ML19289C552
| ML19289C552 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 01/04/1979 |
| From: | Pilant J NEBRASKA PUBLIC POWER DISTRICT |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| REF-PT21-79-093-000 NUDOCS 7901170324 | |
| Download: ML19289C552 (4) | |
Text
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ATTACHED I' PART 21 REPORT FROM IE MAIL UNIT - R00:1 317 E/W s
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January 4, 1979 Mr. Karl V.
Seyfrit, Director l'.S.
Nuclear Regulator Comnission Office of Inspection and Enforcement Region IV (11 Ryan Placa Suite 1000 Arlington. Texas 76011
Subject:
Spent Fuel Storage Rack Weld Cracks /10CFR21 Reportability Cooper Nuclear Station NRC Docket No. 50-293, DPR-46
Dear Mr. Seyfrit:
Pursuant to I&E Inspection Report 50. 50-298/78-20 for Cooper Nuclear S'ation concerning weld cracks identified on the high density fuel s:orage racks, reportable under 10CFR21, the following information is submitted.
The Cocper Nt : lear Station high density spent fuel storage racks were designed by Nuclear Energy Services Incorporated, of Danbury, Connecti-
"Boral" product supplied by Brooks cut, with the neutron poison bein7, a
and Perkins Inc.
The racks were fabricated and constructed by Leckenby Company of Seattle, Washington, and monitored during this time by engi-neering personnel from the District.
On October 24, 197S, during the receipt inspection of the racks by NPPD, crater cracks on some welds were identified in the aluminum structure.
The cracks were found to be confined to the aluminu welds made by Leckenby Company.
Representatives from NPPD, Leckenby, and NES jointly identified the extent of the problem and determined the method and criteria for repair and rework.
Welds critical to the loading and seismic capability of the fuel racks were identified by NES:
a.
The case structural welds are the most critical welds since they are subj ected to the non-cyclic dead weight load of the racks and stored fuel.
The side velds of the lower grid will also see some dead weight loading (thermal loading of all rack welds was determined to be negligible).
Mr. Karl V.
Seyfrit January 4, 1979 Page 2 b.
The upper grid welds (side welds and egg-crate welds) are i=portant since they may be subjected to the substantial seismic loads icposed by the other fuel racks.
Since these welds do not sustain loading under normal conditions the probability of crack propagation in these welds was concluded to be negligible.
c.
The lower egg-crate grid welds are not considered critical since they do not carry any significant load under not:21 operating conditions and since the construction of the lower grid is such that the overall structural integrity of the rack will be main-tained even if all of the egg-crate welds in the lower grids are completely dataged during a seismic event.
The extent of cracking in these egg-crate welds which are internal to the rack structure and noninspectable should be rignificantly less than that found in the rack base and upper grid since these welds are generally smaller and cade between parts having similar thicknesses.
The probability of crack propagatice is concluded to be negligible since the welds do not sustain loading under normal conditions.
A special work procedure was developed to repair the critical welds.
This procedure specified (1) the procedure for visual and dye penetrant examination of the critical welds; (2) the acceptance criteria as specified by NES; (3) the grinding procedure for those welds found defective; and (4) the general recuirements for weld repair.
Weld repair was effected in the following canner:
a.
Rack base structural welds were 100% visual and licuid dye-penetrant tested.
The extent of the weld cracks were determined and all weld filler metal in the vicinity of each crack was removed.
Inter-cittent 3" welds ground to a dimension less than 2h" were revelded to the original 3" dimension.
Continuous fillet welds were rewelded if more than h" cf weld metal was removed in any 3" length of weld.
All ground and repaired welds were reinspected by the dye-penetrant method.
b.
Upper grid egg-crate welds were 100% visual and liquid dye-penetrant tested.
All weld cracks found were removed by grinding.
All weld filler metal in the vicinity of each crack was completely renovec.
Welds ground to less than 2/3 of their original length were rewelded to the original dimensions.
All grcund and repaired welds were inspected by the dye-penetrant method.
Adjacent welds were also inspected.
Side welds on top and lower grid were 100% visually inspected.
All c.
cracks found were ground and repaired.
All ground and repaired welds were reinspected by the dye-penetrant nethod.
A su==ary of the weld repairs on each rack is as follows:
Mr. Earl V.
Seyfrit January 4, 1979 Page 3 Rack Botto:
Upper Requiring Number Base Grid Side Total Reweld 1
133 109 0
242 8
2 188 55 1
244 15 3
191 191 3
365 9
4 SS 252 0
339 9
5 119 257 1
377 11 6
174 152 0
326 9
7 114 244 9
358 18 8
199 165 3
367 8
9 54 266 0
320 8
10 46 106 0
152 9
11 64 101 2
167 2
12 44 219 4
267 13 13 56 167 223 7
0 Total 1450 22S4 14 3748 126 Following the weld repair, Leckenby Company certified that the requirements of applicable codes, standards, specifications, and drawings were cet.
Nuclear Energy Services determined that the evaluation, repair, and rework of the fuel racks was acceptable and that the racks are now adequate to withstand the design loadings.
All aspects of the subject repair work have been reviewed and accepted by CSS Engineering and the CSS Station Operations Review Connittee (SORC).
Complete documentation of the subject repair is available for review.
If you should have any questions, or require further infor=2tien, please do not hesitate to contact L. C. Lessor or cyaelf.
Very truly yours, IAA t
'e, Pilant em; Director of Licensing and Ouality Assurance
/cmk cc:
Director, Office of Inspection and Enforcement (3 copies)
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