05000369/LER-1982-053, Forwards LER 82-053/03L-0.Detailed Event Analysis Encl

Forwards LER 82-053/03L-0.Detailed Event Analysis Encl

ML20055B731
Person / Time
Site:	McGuire
Issue date:	07/13/1982
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20055B732	List: 05000369/LER-1982-053, Forwards LER 82-053/03L-0.Detailed Event Analysis Encl
References
82-53, NUDOCS 8207230216
Download: ML20055B731 (3)

LER-2082-053, Forwards LER 82-053/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
3692082053R00 - NRC Website

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%cr PpCSIDENT ICL EPedON E:Aata704 l SYtaw PaoouCTiou 373-4083 Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re: McGuire Nuclear Station Unit 1 Docket No. 50-369

Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-369/82-53. This report concerns T.S.3.8.2.1, "The following A.C. electrical busses and inverters shall

be operable and energized.. 120 volt A.C. vital bus #1 EKVA energized from inverter #1 EVIA connected to D.C. Channel 1..."; and T.S.3.4.1.4, "Two residual heat removal (RHR) loops shall be operable and at least one RHR loop shall be in operation". This incident was considered to be of no significance with respect to the health and safety of the public.

Ve 'y truly yours, Y M! - (p, ,

William O. Parker, Jr.

PBN/j fw Attachment t

cc: Director Records Center

Office of Management and Program Analysis Institute of Nuclear Power Operations U. S. Nuclear Regulatory Commission 1820 Water Place l Washington, D. C. 20555 Atlanta, Georgia 30339 l

Mr. P. R. Bemis l Senior Resident Inspector-NRC

McGuire Nuclear Station 4

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; OFFICIAL COPY.

1 1E M 8207230216 820713 l PDR ADOCK 05000369 S PDR

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DUKE POWER COMPANY McGUIRE NUCLEAR STATION REPORTABLE OCCURRENCE REPORT NO. 82-53 REPORT DATE: July 13, 1982 FACILITY: McGuire Unit 1, Cornelius, NC IDENTIFICATION: A Malfunctioning Vital Static Inverter Caused the Interruption of Decay Heat Removal During Shutdown Operations DESCRIPTION: On June 13, 1982, Unit 1 experienced a reactor trip initiated by a spurious low flow condition in the Reactor Coolant System (NC) loop C (refer-ence R0-369/82-52). On June 15, after performing maintenance on the power supply which had caused the trip (a 120 VAC Vital Instrumentation and Control Power System (EPG) 15 KVA static inverter) and verifying the inverter's proper operation, the reactor was returned to power operation. On June 24, the unit was shutdown for a scheduled outage. During the plant cooldown and mode deescalation, static inver-ter EVIA again malfunctioned causing a Residual Heat Removal System (ND) isolation valve to close. Operators restored ND flow in short order, but not before the loss of flow effected a transition from mode 5 (s 2000F) to mode 4 (>200 F) operation (NC temperature increased to 2090F). EVIA was subsequently declared inoperable, and bus EKVA was supplied by distribution panelboard KRP.

The closure of the ND suction isolation valve, IND-2, rendered both trains of ND inoperable causing operation under the Action Statement requirements of Technical Specification 3.4.1.4.

This incident is attributed to a Component Failure / Malfunction of the Solidstate Controls, Inc. static inverter.

EVALUATION: The loss of power to NC loop D pressure process control instrumentation, Channel I, caused the overpressurization protection interlock to function, closing IND-2. Normally, the instrumentation provides an open permissive signal to the IND-2 controller on a decreasing NC pressure of 385 psig and the interlock closes the valve on an increasing NC pressure of 560 psig. IND-1, the redundant ND suction isolation valve in series with IND-2, is similarly interlocked by NC loop C pressure I process control instrumentation, channel IV.

Inadvertent loss of residual heat removal flow has been previously reported by McGuire LERs R0-369/81-72,81-129, and 81-185. In this latest instance operators stopped the running NC pump to protect the pump from loss of suction, and were able to restore NC flow six minutes after IND-2 closed. Thus the significance of these events continues to be in their repeatability rather than in their challenge to reactor safety.

In reaction to these events, preventative procedural controls have been implemented at McGuire. Operations Group procedure " Draining the Reactor Coolant System" was amended to provide a step to lock open IND-1 and 1ND-2 valve operator power breakers.

This renders the valves inoperable in the open position. Instrumentation maintenance procedures " Reactor Coolant Wide Range Pressure Calibration", and " Pressurizer Vapor Temperature Calibration", were modified to ensure power is removed from 1ND-1 and IND-2 valve operators prior to maintenance, when ND is in operation. After the

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Report No. 82-53 Page 2 June 24 incident the " Controlling Procedure for Unit Shutdown" was changed to add step 3.2.6.3, "after N2 blanket has been established in the pressurizer, lock open the power supply breakers to IND-1B and IND-2A to prevent inadvertent loss of ND flow". It should be noted that while these administrative measures would reduce the probability of recurrence, none would have prevented this incident.

The inspection and troubleshooting of static inverter EVIA on June 13, 1982 in response to the original failure (LER R0-369/82-52) failed to identify the faulty capacitors which later caused the additional incident. The location of these capacitors in the inverter cabinet was such that visual inspection was significantly obstructed.

In order to see the later discovered deformation in the capscitor casings, the capacitors' soldered connections had to be disconnected, and the capacitors removed from the inverter.

The Vital Inverter Corrective Maintenance Procedure was reviewed pertinent to this subsequent incident. It was found that troubleshooting and/or identifying CVT capacitor failures was not addressed by the procedure.

CORRECTIVE ACTION: Observers present at the inverter during its malfunction on June 26 noted voltage fluctuations of the equipment. The output voltage was 116 volts for several minutes, and had been as low as 100 volts. During maintenance on June 29 and 30, the constant voltage transformer (CVT) capacitors were disconnected and capacitance checks were conducted. Three capacitors had definitely failed,and each of the remaining capacitors measured close to the required 13 microfarads.

All three of the failed capacitors had deformed casings. The failed capacitors in the output CVT capacitor bank were replaced, and proper operation of the inverter was monitored until July 2, when it was placed in service.

Restoration of the ND system was accomplished in accordance with the ND system normal operating procedure.

As a result of this incident, the possibility of CVT capacitor failure, the symptoms, and verification method, will be included in the " Vital Inverter Corrective Maintenance" procedure. Also, the " Controlling Procedure for Unit Shutdown" now includes provisions to preclude the inadvertent loss of ND flow.

SAFETY ANALYSIS: No condition challenging to reactor safety occurred prior to the reactor trip on June 13. Likewise, ND system isolation on June 26 was not initiated because of unsafe conditions. Both incidents occurred as results of conservative reactor protection and control systems design. System control was maintained throughout the event, and the sole consequence of the interruption in ND flow was a short delay in the ND cooldown process. The incidents were considered to be of no significance to the health and safety of the public.