ML20044F186
| ML20044F186 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/14/1993 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Curran D HARMON, CURRAN, SPIELBERG & EISENBERG, LLP. |
| Shared Package | |
| ML20044F187 | List: |
| References | |
| NUDOCS 9305270165 | |
| Download: ML20044F186 (4) | |
Text
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- t UNITED STATES E \\idf f [E NUCLEAR REGULATORY COMMISSION (yjjge' WASHINGTON, D.C. 20556-0001
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May 14, 1993 Diane Curran, Esq.
2001 S Street, N.W.
Suite 430 Washington, DC 20009-1125
Dear Ms. Curran:
t I am responding to your letter of April 2,1993, regarding " intentional disabling of safety systems for purposes of performing at-power repairs."
In your letter, you particularly questioned the practice of Vermont Yankee Nuclear Power Corporation of removing an emergency diesel generator (EDG) from service for the purpose of performing routine repairs during power operation.
You asked whether the staff finds that practice inconsistent with General Design Criterion (GDC) 17 of Appendix A to Part 50 of Title 10 of the Code of Federal Regulations (10 CFR Part 50), the plant Technical Specifications (TS),
and Regulatory Guide (RG) 1.93 " Availability of Electric Power Sources." You also asked how the staff views the safety benefits of this practice and what credit the staff allows for the availability of the Vernon Hydroelectric Station (Vernon Hydro; tie-line while an EDG is unavailable at the Vermont Yankee Nuclear Power Station.
The staff believes that the intentional removal of safety systems for planned maintenance with the reactor at power is not inconsistent with GDC 17, plant TS, or RG 1.93.
The requirements of GDC 17 govern the design of the facility and are intended to provide " reasonable assurance that the facility can be operated without undue risk to the health and safety of the public." However, the Commission recognizes that, in practice, a redundant component may be remosed from service for short intervals for various reasons, which include random failures, surveillance testing, maintenance, and routine repairs.
Therefore, pursuant to 10 CFR 50.36(c)(2), the limiting conditions for operation (LCO) in the TS include remedial actions which permit the licensee to continue operating the reactor for a prescribed interval while restoring --~~~
the component to service.
This contingency is recognized in the discussion of "The Available A.C. Power Sources Are One Less Than the LC0" in RG 1.93, whi:h states, in part,
- each system [i.e., the off-site power system and the on-site power system] retains full capability (one system with redundancy) to effect a safe shutdown and to mitigate the effects of a design basis accident.
Operation could, therefore, safely continue if the availability of the remaining sources of power is verified; however, since the system is degraded below the LCO, a time limit on continued operation is warranted.
The plant TS specify that time limit.
The NRC staff has issued guidance in the NRC Inspection Manual (Enclosure) for consideration of whether or not the conduct of a particular maintenance activity is appropriate and not detrimental to safety while the reactor is at power. This guidance takes into consideration among other things (1) the ty W p m..; m 1
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Ms. Diane Curran
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May 14, 1993 of maintenance activity and its value in improving the reliability of the particular structure, system, or component (SSC); (2) the effect of alternatives (including alternative maintenance schedules or the conduct of the maintenance in an alternative mode of reactor operation) on both the risk and the safety benefits; (3) the recent performance history of the affected SSC, including entries into LC0 action statements; (4) compensatory measures such as assurance of operability of the redundant SSC, assurance of operability of other safety systems, and plant stability while operating in the action statement; and (5) the relative expectation of adverse natural phenomena, such as storms, which may affect the probability of an initiating event.
The staff recognizes that quantification of these considerations is usually impractical. The above considerations are discussed in the NRC l
Inspection Manual and are available for use by both the staff and the l
licensees.
As discussed above, the staff does not consider Vermont Yankee's performance of preventive maintenance on EDGs with the reactor operating at power to be inconsistent with GDC 17.
Therefore, the staff concludes that an alternative power source is not required to " substitute" for the affected EDG to demonstrate compliance with GDC 17 during the period of operation in the LCO action statement.
Rather, the staff views the availability of the Vernon tie-line during LCO maintenance of an EDG, not as an assured on-site power source, but as a measure which provides some reduction of the risk associated with maintenance.
Sincerely, i/riginal signed by Tho:335 E. Murley Thomas E. Murley, Director Office of Nuclear Reactor Regulation
Enclosure:
l NRC Inspection Manual l
Part 9900 Issue Date 4/18/91
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1 Ms. Diane Curran.
May 14, 1993 of maintenance activity and its value in improving the reliability of the particular structure, system, or component (SSC); (2) the effect of alternatives (including alternative maintenance schedules or the conduct of the maintenance in an alternative mode of reactor operation) on both the risk and the safety benefits; (3) the recent performance history of the affected SSC, including entries into LC0 action statements; (4) compensatory measures such as assurance of operability of the redundant SSC, assurance of operability of other safety systems, and plant stability while operating in the action statement; and (5) the relative expectation of adverse natural phenomena, such as storms, which may affect the probability of an initiating event.
The staff recognizes that quantification of these considerations is usually impractical.
The above considerations are discussed in the NRC
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inspection Manual and are available for use by both the staff and the licensees.
As discussed above, the staff does not consider Vermont Yankee's performance of preventive maintenance on EDGs with the reactor operating at power to be inconsistent with GDC 17.
Therefore, the staff concludes that an alternative power source is not required to " substitute" for the affected EDG to demonstrate compliance with GDC 17 during the period of operation in the LCO action statement.
Rather, the staff views the availability of the Vernon tie-lit.e during LCO maintenance of an EDG, not as an assured on-site power source, but as a measure which provides some reduction of the risk associated with maintenance.
Sincerely, W
Thomas E. Murley, Director Offica of Nuclear Reactor Regulation
Enclosure:
NRC Inspection Manual Part 9900, Issue Date: 4/18/91 l
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r Yellow Ticket #0930072 DISTRIBUTION:
Docket File:(50-271)1w/incomingr
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NRC &' L'ocal" PDRs (w/ incoming)
PDI-3 Reading Yellow Ticket File (#0930072 w/ incoming)
IMurley FMiraglia WRussell JPartlow SVarga JCalvo WButler DDorman TClark NRR Mailroom (YT#0930072) 12G18 BClayton RThompson CNorsworthy JLinville, RI JRichardson AThadani BGrimes OGC
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