05000413/LER-2010-001

LER-2010-001, Technical Specification Violation Associated with Failure to Perform Offsite Circuit Verification

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4132010001R00 - NRC Website

BACKGROUND

This event is being reported under the following criterion:

10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications.

Catawba Nuclear Station Units 1 and 2 are Westinghouse four-loop Pressurized Water Reactors (PWRs) [EIIS: RCT].

The unit Essential Auxiliary Power Distribution System [EIIS: EB] AC sources consist of the offsite power sources (normal and alternate), and the onsite standby power sources (Train A and Train B Diesel Generators (DGs) [EIIS: EK]). As required by 10 CFR 50, Appendix A, General Design Criterion 17, the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems [EIIS:

JE].

The onsite Class 1E AC Distribution System is divided into redundant load groups (trains) so that the loss of any one group does not prevent the minimum safety functions from being performed. Each train has connections to two preferred offsite power sources and a single DG.

From the transmission network, two electrically and physically separated circuits provide AC power, through step down station auxiliary transformers [EIIS: XFMR], to the 4.16 kV ESF buses [EIIS:

BU]. A qualified offsite circuit consists of all breakers [EIIS: 52], transformers, switches [EIIS: IS], interrupting devices [EIIS: GFI], cabling [EIIS: CBL], and controls [EIIS: JC] required to transmit power from the offsite transmission network to the onsite Class 1E ESF bus(es).

The onsite standby power source for each 4.16 kV ESF bus is a dedicated DG. DGs A and B are dedicated to ESF buses ETA and ETB, respectively.

Two qualified circuits between the offsite transmission network and the onsite Essential Auxiliary Power System and separate and independent DGs for each train ensure availability of the required power to shut down the reactor and maintain it in a safe shutdown condition after an Anticipated Operational Occurrence or a postulated Design Basis Accident.

TS Limiting Condition for Operation (LCO) 3.8.1 governs the AC sources while in Modes 1, 2, 3, and 4. LCO 3.8.1 requires two offsite circuits and two DGs to be operable for each unit. With one offsite circuit inoperable, Condition A allows for continued operation for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Additionally, Surveillance Requirement (SR) 3.8.1.1 (verify correct breaker alignment and indicated power availability for each offsite circuit) must be performed for the operable offsite circuit within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter.

SR 3.8.1.8 (verify automatic and manual transfer of AC power sources from the normal offsite circuit to each alternate offsite circuit) is required to be performed every 18 months. Transfer of each 4.16 kV ESF bus power supply from the normal offsite circuit to the alternate offsite circuit demonstrates the capability of the alternate circuit distribution network to power the shutdown loads. The alternate circuit distribution network consists of an offsite power source through a 6.9 kV bus incoming breaker, its associated 6.9 kV bus tie breaker, and the aligned 6.9/4.16 kV transformer to the essential bus.

The requirement of this SR is the transfer from the normal offsite circuit to the alternate offsite circuit via the automatic and manual actuation of the 6.9 kV bus tie breaker and 6.9 kV bus incoming breakers upon loss of the normal credited offsite source.

The following table depicts the relationship between the offsite circuits, the tie breakers, and the ESF buses supported for Unit 1 and Unit 2.

Offsite Circuit Tie Breaker� ESF Bus Supported 1A�N/A Normal to lETA 1TD7 Alternate to lETB 1B N/A Normal to lETB 1TA7 Alternate to lETA 2A�N/A Normal to 2ETA 2TD7 Alternate to 2ETB 2B N/A Normal to 2ETB 2TA7 Alternate to 2ETA On February 1, 2010, when this event occurred, Units 1 and 2 were in Mode 1 at 100% power operation.

EVENT DESCRIPTION

(Certain event times are approximate.) Date/Time�Event Description 02/01/10/0445 Tie breaker 1TA7 was racked out for preventive maintenance.

1130 Preventive maintenance work was recognized by Operations as being complete.

1320 Operations experienced difficulty racking 1TA7 back in.

1618 Work request written concerning the difficulty experienced racking 1TA7 back in.

1730-1745 Operations and Regulatory Compliance discussed the implication of 1TA7 being racked out on operability. It was noted that since SR 3.8.1.8 was not met with 1TA7 racked out, that LCO 3.8.1 was not met.

1830�Offsite circuit 1A was declared inoperable.

