ML20215B927
| ML20215B927 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 09/30/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20215B925 | List: |
| References | |
| NUDOCS 8610090466 | |
| Download: ML20215B927 (4) | |
Text
J 8[. a m UNITED STATES NUCLEAR REGULATORY COMMISSION o
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,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.64 TO FACILITY OPERATING LICENSE NPF-9 AND AMENDMENT NO.45 TO FACILITY OPERATING LICENSE NPF-17 DUKE POWER COMPANY DOCKET NOS. 50-369 AND 50-370 McGUIRE NUCLEAR STATION, UNITS 1 AND 2 INTRODUCTION In the August 19, 1985 letter, Duke Power Company proposed a change to Tech-nical Specification 3.5.1.1 to increase the time allowance for restoration of boron concentration in an accumulator that is out of specifications. Also proposed was a change to Technical Specification 4.5.1.1.1, which eliminates i
the need to verify boron concentration in the accumulator within six hours after a volume increase (greater than 1%) from normal makeup.
In the April 17, 1986 letter, Duke Power Company supplemented the proposed changes to the Technical Specification to establish a lower limit of 1500 ppm volume weighted average for the three limiting accumulators and action times and requirements in accordance with the suggested Technical Specifica-tion in an NRC letter to Duke Power Company dated December 5, 1985.
These changes proposed by the August 19, 1985 and April 17, 1986 letters are intended to reduce the number of unnecessary plant mode changes and provide the operator more time in which to diagnose and correct low boron concentra-tion while maintaining plant conditions which satisfy safety analyses assumptions.
EVALUATION l
Current Technical Specifications do not distinguish inoperable status of an ac-cumulator due to reduced boron concentration from other inoperable conditions.
The proposed technical specifications would draw this distinction.
In a large break LOCA analysis, the accumulator in the broken leg is assumed to dump out the break. The ECCS analysis is based on the average boron con-centration of the three accumulators in the intact loops. Neutron Kinetics are not explicitly modelled in the large break LOCA ECCS analysis. Control rods are simply assumed to fail to insert. The reactor is then shutdown due to void formation during blowdown. Sufficient boron concentration is main-tained in the accumulators and refueling water storage tank to ensure that the reactor does not return to criticality following refill and reflood. The mag-nitude of the required boron concentration is detennined by separate analysis peripheral to the ECCS analyses. As long as the average value of boron con-centration is preserved, variation in individual accumulators will not affect the LOCA analysis.
8610090466 860930 DR ADOCK 05000369 PDR
However, since the accumulators are part of the emergency core cooling system, reasonable time requirements for restoration of boron concentration in each accumulator are established.
The changes proposed by Duke Power Company specify time limitations on the permissible boron concentration in the accumulators.
Presently, if boron concentration in any one accumulator is found to be below 1900 ppm, one hour is allowed for restoration of boron concentration to 1900 ppm.
The proposed changes would vary this time allowance relative to boron concentration in the three limiting accumulators. Limiting is defined as the combination of the three accumulators which would deliver the minimum volume weighted average boron concentration. The accumulator which would have provided maximum boron delivery is assumed to be in the broken loop.
Specifically, if baron concentration in only one accumulator were found to be below 1900 ppm and if the volume weighted average boron concentration of the three limiting accumulators were greater than 1900 ppm, (the minimum boron concentration design limit), the licensee has propcsed twenty-four hours to be -
allowed for. restoration of the affected accumulator to a boron concentration of 1900 ppm.
If this time limit were not met, the plant would be in HOT STANDBY in the next six hours, and pressurizer pressure reduced below 1000 psig in the following six hours. This time extension, from the current one to twenty-four j
hours, is acceptable because the volume weighted average of 1900 ppm boron in the limiting accumulators provides reactor shutdown capability without control rod availability and with the designated shutdown margin.
If boron concentration fell below 1900 ppm in a single accumulator and the volume weighted average boron concentration of the three limiting accumulators was less than 1900 ppm, six hours would be allowed for restoration of the volume weighted average to 1900 ppm.
If this requirement were not met, the unit would be in HOT STANDBY in the next six hours and pressurizer pressure reduced below 1000 psig in the following six hours.
The impact of dilution of boron concentration below 1900 ppm raises questions on the ability of the three limiting accumulators to shutdown the reactor.
The purpose of boron in the accumulator water is to maintain subcriticality of the reactor following a design basis LOCA. Although the design limit for boron concentration is 1900 ppm, as specified in McGuire Technical Specifications, the boron concentration necessary to maintain shutdown of the reactor at zero power, k eff = 1.0, all control rod assemblies out, including a 1% uncertainty is 1500 ppm at HOT and 1280 ppm, COLD.
(Table 4.3.2-2 McGuire FSAR, 1984 Update). A 1900 ppm boron concentration gives a 4% subcriticality level.
In order to dilute from 1900 ppm to 1500 ppm boron, the amount of water required would fill the entire volume of the limiting accumulators.
Dual level and pressure controls on each accumulator will prevent extensive dilution of boron concentration in the accumulators. An extension from one to six hours as a time limit on raising volume weighted average boron concentration above 1900 ppm in the three limiting accumulators therefore seems reasonable.
However, if boron concentration drops below 1500 ppm in the limiting accumu-lators, the ability to shutdown the reactor at maximum criticality conditions without control rods is lost. Therefore,1500 ppm is the lower limit on boron
- concentration in the.three limiting accumulators which would be permitted.
If the volume weighted average boron concentration in the three limiting accumu-lators were to drop below 1500 ppm, one hour should be allowed for restoration of the volume weighted average 1500 ppm.
If this requirement is not met, the unit should be in HOT STANDBY in the next six hours and pressurizer pressure reduced below 1000 psig in the following six hours. This additional constraint on boron concentration maintains the margin of safety necessary for reactor shutdown and is no more restrictive than the current Technical Specification.
Accumulator check valve leakage, which appears to be the root cause of the desired Technical Specification modification, should not result in entering this action statement. This action statement would only be entered should in-advertent dilution from the accumulator fill subsystem occur.
In addition to the above arguments, the increase in probability of a LOCA when accumulator down time is increased from one to six and twenty-four hours is small. The loss of an accumulator due to decreased boron concentration over these time periods will have little effect on the safety of the plant.
The second change, concerning elimination of verification of boron concen-l tration after a greater than 1% volume increase from normal makeup, is also reasonable. The nonnal makeup source, the refueling water storage tank, is specified to be maintained at 2000-2100 ppm boron and must be demonstrated as such once every seven days.
No dilution can come from this source and thus, verification of this concentration level six hours after normal makeup is unnecessary.
Based on the foregoing review, the changes submitted by Duke Power Company to Technical Specifications 3.5.1.1 and 4.5.1.1.1 are acceptable.
ENVIRONMENTAL CONSIDERATION These amendments involve changes to the installation of use of facilities' com-i ponents located within the restricted area as defined in 10 CFR Part 20 and changes in surveillance requirements. 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 exposure. The Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration, and there has been no public coment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment i
need be prepared in connection with the issuance of these amendments.
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CONCLUSION The Commission made a proposed determination that the amendments involve no significant hazards consideration which was published in the Federal Register (51 FR 30569) on August 27, 1986, and' consulted with the state of North Carolina. No public comments were received, and the state of North Carolina did not have any comments.
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 Commission's regulations, and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors:
R. Sammons, RSB D. Wigginton, PWRf4 Dated: September 30, 1986 l
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