05000440/LER-1990-014
| ML20055G575 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 07/20/1990 |
| From: | Hegrat H CENTERIOR ENERGY |
| To: | |
| Shared Package | |
| ML20055G573 | List: |
| References | |
| LER-90-014, LER-90-14, NUDOCS 9007230333 | |
| Download: ML20055G575 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4402090014R00 - NRC Website | |
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Perry Nuclear Power Plant. Unit 1 0 l$ l 010 l 0141410 1l0FIOI4 Unexpected Actuation of Both Trains of Control Room Emergency Recirculation System Due to Parannn.1 Errne nurin. rw .n t o. u.- ... .... i..: .r_.
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-asseaner no .se . A. . . _ no On June 21, 1990, at 2056, both trains of the Control Room lleating, Ventilation and Air Conditioning (CEllVAC) System actuated unexpectedly in the Emergency Recirculation mode of operation. At the time of the event, the plant was in Operational Condition 1 (Power Operation) at approximately 100 percent of rated thermal power. All equipment responded as designed, and the system was returned to normal operation.
The root causes of this event were multiple personnel errors by 16C and control room personnel during corrective maintenance activities to replace a relay in-system control circuitry. Activities were inadequately reviewed prior to the start of repair. In addition, inadequate communications and insufficient review of system electrical drawings contributed to a decision not to realign the system to prevent an automatic actuation of the Emergency Recirculation mode.
In order to prevent recurrence, 160 Section Maaagement has issued a directive to all 160 personnel discussing actions to eliminate personnel error. In addition, this event will be discussed in 160 continuing training sessions. Print reading training programs for licensed operators will be revised to strees the importance of using the appropriate drawing for each application. Additionally, as part of the established requalification training program, this event will be discussed with all plant licensed operators. Finally, all personnel concerned with this event were directly involved in the investigation, and have been appropriately counseled by supervision. !
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010 0 l2 0F 0 14 von er . .asma,asc am.amewim On June 21, 1990, at 2056, both trains of the Control Room Heating, Ventilation and Air Conditioning (CRHVAC) [V1] Systems actuated unexpectedly in the Emergency Recirculation mode of operation. At the time of the event, the plant was in Operational Condition 1 (Power Operation) at approximately 100 percent of rated thermal power. The Reactor Pressure Vessel [RPV) was at saterated conditions at approximately 1023 peig.
On June 21, 1990 at 0824, during the performance of surveillance testing on the Control Room Ventilation Radiation Monitor [ MON], the A CRHVAC train inboard isolation damper (DMP] failed to close. Instrumentation and Con 4rols (160) technicians began troubleshooting at 1350. The responsible syrcem engineer determined that both the solenoid valve [V) for the isolation damper and its associated relay [RLY] should be replaced. The root cause of the equipment malfunction would be determined by component testing following replacement. At this time the B CRHVAC train was in normal operation with cooling from the B Control Complex Chiller. The A CRHVAC train was in standby readiness; however, because the A Control Complex Chiller was tagged out for maintenance (i.e. no cooling was available to the A CRHVAC), the Emergency Recirculation mode of A train operation was considered inoperable.
At 2000, 1&C technicians were assigned to replace the defective relay. Control Room personnel did not consider it necessary to change the alignment of CRHVAC Systems for the performance of this work. When initial attempts to remove the relay resulted in additional unexpected cycling of system dampers, Control Room personnel directed the work to be terminated until an additional review of system drawings could be performed, with respect to the troubleshooting / repair efforts.
When the Unit Supervisor (US) was satisfied that additional damper cycling caused by relay removal would not affect plant safety, he gave approval for the work to be resumed. At 2056, 16C technicians momentarily interrupted the neutral current path for a portion of the CRHVAC logic by partially loosening the screw on the.
