ML19210B175
| ML19210B175 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/18/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19210B173 | List: |
| References | |
| NUDOCS 7911040103 | |
| Download: ML19210B175 (2) | |
Text
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BRANCH TECHNICAL POSITION E!CSB 18 APPLICATION OF THE SI?:GLE FAILURE CRITERION TO MA'iUALLY-CONTROLLED ELECTRICALLY-OPERATED VALVES A.
BACKGRC'JND Where a single failure in an electrical system can result in loss of capability to perforr.
a safety function, the effect on plant safety. must be evaluated. This is necessary regard-less of whether the loss of safety function is Caused by a corponent failing to perform a requisite mechanical motion, or by a component performing an undesirable rechanical -otion.
This position establishes the acceptability of disconnecting power to electrical co. ::onents of a fluid system as one means of designing against a single failure that might cause an un-desirable co ponent action. These provisions are based on the assumption that the component is then equivalent to a similar component that is not designed for electrical operation, e.g., a valve that can be opened or closed only by direct canual cperation of the valve.
They are also based on the assu ption that no single failure can both restore rcwer to the electrical system and cause mechanical motion of tne co ponents served by the electrical system. The validity of these assumptions should be verified when applying this position.
i B.
BRAriCH TEC"NICAL POSITION 1.
Failures in both the " fail to function" scnse and the " undesirable functi:9' sese of components in electrical syste s of valves and other fluid system co ::cr.e'.ts s%id be considered in designing against a single failure, even thcugh tne sa've ce ct*.er fluid systen co.panent -ay not be called up:n to (snction in a given safct cperational sequence.
2.
Where it is determined that failure of an electrical system compenent an :ause undesired rechanical motion of a valse or other fluid system c: ponrr, and tnis motion results in loss of the systen safety function, it is accepta-e, in lieu of design changes that also may be acceptable, to disconnect power to the electric systers of the valve or other fluid system co ponent. The plant technical specifications should include a list of all electrically-operated valves, and 'tne recuired positions of these valves, to which the requirenent for removal of electric power is applied in creer to satisfy the single failure criterion.
3.
Electrically-operated valves that are classified as " active" valves, i.e., are recuired to open or close in various safety systen operational sequences, but are ranually-controlled, should be operated from the main control room. Such valves may not be included among those valves from which ower is removed in order to meet the single r
failure criterion unless: (i) electrical power can be restored to the valves frem the main control room,(b) valve operation is not necessary for at least *en minutes
(
following occurrence of the event requiring such operation, and(c) it is cenonstrated 1 l' O 7 nnA IJOI U~ ) 4 7A-27 O3
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jff g that there is reasonable assurance that all necessary operator actions will be per-
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fortned'within the ti e shown to be adequate by the analysis. The plant technical specifications should include a list of the required positions of manually-centrolled, electrically-operated valves and should identify those valves to which the recuire-inent for reinoval of electric power is applied in order to satisfy the single failure criterion.
4.
When the single failure riterion is satisfied by removal of electrical power from valves described in(2) and (3), above, these valves should have redundant position indication in the r.ain control room and the position indication syster should.itself.
reet the single failure criterion.
S.
The phrase " electrically operated valves" includes both valves operated directly by an electrical device (e.g., a rotor-operated valve or a solenoid-operated valve) and tnose valves operated indirectly by an electrical device (eeg., an air-operated valve e.ose air supply is controlled by an electrical solenoid valve).
C.
REFERENCES 1.
fdemorandum to R. C. C, Young and V.' A. Moore from V. Stello, October 1, 1973.
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- s. s' 7A-28
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