05000413/LER-2012-003
| Catawba Nuclear Station | |
| Event date: | 12-22-2012 |
|---|---|
| Report date: | 03-22-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4132012003R00 - 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 (TS).
Catawba Nuclear Station Unit 1 is a Westinghouse four-loop Pressurized Water Reactor (PWR) [EIIS: RCT].
The Auxiliary Feedwater (AFW) System [EllS: BA] (Duke Energy designation "CA") supplies feedwater to the steam generators [EIIS: SG] to remove decay heat from the Reactor Coolant System [EIIS: AB] upon the loss of normal feedwater supply. The AFW pumps [EIIS: P] take suction through suction lines from the Condensate Storage System (CSS) [EIIS: KA] and pump to the steam generator secondary side. The normal supply of water to the AFW pumps is from the CSS. The supply valves [EIIS: V] are open with power removed from the valve operators. The assured source of water to the AFW System is supplied by the Nuclear Service Water System (NSWS) [EIIS: BI]. The turbine and motor driven pump discharge lines to each individual steam generator join into single lines outside containment. These individual lines penetrate the containment and enter each steam generator through the auxiliary feedwater nozzle. The steam generators function as a heat sink for core decay heat. The heat load is dissipated by releasing steam to the atmosphere from the steam generators via the Main Steam Safety Valves (MSSVs) [EIIS: SA] or the steam generator Power Operated Relief Valves (PORVs) [EIIS:
SA]. If the main condenser [EIIS: COND] is available, steam may be released via the steam dump valves [EIIS:
JI] and recirculated to the hotwell.
The AFW System consists of two motor driven AFW pumps and one steam turbine driven pump configured into three trains. Each of the motor driven pumps supplies 100% of the flow requirements to two steam generators, although each pump has the capability to be realigned to feed other steam generators. The turbine driven pump provides 200% of the flow requirements and supplies water to all four steam generators. Travel stops are set on the steam generator flow control valves [EIIS: FCV] such that the pumps can supply the minimum flow required without exceeding the maximum flow allowed. The pumps are equipped with independent recirculation lines to prevent pump operation against a closed system. Each motor driven AFW pump is powered from an independent Class lE power supply. The steam turbine driven AFW pump receives steam from two main steam lines upstream of the Main Steam Isolation Valves (MSIVs) [EIIS: SB]. Each of the steam feed lines will supply 100% of the requirements of the turbine driven AFW pump.
The AFW System is capable of supplying feedwater to the steam generators during normal unit startup, shutdown, and hot standby conditions. One turbine driven pump at full flow is sufficient to remove decay heat and cool the unit to Residual Heat Removal (RHR) [EIIS: BP] entry conditions. During unit cooldown, steam generator pressures and main steam pressures decrease simultaneously. Thus, the turbine driven AFW pump with a reduced steam supply pressure remains fully capable of providing flow to all steam generators. Thus, the requirement for diversity in motive power sources for the AFW System is met.
The AFW System is designed to supply sufficient water to the steam generators to remove decay heat with steam generator pressure at the lowest setpoint of the MSSVs plus 3% accumulation. Subsequently, the AFW System supplies sufficient water to cool the unit to RHR entry conditions, with steam released through the steam generator PORVs or MSSVs.
The motor driven AFW pumps actuate automatically on steam generator water level low-low in one out of four steam generators by the Engineered Safety Features Actuation System (ESFAS) [EllS: JE]. The motor driven pumps also actuate on loss of offsite power, safety injection, and trip of all Main Feedwater (MFW) [EIIS: SJ] pumps. The turbine driven AFW pump actuates automatically on steam generator water level low-low in two out of four steam generators and loss of offsite power.
TS 3.7.5 governs the AFW System. Limiting Condition for Operation (LCO) 3.7.5 requires three AFW trains to be operable in Modes 1, 2, and 3. In Mode 4 when the steam generator(s) are relied upon for heat removal, only one AFW train, which includes a motor driven pump, is required to be operable. Since the ESFAS instrumentation that actuates the AFW System is not required to be operable in Mode 4, manual actuation of the required AFW train in this mode is sufficient.
