used to derive the value for measurement comparison at the 300 ppm ecuilibrium boron concentration point. The most negative MTC value is basec on the limiting moderator density coefficient, (MDC), used in the Chapter 15 of the Final Safety Analysis Report (FSAR) analyses:

OhbOhcS ObObu r

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-2 O

This MDC value is first incrementally adjusted to allow for changing the core from the all-rods-inserted condition, upon which the safety analysis is based, to an all-rods-withdrawn condition consistent with actual measurement conditions.

3 The second conversion translates the MDC value in delta k/k/(g/cm ) to MTC in delta k/k/*F. A derivative of water density with respect to temperature at core operating conditions is used to make this conversion.

The result is the Technical Specification EOC negative MTC limit.

The final conversion translates the EOC negative MTC limit into a TS value at the 300 ppm equilibrium boron concentration measurement point, i

Conservative corrections for MTC change due to burnup and soluble boron concentration are used.

The resulting E0C negative MTC limit and negative MTC value at tge 300 ppm equilibrium bogon concentration measurement point are -4.4 x 10~ delta k/k/*F and -3.3 x 10- delta k/k/*F, respectively. The differences between these values and the current NA-182 TS limits are primarily due to a difference in the derivative of water density with respect to temperature at the current core operating conditions.

Once the equilibrium baron concentration falls below about 60 ppm, dilution operations take an extended amount of time due to the large required volume of dilution water. For example, dilution of the RCS from 50 ppm to 40 ppm requires charging of about 17,000 gallon of primary grade water and would require over 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. These extended oilotion times make re?iable MTC measurements difficult to obtain due to any of a variety of fluctuations in the system conditions which could take place over this time interval.

As a result of this difficulty, t!.e licensec has proposed a change to TS 4.1.1.4.b to eliminate further MTC measurements provided a measurement of 60 ppm equili-brium boron (ay rods withdrawn, rated themal power conditions) is less negative delta k/k/*F. Calculations have shown that for this condition than -4.0 x 10, delta k/k/*F limit will always be met at the licensed end of the -4.4 x 10" cycle, conservatively accounting fca the effects of control rods, burnup, boren concentration and end of cycle coastdown.

The proposed TS continue to ensure that the acceptance criterf a for the NA UFSAR accident analyses are met. The limiting value used in the UFSAR safety analysis is the positive MDC limit value, and this value is not changed by the proposed Technical Specifications. Thus, the current analyses remain bounding.

Fvaluation:

The changes in EOC negative MTC limit and the valut at 300 ppm nre primtfily the result of an increase of 7.52F in Tave which was aporoved by the Commission in March 1984 This temperature change results in a difference in the derative of the water density with respect to tempeyture an( thss allows a sjightly more negative MTC botn at EOC W.3 x 10 delta k/k/'F vs.

-4.0 x 10~4 deltak/k/*F)andat300 ppm (-3.3x10" delta k/k/'F vs.

-3.1 x 10" delta k/k/*F1.

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To support elimination of measurements below 60 ppm, the licensee has shown by calculatignthatthemaximumchangeinMTCfrom60ppmtoEOCislesstgan 0.4 x 10- delta k/k/*F. Thus a measurement of greater than -4.0 x 10-delta k/k/jF at 60 ppm will insure that the MTC will not be less than

-4.4 x 10' delta k/k/*F at EOC.

Thus the changes to the MTC limit at EOC and at 300 gpm are acceptable. Also if the 60 ppm measurement is greater tnan -4.0 x 10- delta k/k/'F further measurements are not necessary.

Environmental Consideration These amendments involve a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.

The staff has detennined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Comission has previously published a proposed finding that these amendments involve no significant hazards consideration and there has been no public comen+ on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 651.22(c)(9). Pursuant to 10 CFR 651.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendments.

Conclusion We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendments will not be inimical to the comon defense and security or to the health and safety of the public.

Date: September 8,1986 Prir.cipal Contributors:

M. Chatterton L. Engle