ML16342B041
| ML16342B041 | |
| Person / Time | |
|---|---|
| Site: | 05000000 |
| Issue date: | 12/29/1978 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | |
| References | |
| IEC-78-19, NUDOCS 7901040236 | |
| Download: ML16342B041 (8) | |
Text
IE Circular No. 78-19 December 29, 1978 Page 1 of 2 MANUAL OVERRIDE (BYPASS)
OF SAFETY SYSTEM ACTUATION SIGNALS Description of Circumstances:
A review of several recent events has raised questions about safety system circuit designs which incorporate manual override (bypass) features.
The two events described below directly relate to the practice of containment purging during normal plant operation by manually overriding containment isolation signals.
In these instances the automatic isolation function of the purge system containment isola-tion valves was unintentionally made inoperable, and this condition was neither continuously indicated in the control room nor known to the plant operators.
During a review of operating procedures on July 25, 1978, the Northeast Nuclear Energy Company discovered that since Hay 1, 1978, intermittent containment purge operations had been conducted at Millstone Unit No.
2 with the safety actuation isolation signals to both inlet and outlet redundant containment isolation valves (48 inch butterfly valves) in the purge inlet and outlet penetrations manually overridden and inoperable.
The isolation signals which are required to automatically close the purge valves for containment integrity were'anually overridden 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 manual operation independent of any safety actuation signal.
This circuitry was designed to permit reopening these valves after an accident to allow manual operation of certain safety equipment.
On September 8, 1978, the Public Service Electric and Gas Company advised the staff that, as a matter of routine, Salem Unit No.
1 has 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.
Overri'de of the containment isolation signal was accomplished by resetting the train A and B reset buttons.
Under these circumstances, six valves in the containment vent and purge systems could be opened with a high particulate isolation signal present.
This override was performed after verifying that the actual containment particulate levels were acceptable V901P 40 g 86
O IE Circular No. 78-19 December 29, 1978 Page 2 of 2 for venting.
The licensee, after further investigation of this practice, determined that the reset of the particulate alarm also bypasses the containment isolation signal to the purge valves and that the purge valves would not have automatically closed in the event of an emergency core cooling system (ECCS) safety injection signal.
These events and information gained from recent licensing actions have raised a generic concern relative to potential design deficiencies that could permit manually defeating a protection function.
Since all plants with construction permits must meet the requirements of IEEE 279, we recommend that you review the design of all safety actuation signal circuits which incorporate a manual override feature to ensure that overr iding of one safety actuation signal does not also cause the bypass of any other safety actuation signal, that sufficient physical features are provided to facilitate adequate administrative controls, and that the use of each such manual override is annunciated at the system level for every system impacted.
Compliance with Federal Regulation 50.55a(h) requirements will be verified by NRC through the licensing review process and during regular onsite inspections for plants with construction permits.
NRC's requirements relative to this matter have been conveyed to all operating plant licensee's via a generic letter.
No written response to this Circular is required.
If you require additional information regarding this matter, contact the Director of the appropriate NRC Regional Office.
IE Circular No. 78-l9 December 29, 1978 LISTING OF IE CIRCULARS ISSUED IN 1978 Circular Subject Date No.
of Issue Issued To 78-01 78-02 78.-03 78-04 Loss of Mell Logging Source Proper Lubricating Oil for Terry Turbines Packaging Greater Than Type A guantities of Low Specific Activity Radioactive Ilaterial for Transport Installation Error That Could Prevent Closing of Fire Doors 4/5/78 4/20/78 5/12/78 5/15/78 All Holders of Mell Logging Source Licenses All Holders of Reactor OLs or CPs All Holders of Reactor OLs, CPs, Fuel Cycle, Priority I.t1aterial and Maste Disposal Licenses All Holders of Reactor OLs or CPs 78-05 Inadvertent Safety Injection 5/23/78 During Cooldown All Holders of Reactor OLs or CPs
'78-06, 78-07 78-08 78-09 Potential Common trode Flooding of ECCS Equipment Rooms at BMR Facilities Damaged Components of a Bergen-Paterson Series 25000 Hydraulic Test Stand Environmental qualification of Safety Related Equipment at Nuclear Power Plants Arcing of General El ectri c Company Size 2 Contactors 5'/23/78 5/31/78 5/31/78 6/5/78 All Holders of Reactor OLs or CPs All Holders of Reactor OLs ol CPs All Holders of Reactor OLs or CPs All Holders of CPs Enclosure Page 1 of 2
IE ircular Ho. 78-19 December 29, 1978 LISTING OF IE CIRCULARS ISSUED IH 1978 Circular Subject Date of No.
Issue Issued to 78-10 78-11 78-12 78-13 78-14 78-15 78-16 Control of Sealed Sources Used in Radiation Therapy Recirculation N-G Set Overspeed Stops HPCI Turbine Control Valve Lift Rod Bending Inoperability of Multiple Service Water Pumps HPCI, Turbine Reversing Chamber Hold Down Bolting Checkvalves Fail to Close In Vertical Position Limitorque Valve Actuators 6/14/78 6/15/78 6/30/78 7/10/78 7/12/78 7/20/78 7/26/78 All Hedical Licensees in Categories G
and Gl All Holders of BWR OLs or CPs All Holders of BWR OLs or CPs for plants with HPCI Terry Turbine All Holders of Reactor OLs and CPs except for plants located in: AL, AK, CA, FL, GA, LA, HS, SC All Holders of BWR OLs or CPs for plants with a HPCI Terry Turbine excepting Duane Arnold and Honticello All Holders of'eactor OLs or CPs All Holders of Reactor OLs or CPs 78-17 Inadequate Guard Training/
10/13/78 gualification and Falsified Training Records All Holders of and applicants for Reactor OLs 78-18 UL Fire Test ll/6/78 All Holders of Reactor OLs or CPs Enclosure Page 2 of 2 u
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