05000369/LER-2007-001

LER-2007-001, 369 5McGuire Nuclear Station Unit 1 05000 1 OF5

Docket Number
Event date:	1-17-2007
Report date:	3-16-2007
3692007001R00 - NRC Website

BACKGROUND

At the time this historical condition was identified, McGuire Unit 1 and Unit 2 were in Mode 1 at 100% power. No systems, structures, or components were out of service at the time of this event which contributed to this event.

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

The 125 VDC Vital Instrumentation and Control Power System [EJ](EPL) is designed to provide a reliable and continuous source of power to a select group of Class lE instrumentation and control equipment required for start up, normal operation, and orderly shutdown of each unit. Should a loss of offsite power (LOOP) or blackout (no voltage or a degraded voltage condition on the 4KV Essential Buses) occur, this equipment is required to safely shutdown the plant.

The EPL system consists of four independent and physically separate load channels. Each channel is comprised of a battery, a charger connection box, a battery charger, a 125 VDC distribution center, and two 125 VDC power panelboards. Each of the batteries is sized to supply the continuous emergency loads and momentary loads fed from its distribution center plus supply the loads of its cross tied distribution center for one hour.

Technical Specification (TS) Surveillance Requirement (SR) 3.8.4.5, in combination with TS SR 3.8.4.4 provide an indication of physical damage or abnormal deterioration that could indicate degraded battery condition by performing a visual inspection and measuring the resistance of inter-cell, inter-rack, inter-tier, and terminal connections. Associated test acceptance criteria (TAC) in SR 3.8.4.5 include:

Verify battery connection resistance is connections, and McGuire TS 3.8.4 specifies that the four channels of DC sources shall be operable in Modes 1, 2, 3, and 4. Condition A requires that, in the event one channel of DC sources is inoperable, the affected channel must be restored to operable status within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> OR verify associated bus tie breakers are closed between DC channels within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and restore the affected channel to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

EVENT DESCRIPTION

12 May 2005 - Maintenance performed procedure IP/0/A/3061/007, "Vital Battery and Terminal Post Inspection," to satisfy TS SR 3.8.4.5 for vital battery EVCC. One (of a total of 59) of the recorded values for inter-cell resistance was 1.7E-4 ohms. This exceeded the acceptance criteria of the SR.

Per step 10.4.2 D of IP/0/A/3061/007, "if inter-cell resistance readings are >1= 1.5E-4 ohms, notify responsible IAE supervisor and Control Room SRO that battery is out of Technical Specification limits and should be declared inoperable." This was not identified at the time and no actions were taken.

This resulted in exceeding the allowed completion time of TS 3.8.4 Condition A.

11 May 2006 - Maintenance performed IP/0/A/3061/007, "Vital Battery and Terminal Post Inspection," to satisfy TS SR 3.8.4.5 for vital battery EVCC, all values recorded met the acceptance criteria of the SR.

21 August 2006 - Maintenance performed PT/0/A/4350/038, "Vital Battery Service Test," to satisfy TS SR 3.8.4.7. The purpose of this SR is to "verify battery capacity is adequate to supply, and maintain in an OPERABLE status, the required emergency loads for the design duty cycle when subjected to a battery service test." All acceptance criteria for the SR were met.

14 December 2006 - Engineering was informed of a potential non-conservative TS value for vital battery inter-cell resistances identified during a Component Design Basis Inspection (CDBI) performed at another licensee's station. Engineering determined the McGuire Technical Specifications did contain a non-conservative value for vital battery inter-cell resistances.

This was entered into the Corrective Action (CA) program (PIP M-06-05905) and an operability evaluation was commenced.

11 January 2007 - Engineering completed the operability evaluation. The vital batteries were declared Operable but Degraded/Non-Conforming (OBDN).

17 January 2007 - During a review of historical data to support the reportability determination associated with the non-conservative TS value discovered above, Engineering discovered the value recorded during the performance of TS SR 3.8.4.5 on 12 May 2005 that did not meet the acceptance criteria.

25 January 2007 - McGuire Regulatory Compliance determined this event was reportable per 10CFR50.73 (a)(2)(i)(B).

05 February 2007 - Maintenance performed IP/0/A/3061/007, "Vital Battery and Terminal Post Inspection," on battery EVCC and all acceptance criteria was met.

CAUSAL FACTORS

The cause of the failure to recognize and report the failed TS SR acceptance criteria was human error. The in-plant investigation determined that the inter-cell resistance value was recorded in error and was not truly outside the TS SR acceptance criteria.

There has not been another case of a vital battery inter-cell resistance value being outside the acceptance criteria. Additionally, resistance values have been taken twice on battery EVCC following this event and all acceptance criteria was met.

IMMEDIATE

1.IP/0/A/3061/007 placed on technical hold pending incorporation of changes deemed necessary in the root cause evaluation.

2.The importance of immediately reporting any data that does not meet Technical Specification acceptance criteria to Supervision and the Control Room Senior Reactor Operator was conveyed to the maintenance technicians involved.

3.McGuire Regulatory Compliance group was immediately informed of the past failure to meet TS SR 3.8.4.5 acceptance criteria.

SUBSEQUENT

1.Maintenance Superintendent issued a communication emphasizing the roles and responsibilities of the Procedure Verifier and Approver.

2.Placed all procedures on Hold that take the same data for the remaining affected batteries.

PLANNED

1. Revise IP/0/A/3061/007 to have Acceptance Criteria Met signoff that verifies Technical Specification data taken is acceptable.

2. Review and revise all Maintenance Procedures which document TS and SLC compliance to require a Acceptance Criteria Met verification by documented signature.

3. Operations, Chemistry, Radiation Protection and Engineering will review procedures that take TS or SLC data to evaluate if applicable signoffs for criteria met are required.

SAFETY ANALYSIS

The battery's ability to perform its safety function is conducted in TS SR 3.8.4.7 - the battery service (duty cycle) test, which is conducted every 18 months. This test was completed successfully on battery EVCC on October 19, 2004 and August, 21, 2006. Both tests demonstrated a battery terminal voltage margin in excess of 4.0 VDC following the most limiting portion of the duty cycle. This voltage margin along with total battery resistance was used to determine the amount of additional battery degradation (increased resistance) required before the battery would be considered inoperable. The Operability analysis revealed that the "TOTAL" EVCC battery inter-cell, inter-tier, and inter-rack connection resistance would have to increase by 2.048E-3 ohms for the available battery terminal voltage margin to decrease to zero. The average battery inter-cell connection resistance measurement during the May 12, 2005 surveillance was 4.37E-5 ohms. The number of battery inter-cell terminal connections required to reach 1.7E-4 ohms and eliminate all available margin (2.048E-3 ohms) would have been 16 connectors. 16 connectors would have had to be at the 1.7E-4ohm value for the battery operability to be in question [(1.7E-4 - 4.37E-5) x 16] = 2.021E-3 ohms.

Even though it was determined that the resistance value was recorded in error and was not truly outside the acceptance criteria, the above evaluation determined that vital battery EVCC would have been operable and completely capable of meeting its design and safety function requirements.

Therefore, it has been determined that there is no impact on either the estimated core damage frequency (CDF) or large early release frequency (LERF) due to this event such that the event described in this LER was not significant with respect to the health and safety of the public.

ADDITIONAL INFORMATION

A review of the McGuire corrective action database did not identify any other events within the past three years having similar circumstances, cause, and corrective actions. Therefore, the event described in this LER is not considered a recurring event.