4 neutral terminal of the coil of the relay. This resulted in a momentary loss of power to two chlorine monitors which caused a High Toxic Gas alarm and both trains of the CRHVAC to shift into the Emergency Recirculation mode. 't he operators verified that both trains were in the proper damper line-up. At 2114 the chlorine monitors were reset and at 2200 A CRHVAC was returned to standby readiness, and the "B" train was returned to normal operation. At 0615 on June 22, 1990, after appropriate re-evaluation of the work to be performed, the defective relay was replaced with the CRHVAC aligned to prevent automatic initiation of Emergency Recirculation.
The root causes of this event were multiple personnel errors, inattention to.
detail / failure to recognize and inadequate communication, by 160 and Control Room personnel. The following errors were identified:
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- 1. Inadequate preparation and review of work scope by 1&C perconnel prior to requesting permission to commence work. The technicians did not review )
drawings, assuming that control room personnel would realign the CRHVAC i system to prevent any unanticipated Emergency Recirculation initiations. ,
l l 2. During discussions between technicians and the Unit Supervisor prior to '
j approval to commence work, the scope of the repair activity was not
! adequately clarified. The US believed the subject relay to be a plug-in type, which would not necessitate the remnval/ replacement of wires from terminals.
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- 3. After the initial unexpected damper actuation, 160 personnel, the.US and the ]
Shift Technical Advisor reviewed elementary electrical drawings to evaluate effecto of the repair activities. These drawings, however, do not adequately represent physical configuration of the electrical system. More detailed Control Room wiring diagrams should have been reviewed in conjunction with the elementary drawings. Additionally, although 160 personnel inspected the actual relay installation and recognized that additional wires were installed !
on the neutral relay terminal, this observation was not adequately 1 communicated to the unit Supervisor. I As a result of the above errors, the personnel involved failed to recognize the potential for Emergency Recirculation actuditon due to the momentary interruption )
of circuit continuity for the chlorine meaitors. Also, becaus,e of the above '
considerations, and because the A Controt C(mplex Chiller was out of service for j maintenance, the US decided not to align the CRHVAC systems to prevent Emergency i Recirculation actuation at the time the work was to be performed. This would require placiag the A train in secured status (without cooling), and j 9
unnecessarily exercising the operable B train by placing it into the Emergency 4 Recirculation mode.
The CRHVAC system provides :0611:3. heating, v9ntilation, and when required, ,
smoke removal for the centrol room and equipment areas during normal plant operation, and.during periods of emergency'(LOCA o,r high ra'diation conditions or l high chlorine gas level). The Emergency Recirculation mode provides the l necessary supplementary particulate and balogen filtrat. ion of the air supplied to i the control room areas during emergency cen'ditions and other abnormal conditions I to reduce the radiation dose for personnel protection. The Emergency l Recirculation mode will auto initiate for a high chlorine gas alarm, high rad alarm, Loss of Offsite Power (LOOP) or Loss of Coolant Accident (LOCA) signal.
In this event, both trains properly responded as designed to the automatic initiation signal. Although the A chiller train was tagged out for maintenance and only one chiller was in service, the B train was operable and operated as necessary to satisfy the safety function. Therefore, this is not considered a safety significant event. A review of previous events identified eight CRHVAC Emergency Recirculation actuations since 1986. None of there events were considered to be simline to the June 21 evnnt.
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,... .exe enn Perry Nuclear Power Plant. Unit 1 0 l5 l0 l01814 l 410 910 -
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010 014 W D 14 vs., n . a m .ac so anawim In order to prevent recurrence 16C Section Hanagement has issued a directive to all 160 personnel discussing actions to eliminate personnel error. In addition, this event will be discussed in 160 continuing training sessions. Print reading training programs for licensed operators will be revised to stress the importance of using the appropriate drawing ror each application. Additionally, as part of the established requalification training program, this event will be discussed with all plant licensed operators. Finally, all personnel concerned with this event were directly involved in the investigation and have been appropriately counseled by supervision.
Energy Industry Identification Codes are identified in the test as [XX).
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