ML20236S367
| ML20236S367 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/13/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20236S364 | List: |
| References | |
| TAC-65852, TAC-66116, NUDOCS 8711250108 | |
| Download: ML20236S367 (2) | |
Text
1 9 5tC0 f[6 g
'o UNITED STATES g
NUCLEAR REGULATORY COMMISSION l;,
j W ASHINGTON, D. C. 20555 i
/
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT NO.121 TO DPR-65 l
l NORTHEAST NUCLEAR ENERGY COMPANY, ET AL.
l MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 1
DOCKET NO. 50-336 INTRODUCTION By applications for license amendments dated July 14, 1987 and September 4, 1987, Northeast Nuclear Energy Company, et al. (the licensee), requested changes to the Technical Specifications (TS) for Millstone Unit 2 as follows:
(1) TS 4.4.5.1.4, " Acceptance Criteria", is modified to address the wall thinning criteria for steam generator sleeves and to remove a footnote and (2) TS 3.4.6.2, " Reactor Coolant System Leakage", would be changed to decrease the allowable primary-to-secondary leakage (through any one steam generator) from 0.5 to 0.15 gpm.
DISCUSSION AND EVALUATION With regard to sleeving of steam generator tubes, on December 30, 1983, the NRC staff issued Amendment 89 to the Millstone Unit 2 Operating License, DPR-65. Amendment 89 permitted the licensee to repair degraded steam l
generator tubes by inserting thin wall tubes (sleeves) in the existing i
steam generator tubes.
In the safety evaluation for Amendment 89, the NRC staff expressed the need for the licensee to develop criteria to address potential degradation of sleeved steam generator tubes. This need was subsequently ref1".:ted in a footnote to TS 4.4.5.1.4 as follows:
"The plugging limit Gr sleeves will be determined prior to next refueling
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outage." Sub%quently, on May 24, 1984, the licensee submitted a letter which propor J that sleeved steam generator tubes, degraded forty percent (40%) thro'sn wall, should be plugged.
By letter dated January 28, 1985, y
the NRC r sponded by approving the licensee's plugging criteria for sleeved steam r ierator tubes. The proposed changes to TS 4.4.5.1.4 would delete the e'; sting footnote and incorporate the plugging criteria for sleeved i
ster generator tubes in the TS by changing the definitions of imperfection,
,g de'y6dation, degraded tube, % degradation, and plugging limit, as they r aear in TS 4.4.5.1.4.
55 In order to demonstrate the adequacy of the 40% plugging criteria for sleeved "O
steam generator tubes, the NRC staff required the licensee to demonstrate
@f that a 40% degraded sleeve is equivalent in strength to a 40% degraded steam y
generator tube. Based upon information supplied by the licensee in their 7
letter dated May 25, 1984, we conclude that the sleeve design is such that it
,e,
is not as stiff as the parent tube. As a result, the bending stresses for a:
the sleeve are less than for a tube under both normal operation and accident conditions. We conclude that a sleeve degraded 40% through wall has a factor of safety of three or more against burst under all conditions specified in Regulatory Guide 1.1 21. Accordingly, the proposed change te the TS which provides for a 40% throughwall plugging criteria for sleeved steam generator tubes, is acceptable.
o
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The second proposed change to the TS involves the limit for primary-to-secondary leakage through a single steam generator. At the present time, TS 3.4.6.2 limits the primary-to-secondary leakage, in a single steam generator, to 0.5 gpm. The proposed change to TS 3.4.6.2, which would decrease the allowed leakage from 0.5 to 0.15 gpm, resulted from the licensee's January 1987 shutdown of Millstone Unit 2 for high primary-to-l secondary leakage. Following the plant shutdown, the licensee identified a steam generator tube with a circumferential crack which was through-wall over at least a portion o# the 220* circumferential extent.
I Assessments of the safety significance of the leaking tube were performed by the licensee and concluded that operation of the steam generator con-tinued to be safe provided that structural limits could be met for a circumferential1y oriented crack. Based on calculations which concluded i
that a circumferential crack of the size which would allow 0.15 gpm primary-to-secondary leakage was structurally acceptable, an administrative reduction of.the allowable leakage from 0.5 gpm to 0.15 gpm per steam generator was adopted for subsequent reactor operation. The pro >osed change to TS 3.4.6.2 incorporates this limit in the TS. The proposed c1ange to TS 3.4 6.2 pro-vides a more conservative limit on primary-to-secondary leakagc that reflects the plant-specific experience of the licensee. Accordingly, the proposed change to TS 3.4.6.2 is acceptable.
ENVIRONMENTAL CONSIDERATION This amendment changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, j
and no significant change in the types, of any effluents that may be released
{
offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously published a proposed finding that the amendment involves no significant hazards consideration j
2 and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental imsact statement or environmental assessment need be prepared in connection wit 1 the issuance of the amendment.
l CONCLUSION We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendment will not be inimical to the comon defense and security or to the health and safety of the public.
Dated: W 2 8 gy Principal Contributor:
D. H. Jaffe
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