ML19317E743
| ML19317E743 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/16/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19317E739 | List: |
| References | |
| NUDOCS 7912180898 | |
| Download: ML19317E743 (2) | |
Text
I
/
i\\/y. 6 t
.i
.g.
i
~
BRANCH TECHNICAL POSITIO*; EICSB 18 APPLICATI.ON OF THE 51r:GLE FAILURE CRITERICN TO V"*cALLY-CONTROLLED ELECTRICALLY-OPERATED VAL'.'ES A.
BACKGROU';D Where a single failure in an electrical system can result in loss of capability to perfom g
{
a safety function, the effect on plant safety r.ust be evaluated. This is necessary regard-less of whether the loss of safety function is Caused by a cc ponent failing to perform a requisite r,echanical motion, or by a component perfcming an undesirable cechanical r.otion.
This position establishes the acceptability cf disconnecting poner to electrical co conents of a fluid systen as one ; mans of designing against a single failure that r.ignt cause an ur.-
desirable component action. These provisions are based on the assu ption that the cccponer.t is then equivalent to a similar compenent that is not designed for electrical cperation, l,
e.g., a valve that can be opened or closed caly by direct ranual cparaticn of the valve.
They are also based on the assu.ption that no single failure can both restore gener to the electrical system and cause mechanical cotien of the cocponents served by tne electrical systt.a. The validity of these assu ptions should be verified
- hen applying this pcsiticn.
B.
BRANCH TECP:ICAL POSITIO*i IO 1.
Failures in both the " fall to function" sense and the " undesirable function *' sense of crenponents in electrical systens of valves and other fluid system cc ponents s*.ould be considered in designirg against a single failur2, even though the valve or other fluid system ccaponent may not be called upon to function in a given safety operational sequence.
2.
Where it is detemined that failure of an electrical syste. co penent can cause undesired rechanical cotion of a valve'er other fluid syste-' co ;ccent ar.d this motion results in loss of the system safety function, it is acceptable, in lieu of design changes that also may be acceptable, to disconnect pc er to the electric syste s of the valve or other fluid system component. The plant technical specificatiens should, include a list of all electrically-operated valves, and the required positiers of these valves, to which the requirement for re= oval of electric power is applied in order to satisfy the single failure criterion.
?
~
3.
Electrically-operated valves that are classified as " active" valves, i.e., are required g
to open or close in various safety system operational sequences, but are manually-controlled,' should be operated from the c:ain control roo.9 Such valves ray not be included among those valves from which power is removed in order to meet the single '
failure criterion unless: (t) electrical power can be restored to the valves frcm the main control room,(b) valve operation'is not necessary for at least tm minutes f.ollowing occurrence of the event requiring such~ operation, and(c) it is denonstrated
~
-y eo@yy y
?*.
that there is reascnabis assuranc7 that all necessary operater actions will be per-D formed ylthin the tire shown to be adequate by the analysis.
The plant technical specifications should include a list of the required positions of rianually-controlled.
electrically-operated valves and should identify those valves to which the require-ment for removal of electric power is applied in order to satisfy the single failure criterion.
4.
[
ilhen the single fcilure criterion is satisfied by reroval of electrical pc.ar fron valves described in(2) and(3), above these valves should have redandant position indication in the main control room and the positicn indication system should itself v
j meet the single failure criterion.
t 5.
The phrase " electrically-operated valves" incit, des both valve operated directly by an electrical device (e.g.. a motor-operated valve or a solenoid.orerated valve) and those valves operated indirectly by an electrical device (e.g., an air-operated valve whose j -
air supply is controlled by an electricel solenoid valve).
-t
, [
C.
REFERENCES 1.
Pemorandum to R. C. DeYoung and Y. A. P. core from V. Stello. October 1. 1973.
t l
y e
,t I
p 4
g l
l l
-l 9
t
'6 P
I 7A-28
'i j
.