ML20004D181
| ML20004D181 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/02/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20004D179 | List: |
| References | |
| NUDOCS 8106080542 | |
| Download: ML20004D181 (4) | |
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SUPPLEMENT TO THE SEPTEMBER 19, 1980 SAFETY EVALUATION SUPPORTING AMENDMENT NOS. 47 AND 30 TO FACILITY OPERATING LICENSES HOS. DPR-53 AND DPR-69 CALVERT CLIFFS NUCLEAR PGWER PLANT, UNIT NOS.1 & 2
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SPENT FUEL STORAGE RACKS BALTIMORE GAS AND ELECTRIC COMPANY DOCKET NOS. 50-317 AND 50-318 INTRODUCTION By letter dated January 29, 1981, Baltimore Gas and Electric Company (BG&E or the licensee) provided infomation that certain design aspects of the as-built high-density borated spent fuel storage racks (SFSR) for Calvert Cliffs Nuclear Power Plant, (CCNPP), Units No.1 and 2 were not as documented in their applications and our September 19, 1980 Safety Evaluation supporting Amendments No. 47 and 30. The problems were the subject of:
(1) the NRC Office of Inspection and Enforcement's " Notice of Violation" resulting from Inspection No. 50-317/80-21 (Decmber 11, 1980); (2) several telephone conversations between the BG&E and NRC respective staffs including the one BG&E referenced on January 27,1981, and (3) the meeting held in Bethesda, Maryland on February 26,1981 (Summary of Meeting ern:losed). BG&E has provided additional infomation in their submittals of" February 13 and March 11, 1981.
The problems to be addressed in this Supplement are:
1.0 The SFSR were not (as indicated in the BG&E submittals) designed and RA '.G.mi...p gi,, jui:l t,to fSME,-B&PV, C. ode Supection;N,Fz:3.
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n 1.1 Arc Spot welding was used in the 2 by 2 cell module construction.
1.2 Composition of weld rods.
1.3 Material traceability.
2.0 Defective spot welds.
DI QJSSION AND EVALUATION 1.0 SFSR Code In our April 12, 1978 letter "To All Power Reactor Licensecs" as repeated in our letter of September 21, 1979 to BG&E, we provided the following guidance.
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"(2) App 1'ca51e Codes Standards and Specifications Cor.struction materials should conform to Section III, Subsec-tion NF of the ASME*-Code. A?1 material should be selected to b2 compatible with the fuel pool environment to minimize corro-sion and galvanic effects.
Design, fabrication, and installation of spent fuel racks of stainless steel m'aterial may be performed based upon the AISC**
specificatien or Subseccion NF requirements of Section III of the ASME B&PV Code for Class 3 component supports. Once a code is chosen its provisions must be followed in entirety. When the AISC specification procedures are adopted, the yield stress values for stainless steel base metal may be obtained from the 3ection III of the ASME B&PV Code, and the design stresses de-fined in the AISC specifications as percentages of the yield stress may be used. Permissible stresses for stainless steel welds used in accordance with the AISC Code may be obtained from Table NF-3292.1-1 of ASME Section III Code.
Other materials, design procedures, and fabrication techniques will be reviewed on a case by case basis.
"American Society of Mechanical Engineers Boiler and Pressure Vessels Codes, Latest Edition.
- American Institute of Steel Construction,,,, Latest Edition."
In the January 29, 1981 letter and at the February 26, 1981 meeting, BG&E explained how the problem of the code to be used developed. Although the BG&E purchase order specified Section III, Subsection NF of the ASME Code, the SFSR designer, Nuclear Energy Services, Inc. (HES) and the manufacturer, Metal Products of Greenv M, South Carolina, had designed and built SFSR
. g.q ; fo.r;other.. facilities;.cq13 h;the ALSC.. Code.9c,They stat.e tnat.NES. f avoge.d 'us.ing. s.,;.
n; the AISC'Specificaffon because it is'more directly applicable to fue'l rack structures. However a communication problem existed between B3&E and MES; i
each believing the other was proceeding using their favored code /specifica-
-tion.
1.1 Use of Arc Spot Welds l
The basic unit of the HES designed SFSR for CCNPP is the 2 by 2. cell module (providing storage of 4 fuel assemblies). Each cell is made of 0.060 inch cold-formed thin walled stainless steel with sheets of poison material retained between two stainless steel sheets. The preformed components are united into a 2 by 2 module with 2,360 arc spot welds. This type of construction is not directly addressed by AISC or Subsection NF of ASME.
O OO However, BG&E presented their reasoning why this type of welding is allowed.
prov,ided it is qJalified by applicable tests and approved by the Engineer, in their January 29, 1981 letter.
