ML20198L031
| ML20198L031 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 12/29/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20198L028 | List: |
| References | |
| NUDOCS 9901040030 | |
| Download: ML20198L031 (2) | |
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UNITED STATES g
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WASHINGTON, D.C. 20066-0001 e%...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION EXEMPTION FROM 10 CFR PART 50. APPENDIX A.
l GENERAL DESIGN CRITERION 57. CLOSED SYSTEM ISOLATION VALVES CATAWBA NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50-413 AND 50-414
1.0 INTRODUCTION
Title 10 of the Code of Federal Reaulations (10 CFR), Part 50, Appendix A, General Design Criterion (GDC) 57, regarding closed system isolation valves, states that:
Each line that penetrates primary reactor containment and is neither part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere shall hav = at least one containment isolation valve which shall be either automatic, or locked closed, or capable of remote manual operation. This valve shall be outside containment and located as close to the containment as practical. A simple check valve may not be used as the automstic isolation valve.
l By letter dated September 2,1997, Duke Energy Corporation (the licensee) submitted a request for an exemption from GDC 57 for Containment Penetrations M261 and M393 (erroneously stated as M363 in the submittal).
2.0 EVALUATION Containment Penetrations M261 and M393 are main steam penetrations. These lines penetrate the containment and are not part of the reactor coolant pressure boundary or connected directly to the containment atmosphere. Outside of containment, these lines branch into various separate, individual lines before reaching the respective main steam isolation valves. From each of these main steam li6es, one branch supplies main steam to the I
turbine-driven auxiliary feedwater pump (CAPT, using the licensee's abbreviation). Figure 10-6 of the Updated Final Safety Analysis Report (UFSAR) provides details of the line arrangement.
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Valves SA-1 and SA-4 are manual gate valves located in the Interior Doghouse immediately.
l downstream of the respective main steam piping. These valves are locked open (with break t
away locks) and capable of local manual operation only. These valves are required to be open (Technical Specification SR 3.7.5.1) to supply steam to the CAPT, which is part of the j
engineered safety features. The CAPT can operate with one of these valves closed, providing that steam is available from the opposite main steam piping. (Penetrations M261 and M393, and corresponding Valves GA-1 and SA-4, are listed in Table 6-77 of the UFSAR.
Requirements for containment isolation valves are set forth in Section 3.6.3 of the Catawba l
Technical Specifications.) From a probabilistic risk assessment perspective, the CAPT is one of the most risk-significant safety system components. Adding motor operators to SA-1 and l
9901040030 981229 PDR ADOCK 05000413 p
. SA-4 such that they become automatic or capable of remote operation (i.e., meeting GDC 57) would, thus, adversely impact the reliability of the CAPT to mitigate an accident because the motor operators would introduce a new failure mode. Keeping SA-1 and SA-4 closed (i.e.,
meeting GDC 57) during plant operation would violate a Technical Specification requirement.
The licensee indicated that under certain postulated accident conditions, SA-1 and SA-4 would be in environmental conditions inaccessible to operators. In that circumstance, stop check valves SA 3 and SA-6, which are beated downstream of SA-1 and SA-4 in the Auxiliary Building, respectively, would be used to isolate steam flow if needed. The licensee listed all the emergency proceduras currently in existence that direct the operators to preferentially close SA-1 and SA 4, then SA-3 and SA-6. The licensee indicated that the times needed by operators to isolate steam using SA-1 and SA-4, or SA-3 and SA-6, have been factored into the accident analyses and resultant dose calculations in the UFSAR.
3.0 CONCLUSION
The staff finds that (1) modifying valves SA-1 and SA-4 such that they can meet the operational requirement specified by GDC 57 would reduce reliability of the CAPT, violate an existing TS, or both; and (2) the times needed by operators to manually close SA-1 and SA-4, or SA-3 and SA-6, during an accident have been factored into accident analyses and are bounded by the design-basis accident scenarios and consequences. On such bases, the staff concludes that literal compliance with the operational aspect of GDC 57 is not desirable and therefore an exemption is acceptable.
Principal Contributors: James Pulsipher Peter S. Tam Date: December 29, 1998 fW
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