ML20212D191
| ML20212D191 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 09/20/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212D171 | List: |
| References | |
| NUDOCS 9909230029 | |
| Download: ML20212D191 (2) | |
Text
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UNITED STATES 8y')*
E NUCLEAR REGULATORY COMMISSION f
WASHINGTON, D.C. 20555-0001
.....,5 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION EXEMPTION FROM 10 CFR PART 50. APPENDIX A.
GENERAL DESIGN CRITERION 57. CLOSED SYSTEM ISOLATION VALVES j
MCGUIRE NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50-369 AND 370
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 have 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 automatic isolation valve.
By letter dated April 20,1999, Duke Energy Corporation (the licensee) submitted a request for an exemption from GDC 57 for Containment Penetrations M261 and M393.
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 lines, one branch supplies main steam to the turbine-driven auxiliary feedwater pump (TDCA, using the licensee's abbreviation). The attached sketch provides details of the line arrangement. Figure 10-13 of the Updated Final Safety Analysis Report (UFSAR), also shows this line arrangment.
Valves SA-1, SA-2, SA-77, and SA-78 are manual gate valves located in the Interior Doghouse immediately downstream of the respective main steam piping, in the branch lines that supply main steam to the TDCA. These valves are locked open (with break away locks) and capable of local manual operation only. These valves are required to be open (Technical Specification (TS) SR 3.7.5," Auxiliary Feedwater System") to supply steam to the TDCA, which is part of the engineered safety features. The TDCA can operate with one of these valves closed, providing that steam is available from the opposite main steam piping. (Requirements for containment isolation valves are set forth in Section 3.6.3 of the McGuire TS.) From a probabiiistic risk assessment perspective, the TDCA is one of the rnost risk-significant safety system components. Adding motor operators to SA-1, SA-2, SA-77, and SA-78 such that they become 9909230029 990920 PDR ADOCK 05000369 P
. automatic or capable of remote operation (i.e., meeting GDC 57) would adversely impact the reliability of the TDCA to mitigate an accident because the motor operators would introduce a new failure mode. Keeping SA-1, SA-2, SA-77, and SA-78 closed (i.e., meeting GDC 57) during plant operation would violate a TS requirement.
Valves SA-1, SA-2, SA-77, and SA-78 can be manually closed, as needed during certain accidents, to isolate the steam lines they serve. However, the licensee indicated that under certain postulated accident conditions, SA-1, SA-2, SA-77, and SA-78 would be in environmental conditions inaccessible to operators. In that circumstance, stop check valves SA-5 and SA-6, which are located downstream of SA-1, SA-2, SA-77, and SA-78 in the Auxiliary Building, respectively, would be used to isolate steam flow if needed. The licensee listed all the emergency procedures currently in existence that direct the operators to preferentially close SA-1, SA-2, SA-77, and SA 78, then SA-5 and SA-6. The licensee indicated that the times needed by operators to isolate steam using SA-1, SA-2, SA-77, and SA-78, or SA-5 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, SA-2, SA-77, and SA-78 such that they can meet the operational requirement specified by GDC 57 would reduce reliability of the TDCA or violate an existing TS, or both; (2) the times needed by. operators to manually close SA-1, SA-2, SA-77, and SA-78, or SA-5 and SA-6, during an accident have been factored into accident analysos, and (3) the applicsble design-basis accident scenarios and consequences continue to be bounding. 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.
Attachment:
As stated l
Principal Contributors: James Pulsipher Frank Rinaldi l
Date:
September 20, 1999
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