05000244/LER-2003-001

LER-2003-001, Inadequate Consideration of System Interactions for Bus Tie Breaker Maintenance Results in a Condition Prohibited By Technical Specifications

R. E. Ginna Nuclear Power Plant
Event date:	04-02-2003
Report date:	05-23-2003
2442003001R00 - NRC Website

I. PRE-EVENT PLANT CONDITIONS:

On April 2, 2003 the plant was in Mode 1 at approximately 100% steady state reactor power. Unrelated to plant activities, plant staff identified that operation in a condition prohibited by Technical Specifications had previously occurred related to Limiting Condition for Operation (LCO) 3.7.3, "Main Feedwater Regulating Valves (MFRVs), Associated Bypass Valves, and Main Feedwater Pump Discharge Valves (MFPDVs)".

II. DESCRIPTION OF EVENT:

A. � EVENT:

On April 2, 2003, Operations and Engineering personnel determined that over the last three years, on two separate occasions, maintenance activities associated with non-safety-related bus tie breakers 52/BTA-A and 52/BTB-B had rendered the MFPDVs inoperable with respect to the Ginna Station Technical Specifications. This inoperability was not recognized by plant staff at the time of the maintenance. As a result, LCO 3.7.3 Condition A was not entered and the Required Action Completion Time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> was not met.

The two MFPDVs (MOV 3976 and MOV 3977) are located on the discharge of the two Main Feedwater (MFW) pumps and function to provide isolation of feedwater to the steam generators following a feedline or steamline break. This effectively limits the mass and energy release within containment, and reduces the reactor coolant system cooldown effects following a steamline break.

The MFPDVs are motor-operated valves which close when the associated MFW pump breaker trips open following receipt of a safety injection signal or any other signal which trips the pump breaker. The power supply for MOVs 3977 and 3976 is from MCC A and MCC B, respectively.

These MCCs are supplied by Buses 13 and 15, respectively, which are in turn supplied by Buses 11A and 11B. During normal plant operation, Buses 11A and 11B are supplied by Unit Auxiliary Transformer 11 which is provided power directly from the Ginna Station turbine/generator. Following a turbine/generator trip and an approximately 60 second time delay, the feeder breakers to Buses 11A and 11B are tripped and bus tie breakers to Buses 12A and 12B, respectively, are closed. These bus tie breakers (52/BTA-A and 52/BTB-B) then supply Buses 11A and 11B from offsite power sources.

On March 5, 2003, a Plant Operations Review Committee (PORC) meeting was held at the request of the Scheduling Manager (Meeting #2003-007). This meeting was held in accordance with procedure IP-PSH-2, "Integrated Work Schedule Risk Management" which requires PORC authorization to voluntarily enter conditions of elevated risk as determined by the Equipment Out-Of-Service (BOOS) computer risk monitor code. This elevated risk was due to planned activities to remove bus tie breaker 52/BTB-B from service at power for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> to perform elective maintenance (Work Order #20202410). While the reasons for the elevated risk within EOOS was qualitatively determined to be conservative modeling, based on discussions within the PORC meeting, Operations management decided to reject this activity due to the potential risks involved. These risks included the potential consequences if a turbine/generator trip were to occur during the 36 hour4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> window which would result in the loss of one train of non-safety- related plant loads including a reactor coolant pump and an instrument bus.

Subsequent to the PORC meeting, efforts continued among plant staff to support performance of this activity at power with more effective management of the potential risks involved. On April 2, 2003, it was identified that this activity would prevent the MFPDVs from performing their Technical Specification function. Specifically, with either bus tie breaker 52/BTA-A or 52/BTB-B removed from service, the respective MFPDV would not have power available to perform their isolation function following a turbine/generator trip. This is due to the approximate 72 second stroke time associated with the MFPDVs and the 60 second time delay for transfer to offsite power via the bus tie breakers. It was also identified that these bus tie breakers had been removed from service at power in two instances over the last three years (June 8, 2000 for 52/BTB-B and January 16, 2002 for 52/BTA-A) for 51.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> and 34.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, respectively, which exceeded the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Completion Time specified by LCO 3.7.3, Condition A. This resulted in a condition prohibited by Technical Specifications.

Ginna Station ACTION Report 2003-0717 was initiated to document this condition. Since this issue was related to a past occurrence, no immediate NRC notification was required.

THE EVENT:

None

C. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

• June 8, 2000, 0609 EDT: Event date and time for 52/BTB-B being inoperable 34.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />.

• January 16, 2002, 0616 EST: Event date and time for 52/BTA-A being inoperable for 51.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

• April 2, 2003, 0930 EST: Discovery date and time.

D. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

None E. M METHOD OF DISCOVERY:

The condition was self-identified by Engineering and Operations personnel performing planning activities associated with Work Order #20202410.

