05000370/LER-2005-007

LER-2005-007, Power Reduction Due to Entry into LCO 3.0.3 Caused by Inoperable Control Room Area Cooling Water System

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3702005007R00 - NRC Website

BACKGROUND

Applicable Energy Industry Identification System (EIIS) system and component codes are enclosed within brackets. McGuire unique system and component identifiers are contained within parentheses.

The Control Room Area Cooling Water System [KM] (CRACWS) provides temperature control for the control room following isolation of the control room. The CRACWS consists of two independent and redundant trains that provide cooling of recirculated control room air. Each train consists of the equipment, instrumentation, and controls needed to maintain control room temperature. The CRACWS is a subsystem providing air temperature control for the control room. The CRACWS is an emergency system, parts of which may also operate during normal unit operations. A single train provides the required temperature control to maintain the control room at approximately 75°F.

Each train of the CRACWS has a chiller that is equipped with an oil pressure switch. This switch is provided as an equipment protective function to shutdown the chillers on low oil pressure. Even though this is not a safety related function, the oil pressure switch is purchased, installed, and maintained as safety related because it is electrically connected to an essential circuit. Installation of a new oil pressure switch requires removal and replacement of the chiller refrigerant, which is a time consuming process.

Technical Specification (TS) 3.7.10 specifies that two CRACWS trains shall be operable in Modes 1, 2, 3, 4, 5, and 6, during movement of irradiated fuel, and during core alterations. TS 3.7.10 Condition E applies when two CRACWS trains are inoperable in Modes 1, 2, 3, and 4. The required action for this condition is an immediate entry into TS Limiting Condition for Operation (LCO) 3.0.3. LCO 3.0.3 requires that action be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the affected unit in Mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, Mode 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.

EVENT DESCRIPTION

On October 8, 2005, at 03:20, both trains of the McGuire CRACWS were declared inoperable. At the time McGuire Unit 1 was in Mode 6 at 0% power during an ongoing refueling outage and McGuire Unit 2 was in Mode 1 at 100% power operation. This placed Unit 2 in a state of non-compliance with TS 3.7.10, Condition E, because two CRACWS trains were inoperable in Mode 1.

On October 8, 2005, McGuire Unit 1 was in the latter stages of Refueling Outage 1 End-of-Cycle 17. Earlier on October 7, 2005, the CRACWS "B" (the outage unit) to support "B" train Engineering Safety Features (ESF) testing. The "B" Chiller, while available and fully functional, was declared administratively inoperable because of its reliance on shared and unit designated equipment aligned with the outage unit. Shared portions of the CRACWS must be operable for each unit that is in a Mode of applicability for the TS. Therefore, in order to support the operation of Unit 2 in Mode 1, CRACWS "B" must have emergency power and supporting systems available.

The CRACWS "B" emergency power supply was inoperable due to its support system (the nuclear service water system) being considered inoperable. It is noted, however, that all CRACWS "B" support systems had met the required TS surveillance requirements for Modes 1 thru 4. Procedurally, as part of the ESF testing, the CRACWS "B" Chiller was nonetheless successfully started, and the CRACWS "A" Chiller shutdown to ensure functionality of the CRACWS "B" Chiller. Since the "B" ESF testing requires the CRACWS "B" Chiller to be off and the CRACWS "A" Chiller in operation, an attempt was made to swap to the CRACWS "A" Chiller. However, the CRACWS "A" Chiller failed to start.

Investigation concluded that the "A" Chiller failed to start due to the absence of an oil pressure permissive following system alignment activities to support ESF testing on Unit 1. The oil pump started as expected, but the chiller did not start. The chiller failure investigation revealed that the suspected cause was a defective oil pressure switch. The current TS required action to immediately enter LCO 3.0.3 did not provide enough time to address needed repairs to the defective oil pressure switch, nor did it provide sufficient time to implement alternate measures. In a telephone conference call held with NRC officials on October 8, 2005, Duke Energy Corporation (Duke) requested a Notice of Enforcement Discretion (NOED).

However, prior to the NRC approval of the NOED, an orderly shutdown of Unit 2 had already begun in accordance with LCO 3.0.3, but upon receipt of the NRC's verbal approval shortly after the conference call, the shutdown was returned to 100% power at approximately 15:00 on October 8, 2005. Since Unit 2 began a shutdown in accordance with LCO 3.0.3, this event is considered reportable as a TS prohibited condition in accordance with 10 CFR 50.73(a)(2)(i)(B). The NRC granted the NOED for TS 3.7.10 and LCO 3.0.3, which extended to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (from 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />) the time allowed before Unit 2 was required to be in Mode 3 in accordance with LCO 3.0.3. The NRC's subsequent formal approval of this NOED was documented in a letter to Duke dated October 14, 2005. The additional time allowed by the NOED permitted the "A" Chiller to be returned to an operable but degraded/nonconforming condition using compensatory measures, while the "B" Chiller supplied the cooling function for the control room.