1938 SR 3.8.1.1 was performed for Unit 1.

-2210 �1TA7 was racked in 02/02/10/0030 Operations logged the inoperability into the Technical Specification Action Item Log (TSAIL) and noted the impact on Unit 2. SR 3.8.1.1 was subsequently performed for Unit 2.

CAUSAL FACTORS

The root cause of this event was that the TS Bases for SR 3.8.1.8 are unclear in relation to the design basis requirements for the 6.9 kV bus tie breakers. This is a legacy issue and the lack of clarity subsequently led to a lack of understanding of the importance of the tie breakers by various plant groups.

The TS Bases for SR 3.8.1.8 do not delineate which offsite circuit is to be considered inoperable if a particular tie breaker is incapable of performing its function. Additionally, there is no design basis document information available related to this issue. From a review of design documents, this lack of clarity dates back to the original design of the system and to the documentation of the TS SR Bases. This lack of clarity has therefore affected the operational control of the tie breakers since 1996 (refer to the last paragraph of this section).

Once it was recognized that an offsite circuit was inoperable, SR 3.8.1.1 was not performed within one hour as required by TS 3.8.1, Required Action A.1. Due to multiple ongoing activities, licensed Operations personnel failed to adequately evaluate and perform the required actions associated with the inoperability of the 1A offsite circuit in a timely manner. Additionally, personnel failed to adequately apply 1TA7's cascading effects to Unit 2. (The cascading effects result from the fact that Catawba has two safety related shared motor control centers, one for each train, which can be powered from either unit and which support the operation of certain shared safety related equipment.) Timely application of these cascading effects would have led to verification of the operable offsite circuit within the one-hour time limit.

Events similar to this could have potentially occurred at Catawba as far back as 1996. In 1996, the preventive maintenance work on the 6.9 kV bus tie breakers was moved from outage to innage with a five-year maintenance frequency. Prior to 1996, work on these tie breakers would have occurred during the respective unit outage(s); therefore, this event was not considered to have been a credible occurrence prior to 1996.

CORRECTIVE ACTIONS

Immediate:

1.Tie breaker 1TA7 was racked in, thereby restoring operability to the affected offsite circuit.

2.Plant personnel verified that the breaker issue had no impact on the overall plant risk profile.

3.A comment was placed within the tagging system to alert plant personnel as to the importance of the tie breakers relative to offsite circuit operability.

Subsequent:

1.A lessons learned communication was provided to all shift Operations personnel concerning this event.

2.PT/1,2/A/4350/003, "Electrical Power Source Alignment.

Verification" were revised to add a weekly check of the applicable tie breakers being racked in and open. Information was also added regarding the critical nature of the tie breakers.

3.OP/0/A/6350/010, "Operation of Station Breakers and Disconnects" was revised to add information regarding the tie breakers and their relevance to TS 3.8.1.

Planned:

1.The TS Bases for SR 3.8.1.8 will be revised to clarify the design basis of the offsite circuits and the relationship to the tie breakers.

2.The Design Basis Document for the 4.16 kV Essential Auxiliary Power System will be revised to include a clear design basis for the tie breakers.

There are no NRC commitments contained in this LER.

SAFETY ANALYSIS

There was no safety significance to:this .event. At no time was offsite power lost to either of the 4.16 kV ESF buses ETA 'or ETB. With the tie breaker removed from service, the only adverse- effect: upon,the plant was the inability to comply with SR 3.8.1..8. Although SR 3.8.1.1 was performed late, the surveillance demonstrated that the required offsite circuits were, in fact, operable. Also, both train's DGs remained available throughout this event, thereby ensuring that standby emergency power was available to the ESF buses, ha.d it been required.

The health and safety of the public were not adversely affected by this event.

ADDITIONAL INFORMATION

'Within the previous three years,.there.were no LER .events involving the failure to perform SR 3.8.1.1 within one hour as required by TS 3.8.1.

Therefore, this event .is considered to be non-recurring.

Energy Industty Identification System (EIIS) codes are identified in the text'as [EIIS: XX]. 'This event-is not considered reportable to the EqUipment Performance and Information Exchange (EPIX)'.program.

This event is not considered to constitute. a Safety System Functional Failure.

• There was no release.of radioactive 'material, radiation overexposure, or personnel injury associated with the event described in this LER.