ML19309B606
| ML19309B606 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/13/1980 |
| From: | Parr O Office of Nuclear Reactor Regulation |
| To: | Ferguson J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 8004040428 | |
| Download: ML19309B606 (5) | |
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Docket No. 50-339 MAR 13 1980 Mr. J. H. Ferguson Executive Vice President - Power Operations Virginia Electric & Power Company P. O. Box 26666 Richmond, Virginia 23261
Dear Mr. Ferguson:
SUBJECT:
POTENTIAL DESIGN DEFICIENCIES IN BYPASS, OVERPIDE, AND RESET CIRCUITS OF ENF "ERED SAFETY FEATURES Discussion Of Deficiencies Several instances have been reported where automatic closure of the containment ventilation / purge valves would not have occurred because the safety 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 isola-tion signals which are required to automatically close the purge valves to assure containment integrity were manually overriden to allow purging 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 enual operation independent of any safety actuation signal. This circuitry was designed to permit reopen.ng of certain valves after an accident to allow manual operation of required safety equipment.
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Mr. J. H. Ferguson 3 ISSO On September 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 overridden.
The override of this containment isolation signal was accomplished by re-setting the train A and B reset buttons. Under these circumstances, six valves in the containment vent and purge systems could be opened with the radiat 9r 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 t'1e containment isolation signal to the purge valves such that the purge valvet would not have automatically closed on an emergency core cooling system (ECC3) 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 certs 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 for all operating license applications currently under review:
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Mr. J. H. Ferguson MAR 13 1980 a
- 1) The overriding of one type of safety actuation signal (e.g., parti-culate 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 en-sure adequate administrative controls.
- 3) A system level annunciation of the overridden status should be provided for every safety system impacted when any override is active.
(See RegulatoryGuide1.47).
- 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 ventila-tion isolation should be designed and qualified to Class 1E criteria.
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- 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 tt deter-mine its degree of conformance to these criteria.
You should report the results of your review to us by Ap'ril 15, 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, fan 6.t
.ParrMhief Light Water Reactors Branch No. 3 Division of Project Management CC: See next page The following definitions are given for clarity.
a0verride: 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.
M'r. J. H. Ferguson ~
cc: Mr. Anthony Gambaradella Clarence T. Kipps, Jr., Esq.
Office of the Attorney General 1700 Pennsylvania Avenue, N.W.
11 South 12th Street - Room 308 Washington, D. C.
20006 Richmond, Virginia 23219 Carroll J. Savage, Esq.
Richard M. Foster, Esq.
1700 Pennsylvania Avenue, N.W.
Musick, Williamson, Schwartz Washington, D. C.
20006 Leavenworth & Cope, P. C.
P. O. Box 4579 Mr. James C. Dunstan Boulder, Colorado 80306 State Corporation Commission Commonwealth of Virginia Michael W. Haupin, Esq.
Blandon Building Hunton, Williams, Gay & Gibson Richmond, Virginia 23209 P. O. Box 1535 Richmond, Virginia 23212 Alan S. Rosenthal, Esq.
Atomic Safety and Licensing Appeal Board Mrs. June Allen U.S. Nuclear Regulatory Commission 412 Owens Drive Washington, D. C.
20555 Huntsville, Alabama 35801 Michael C. Farrar, Esq.
Mrs. James Torson Atomic Safety and Licensing Appeal Board 501 Leroy U.S. Nuclear Regulatory Commission Socorro, New Mexico 87801 Washington, D. C.
20555 Mrs. Margaret Dietrich Dr. John H. Buck Route 2, Box 568 Atomic Safety and Licensing Appeal Board Gordonsville, Virginia 22942 U.S. Nuclear Regulatory Commission Washington, D. C.
20555 William H. Rodgers, Jr., Esq.
Georgetown University Law Center Atomic Safety and Licen.ing Board Panel 600 New Jersey Avenue, N. W.
U.S. Nuclear Regulatory Commission Washington, D. C.
20001 Washington, D. C.
20555 Mr. Peter S. Hepp Mr. Michael S. Kidd Executive Vice President U.S. Nuclear Regulatory Commission Sun Shipping & Ory Dock Company P. O. Box 128 P. O. Box 540 Spotsivania, Virginia 22553 Chester, Pennsylvania 19013 Dr. Paul W. Purdom Mr. R. B. Briggs Department of Civil Engineering Associate Director Drexel University 110 Evans Lane Philadelphia, Pennsylvania 19104 Oak Ridge, Tennessee 37830 l
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M. J. H. Ferguson MAE 131980 cc: Dr. Lawrence R. Quarles Apartment No. 51 Kendal-at-Longwood Kennett Square, Pennsylvar.ia 19348 Mr. Irwin B. Kroot Citizens Energy Forum P. O. Box 138 McLean, Virginia 22101 James B. Dougherty, Esq.
Potomac Alliance 1416 S Street, N.W.
Washington, D. C.
20009 W. R. Cartwright, Station Manager P. O. Box 402 Mineral,. Virginia 23117 W. L. Stewart, Manager P. O. Box 315 Surry, Virginia 23883 i
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