05000416/LER-2012-001
| Grand Gulf Nuclear Station | |
| Event date: | 11-19-2009 |
|---|---|
| Report date: | 03-14-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4162012001R00 - NRC Website | |
A. Reportable Occurrence This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications (TS) when it was discovered the acceptance criteria of TS Surveillance Requirement (SR) 3.5.3.1 did not fully implement the requirement.
B. Description of Structure(s), System(s) and Component(s) As discussed in TS 3.5.3 Bases, the reactor core isolation cooling (RCIC) System (EllS:BN) is not part of the Emergency Core Cooling System (ECCS), is not an Engineered Safety Feature (ESF) System, and is not credited in the safety analyses; however, the RCIC System is included with the ECCS TS section because of its similar functions. The RCIC System is designed to operate either automatically or manually following a reactor pressure vessel (RPV) isolation accompanied by a loss of coolant flow from the feedwater system to provide adequate core cooling and control of RPV water level. Under these conditions, the High Pressure Core Spray (HPCS) (EllS:BJ) and RCIC systems perform similar functions.
From the Updated Final Safety Analysis Report (UFSAR), the RCIC System consists of a steam driven turbine pump unit, piping, and valves to provide steam to the turbine, as well as piping and valves to transfer water from the suction source to the core via the feedwater system line. RCIC is designed to respond to transient events by providing makeup coolant to the reactor. RCIC is designed to assure that sufficient reactor water inventory is maintained in the reactor vessel to permit adequate core cooling to take place. This prevents reactor fuel overheating, should the vessel be isolated and maintained in the hot shutdown condition; or should the vessel be isolated accompanied by loss of coolant flow from the reactor feedwater system; or should a complete plant shutdown under conditions of loss of normal feedwater system be started before the reactor is depressurized to a level where the shutdown coolant system can be placed into operation.
C. Initial Conditions The reactor was in operational mode 1 with reactor power at approximately 100 percent. There were no inoperable structures, systems, or components that contributed to this event.
D. Description of Occurrence During the 2011 NRC PI&R Inspection at GGNS, the NRC reviewed a previous 2009 NRC PI&R Inspection non cited violation concerning whether a procedure was sufficient to meet a TS SR. SR 3.5.3.1 requires a monthly verification that the Reactor Core Isolation Cooling (RCIC) system piping is filled with water from the pump discharge valve to the injection valve. The procedure allowed the SR to be considered met after a vent of two minutes was performed. The NRC questioned in 2009, whether the procedure was sufficient to meet the TS SR because there was no visual means of confirming water flow through the vent line when performing venting of the RCIC system. During the 2011 Pl&R Inspection, it was determined that the acceptance criteria to satisfy TS (SR) 3.5.3.1 was inadequate and that in November 2009, when Description of Occurrence (continued) the NRC first raised the RCIC venting concern, GGNS provided a bases (calculation) for the venting but failed to determine whether the surveillance acceptance criteria was adequate. In 2009, GGNS determined that the surveillance was satisfactorily performed, however, as an enhancement to the procedure, Surveillances 06-OP-1E51-M-0001 (RCIC System Operability Verification) and 06-OP-1E51-Q 0003 (RCIC System Quarterly Pump Operability Verification) were revised to incorporate ultrasonic testing (UT) to ensure the piping was full of water.
In 2009, GGNS did not identify this procedure as an inadequate surveillance test and considered the TS SR met and that the RCIC system had successfully completed the required surveillance testing. As GGNS did not consider this an inadequate surveillance, GGNS failed to utilize TS SR 3.0.3 to address the inadequate TS surveillance as a missed surveillance. TS SR 3.0.3 states that if the surveillance was not performed within an allowed delay period, the limiting condition for operation (LCO) must immediately be declared not met. The LCO was not declared not met for this condition. LCO 3.5.3 requires the RCIC system to be operable in mode 1 and in modes 2 and 3 with reactor steam dome pressure greater than 150 psig. The TS Actions for an inoperable RCIC system require verification within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> that HPCS is operable and restoration of RCIC to operable status within 14 days. If those Actions are not met, then the plant must be placed in mode 3 with reactor pressure less than 150 psig. There were limited occasions where the HPCS system was inoperable for maintenance resulting in other TS required actions to be entered for those situations.
GGNS performed UT testing February 5, 2010 which verified the piping was full of water and restored full compliance with TS SR 3.5.3.1.
E. Cause of Occurrence The cause of the occurrence was an inadequate surveillance procedure acceptance criterion which resulted in the requirements of SR 3.5.3.1 not being met.
The contributing factor was the lack of technical rigor in evaluation of a potential inadequate surveillance procedure.
F. Corrective Actions
1. When identified in the 2009 PISA Inspection, Surveillance 06-OP-1E51-M-0001 (RCIC System Operability Verification), and 06-OP-1E51-Q-0003 (RCIC System Quarterly Pump Operability Verification) were revised to incorporate UT to verify the piping was full of water.
2. UT testing of the affected piping was performed to verify piping was full of water.
The corrective actions were developed as required by the GGNS Corrective Action Program under Condition Report (CR) GGN-2009-6249 on November 24, 2009 and were implemented on February 5, 2010 for the UT testing and March 17, 2010 for the procedure changes.
G. Safety Assessment RCIC is credited in the Control Rod Drop Accident (CRDA) and is an ESF system for this event only. The rod pattern controller (EDS:AA) and reactor protection system (RPS) (EllS:JC) average power range monitoring (APRM)(EllS:IG) flux scram are the mitigating functions credited in the CRDA (short-term).
Core cooling is required for long-term mitigation of this accident (decay heat removal). The available core cooling systems are RCIC and HPCS. RCIC is also the only system available for providing cooling water to the core in the event of a station black out (SBO) and is used to demonstrate GGNS compliance to 10 CFR 50.63 requirements.
At no time during this issue resolution was RCIC unable to perform its safety function. The RCIC system has successfully completed the required surveillance runs. The RCIC surveillance running from condensate storage tank (CST) to CST would have been ideal conditions for the formation of an isolated bubble at the injection valve to cause pressure oscillations due to the RCIC system running in this mode.
An evaluation done for condition report (CR) CR-GGN-2007-03818 determined there was enough pressure from the CST to prevent gas from disassociating from the water and analysis indicated that two minute vent time was enough time to vent the RCIC discharge line volume from the pump discharge check valve to the injection valve. The system surveillance testing was performed per procedure and the system is vented every 31 days. As explained above, the two minute vent time was adequate to ensure the RCIC discharge piping at the injection valve was adequately vented and the condition would not have prevented the fulfillment of a safety function.
There were no actual adverse safety consequences as a result of this condition.
H. Additional Information
Previous Occurrences - There has not been any occurrence of a failure to submit an Licensee Event Report (LER) in the past three years at Grand Gulf Nuclear Station involving reportability under 10CFR50.73(a)(2)(i)(B) or involving these same conditions.