Condition B states in part that with one AFW train inoperable in Mode 1, 2, or 3 for reasons other than one inoperable turbine driven AFW pump steam supply, the AFW train must be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If this is not accomplished, then the unit must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> according to Condition C.
Surveillance Requirement (SR) 3.7.5.2 requires verification that the developed head of each AFW pump at the flow test point is greater than or equal to the required developed head. SR 3.7.5.2 is modified by a Note that states that the SR is not required to be performed for the turbine driven AFW pump until 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after achieving greater than or equal to 600 psig in the steam generators. The purpose of the Note is to provide an allowance for deferring the SR until sufficient steam pressure exists to operate the turbine driven AFW pump. The SR Frequency is specified as being in accordance with the Inservice Testing Program.
Procedure MP/0/N7200/005, "Auxiliary Feedwater Pump Turbine Corrective Maintenance and Overspeed Trip Test Procedure", provides governance for corrective maintenance on the turbine section of the turbine driven AFW pump. The turbine is a Terry Model GS-2N.
On December 22, 2012, when this event occurred, Unit 1 was in Mode 3 at 0% power operation, in the process of starting up following the completion of the End of Cycle (EOC) 20 Refueling Outage (RFO). No other structures, systems, or components were out of service that had any effect on the event.
EVENT DESCRIPTION
Date/Time Event (Some event times are approximate.) 11/24/12/0938 Unit 1 entered Mode 4 in preparation for the EOC 20 RFO.
1018 The turbine driven AFW pump was logged in the Technical Specification Action Item Log (TSAIL) as inoperable under a tracking entry to support maintenance work during the EOC 20 RFO (TSAIL entry C1-12-03298).
EOC 20 RFO Maintenance work was performed on the turbine driven AFW pump. The scope of work included a 6-year overhaul of the pump turbine.
12/17/12/ The uncoupled overspeed trip test was successfully completed. The turbine was subsequently coupled to the pump.
12/22/12/0531 The turbine driven AFW pump was declared operable (TSAIL entry C1-12-03298).
0553 Unit 1 entered Mode 3 during startup from the EOC 20 RFO.
1053 Steam pressure reached 600 psig, which initiated the 24-hour testing deferral period allowed by the Note to SR 3.7.5.2.
1307 The turbine driven AFW pump tripped on mechanical overspeed during inservice testing.
The pump was examined by Engineering, reset, and run a second time. It tripped again on mechanical overspeed. The pump was subsequently declared inoperable using 1307 as the start time of pump inoperability (TSAIL entry C1-12-03590).
12/25/12/1837 Unit 1 entered Mode 4 per TS 3.7.5 Condition C. (During a reportability review the pump was determined to have been retroactively inoperable when Unit 1 entered Mode 3; the required Completion Time for being in Mode 4 was exceeded by 44 minutes.) 12/25-26/12/ Troubleshooting and corrective maintenance work were performed on the turbine driven AFW pump.
12/26/12/1134 Unit 1 reentered Mode 3 following completion of troubleshooting and corrective maintenance work on the turbine driven AFW pump.
1620 Steam pressure reached 600 psig, which initiated the 24-hour testing deferral period allowed by the Note to SR 3.7.5.2.
12/27/12/0148 The turbine driven AFW pump was declared operable following successful completion of the required inservice testing (TSAIL entry C1-12-03612).
01/22/13/ Catawba conclusively determined that the turbine driven AFW pump inoperability resulted from the maintenance activity performed during the EOC 20 RFO. This determination started the 60-day clock for LER submission.
