ML17252A714
| ML17252A714 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/26/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Abel J COMMONWEALTH EDISON CO. |
| References | |
| TASK-03-10.A, TASK-3-10.A, TASK-RR LSO5-81-06-119, LSO5-81-6-119, NUDOCS 8107020369 | |
| Download: ML17252A714 (5) | |
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Docket No. 50-237
- LSOS06-119 Mr. J. S. Abel Director of Nuclear Licensing Conunonwealth Edison Company Post Office Box 767 Chicago~ Illinois 60690
Dear Mr. Abel:
June 26, 1981
SUBJECT:
SEP TOPIC III-10.A, THERMAL-OVERLOAD PROTECTION FOR MOTORS OF MOTOR-OPERATED VALVES, SAFETY EVALUATION REPORT FOR DRESDEN UNIT 2 The enclosed staff safety evaluation supplements our contractor's evaluation that has been made available to you previously. This evaluation supports
.the find1pgs of the enclosed staff safety evaluation on Topic III-10.A that
- proposes' inodifications to the valve protective trips.
'The need to actually implement these changes will be detennined during the integrated plant safety assessment. This topic ass~ssment may be revised 1n the -future if your facility design is changed or if NRC criteria relating to
~his topic are 100dified before. the-.integrated assessment 1s completed.
Enclosure:
As stated cc w/enclosure:
See next page 81070 2.0:J<o9 f
Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 Division oflicensing OFFICE~
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UNITED STATES NU~EAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket No. 50-237
- LS05 06-119 Mr. J. S. Abel Director of Nuclear Licensing Conunonwealth Edison Company Post Office Box 767 Chicago, Illinois 60690
Dear Mr. Abel:
June 26, 1981
SUBJECT:
SEP TOPIC III-10.A, THERMAL-OVERLOAD PROTECTION FOR MOTORS OF MOTOR-OPERATED VALVES, SAFETY EVALUATION REPORT FOR DRESDEN UNIT 2 The enclosed staff safety evaluation supplements our contractor's evaluation that has been made available to you previously. This evaluation supports the findings of the enclosed staff safety evaluation on Topic III-10.A that proposes modifications to the valve protective trips.
The need to actually implement these changes will be determined during the integrated plant safety assessment. This topic assessment may be revised in the future if your facility design is changed or if NRC criteria relating to this topic are modified before t~e integrated assessment is completed.
Enclosure:
As stated cc w/enclosure:
See next page Sincerely;
~/J'/.LJ-~L~
Dennis M. Crutchfield, ~
Operating Reactors_Branch No. 5 Division of Licensing
Mr. J. s. Abel cc Isham, Lincoln & Beale Counselors at Law One First National Plaza, 42rid Floor Chicago, Illinois 60603 Mr. B. B. Stephenson Plant Superintendent Dresden Nuclear Power Station Rura 1 Route #1 Morris, Illinois 60450 Natural Resources Defense Council 917 15th Street, N. w.
Washington, D. c.
20005
- u. s. Nuclear Regulatory Commission Resident Inspectors Office Dresden Station RR #1 Morris, Illinois 60450 Mary Jo Murray Assistant Attorney General Environmental Control Division 188 w. Randolph Street Suite 2315 Chicago, Illinois 60601 Morris Public Library
.604 Liberty Street Morris, Illinois.60451 Chairman Board of Supervisors of Grunqy County Grundy County Courthouse Morris, Illinois 60450 John F. Wolfe, Esquire 3409 Shepherd Street Chevy Chase, Maryl~nd 20015 Dr. Linda w. Little 500 Hermitage Ori ve Raleigh, North Carolina 27612
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Illinois Department of Nuclear Safety 1035 Outer Park Drive, 5th Floor Springfield, Illinois 62704
- u. S. Environmental Protection Agency Federal Activities Branch Region V Office ATTN:
EIS COORDINATOR 230 South Dearborn Street Chicago, Illinois 60604 Dr. Forrest J. Remick 304 East Hamilton Avenue Chicago, Illinois 60604
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~~TOPIC: III-10.A THERMAL-OVERLOAD PROTECTION FOR MOTORS OF MOTOR-OPER/\\TED VALVES I.
INTRODUCTfON The primary objective of thermal overload relays is to protect motor windings of motor-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-
- l ear pl ant safety systei11 application, the ultimate criterion should -
be to drive the valve to its proper position to mitigate the conse-quences of an ~ccidents, rather than to be concerned with degradation or failure of the motor due to excessive heating.
II.
- R~VIEW C~ITERIA The primary review criteria are:
l~
IEEE Std. 279-1971, and 2.. Regulatory Guide 1.106.
As a result of numerous operating plant events resulting from torque switch problem~ the following supplemental criteri9n was used:
11 (3)
In MOV designs that use a torque switch.to limit the opening or closing of the v~lve, the automatic opening or closing signal*
should be used in conjun~tion with a correspondi~g 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 Topics nor are any other topics depend~nt on the results of t~i~ review.
IV.
REVIEW GUIDELINES The review should assure that: (1) thermal. overload protection, if.
provided, for MOV's s*hould have the trip setpoin:t.at a value high enough to prevent spurious trips due to design inaccuracies, trip set-point drift, or variation in the ambient temper~ture *at the installed location; (2) the circuits that bypass the thermal overload.'protection under accident conditions are designed to IEEE Std. 279-1971 criteri~,
as appropriate for the rest of the safety related system; and (3} in MOV designs that use a torque switch instead of a limit switch to limit the opening or closing of the valve, the automatic opening or closin~ signal should be used in conjunction with a corresponding limit switch and thermal overload should remain as backup protection over the first 10% of valve travel.
V.
EVALUATION The design provisions for motor-operated valve protection are described in EG&G Report 1645F, "Thermal-Overload Protection for Motors of Motor-Operated Valves."
Furthermore, a staff review of Licensee Event Reports for Dresden 2 indicates that torque switch problems have accounted for more than 34% of all motor-operated valve failures.
VI.
CONCLUSIONS The Dresden 2 design does not satisfy the current licensing criteria for safety related valve functions, and torque switch problems have been a significant contributor to valve reliability problems.
Because poor valve reliability may lead to the failure of more th.an ofre valve during emergency conditions, and multiple valve failures have not been analyzed for th~ir affect upon system performance and plant safety, the staff recommends that action should be taken to improve valve reliability (i.e., bypassing torque switches with a limit switch during automatic actuation of the valve and bypassing thermal overloads with an ECCS signal).