ML19320C818
| ML19320C818 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 07/09/1980 |
| From: | Youngblood B Office of Nuclear Reactor Regulation |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 8007180069 | |
| Download: ML19320C818 (5) | |
Text
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't NUCLEAR REGULATORY COMMISSION 3
WASHINGTOrJ, D. C. 20555 E,&.s
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JUL 9 1980 Docket Nos.
50-369 and 50-370 Mr. William 0. Parker, Jr.
Vice President - Steam Production Duke Power Company P. O. Box 33189 422 S. Church Street Charlotte, North Carolina 28242
Dear Mr. Parker:
SUBJECT:
POTENTIAL DESIGN DEFICIENCIES IN BYPASS, 0VERRIDE, AND RESET CIRCUITS OF ENGINEERED SAFETY FEATURES Discussion Of Deficiencies l
Several instances have been reported where automatic closure of the contain-ment ventilation / purge valves would not have occurred because the safety L
actuation signals were either manually overriden or bypassed (blocked) during normal plant operations.
In addition, a related design deficiency with regard to the resetting of engineered safety feature actuation signals has been found at several operating facilities where, upon the reset of an ESF signal, certain safety related equipment would return to its non-safety mode.
Specifically, on June 25, 1978, Northeast Nuclear Energy Company discovered that intermittent containment purge operations had been conducted at Millstone Unit No. 2 with the safety actuation signals to redundant containment purge isolation valves (48 inch butterfly valves) manually overriden and inoperable.
The isolation signals which are required to automatically clcr W purge valves to assure containment integrity were manually overriden N
..ow purg-ing of containment with a high radiation signal present. The manual override circuitry designed by the plant's architect / engineer defeated not only the high radiation signal but also all other isolation signals to these valves.
To manually override a safety actuation signal, the operator cycles the valve control switch to the closed position and then to the open position.
This action energized a relay which blocked the safety signal and allowed manual operation l
indepdendent of any safety actuation signal. This circuitry was designed to permit reopening of certain valves after an accident to allow manual operation of required safety equipment.
80[7180063
Mr. W. Parker JUL 9 1330 On Serember 8,1978, the staff was advised that, as a matter of routine, Salem Unit No. I had been venting the containment through the containment ventilation system valves to reduce pressure.
In certain instances this venting has occurred with the containment high particulate radiation monitor isolation signal to the purge and pressure-vacuum relief valves overriden.
- The override of this containment isolation signal was accomplished by resetting the train A and B reset buttons. Under these circumstances, s1x valves in the containment vent and purge systems could be opened with the radiation isolation signal present. This override was performed after verifying that the actual containment particulate levels were acceptable for venting.
The licensee, after further investigation of this practice, determined that the reset of the particulate radiation monitor alarm also overrides the containment isolation signal to the purge valves such that the purge valves would not have automatically closed on an emergency core cooling system (ECCS) safety injection signal.
A related design deficiency was discovered during a review of system operation following a recent unit trip and subsequent safety injection at North Anna No. 1.
Specifically, it was found that certain equipment important to safety (for example, control room habitability system dampers) would return to its non-safety mode following the reset of an ESF signal.
In addition, many utilities do not have safety grade radiation monitors to initiate containment isolation.
Safety Significance The overriding of certain containment ventilation isolation signals could also bypass other safety actuation signals and thus prevent valve closure when the other isolation signals are present. Although such designs may be acceptable, and even necessary, to accomplish certain reactor functions, they are generally unacceptable where they result in the unnecessary bypassing of safety actuation signals. Where such bypassing is also inadvertent, a more serious situation is created especially where there is no bypass indication system to alert the operator.
Where the resetting of ESF actuation signals, such as safety injection, directly causes equipment important to safety to return to its non-safety mode, protec-tive actions of the affected systems could be prematurely negated when the associated actuation signal is reset.
Prompt operator action would be required to assure that the necessary equipment is returned to its emergency mode.