The additional time requested within the NOED allowed Duke to bypass (jumper around) the defective oil pressure switch and return the "A" Chiller to an operable but degraded/nonconforming condition. The 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided sufficient time to make the physical change to the plant and complete the engineering and administrative processes to complete the temporary station modification. During the extension period, the control room was cooled by the "B" Chiller which (at the time of the NOED request) was operating and fully functional, although administratively inoperable, as discussed above.

The events are shown below in the approximate sequence in which they occurred. All times are approximate.

At 18:18 on 10/7/2005 CRACWS "B" was declared inoperable in preparation for shifting the power supply and nuclear service water supply from Unit 2 to Unit 1.

At 02:59 on 10/08/2005 CRACWS "B" was started and CRACWS "A" was shut down to ensure "B" train functionality after the power supply swap.

At 03:20 on 10/08/2005 CRACWS "A" failed to start. CRACWS "B" continued to operate satisfactorily.

entered LCO 3.0.3 due to both trains of CRACWS being inoperable with Unit 1 in Mode 6 and Unit 2 in Mode 1 at 100% power.

At 03:47 on 10/08/2005 a corrective work order was written to repair CRACWS "A".

At approximately 05:00 contacted the NRC Resident Inspector to discuss the NOED process.

At 07:23 on 10/08/2005 Unit 2 commenced power reduction to comply with the LCO 3.0.3 action statement.

At 07:26 commenced NOED discussion with NRC management.

At 08:09 on 10/08/2005 load reduction was terminated following NOED approval from NRC.

At 15:00 on 10/8/05 Unit 2 reached 100% power.

At 20:06 on 10/08/2005 CRACWS "A" was returned to operable status and Unit 2 exited the NOED.

CAUSAL FACTORS

The cause of this event was a defective oil pressure switch on the "A" Chiller. It was concluded that the chiller failed to start due to an invalid low oil pressure interlock following system alignment activities to support ESF testing on Unit 1.

A contributing cause for this event is that the current McGuire licensing basis does not address the situation of the reliance on shared and unit designated equipment aligned with the outage unit to support the operating unit.

CORRECTIVE ACTIONS

Immediate: None.

Subsequent:

1.A NOED was obtained to allow a 24-hour period prior to completing initial action in accordance with LCO 3.0.3.

2.A temporary modification was implemented to restore the "A" Chiller to an operable but degraded/nonconforming condition by means of bypassing the low oil pressure protective interlock. An individual was stationed at the "A" Chiller to monitor the oil pressure by local indication.

3.Permanent repairs were made to the "A" Chiller on 10/25/05 by means of replacing the defective oil pressure switch.

Planned:

1. A future license amendment request (LAR) will be developed and submitted to the NRC. This LAR will address operability requirements for shared and unit designated equipment on a shutdown unit when this equipment is relied on to support an operating unit in Modes 1 thru 4.

SAFETY ANALYSIS

The safety significance of the CRACWS system is low because of the opportunity to mitigate the consequences of its loss with preplanned

• measures as described in plant Abnormal Procedures. As a result, the loss of the CRACWS System, including the control room chillers, has been screened out of the McGuire PRA as either an initiating event or as a support system failure. Therefore, the CRACWS System has no impact on the calculated Core Damage Frequency (CDF) or Large Early Release Frequency (LERF) at McGuire.

During the period allowed by the NOED, the "B" Chiller was recorded as inoperable, but it was available and did perform its safety function of cooling the control room.

Based on the opportunity to mitigate the consequence of this event, and the fact that the "B" chiller was available to perform its intended safety function, the impact on the incremental conditional core damage probability (ICCDP) was expected to be much less than 5E-07 and the impact on the incremental conditional large early release probability (ICLERP) was expected to be much less than 5E-08.

This event was determined to be of no significance to the health and safety of the public.

ADDITIONAL INFORMATION

A review of the McGuire corrective action database identified no previous LERs, within the past three years, caused by a CRACWS chiller failing to start due to a defective oil pressure switch. Therefore, this is not considered a recurring event.