ML19241C098
| ML19241C098 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/15/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Ahearne J NRC COMMISSION (OCM) |
| References | |
| NUDOCS 7907260641 | |
| Download: ML19241C098 (3) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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2 WASHINGTON D. C. 20555
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MEMCRANDL?l FOR: Comm'ssioner John Ahearne FROM:
H. R. Denton, Director Office of Nuclear Reactor Regulation THRU:
L. V. Gossick, Executive Director for Ccerations EUSJECT:
LER TRENDS Your memorandum to R. J. Mattson on the above subject dated April 19, 1979, cited the briefing given on operational data by Dr. W. Vesely on the same date. At this briefir.g Dr. Veselv reported that an analysis of LER's re-lated to valve failure indicated that a cocron problem was the leaving of valves incorrectly aligned (open or closed) fol{owing maintenance. The pro-bability cited for this type of failure was 10- per maintenance act. Your memorandum asked:
(1) if we had a preliminary list of other similarly high probability failurer, and (2) if we had developed or knew of a mechanism for autcmatically detecting and alaming such safety violations.
In sumary:
(1) We do not have a list, but are aware of some high failure rates shown by LERs and are studying these items; (2) Systems exist for auto-matic detection and alarming of incorrect valve positions; the degree of sophistication of such systems has been increasing on recent designs.
1.
With regard to the first question, we do not have a formal preliminary list of "other similarly high probability failures." We are aware, hcwever, that LER's seem to indicate a higher incidence of failures of some components than we would like to see. These include:
(1) valves and valve operators, (2) pumps, (3) control rods and drive mechanisms, (4) instrumentation and control components, (5) circuit breakers, and (6) diesel generators. On April 24, 1979, Mr. Gossick appointed a task force on " Operational Safety Data Analysis and Evaluation," with Mr. D. Davis of NRR as chaiman. Some time ago, RES initiated (Ref.1) a major LER Evaluation Program which has as its goal the extraction of component failure data from the NRC LER file, including studies of human-caused failures and multiple failure occurrences.
Dr. Vesely's briefing to you on April 19, 1979, was the first result of this program.
Items one through five cited above will be analy:ed first in acproximately that order and other items are likely to be added to the program later.
Similarly, an evaluation of diesel generator LER's will be included in the Task Action Plan A-44, Station Blackout, when it is developed. A recent study of diesel-generator reliability (Ref. 2) was perfomed under the Technical Assistance Program. The results of these programs, when available, will be considered in reassessment of the adequacy of existing eystem designs and safety criteria.
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Cor:r.issioner John Ahearne 2.
All nuclear plant designs include a control rocm annunciator system which automatically inc'icates and alarms a: normal plant conditions, including the incorrect position of scme (but not all) critical valves. Technical Specifications ard the supporting administrative procedures are relied on to assure that these other critical valves are ccrrectly positioned.
Various types of valves are used in nuclear power plants: motor operated valves (MGV's), manual valves (MV's), flow control valves (FCV's - either air or hydraulically operated), and solenoid valves (SV's). Most of the valves used in engineered safety feature systems are MOV's or MV's.
MCV's are all provided with position sensing limit switches integral with the motor operator which are used in the valve motor control circuitry and for remote position indication (open or closed). FCV's are provided with con-tinuous position sensors used in the flow control circuitry and for remote reading (". open). MV's and SV's are not usually provided with position sensing devices, although the position indication of SV's is scmetimes de-rived indirectly from the energized or deenergized status of the solenoid.
Hcwever, all these valve typer can be modified to provide position sensing devices; these devices then could be used to provide input to an automatic incorrect valve position indication and alarm system.
Monitoring is required of all safety systems, including indication when iney are bypassed or otherwise inoperable. This include incorrectly positionea valves. The requirements are contained in Criterion XIV of Appendix B to 10 CFR Part 50 (Enclosure 1), Section 4.13 of IEEE Std 279-1971 (Enclosure 2),
and Regulatory Guide 1.47 (Enclosure 3).
It should be nc.ted that only RG 1.47, which provides the most explicit requirements, includes a requirement for automatic indication of inoperable status at the system level. This guide was issued in 1973 and is applicable to plants with CP applications docketed after issuance of the guide. However, our reviews of CP's and OL's to which this guide is not applicable have attained a measure of confomance to its requirements, the degree depending on the degree of confomance of the origi-nal design and its stage of completion at the time the guide was issued.
In this regard, the status monitoring system design for Watts Bar Units 1 and 2 is probably the most advanced design proposed to date. The monitor is com-oletely computerized and includes audible alarms, and light displays indicat-ing system status, cathoderay tube graphic display, alann recorder, and inter-rogation capability for the operator to determine the status of components of the monitored systems. Enclosure 4, Section 7.7.1.3.6 of the Watts Bar FSAR, provides a more detailed description of this system.
In addition to monitoring the positions of critical valves, we recuire that some be interlocked so that signals initiating their safety functions also act to place the valves in their correct pcsitions if they are nc,t there already.
In view of the Three Mile Island incident, we are considering both the need for l
revision of existing requirements for safety system status monitoring systems bl9122
Commissioner John Aheerne and interlocks, and also the need for backfitting of the revised requirements to operating plants and plants now in licensing review.
Harold R. Denton, Director Office of Nuclear Reactor Regulation References 1.
Memorandum frem A. R. Buhl to NRR Division Directors dated October 30, 1978, LER, Evaluation Program: Draft Report on ECCS Valve Failure Rate Analysis.
2.
NUREG CR 0660, Enhancement of On-Site Energency Diesel Generator Reliability.
Enclosures:
1.
Cri.erion XIV, Inspection Test and Operating Status, of Appendix B to 10 CFR Part 50.
2.
Section 4.13, Indication of Bypasses, of IEEE Std 279-1971.
3.
R.G. 1.47, Bypassed and Inoperable Station In-dication for Nuclear Power Plant Safety Systems.
4.
Section 7.7.1.3.6, Safety Systen Status Moni-toring System, Watts Sar FSAR.
cc: Chairman Hendrie Commissioner Gilinsky Commissioner Kennedy Commissioner Bradford Secy EDO 319123