ML20088A664
| ML20088A664 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/26/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20088A663 | List: |
| References | |
| NUDOCS 8404120375 | |
| Download: ML20088A664 (3) | |
Text
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! aux UNITED STATES 8
NUCLEAR REGULATORY COMMISSION o
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WASHINGTON, D. C. 20555 g,
f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AliENDMENT N0. 53 TO FACILITY OPERATING LICENSE NO. NPF-6 ARKANSAS POWER & LIGHT COMPANY ARKANSAS NUCLEAR ONE, UNIT 2 DOCKET N0. 50-368 i
Introduction In a letter dated July 12, 1983, Arkansas Power and Light Company requested a change to the Arkansas Nuclear One Unit 2 (AN0-2) Technical Specification 3.3.3.2 which states the requirements for operability of the incore detection system. Additional supporting information was submitted in letters dated September 30, 1983 and January 6, 1984.
Evaluation The current technical specification requires 75% of the detector locations to be operable and defines an operable location as one which has a minimum 4
of four operable detectors.
(Each location has a detector at each of five axial levels.)
It also requires that a ninimum of two quadrant symmetric incore detector locations per core quadrant be operable.
The proposed specification requires the same number of operable locations but it redefines an operable detector location as one having at least three operable detectors.
It adds the requirement that 75% of all detectors must be operable and changes the requirements on spatial distribution of the operable detectors.
The proposed specification has a requirerent of at least one operable detector in each quadrant at each level and sufficient operable detectors to perform at least six tilt estimates with at least one tilt estimate at each of three levels.
The change in the definition of operable locations from four operable detectors to three operable detectors is consistent with definitio'ns of operability in other plants which have four detectors per location and require three oper-able detectors. The requirement that 75% of the detectors be operable was added to limit the total number of detector failures allowed. The proposed tilt estimate requirement ensures that at least six-4 detector-tilt estinates are available and that there is at least one tilt estimate from at least three levels.
The previous spatial distribution requirenents ensured at least i
six tilt estimates but these could be made with three of the four symmetric
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-2 The purposes of the incore instrumentation system are.to evaluate core power distributions, perform calibrations of the out of core flux measurement system and provide inputs to the Core Operating Limit Supervisory System (COLSS).
A study was performed to determine which criterion would be violated first if the detector failures were random.
For the current requirements, the detector location operability criterion was violated first in all cases (200 cases run).
In these cases, only 12% to 20% of the detectors had failed when the location operability criteria was reached. For the proposed re-quirements, the criterion of 75% of detectors operable was violated first in all cases (500 cases run).
For these cases, only 3 to 8 locations were.
inoperable when the 75% of detectors criterion was violated.
Arkansas Power and Light Company has shown.that the proposed operability requirements are consistent with the data base used for the approved CECOR j
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j Topical CENPD-153-P Per'l-P-A, May 1980.
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The data base cases with the most failures were examined.
These cases support operation with up to 25% of the detectors failed and 25% of the locations failed.
In addition, Arkansas Power and L.ight Company has done simulation studies for ANO-2 to evaluate synthesis uncertainties for F, F F and F using the proposed detector operability requirements.
FivedYffe9ent 7
cEses were used for the study.* The results of the study were presented and they indicate no increase in the uncertainties. As a matter of fact the I
uncertainties are well below those used in the topical which is based on 4 l
detectors per location because AN0-2 is a five detector per location plant.
The five dtectors and five axial nodes gives lower synthesis uncertainties l
j than four detectors because of the better axial representation. Similar i
results have been obtained in other studies on five detector plants.
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Based on our review of the material submitted by the licensee and the randon detector study, we conclude that the proposed technical specification change 1
is acceptable. There is however no justification for operation with fewer than 75% of the detectors. Any operation with fewer than 75% of the detectors would require a complete reevaluation.
Case 1 - Most detectors ANO-2 ever had failed.
l Case 2 - Case 1 plus random failure to fail 25% of detectors failed and 25% failed locations.
Case 3 - Entire core central region axially and radially failed.
Case 4 - Two quadrants contained only 1 live detector each at axial levels and selected failures in other quadrants.
Case 5 - Eleven detectors failed in one quadrant, leaving only one live string in that quadrant.
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Environmental Consideration We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is in-significant from the standpoint of environmental impact and, pursuant to 10 CFR 651.5(d)(4), that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance-of this amendment.
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 Conmission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date:
March 26, 1984 Principal Contributor:
M. Chatterton