CAUSAL FACTORS
When the turbine driven AFW pump was reassembled following the EOC 20 RFO maintenance work, the drive coupling between the turbine governor and the turbine was installed in the wrong orientation (180 degrees reversed from the required orientation). This resulted in incomplete engagement between the governor and the turbine. The maintenance technician performing the reassembly did not utilize all applicable human performance tools (i.e., self-checking, questioning attitude, and stop when unsure) during the reassembly process. The technician failed to match mark the affected components during the disassembly process. The cause of this event was therefore determined to be human performance error. In addition, procedure MP/0/A/7200/005 was deficient in that it lacked detail concerning the required orientation of the drive coupling when performing the installation process, which resulted in this task being performed as "skill of the craft".
CORRECTIVE ACTIONS
Immediate:
1. The turbine driven AFW pump was declared inoperable when it tripped on mechanical overspeed during its inservice testing.
Subsequent:
1. Unit 1 was placed in Mode 4 in a time frame commensurate with TS 3.7.5 Condition C requirements once the inoperability was discovered.
2. A new drive coupling was installed in the required orientation and the turbine was recoupled to the pump. All required pump testing was successfully completed. Unit 1 startup activities resumed.
Planned:
1. Remedial actions will be provided as necessary to ensure maintenance technicians understand the requirements of human performance tool use.
2. Procedure MP/0/N7200/005 will be enhanced to include steps, sketches, and verification requirements for required orientation of the drive coupling. In addition, a complete review of the procedure will be performed for inadequate detail in other steps that are considered vital for the proper assembly and adjustment of the pump turbine.
There are no NRC commitments contained in this LER.
SAFETY ANALYSIS
There was no safety significance to this event. During the time that the turbine driven AFW pump was inoperable while Unit 1 was in Mode 3, both motor driven AFW pumps were operable and remained capable of automatically starting and providing the required flow to the steam generators, had a Design Basis Accident (DBA) occurred requiring an automatic start of the AFW System. In addition, when this event was discovered, core decay heat was at a low level, since Unit 1 was in the process of starting up from the EOC 20 RFO. Throughout this event, no situation existed that would have resulted in a demand for an AFW System automatic start. The total time that Unit 1 was in Mode 3 with the turbine driven AFW pump unknowingly inoperable was 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and 14 minutes.
Following the discovery of the pump inoperability, the applicable TS requirements were complied with.
Therefore, this event is considered to be of no significance with respect to the health and safety of the public.
ADDITIONAL INFORMATION
Within the previous three years, the following LERs were submitted which have been evaluated against this LER for recurring event similarity:
Auxiliary Feedwater System Train Due to Closed Pump Discharge Valves". The root cause of this event was determined to be that the operating procedure for the AFW System was not structured to provide clear guidance to the operators for the status of AFW System alignments for Mode 4 and Mode 3.
Associated Technical Specification Violation Involving Notice of Enforcement Discretion Due to Two Inoperable Trains of the Control Room Area Chilled Water System". One of the root causes of this event was determined to be insufficient maintenance procedural guidance for alignment of a chilled water pump.
Motor Cable Resulted in Zone G Relay Lockout and Subsequent Loss of Offsite Power and Emergency Diesel Generator Automatic Start for Both Units". One of the root causes of this event was determined to be inadequate design input specification and insufficient control over vendor outsourcing in conjunction with a Zone G relay modification.
10/23/12 Due to Failed Tachometer Relay Power Supply'. The root cause of this event was determined to be an inadequate technical evaluation following a DG 2B engine tachometer malfunction.
These events all involved entering or operating in a plant mode with an inoperable TS required component. In addition, LER 413/2011-003 involved insufficient maintenance procedural guidance. The procedural corrective actions resulting from that event were specific to controllers and pump impeller alignment associated with the Control Room Area Chilled Water System. The specifics of the root causes and corrective actions associated with the other events were also different. Therefore, Duke Energy concludes that the event being reported in this LER is considered to be non-recurring in nature.
Energy Industry Identification System (EIIS) codes are identified in the text as [EIIS: )0(].
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.
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