ML13310B357
| ML13310B357 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/17/1984 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Baskin K Southern California Edison Co |
| References | |
| LSO5-84-04-035, LSO5-84-4-35, NUDOCS 8404230077 | |
| Download: ML13310B357 (7) | |
Text
0 0R UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 April 17, 1984 Docket No. 50-206 LS05-84-04-035 Mr. Kenneth P. Baskin, Vice President Nuclear Engineering Licensing and Safety Department Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770
Dear Mr. Baskin,
SUBJECT:
SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 -
BENT BRACES ON SPENT FUEL PIT STORAGE RACKS By letter dated July 13, 1983, you submitted Licensee Event Report (LER)83-002, which noted that two upper lateral braces of the spent fuel pit storage racks had been found to be bent. You concluded, based on structural analysis of this configuration, that the storage racks meet the original design criteria (FSAR) in the current "as-loaded" condition but would not in the "fully-loaded" condition. Your calculations were submitted by letter dated October 17, 1983.
The staff.has reviewed your analyses and, as discussed in the enclosed Safety Evaluation Report, concurs with your conclusions regarding the spent fuel racks. Therefore, we request that you do the following:
(a) Propose a program and schedule for repairing the racks for staff review and approval.
Justification for the repair schedule should be provided considering anticipated needs for addition of assemblies to the racks.
(b) If the actual fuel rack load to be imposed before repair will significantly exceed the presently applied load level (the current 96 cells filled), a stress analysis of the fuel rack should be submitted to demonstrate that the rack stresses still remain below the FSAR criteria prior to the actual loading.
8404230077 840417 PDR ADOCK 05000206 p
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Mr. Kenneth April 17, 1984 The reporting and recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely, Original signed by Walter Paulson for Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing
Enclosure:
Safety Evaluation Report cc w/enclosure See next page DISTRIBUTION Docket NRC PDR Local PDR ORB #5 Reading NSIC DCrutchfield LA EMcKenna OELD EJordan JGrace ACRS (10)
SEPB DL:ORB #5 DL:2.RB #5
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Mr. Kenneth P. Baskin cc Charles R. Kocher, Assistant General Counsel James Beoletto, Esquire Southern California Edison Company Post Office Box 800 Rosemead, California 91770 David R. Piqott Orrick, Herrington & Sutcliffe 600 Montogmery Street San Francisco, California 94111 Dr. Lou Bernath San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 Resident Inspector/San Onofre NPS c/o U.S. NRC P. 0. Box 4329 San Clemente, California 92672 Mayor City of San Clemente San Clemente, California 92672 Chairman Board of Supervisors County of San Diego San Diego, California 92101 California Department of Health ATTN:
Joseph 0. Ward, Chief Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814 U.S. Environmental Protection Agency Region IX Office ATTN:
Regional Radiation Representative, 215 Freemont Street San Francisco, California 94111 John B. Martin, Regional Administrator Nuclear Reaulatory Commission, Region V 1.450 Maria Lane Walnut Creek, California 94596
REVIEW OF RE-EVALUATION OF SPENT FUEL STORAGE RACKS FOR SONGS-1 As reported in LER 83-022/OIT, an inspection of the spent fuel storage racks revealed that the upper grid lateral braces located at the north east and southeast corners on the east end of the rack were bent and no longer in contact with the spent fuel pool wall.
Southern California Edison Company submitted analyses, performed by their contractor, by letter
.dated October 17, 1983. Bechtel's calculation of the seismic adequacy of the spent fuel storage racks was performed for this damaged condition with two bent braces.
The damage of braces was not caused by earthquakes because no strong ground motion has been recorded since the plant was in operation. It is believed that these braces were accidentally hit by a crane or equipment during a loading operation of spent fuel.
In the LER the licensee noted the corrective actions for future operations so that such damage will not happen again. The damaged braces will be repaired eventually but not right away.
The purpose of Bechtel's calculation is to determine the structural integrity of the spent fuel storage racks without the use of the two damaged struts.
Its original total of nine struts in the upper grid bracing scheme are then reduced to seven. Two loading conditions have been considered for analysis:
the "fully loaded" and the "as loaded".
The seismic civil/structural reanalysis criteria of the spent fuel storage racks at San Onofre Nuclear Generating Station, Unit 1 were based on the design criteria and analysis methodology stated in the FSAR which in many respects differ significantly from the present (1984) SRP requirements,
-2 such as the stipulation of an equivalent static load factor of 1.5 and the need to consider an additional 5% eccentricity for accidental torsion. It is not the intention of the Bechtel re-evaluation to compare or to comply with the present SRP requirements; rather the stress and strain conditions under the design environments are of interest in the reanalysis.
The basic assumptions on physical properties of structural material and systems, such as 7% damping for submerged structures, are reasonable and acceptable. Frictional resistance at the floor is ignored for analysis because of its uncertainty; this would result in conservative calculations. The method of analysis is straight-forward and conventional.
Calculations based on the existing 7 struts are summarized as follows:
A. Racks fully loaded OBE:
13.3% overstressed*
DBE:
41.7% overstressed*
- Compared with Fa=14 ksi computed for the struts, where Fa is the axial stress permitted in the.absence of bending moment based on Eq 1.5-1 of AISC. Even.
with end struts undamaged (i.e. 9 struts acting) the safety factor for DBE is marginal; thereforethe DBE condition for the existing 7 struts is un acceptable if racks are fully loaded.
-3 B. Actual loading as of June 1983 when 96 of the 216 cells are filled:
For the existing 7 struts, assuming uniform load distribution, the Factor of Safety (F.S.) is as Follows:
OBE:
F.S. = 1.96 (Compared with the computed Fa=14 ksi for both OBE and DBE case)
DBE:
F.S. = 1.57 The licensee also performed analyses at the NE and SE corners of the rack assuming interconnection of 2 rows of rack elements and allowing for load redistribution. Two additional analyses were performed at the NE and SE corners assuming 100 percent of the load from the damaged struts being transferred to the next closest strut. The calculations from these analyses
.showed that the struts analyzed were adequate in meeting the stress requirement for both OBE and DBE.
In summary, the licensee has shown that the damaged fuel racks under the present "as-loaded" condition above do meet the stress criteria of the FSAR.
However, under a fully loaded condition, the FSAR stress criteria are not met; therefore, we require a rack repair and strengthening work as soon as practicable in the future.
The licensee may maintain it present usage (96 cells filled) of the damaged fuel racks until such a time that the repair and strengthening of the racks can be implemented without undue hardship,
-4 provided that the following two conditions are met:
- a. The licensee should propose a program and schedule for repairing the racks for staff review and approval.
Justification for the repair schedule should also be provided in light of anticipated additional loading of the rack.
- b. If the actual fuel rack load to be imposed before repair will signifi cantly exceed the presently applied load level (the current 96 cells filled), a stress analysis of the fuel rack should be submitted to demonstrate that the rack stresses still remain below the FSAR criteria prior to the actual loading.