ML19269C758
| ML19269C758 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/07/1979 |
| From: | Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 543A-092818, 543A-92818, NUDOCS 7902120154 | |
| Download: ML19269C758 (2) | |
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eg VIRGINI A ELECTRIC AND POWER COMP ANY, PICHMOND, VIRGINI A 23261 February 7,1979 Mr. -James P. O'Reilly, Director Serial No. 543A/092878 Office of Inspection & Enforcement PSE&C/RIN:adw U. S. Nuclear Regulatory Comission Region II Docket No. 50-339 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303
Dear Mr. O'Reilly:
In our previous letter of September 28, 1978, Serial No. 543, we presented our final report on a deficiency concerning the embedded restraint assemblies of the upper supports for the steam generators at-North Anna, Unit 2 as required by 10CFR50.55(e)(3). Subsequent analysis was performed to incorporate modifica-tions of the assumptions concerning the distribution of loads in the upper support system. This analysis results in changes to some of the numbers mentioned in our previous letter; however, it does not change our position that the assemblies are still capable of performing their design functions without jeopardizing the safety of the system.
Our previous letter, Serial No. 543, is ammended as stated below.
Paragraph five should be changed to read:
"Considering the gross sectional properties of the embedded plate, the design stress in all twelve plates is below the yield strength of the steel and the stress in six of these plates exceeds the allowable.
Considering a net section through the clevis bolt holes, all twelve plates have stress-es that exceed the allowable. The stress in two of these plates is less than the yield strength.
In the other 10 plates the extreme fiber strain in the plate is above the strain required to produce yield snd this plastic behaviour is localized to the section at the clevis bolt holes. The full plastic noment capability is well in excess of the applied moment, thus preventing excessive deflections. The plastic section capacity at this section exceeds the applied moment by a ratto of 1.26.
Therefore, the restraint assembly remains functional, since strains and deflections of the front plate are limited by its reserve flexurrl capacity."
MDy 790212olP
Mr. James P. O'Reilly 2
The' third sentence of paragraph six should be changed to read:
"In the worst case at the localized' net section the extreme fiber strain exceeds the yield strain by 26 percent, however this represents only 0.58 percent of the ultimate strain."
These changes do not jeopardize the safety of the system which is still capable of perfoming its design function. This letter is to be considered an addition to our final report on this item and no further_ correspondence is anticipated.
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'Ver ;truly yours!
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' Sam C. Brown, Jr.
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f Senior Vice President cc: Mr. John G. Davis, Acting Director Office of Inspection & Enforcement Harold R. Denton, Director Office of Nuclear Reactor Regulation