ML20044F199
| ML20044F199 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 04/18/1991 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20044F187 | List: |
| References | |
| NUDOCS 9305270187 | |
| Download: ML20044F199 (3) | |
Text
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Enclosure
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UNITED STATES f
' i NUCLEAR REGULATORY COMMISSION
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j WASHINGTON. o. C. 20555 G
NRC INSPECTION MANUAL OTSB PART 9900: TECHNICAL GUIDANCE MAINTENANCE - VOLUNTARY ENTRY INTO LIMITING CONDITIONS FOR OPERATION ACTION STATEMENTS TO PERFORM PREVENTIVE MAINTENANCE A.
PURPOSE To provide a set of safety principles for guiding the performance of preven-tive maintenance (PM) at licensed nuclear reactor facilities when the performance of the PM requires rendering the affected system or equipment a
l inoperable (on-Line PM).
Although these principles apply primarily to PM during power operation, they also apply to PM on equipment that must be OPERABLE during shutdown evolutions such as fuel handling or mid-loop operation.
This guidance provides qualitative criteria to assist in recognizing abuses I
of on-line PM.
If such abuses are noted, they should be discussed with NRC management before they are discussed with the licensee.
This should ensure that the guidance is applied in a reasonable and consistent manner for all licensees.
l B.
BACKGROUND
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The NRC has not previously established guidance on taking equipment out of service to perform PM because the NRC did not expect licensees to routinely perform such PM when technical specifications require the equipment to be OPERABLE.
Rather, it was expected that most PM that necessitated taking
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equipment out of service would be accomplished at a time when the safety function performed by the equipment was not needed, (e.g., when the facility
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is shutdown).
Performing such PM (e.g., emergency diesel generator overhaul i
at power) requires intentionally entering the technical specifications (TS)
~1 limiting conditions for operation (LCO) for the affected system.
If a i
licensee does this, it must complete the PM and restore compliance with the LC0 OPERABILITY requirements within the time specified in the appropriate i
action statement of the LC0 (i.e., the allowed outage time (A0T)).
Inten-j tional entry into an action statement of an LCO is not a violation of the TS (except in certain cases, such as intentionally creating a loss of func-tion situation or entering LC0 3.0.3).
For example, TS allow licensees to perform much surveillance testing during power operation, even though such testing requires entry into LC0 action statements.
TS permit entry into LC0 action statements to perform surveillance testing for a number of reasons.
One reason is that the time needed to perform most surveillances is usually only a small fraction of the A0T specified in the action statement.
9305270187 930514 PDR ADDCK 05000271 1ssue Date: 04/18/91 P
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Another reason is that the benefit to safety (increased level of assurance of reliability and verification of OPERABILITY) derived from meeting surveil-lance recuirements is considered to more than compensate for the risk to safety from operating the f acility in an LC0 action statement for a small fraction of the A0T.
The !4?C staff has noticed a trend at many licensed nuclear f acilities to perform increasing amounts of PM during power operation (on-line PM) rather than during shutdown conditions.
By performing more on-line PM, licensees must intentionally enter into LCOs more frequently than before and use more of the A0Ts than would normally be used by surveillance testing alone. This could cause the total unavailability of equipment over each operating cycle (or the total time that a facility operates at increased risk because it is not compl f ailures)ying with LC0 OPERABILITY requirements and is vulnerable to single to become greater than originally contemplated when TS were estab-lished. Of special concern is intentional entry into LCOs to perform PM near the end of an operating cycle primarily in order to shorten the refueling outage.
The NRC is only beginning to quantitatively study the significance to safety (risk) of the trend to perform more PM during power operation.
Therefore, the NRC can not yet establish quantitative criteria by which the NRC or a licensee can determine the net effect on safety that on-line PM would have at a f acility.
Until studies concerning the risk of on-line PM are completed, this guidance establishes conservative principles for safely performing PM that involves entering into LC0 action statements.
C.
DISCUSSION A licensee may take equipment out of service to perform PM during power operation of the facility (on-line PM) if it expects the reliability of the equipment to improve such that the overall risk to safe operation of the facility shoulo decrease.
Licensees' expectations should take into account that such practice may increase the unavailability of the equipment.
When performing PM on equipment not in TS (i.e., equipment that has no T5 A0T),
licensees should be sensitive to the principles embodied by the TS definition of OPERABILITY and the effect upon the OPERABILITY of TS equipment.
If a licensee has a reasonable expectation that an on-line PM program will improve safety by making equipment more reliable, then the licensee can implement that program even though it may increase the unavailability of equipment.
The licensee should be able to justify such an expectation of improved safety.
Part of this justification should be based upon adherence to the following conservative safety principles:
1.
Performance of a FM action on-line rather than during shutdown should i
improve safety (as described above) and be warranted by operational necessity, not just by the convenience of shortening a refueling outage.
2.
The licensee should not abuse the allowance to perform a PM action l
on-line by repeatedly entering and exiting LC0 action statements. The licensee should carefully plan the PM action to prevent such abuse.
Issue Date: 04/18/91 9900 i
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3.
While performing an on-line PM action, the licensee should avoid removing other equipment from service.
Confidence in the OPERABILITY of the independent equipment that is redundant (or diverse) to the affected equipment should be high.
If a piece of equipment is OPERA-BLE, but is degraded, or is trending towards a degraded condition, the i
licensee should not remove its redundant counterpart equipment from service for a routine PM action.
4 While performing an on-line PM action, the licensee should avoid per-forming other testing or maintenance that would increase the likeli-hood of a transient.
The licensee should have reason to expect that the facility will continue to operate in a stable manner.
(The basis of this expectation should include a consideration of degraded or out of service balance of plant equipment.)
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9900 Issue Date: 04/18/91