ML20236B127
| ML20236B127 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 03/10/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20236B121 | List: |
| References | |
| NUDOCS 8903200360 | |
| Download: ML20236B127 (3) | |
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,a orog#o UNITED STATES 8
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SAFETY EYALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT N0. 56 TO FACILITY OPERATING LICENSE'NO. NPF-29 SYSTEM ENERGY RESOURCES, INC., et al.
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GRAND GULF NUCLEAR STATION, UNIT 1 DOCKET NO. 50-416
1.0 INTRODUCTION
Dy letter dated July 25, 1988,. System Energy Resources, Inc. (SERI, the licensee), requested an amendment to Facility Operating License No. NPF-29=
for the Grand Gulf Nuclear Station, Unit 1.
The proposed amendment would change Technical Specifications (TS) 3/4.7.4, Snubbers, and the ' associated Bases 3/4.7.4.by:- (1) changing sampling plan No. 2 to eliminate the requirement to test all snubbers if the number of rejected snubbers exceeds a specified number, and (2) deleting sampling plan No. 3.
2.0. DISCUSSION TS Section 4.7.4, concerning survefilance requirements for snubbers, contains three alternative sampling )lans one of which must be selected prior to surveillance, testing of snu)bers. Plan ho. I requires at least 10 percent of the total number of each type.of snubber to be functionally tested.
If acceptance criteria are not met, an additional 5 percent are-required to be tested until no failures are found, or until all snubbers are tested.
Plan No. 2 requires an initial sample of at least 37 snubbers to be tested. The plan contains criteria for acceptance of the remainder of the untested population, criteria for continued testing and the rejection criteria. The rejection criteria require that if the number of failures exceeds a specified small percentage of snubbers tested (7.5 percent to 10 percent), then all the remainder of the snubbers must be tested. Plan No. 3 requires an initial sample of at least 55 snubbers to be tested.
For 1
each snubber which fails to meet acceptar:e criteria, another sample of at least one-half of the size of the initial sample is required to be. tested until the total number tested equals the initial sample size times the factor 2
(1 + C/2) where C is the number of failed snubbers. Testing continues until acceptance criteria are met or until all snubbers are tested.
For Plan No. 2, test results for a given snubber type are plotted on TS l
Figure 4.7.4-1, where N is the number of snubbers tested and C is the number i
of test failures.
The plot of test results falls into one of three regions:
1 (1) the " accept" region which indicates that snubber type can be terminated; (2) the " continue testing" region which indicates that testing of that snubber type must continue, or (3) the " reject" region which indicates that i
all snubbers of that type are required to be tested. The " reject" region 8903200360 890310 PDR ADOCK 03000416 P
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of TS Figure 4.7.4-1 provides the possibility of rejecting a good popula -
tion of snubbers and requiring functional testing of the entire snubber.
population. Functional testing of the entire population requires increased radiological exposure of test personnel.
l 3.0' EVALUATION The first change in the licensee's preposal is based on an analysis of Wald's sequential' sampling plan. An evaluation of the Wald's sequential sampling plan fonnulas for acceptance and rejection numbers shows that reducing the-
. probability of accepting a go_od population to zero, while holding constant the probability of accepting a bad population, has the effect of eliminating the " reject" region without significantly changing the accept region.
Therefore, acceptance is essentially independent of rejection.
The proposed change to eliminate the " reject" region maintains the currently approved-acceptance criteria, while eliminating the )otential for excessive snubber testing. These results were developed by tie American National 3tandards 1
Institute /American Society.of Mechanical Engineers Code Comittee (ANSI /ASME OM4 Comittee) which develops standards for testing snubbers.
Although, the acceptance criteria in the Wald's sequential sampling plan are essentially independent of the rejection criteria, a slight dependence exists.
The elimination of the rejection criteria without a corresponding l
change to the acceptance criteria will result in a very small increase in the probability of accepting a bad population. For the change being proposed, SERI has determined this negligible increase in probability to be less than 0.003. This determination was made by setting the probability of rejecting a good population to zero and then calculating the change in the probability I
of accepting a bad population required to duplicate the " accept" region of 1
TS Figure 4.7.4-1.
j In' the first refueling outage, 3.2 man-rem of exposure was accumulated during the mechanical snubber inspections using sample plan No. 2.
During j
the second outage, 29 man-rem exposure was accumulated performing mechanical snubber inspections using this same plan.
There is a potential for over 60 man-rem exposure during the third outage if sample plan No. 2 is used without the proposed change. Therefore, this proposed change will reduce man-rem exposure by a substantial amount.
In addition, the change will elim-inate the probability of excessive tests of a good snubber population.
The second change in the licensee's proposal is deletion of sample plan No. 3.
This change is consistent with recent developments by the ANSI /ASME OM4 Comittee.
The licensee has no plans to use plan No. 3.
1 The associated TS Bases are being changed to be consistent with the proposed changes to the TS. A reference to the work of the ANSI /ASME OM4 Comittee is added to provide the bases of TS Figure 4.7.4-1.
Additionally, references l
to plan No. 3 are deleted.
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On the basis of this evaluation, we conclude that the proposed changes to the TS are acceptable because the acceptance criteria for surveillance testing of snubbers remain essentially unchanged. Also, the proposed t
changes do not significantly. reduce the previous confidence level of snubber i
population acceptance and have no significant effect on the structural 4
integrity of safety-related systems or margins of safety.
In addition, i
radiological exposure to test personnel would be reduced with little, if any, increase in the probability of accepting a bad population of snubbers.
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4.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant. impact have been prepared and published in the Federal Register on March 7,1989 (54 FR 9580)
Accordingly,
bused upon the environmental assessment, the Consission has determined that the issuance of this amendment will not have a significant impact on the quality of the human environment.
5.0 CONCLUSION
The Connission has issued a Notice of Consideration of Issuance of Amendment to Facility Operating License and Opportunity for Hearing which was published on August 25, 1988 in the Federal Register (53 FR 32488).
No petition to intervene or request for hearing has been filed on this action.
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The~ staff 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, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuence of this amendment will not be inimical to the common defense and the security, or to the health and safety of the public.
Principal Contributor:
J. Rajan, Mechanical Engineering Branch Dated:
March 10,1989
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