ML20077G016
| ML20077G016 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 06/12/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077G012 | List: |
| References | |
| NUDOCS 9106210196 | |
| Download: ML20077G016 (3) | |
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UNITED STATES d-i,
- i NUCLEAR REGLh.ATORY COMMISSION D,
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%,.....f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT NO.120 TO FACILITY OPERATING LICENSE NPF-9 AND AMENDMENT NO.102 TO FACILITY OPERATING LICENSE NPF-17 DUKE POWER COMPANY MCGUIRE NUCLEAR STATION. UNITS 1 AND 2 DOCKET N05. 50-369 AND 50-370
1.0 INTRODUCTION
By letter dated ilune 7, 1990, as supplemented Octa er 1990, and April 30, 1991, the Duke power Company (licensee) submitted a regnst Tor changes to the Mt.Guire Nuclear Station, Units 1 and 2, Technical Specifications (TSs). The requested changes would revise TS 3/4.6.5.1, " Ice Condenser Containment Systems,"
to reduce the ice weight required to be maintained in the containment ice condenser ice baskets.
The supplemental information provided by letters dated October 4,1990, and April 30, 1991, was clarifying in nature and did not affect the scope of the noticed action or the NRC staff's proposed significant hazards consideration analysis.
2.0 EVALUATION 2.1 ICE WEIGHT REDUCTION The function of the ice in the ice condenser is to absorb thermal energy released into the containment by accidents, particularly by the design-basis loss of coolant accident (LOCA) which provides the most limiting challenge to the ice condenser and determines the minimum required amount (weight) of ice. All of the ice will melt during a design-basis LOCA (after about an hour), so the amount of ice and the amount of heat it absorbs has a direct impact on the peak containment pressure which occurs after the ice has melted.
Current McGuire TS 3/4.6.5.1 requires a minimum total ice weight of 2 466,420 lbs.
which, when divided evenly among 1944 ice baskets, yields 1269 lbs, of ice per basket. This contains a 10% allowance for ice loss through sublimation during the periods between ice weighing surveillances (required every 9 months) and an additional 1.1% allowance to account for systematic error in the weighing instruments. Thus, the actual ice weight assumed in the safety analysis was
?,220,000 lbs.
In the licensee's current safety analysis, called the "FSAR 1989 Containment Pressure Calculation," 2,220,000 lbs. of ice results in a peak containment pressure of 12.36 psig. Containment design capability is 15.0 psig.
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. The McGuire ice condensers have suffered from a significantly higher sublimation rate than the 1% per fuel cycle assurred in the Westinghouse design. As a result, the licensee must replenish the ice in a large fraction of the ice baskets at each refueling outage by removing all the ice from a basket (by mechanically breakinguptheice)andreloadingitwithflakadice.
Even with this, the individual ice baskets with the worst sublimation problems, i.e., those in the row nearest the ice condenser compartment inner wall which borders on the (hot) containment upper and lower compartments, are in danger of dropping below the minimum required ice weight between ice weighing surveillances.
The licensee is working to reduce the sublimation rate, but so far has met with limited success. To alleviate the existing sublimation problem, the licensee has proposed a reduction in the TS required minimum ice weight.
The proposed total ice weight is 2,099,790 lbs. which gives 1081 lbs, per bas 6et. This is based on a safety-analysis ice weight of 1,890,000 lbs., with 11.1% margin added as discussed above. The licensee had a new safety analysis performed by Westinghouse using the LOTIC-1 computer code, in which the only input parameter changed from the previous analysis, cited dbove, was the ice weight which was lowered to 1,890,000 lbs.
The LOTIC-1 code is specified in Standard Review Plan 6.2.1.1.B.
NUREG-0800, dated July 1981, as an NRC staff-approved code for calculation of ice condenser containment pressure and temperature response to LOCAs. The resultant peak containment presst re is 14.07 psig, which is less than the containment design pressure of 15.0 psig and the containment integrated leakage rate test pressure of 14.9 psig specified by TS 3/4.6.1.2.
Since the only input parameter changed for the new LOTIC-1 analysis was the ice weight, the hRC staff finds the input purameters to be acceptable. Since the LOTIC-1 code is staff-approved, the new safety analysis of containment pressure response is acceptable.
Because the new analysis results in a peak containment pressure below the containment design pressure, the new safety-analysis ice weight of 1,890,000 lbs., and therefore, the new TS ice weight of 2,099,790 lbs, total and 1081 lbs, per basket, are acceptable.
2.2 CORRECTION TO BASES Bases section 3/4.6.5.1 states that the TS minimum ice weight contains a 10%
allowance for ice loss through sublimation and an additional 1% allowance for systematic error in weighing instruments. The licensee submits that this is in error because the total allowance or margin is 11.1%; thus, the 1% figure should be changed to 1.1%.
The correct margin is 11.1%; however, the existing Basis is not, strictly speaking, in error, but is sgbject to two interpretations. The licensee's interpretation is straightforvard: 10% margin for sublimation and another 1.1%
for systematic error. The second interpretation, which was the intended meaning of-the existing Basis, is best explained by the following hypothetical example.
For example, if the safety-analysis total ice weight is 100 lbs, then a 10% margin for sublimation would increase this to 110 lbs. A further 1% of that resultant weight (i.e. 1% of 110 lbs.) equals another 1.1 lbs. to be added on, giving a final total of 111.1 lbs. Thus, the total margin is 11.1% of the original weight.
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Although the intended meaning of the existing Basis is correct, it is obviously ambiguous and could be interpreted as allowing a less conservative 11.01 margin.
The licensee's proposal to change the li figure to 1.1% would clarify the Basis in a conservative way since a misinterpretation of the revised Basis would give a tvial margin of 11.211.
Finally, the proposed revision is more straightforward and easier to understand.
Therefore, the NRC staff finds the proposed revision to Eases section 3/4.6.5.1 to be acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the North Carolina State official was notified of the proposed issuance of the amendments. The State official had no consents.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 end change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released of fsite, and that there is 'no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (55 FR 32326). 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 need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
The Commissicn has 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, (2) such activities will be conducted in compliance with the Comission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Jim Pulsipher, PSLB/ DST Date: June 12, 1991 l
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