ML20043F000
| ML20043F000 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 06/04/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20043E998 | List: |
| References | |
| NUDOCS 9006140080 | |
| Download: ML20043F000 (3) | |
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NUCLEAR REGULATORY COMMISSION 5
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOP REGULATION SUPPORTING AMENDMENT N0.122 TO FACILITY OPERATING LICENSE NO. OPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271 INTRODUCTION-By letter dated March 9, IMO, the Vermont Yankee Nuclear Power Corporation (the licensee) requested an amendment to Facility Operating License No. OPR-28 for-the Vermont Yankee Nuclear Power Station. The proposed amendment would revise the Technical Specification Table of primary containment isolation.
valves subject to Type C leakage tests, Table 4.7.2.a.
The change is to accommodate the installation of two new outboard feedwater check valves, V2-27A and 96A which are leak-testable and are now included in the Type C leakage test program. During the upcoming 1990 scheduled refueling outage, Vero nt Yankee plans to implement a design change which will replace the existing inboard feedwater check valves V2-28A and 28B with new check valves Jimilar to the outboard check valves. Leak testing the feedwater check valves also redefinas the primary containment boundary, so that two valves that previously require.d Type C testing, reactor water cleanup system valve V12-68 and control rod drive system valve V3-181, no longer require Type C testing and are removed from Table 4.7.2.a.
BACKGROUNO Section ll.H-of 10 CFR 50, Appendix J requires Type C testing of containment valves (two inboard of containment and two outboard of containment)ystem check isolation valves in the feedwater system of a BWR. The feedwater s were installed to provide the containment isolation function on the two feedwater lines. The feedwater check valves as originally installed at Vermont Yankee were not testable; Appendix J, which was issued after Vermont Yankee was licensed, would call for leak testing these valves. The licensee recognized the importance of testing the feedwater check valves for compliance with Appendix J
_ and in 1981, replaced the originally installed outboard valves with valves capable of meeting Appendix J requirements. On August 19, 1983, the staff issued an exemption from Section II.H of the Appendix J requirement pertaining to the Type C testing of inboard feedwater check valves, in granting the exemption the staff considered that:
"1. ' The closing of a check valve is very reliable. The outboard valves will fail to close only if they are physically blocked by some foreign material
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Even if the outboard valve fails to close, the inboard valve will remain water covered until all remaining feedwater has leaked through, providing a period of time to shut the motor-operated valves before there is any escape of containment atmosphere.
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Even if the outboard valve fails to close, and the motor-operated valves are'left open, system operating pressure greater than Pa can be maintained which will prevent leakage through the inboard valve out into the system."
In view of the above factors and the predicted man-rem exposure of 484 to 715 man-rem for replacing the inboard check valves, the staff concluded that
" anticipated radiation exposures associated with replacing inboard check valves far exceed the benefits of replacing these valves," and "we do not require testing the feedwater system motor operated valves as a basis for exempting thi inboard feedwater system check valves from Appendix J testing."
The Vermont iankee Technical Specifications presently do not require testing either the outboard check valves (V2-27A and 96A) or the inboard check valves (V2-28A and 28B), and include the inboard check valves in Table 4.7.2.b which lists " Valves Not subject To Type C Leakage Tests."
EVALUATION The radiation-field in the region of the inboard feedwater check valves has been reduced substantially since 1983, due in a large part to the recirculation pipe replacement outage during 1985-6. The projected exposure for replacing the inboard-feedwater check valves is 26 Man-rem.
Replacement of feedwater check valves V2-78A&B with valves that are leak-testable and inclusion of leak testino of the feedwater check valves in Vermont Yankee's Type C testing program and Technical Specifications will result in the addition of new testing rcquirements. The licensee stated that:
"The newly installed valves will not alter the manner in which the feedwater system operates. The feedwater check valves function to allow flow in one direction only, toward the reactor vessel. When flow either reverses or stops, the valve will seat itself and prevent reverse flow. The primary difference between the new spring check valves and the older "Y" lift check valves is the inclusion of a resilient seat. The new valves will be able to seat under feedwater system design pressures as well as under the containment design basis accident pressures. Because of the dual seat design of the new feedwater check valves, the integrity of the feedwater line primary containment penetrations.is improved."
The staff agrees that the new valve and new testing requirements should improve the integrity of the feedwater line primary conta! ament penetration. Given that the valves are now testable, the Appendix J requirement for Type C leakage testing should be observed.
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After the new inboard feedwater check valves are installed, the feedwater system will be equipped with check valves both inside and outside of the primary containment that are required to be tested in accordance with Appendix J.
Previously, the= reactor water cleanup system valve, V12-68, and control rod drive. system valve V3-181, which are outboard of the feedwater check valves, were also required to be tested. The addition of the inboard and outboard feedwater check valves to Table 4.7.2.a. Valves Subject to Type C Leakage Tests, allows valves V12-68 and V3-181 to be removed from Table 4.7.2.a.
The feedwater check valves are closer to the reactor and seal all flow in the feedwater flow path, as compared to valves V12-68 and V3-181 which seal only two side streams. Leak testing of the inboard and outboard feedwater check valves rather than valves V12-68 and V3-181, therefore, provides improved assurance of the leak tightness of the primary containment penetration.
ENVIRONMENTAL CONSIDERATION This amendment involves a change in 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. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no i
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 and there has been no public corsent on such finding. Accordingly, this amendment meets the l
eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assesment need be prepared in connection with the issuance of this amendment.
' CONCLUSION l
The Commission made a proposed determination that the amendment involves no significant hazards consideration which was published in the Federal Qe is'.er L
(55 FR 18415) on May 2, 1990, and consulted with the State of Vermont. Fo L
public comments were received and the State of Vermont did not have any comments. The staff concludes that the proposed changes to the Technir.a1 Specifications are acceptable.
. Principal Contributor: Vernon L. Rooney Dated: June 4,1990 1
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