In response to our questions regarding such qualification test and approval of tne BG&E engineering staff, BGSE provided, under cover letter dated February 23, 1981, an approval letter (with comments); Ms. Christine Key, BG&E Engineer to.Mr. R. A. Milos, NES, dated May 21, 1980.
After reviewing the new information provided, we find that SFSR contruction using arc spot welding for single cells and for the 2 by 2 modules (the rest of the rack is made with ASME Code welds) produces a structural component that is equally acceptable to the structure evaluated in our September 19, 1980 Safety Evaluation. Nevertheless, BG&E should be challenged to improve their internal quality assurance to insure that the design, construction and installation of future plant modifications are in accordance with their requirements and that all docketed information is materially accurate.
1.2 Composition of Weld Rods If we assume that the _SFSR were actually made to the AISC Specifications, the use of stainless s'tael welding rods of the fillet welds is not covered.
However, our previously quoted guidance says that construction materials should conform to Section III, Subsection NF of the ASME Code. This code does cover the use of stainless steel welding rod. Therefore, we conclude that the welding rod material used in the construction of these SFSR is acceptable.
1.3 Material Traceability Paragraph NF-2121 of the ASME Code requires all material used in the fabrication of a reactor component such as SFSR to conform to the requirements of the specifications for materials listed in the applicable tables of Appendix I of the ASME Code. BG&E states that traceability of materials used in individual rack components is maintained through assurance
%.4hata.1,1.,1,tems..pti).f zed.during f Abri.gationiaregf. rom.a; sing,le:. cont,rol;1edThere
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,,.~ ' '.. e lot of certified mate' i'al from several heats.
r stainless steel available in the manufacturing shop that was not properly certified material. We find this method of control meets the Code and Regulations requirements. However, this method of control should have been described in earlier B3&E documentation.
2.0 Defective Spot Welds j
As the result of an accidental drop of a 2 by 2 module during handling, NES discovered a problem with spot weld fusion of the third vertical row of spot welds on each side.
It was postulated that as many as S0 modules could be suspected of having unfused spot welds in each third vertical row. However, it is now believed that only a few mcdules were affected with this problem.
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--n 4-5 f4ES perfo'rmed a seismic structural analysis assuming that thirteen 2X2 modules (out of a matrix of twenty-five which comprise a rack assembif).
were defective. This assumption was considered conservative-based on the results of an ultrasonic test program conducted on. seventeen production modules.. _ for the purposes of _the analysis, the postulated defective modules were placed at the most critical locations in a rack and the moment of inertia of those defective modules was reduced to account for cell wall buckling. Stress levels tabulated by the applicant were found to be conservative with respect to allowable values.
Bassd on our review of the information~ submitted by the applicant we concur that the tabulated stress levels as well as the postulated loading conditions and assumptions regar~ dins defective assemblies are conservative. Therefore, the spent fuel storage racks, as fabricated, are acceptable seismic Category 1 structural components.
Date: June 2, 1981 3
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April 1, 1981 C::%et i:s. 50-317 a.pd E3-318 FACILITY:
Calvert Cliffs Nuclear Power Plant (CCNPP) Units No. 1 and 2
'ICEUSEE:
Baltimore Gas and Electric Company (BG&E)
I'JEJECT:
SUMMARY
OF MEETING MELD ON FEBRUARY 26, 1981 WITH BGLE IN REGARDS TO SPENT FUEL STORAGE RACK PROBLEMS AT CCNPP Eac:<;round iy litter dated January 29, 1981, BGLE indicated that the higt.-density.
- orated spent fuel storage racks (SFSR) for the CCNPP units da not meet certain design aspects approved by our review as documented in the September 19, 1950 Safety Evaluation (SE) supporting Amendments No. 47 and 30.
In addition, 13LE inspections have indicated that a limited number of defective welds may exist in the racks.
These problems have been the subject of NRC Inspection in: Enfcrcement (IE) investigations and are addressed in IE Inspection Report
'o. 50-317/80-21.
A tabular listing of the problems follows.
1.0 The SFSR were not (as indicated in the licensee's submittals) designed and built to ASME-S&PV Code, Subsection NF.
1.1 Spot welding was used in the' module construction.
1.2 Compcsition of weld rods.
1.3 Material traceability.
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- - Defective spot welds.
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w he January 29, 1981 letter provides data on all of the above problems.
-ne c;estion of material traceability (Item 1.3) was resolved by telephone
- n January 27, 1981.
- ntrctuction ISLE had requested this meeting to provide the staff with supporting data.
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No. of pages:
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