The use of a non-safety grade monitor to initiate containment isolation could seriously degrade the reliability of the isolation system.
Staff Position It is our position that, in addition to other applicable criteria, the following should be satisified fer all operating license applications currently under review:
Mr. W. Parker JUL s'E
- 1) The overriding of one type of safety actuation signal (e.g., particulate radiation) should not cause the blocking of any other type of safety actuation signal (e.g., iodine radiation, reactor pressure) for those valves that have no function other than containment isolation.
- 2) Physical features (e.g., key lock switches) should be provided to ensure adequate administrative controls.
- 3) A system level annunciation of the overriden status should be provided for every safety system impacted when any override is active.
(See Regulatory Guide 1.47).
- 4) The following diverse signals should be provided to initiate isolation of the containment purge / ventilation system: containment high radiation, safety injection actuation, and containment high pressure (where con-tainment high pressure is not a portion of safety injection actuation).
- 5) The instrumentation systems provided to initiate containment purge ventilation isolation should be designed and qualified to Class IE criteria.
- 6) The overriding or resetting of the ESF actuation signal should not cause any equipment to change position.
Accordingly, you are requested to review your protection system design to determine its degree of conformance to these criteria.
You should report the results of your review to us by August 4,1980, describing any departures from the criteria and the corrective actions to be implemented. Design departures for which no corrective action is planned should be justified.
Please advise if you have any questions on this matter.
Sincerely, i.
./
B. J. Youngblood', Chief Licensing Branch No. 1 Division of Licensing, NRR cc: See next page The following definitions are given for clarity.
Override: The signal is still present, and it is blocked in order to perform a function contrary to the signal.
Reset:
_The signal has come and gone, and the circuit is being cleared in order to return it to the normal condition.
t Mr. William 0. Parker, Jr.
Vice President, Steam Production Duke Power Company P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242 cc:
Mr. W. L. Porter David Flesichaker. Esq.
Duke Power Company 1735 Eye Street. N. W.
P. O. Box 2178 Suite 709 422 South Church Street Washinoton, D. C.
20006 Charlotte, North Carolina 28242 Richard P. Wilson Esa.
Mr. R. S. Howard Assistant Attorney General Power Systems Division State of South Carolina Westinghouse Electric Corporation 2600 Bull Street P. O. Box 355 Columbia. South Carolina 29201 Pittsburgh, Pennsylvania 15230 Mr. E. J. Keith EDS Nuclear Incorporated 220 Montgomery Street San Francisco, California 9410?
Mr. J. E. Houghtaling NUS Corporation 2536 Countryside Boulevard Clearwater, Flor ida 33515 Mr. Jesse L. Riley, President The Carolina Environmental Study Group 854 Henley Place i
Charlotte, North Carolina 28207 J. Michael McGarry, III, Esq.
Debevoise & Liberman 1200 Seventeenth Street, N. W.
Washington, D. C.
20036 Rober t M. Lazo, Esq., Chairman Atomic Safety and Licensing Board U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Dr. Emmeth A. Luebke Atomic Safety and Licensing Board U. S. Nuclear Regulatory Commission WashingtDn, D. C.
20555 Dr. Cadet H. Hand, Jr., Director Bodega Marine Lab of California P. O. Box 247 Bodega Bay, California 94923
Mr. William 0. Parker, Jr.
cc: David Flesichaker, Esq.
1735 Eye Street, N. W.,
Suite.709 Washington, D. C.
20006
'K1 chard P. Wilson, Esq.
Assistant Attorney General State of South Carolina 2600 Bull Street Columbia, South Carolina 29201 Office of Intergovernmental Relations 116 West Jones Street Raleigh, North Carolina 27603 County Manager of Mecklenburg County 720 East fcu th Street Charlotte, North Carolina 28202 U. S. Environmental Protection Agency ATTN: EIS Coordinator Pegion IV Office
'45 Courtland Street, N. W.
Atlanta, Georgia.30308 0
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