ML20008G098
| ML20008G098 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 06/29/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20008G097 | List: |
| References | |
| TASK-03-10.A, TASK-3-10.A, TASK-RR NUDOCS 8107020236 | |
| Download: ML20008G098 (2) | |
Text
- _ _ _ _ _ _ _ -_
TOPIC:
III-10.A THERMAL-0VERLOAD PROTECTION FOR MOTORS OF MOTOR-OPERATED VALVES O
I.
INTRODUCTION The primary objective of thermal overload relays is to protect motor windings of motcr-operated valves (MOV) against excessive heating.
This feature of thermal overload relays could, however, interfere with the successful functioning of a safety related system. In nuc-lear plant safety system application, the ultimate criterion should -
be to drive the valve to its proper position to mitigate the conse-quences of an accidents, rather than to be concerned with degradation or failure of the motor due to excessive heating.
II. REVIEW CRITERIA 1
The primary review criteria are:
1.
IEEE Std. 279-1971, and 2.
As a result of numerous operating plant events resulting from torque switch problems the following supplemental criterion was used:
"(3) In MOV designs that use a torque switch tr' limit the opening or g~
closing of the' valve, the automatic opening or closing signal
- should be used in conjunction with a corresponding limit switch."
III. RELATED SAFETY TOPICS AND INTERFACES There are no safety areas related to the scope of this review that are addressed by other SEP To Ms nor are any other topics 6 pendent on the results of tljis review.
IY. REVIEW GUIDELINES l
The review should assure that:
(1) thermal overload protection, if provided, for M0V's should have the trip setpoint.at a value high l
l.
enough to prevent spurious trips due to design inaccuracies, trip set-point drift, or variation in the ambient temperature at the installed location; (2) the circuits that bypass the themal overload: protection under ac ident conditions are designed to IEEE Std. 279-1971 criteria, as appropriate for the rest 6f the safety related system; and (3) 1'n MOV designs that use ? torque switch instead of a limit switch to limit the opening or closing of the valve, the automatic opening or closing signal should be used ia conjunction with a corresponding limit switch and thermal overload should remain as backup protection over the first 10% of valve travel.
8-15702 0 M5 i
7'
/
.p c;, ;4 m,: y
.,,... > >e-
.c.
n, W/ u. c, <,, -
V' c
. -. - +.. _
m_,.
-_-..-,..-__,_,,,.,,.-.m-,
2-V.
EVALUATION' The design provisions for motor-operated valve protection are described in EG&G Report 1653F, " Thermal-Overload Protection for Motors of Motor-Operated Valves."
VI. CONCLUSIONS The Oyster Creek designs do not satisfy the current licensing criteria, for all safety related valve functions, because the adequacy of the setooints for unbypassed thermal overloads and torque switches has not been established.
The licensee should provide design modificatbns to bypass thermal overloads during ECCS operations or demonstrate the setpoint adequacy as specified by Regulatory Guide 1.106. Furthennore, torque switches should be bypassed by limit switches over the first 10% of travel to permit valve acceleration without tripping the valve motor supply.
I l
1 9
E 6.
m
' qS p $
g q}
Q q
p y
_ _. _.,, _ _ _ _, - - - -. - -,. -,,, _ _ _ -...., - ~....,. -,.. - _,,
,