F. SAFETY SYSTEM RESPONSES:

None III. M CAUSE OF EVENT:

The cause of operating in a condition prohibited by Technical Specifications was plant staff not recognizing the impact of removing bus tie breakers 52/BTA-A and 52/BTB-B from service with respect to the MFPDVs. During normal power operations, the MFPDVs are supplied power from Unit Auxiliary Transformer 11 which is provided power directly from the Ginna Station turbine/generator.

This power source was unaffected by the maintenance activities on the bus tie breakers causing plant staff to believe that there was no impact on Technical Specifications. The definition of operability within the Ginna Station Technical Specifications requires that the component be capable of performing its specified safety function. Since the stroke time of the MFDVs (approximately 72 seconds) exceeded the time duration that power would be available following a turbine/generator trip without the bus tie breakers (60 seconds), the MFDVs were incapable of performing their safety function as specified within the Technical Specifications.

The reason that plant staff did not recognize that the plant configuration during the subject maintenance activity resulted in entry into LCO 3.7.3 is due to inadequate consideration of system interactions. A contributing reason is that the MFDVs were added to the Ginna Station Technical Specifications during the conversion to Improved Technical Specifications in 1996 and this system interaction was not considered. Consequently, plant procedures did not adequately address this plant configuration.

IV. � ASSESSMENT OF THE SAFETY CONSEQUENCES OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73, Licensee Event Report System, item (a)(2)(i)(B), which requires a report of, "any operation or condition which was prohibited by the plant's Technical Specifications." The maintenance activities which removed bus tie breakers 52/BTA-A and 52/BTB-B from service for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> resulted in a condition prohibited by LCO 3.7.3, Condition A.

An assessment considering the consequences and implications of this event resulted in the following conclusions:

There were no operational or safety consequences and implications attributed to the inoperability of the MFPDVs for a greater period of time than allowed by Technical Specifications because:

• The specific condition of having a single MFPDV inoperable is allowed by Technical Specifications for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is "based on operating experience" taking "into account the low probability of an event occurring during this time period that would require isolation of the MFW flow paths." For the two events, the time period in which a single MFPDV was inoperable was 34.9 and 51.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. This is a relatively short period of time in which the LCO Completion Times were not being met. Based on the Ginna Station Probabilistic Safety Assessment (PSA), the likelihood of a steamline or feedline break within containment is 1.47E-08/hour. During the additional time of being in this condition beyond the Technical Specification limit of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the probability of having a steamline or feedline break within containment was only 1.60E-07 and 4.04E-07, respectively.

• The MFPDVs are in series with Main Feedwater Regulating Valves (MFRVs), and their associated bypass valves, which isolate each steam generator. The closure of either the two MFPDVs or the MFRVs and their bypass valves ensures that the steam generator is isolated within containment following a steamline or feedline break within containment.

The MFRVs and bypass valves are air-operated valves which close on a safety injection signal, a high steam generator level signal, or a reactor trip with Tavg of plant records shows that these valves remained operable during the entire time that the MFPDVs were inoperable. The review also determined that there has not been a functional failure of a MFRV, or their bypass valves to close, since 1996. Consequently, isolation of the steam generators would be expected to occur for these two cases.

• For the two cases where the MFPDVs were inoperable, power would be available to allow the valves to close for approximately 60 seconds until the transfer to Buses 12A and 12B would occur. Given an average stroke time of 72 seconds, the MFPDVs would be expected to be approximately 80% closed. As such, the MFPDVs would provide a portion of their isolation function under these conditions. In addition, should containment pressure exceed its 60 psig design pressure, there are no significant radiological consequences associated with a feedline or steamline break.

Based on the above, it is concluded that the plant operated as designed, that there were no unreviewed safety questions, and that the public's health and safety was assured at all times.

V. � CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

STATUS:

None

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

• The bases for LCO 3.7.3 will be revised to state that bus tie breakers 52/BTA-A and . � 52/BTB-B are required for operability of the MFPDVs.

• Operators will be trained on the impact of bus tie breakers 52/BTA-A and 52/BTB-B with respect to the operability of the MFPDVs.

VI. � ADDITIONAL INFORMATION:

A. FAILED COMPONENTS:

None B. � PREVIOUS LERs ON SIMILAR EVENTS:

An historical search of LERs was conducted with the following results: No documentation of similar LER events with the same root cause at the Ginna Nuclear Power Plant could be identified.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

IN THIS LER:

IEEE 803 � IEEE 805 COMPONENT � FUNCTION IDENTIFIER � SYSTEM IDENTIFICATION Flow Control Valve � FCV � SJ � (Feedwater System) Isolation Valve � ISV � SJ

D. SPECIAL COMMENTS:

None r