05000440/LER-1990-033, :on 901120,Train B of Control Room HVAC Sys Actuated Unexpectedly in Emergency Recirculation Mode.Caused by Inadequate Instruction.Procedure Revised Re Correct Guidance During Loss of Power to Bus K-1-N

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:on 901120,Train B of Control Room HVAC Sys Actuated Unexpectedly in Emergency Recirculation Mode.Caused by Inadequate Instruction.Procedure Revised Re Correct Guidance During Loss of Power to Bus K-1-N
ML20024F742
Person / Time
Site: Perry 
Issue date: 12/14/1990
From: Hegrat H
CENTERIOR ENERGY
To:
Shared Package
ML20024F740 List:
References
LER-90-033, LER-90-33, NUDOCS 9012170125
Download: ML20024F742 (3)
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LER-1990-033, on 901120,Train B of Control Room HVAC Sys Actuated Unexpectedly in Emergency Recirculation Mode.Caused by Inadequate Instruction.Procedure Revised Re Correct Guidance During Loss of Power to Bus K-1-N
Event date:
Report date:
4401990033R00 - NRC Website
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, aa an.a-. - - aa. o o On November 20, 1990 at 0248, the B train of the Control Room Heatingt i

Ventilation and Air Conditioning (CRHVAC) System actuated unexpectedly in the Emergency Recirculation mode of operation when temporary power to a power distribution panel, K-1-N, was removed to allow restoration of the normal power supply.

All equipment responded as designed, and the system was returned to normal operation.

The root cause of this event was an inadequate instruction.

The Unit Supervisor, reviewing the tagout for system restoratien, ref erred to Of f-Normal Instruction j

(ON1-R25-2) " Leap of a Non-essential 120V Bus (Unit 1)" to determine expected plant response to the evolution; however, the instruction was inadequate as it did not provide the correct guidance concerning the effects on the CRHVAC system when K-1-N was doenergized.

To prevent recurrence, ONI-R25-2 has been revised to reflect the correct guidance during loss of power to the K-l-N bus.

Additionally, Operations is developing more detailed system operating instructions to provide better guidance for the operations of low voltage electrical systems.

Finally, as part of the established roqualification training program, this event will be discussed with all plant licensed operators.

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., - wc w m a n On November 20, 1990 at 0248, the B train of the Control Room Heating, Ventilation and Air Conditioning (CRHVAC) [V1] System actuated unexpectedly in the Emergency Recirculation mode of operation when temporary power to a power distribution panel, K-1-N, was removed to allow restoration of the normal power supply. At the time of the event, the plaM was in Operational Condition 5 (Refuel), with the Reactor Pressure Vesse' [RPV) at atmospheric conditions and reactor water temperature at approxi% rely 78 degrees.

On November 20, 1990, the Unit Supervisor authorized clearance of a tagout which would remove temporary power that was supplying power to distribution panel K-1-N.

Prior to this, the Unit Supervisor reviewed Of f Normal Instruction (ON1-R25-2) " Loss of a Non-essential 120V Bus (Unit 1)" to determine the effects of a loss of power to K-1-N on plant systems and determine if any mitigating actions should be taken. At this time, both of the CRHVAC trains were considered inoperable due to duct work modifications; however, the A train was operating in the Emergency Recirculation mode and the B train was in the standby readiness mode. At 0248, plant operators removed temporary power from panel K-1-N to enable restoration of its normal power supply. When power to the distribution panel was removed, the Common Airborne Radiation Monitor Panel (IL] and an associated instrument, Control Room Airborne Gas Radiation Monitor (R1], were deenergized. Upon the loss of power to thir. instrument, the CRHVAC B train received an automatic initiation signal and started in the Emergency Recirculation mode.

The A train continued to operate in the Emergency Recirculation mode throughout the event. At 0258, normal power was restored to K-1-N.

At 1216 the A train was returned to normal operation and the B train was placed in the standby readiness mode.

The root cause of this event was an inadequate instruction. The Unit Supervisor reviewed the tagout with the appropriate Off-Normal Instruction for a lose of power to K-1-N.

The instruction was inadequate in that it did not provide the correct guidance concerning the effects on the CRHVAC system when K-1-N was deenergized. This instruction had previously included information regarding initiation of Emergency Recirculation when power is lost to K-1-N.

However, a previous revision to the instruction in November of 1988 removed the subject information. The tevision was made in response to a design change which removed the automatic initiation of the Emergency Recirculation mode due to a loss of l

power to Ethylene Oxide Monitors (45).

The review of this change only focused on

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the effect of Ethylene Oxide monitors. Therefore, it was not recognized that a loss of power to K-1-N would still cause an automatic initiation of the Emergency Mode of the CRHVAC system due to a loss of power to the Control Room Airborne Cas Radiation Monitor.

The CRHVAC system provides cooling, heating, ventilation, and when required, smoke removal for the control room and equipment areas during normal plant operation, and during periods of emergency (LOCA or high radiation conditions or high chlorine gas level). The Emergency Recirculction mode provides the necessary supplementary particulate and halogen flitration of the air supplied to oc.. m. u,

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1 the control room areas during emergency conditions and other abnormal conditions to reduce the radiation dose for personnel protection. The Emergency Recirculation mode will automatically initiate upon receipt of a high chlorine l

gas, high radiation, Loss Of Offsite Power (LOOP) or Loss Of Coolant Accident (LOCA). signal.

In this event, the B train properly responded as designed to the automatic initiation signal, while the-A train continued to operate in Emergency Recirculation. This even' is not considered to be safety significant. A review of previous events identified two CRHVAC Emergency Recirculation actuations since 1986 that were a result of inadequate surveillance and operating instructions (refer to LERs 86073 and 89008).

In both cases, precautions were added to these instructions; however, none of the procedural changes implemented as corrective actions would have prevented the November 20 event.

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_As a result of previous events, and the recognized need to provide complete guidance for loss of various plant power supplies,.the 1 ent Operations Section has maintained a continuing effort to ensure that Electrical Operating Instructions are complete and accurate.

For example, detailed load lists have been developed for 125 VDC distribution systems and included in the Plant Data Book. The inaccuracy in ON1-R25-2 was the direct renuit of an error in the procedure revision process and in considered to be an isolated event.

To prevent recurrence, ON1-R25-2 has been revised to reflect the correct guidance during loss of power to the K-1-N bus. Additionally, Operations is developing more detailed system operating instructions to provide better guidance for the operation of low voltage electrical system.

Finally, as part of the established requalification training program this event will-be discussed with all plant licensed operators.

Energy Industry Identification Codes are identified in the test as [XX).

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