ML20209C314
| ML20209C314 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 03/20/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20209C152 | List:
|
| References | |
| FOIA-87-185 NUDOCS 8704280647 | |
| Download: ML20209C314 (2) | |
Text
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UNITED STATES g*
NUCLEAR REGULATORY COMMISSION o
WASHINGTON. D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING SHROUD HEAD CONNECTION REPLACEMENT l
PHILADELPHIA ELECTRIC COMPANY PUBLIC SERVICE ELECTRIC AND GAS COMPANY DELMARVA POWER AND LIGHT COMPANY ATLANTIC CITY ELECTRIC COMPANY PEACH BOTTOM ATOMIC POWER STATION, UNIT NO. 3
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DOCKET N0. 50-278 1
DESCRIPTION By letter dated January 7,1986, the Philadelphia Electric Company submitted a two-part safety evaluation addressing the intergranular stress corrosion cracking failure of four shroud head stress bolts in the Peach Bottom Atomic 1
Power Station Unit 3 (Peach Bottom 3). The second part of the evaluation,
" Safety Evaluation for the Replacement of Twenty-four Shroud Head Bolt l
Assemblies," demonstrating the adequacy of using 24 instead of the 48 bolts j
for the shroud head connection as originally designed, is being reviewed and evaluated by this report.
DISCUSSION A reanalysis of the shroud head bolting connection was performed by the licensee for the Peach Bottom 3 plant to determine the minimum number of bolts required for the connection.
The reanalysis used the linear failure correlation for combined axial and bending loads as the criterion to evaluate combined SSE and LOCA loadings. The minimum number of bolts required was determined to be
- 24. This calculation did not take into account of the structural strength in the 3" diameter alignment pins and steam dam.
Both the original analysis and the reanalysis take SSE and LOCA events into consideration. However, the original analysis considered these two events separately, while the reanalysis considers them on a concurrent basis. The resultant loadings from the reanalysis are more conservative, and therefore, are acceptable.
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The reanalysis assumed that all shear forces are resisted by shroud head bolts. This resulted in a conservative bending moment. The assumption is conservative and acceptable.
The acceptance criterion employed by the reanalysis was the linear failure correlation of combined axial and bending loadings. Since the connection is not a part of the primary coolant pressure boundary, it does not have to be constructed according to the ASME B&PV Code. The linear failure correlation for combined loadings has been used frequently by mechanical and structural designers.
For non-code construction, the use of this acceptance criterion is acceptable.
CONCLUSION Based on the above evaluation, the staff concludes that the approach used to establish loadings and the design acceptance criterion are acceptable. Since the reanalysis conservatively shows that 24 bolts are required without assuming any structural strength in alignment pins and steam dam, operation with 24 bolts is acceptable.
Principal Contributor:
W. Koo Dated : March 20,1986
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