ML19224C755
| ML19224C755 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/25/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19224C756 | List: |
| References | |
| SER-790525, NUDOCS 7907060145 | |
| Download: ML19224C755 (2) | |
Text
.
ga ascy g
UNITED STATES y ; "ec, g
NUCLEAR REGULATORY COMMISSION
~
E WASHINGTON. D. C. 20555 t
jf
~% *.... e' SUPPLEMENT NO. 1 TO SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 52 TO FACILITY OPERATING LICENSE NO. OPR-65 NURTHEAST NUCLEAR ENERGY COMPANY, ET AL MILLSTONE NUCLEAR POWER STATION, UNIT t.u. 2 DOCKET NO. 50-336 Introduction By letter dated May 12, 1979, we issued Amendment No. 52 authcrizing Cycle 3 operation for Millstone Nuclear Power Station, Unit No. 2 (Millstone-2).
Section 2.4 of the supporting Safety Evaluation addressed Control Element Assembly (CEA) guide tube integrity and our review of the results of the Millstone-2 testing program provided by letters dated April 17 and 26,1979 and May 7, 1979. These results were from eddy-current test (ECT) and pull tests on sleeved fuel assemblies irradiated for one cycle. The results confirmed earlier tests and calculations to show that sleeving is an acceptable repair to alleviate CEA guide tube wear for Cycle 3.
Subsequent to the issuance of Amendment No. 52, test results have been reported by Baltimore Gas & Electric (BG&E) and Combustion Engineering (CE) Ccmpanies revealing a significant number of sleeved fuel assemblies from Calvert Cliffs Nuclear Power Plant, Unit No.1 (Ca' vert Cliffs-1) are outside the ECT and pull test acceptance criteria used at Millstone-2.
Discussion and Evaluation The planned scope of the ECT and pull test program planned for Calvert Cliffs-1 and also for the St. Lucie Plant, Unit No.1 (St. Lucie-1), relied upon the results from the Millstone-2 test program. These three reactors are very similar (designed by CE), and each licensee installed stainless steel sleeves in the CEA guide tubes to remedy the guide tube wear problem during their spring of 1978 refueling outages. An ECT program was planned for Calvert Cliffs-1 and St. Lucie-1 to verify that the results at these plants were at least as good as those observed at Millstone-2. The results of the ECT at St. Lucie-1 favorably compared with those at Millstone-2. Hcwever, the adverse results from the
,c,
, r)
_//
C*
7907060 /I/jI' testing at Calvert Cliffs-1, reported to the NRC staff on May 16, 1979, prompted our concern with regard to the resistance to axial motion of the sleeves in the guide tubes.
Following discussions between the NRC staff, Northeast Nuclear Energy Company (NNECO) and CE to detemine the cause and effect of the abnomalities, NNECO documented their explanation of the Calvert Cliffs-1 results in com-parison with results from Millstone-2 and St. Lucie-1 by letter dated May 17, 1979. They report that the sleeving sequence used at Millstone-2 and St.
Lucie-1 in 1978 differed from that used at Calvert Cliffs-1. At Millstone-2 and St. Lucie-1, pull tests were perfomed on the sleeves afte" the crimping step to verify the adequacy of the crimp. Following the "crirrp verification" pull test, expanding steps were then perfomed on the sleeves, However, at Calvert Cliffs-1, the pull tests were not performed until after both the crimping and the expanding steps were completed. NNECO and CE have concluded that this sequence change added frictional resistance between the expanded sleeve and the guide tube wall to mask the presence of inadequate crimps that would nave been identified by an intemediata " crimp verification" pull test.
In addition, the low ECT results at Calvert Cliffs-1, which indicate inadequate crimps, were unique to a particular fuel category. This fuel category consists of those assemblies that had been irradi'.ted prior to sleeving in 1978. In this fuel category at Calvert Cliffs-1, the eddy-current signals were low for approximately 50% of the 23? f eeve:, 'ested. The low signals for irradiated fuel were not evident at either Millstone-2 or St. Lucie-l.
Thus, it appears that the increased yield strength of irradiated guide tubes may reduce the displace-ment of the crimp. This conditic,a magnifies the importance of the intemediate
" crimp verification" pull test which was not performed at Calvert Cliffs-1.
Conclusion Based upon the data reported in NNECO's submittal datei May 17, 1979, we agree that the CEA guide tube sleeve integrity abnomalities observed at Calvert Cliffs-1 are un.que to the irradiated fuel assemblies sleeved in 1978 at that plant.
Therefore, the Calvert Cliffs-1 test program data has no affect on our conclusion, documented in Section 2.4 of our May 12, 1979 Safety Evaluation, that sleeving of CEA guide tubes provides an acceptable interim repair to alleviate the guide tube wear problem for Cycle 3 operation of Millstone-2.
Dated:
May 25, 1979 I