05000482/LER-2012-004
| Docket Number | |
| Event date: | 05-09-2012 |
|---|---|
| Report date: | 07-03-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4822012004R00 - NRC Website | |
There were no inoperable structures, components or systems that were inoperable at the start of the event and that contributed to the event.
DESCRIPTION OF THE EVENT:
On May 9, 2012, a Nuclear Regulatory Commission (NRC) regional inspector identified that a potential violation of Technical Specification (TS) 3.4.12, "Low Temperature Overpressure Protection (LTOP) System," occurred during the recent forced outage and in prior refueling outages. Limiting Condition for Operation (LCO) 3.4.12 requires an LTOP System shall be operable with a maximum of zero safety injection pumps [ENS: BQ,P] and one centrifugal charging pump (CCP) [EllS: BQ,P] capable of injecting into the Reactor Coolant System (RCS) [ENS: AB]. During the recent forced outage and during refueling outages, one safety related centrifugal charging pump and the non-safety related normal charging pump (NCP) [EllS: CB,P] were capable of injecting into the RCS.
A review of the Wolf Creek Generating Station (WCGS) licensing basis and the NRC safety evaluations related to License Amendment Nos. 123 and 130 establishes the following position:
LCO 3.4.12 requires, in part, an LTOP System shall be operable with a maximum of zero safety injection pumps and one CCP capable of injecting into the RCS. The LCO is applicable in Mode 3 with any RCS cold leg temperature reactor vessel head is on. The LCO is considered to be met when both safety injection pumps and one CCP are not capable of injecting into the RCS with the second CCP and the NCP capable of injecting into the RCS.
The mass input transient analysis assumes simultaneous injection of both a CCP and the NCP into the water-solid RCS while the Residual Heat Removal (RHR) System and the letdown line are isolated. This assumption is consistent with the TS LCO, which requires all safety injection pumps and one of the two Emergency Core Cooling System (ECCS) CCPs be made incapable of injecting into the RCS and therefore, allows a CCP to be operable and the NCP to be functional under these modes of operation. The safety evaluation in Amendment No. 123 for the conversion from current TSs to the improved TSs indicates that the requirements associated with LCO 3.4.12 is specific to ECCS pump capability to inject into the RCS. The NCP is not an ECCS pump. The safety evaluation for Amendment No. 130 specified that the operability of two power operated relief valves (PORVs) [EllS: AB,RV] or two RHR suction relief valves [EllS: BP,RV] or an RCS vent [EllS: AB,VTV] opening of at least 2 square inches ensures adequate flow capacity to protect the RCS from overpressurization from the start of a CCP and/or the NCP injecting into the RCS.
The full basis for this position was submitted to the NRC in Wolf Creek Nuclear Operating Corporation (WCNOC) letter WO 12-0047, "Request for Interpretation of Technical Specification 3.4.12, "Low Temperature Overpressure Protection (LTOP) System"," dated May 31, 2012.
The NCP is a non-safety related single speed, horizontal, centrifugal type pump and is powered from a non-Class 1E source. The NCP is not an ECCS pump.
BASIS FOR REPORTABILITY:
LCO 3.4.12 requires an LTOP System be operable with a maximum of zero safety injection pumps and one centrifugal charging pump capable of injecting into the RCS in Mode 3 with any RCS cold leg temperature two centrifugal charging pumps capable of injecting into the RCS, Required Action B.1 requires the immediate initiation of action to verify a maximum of one centrifugal charging pump is capable of injecting into the RCS. If the Completion Time of Required Action B.1 is not met, Required Action G.1 requires depressurizing the RCS and establishing an RCS vent of >1= 2.0 square inches.
This event is being conservatively reported under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TSs as the Required Actions of TS 3.4.12 would not have been met during certain periods of time if the NCP were to be considered a CCP. The following table identifies the dates in the prior 3 years in which a CCP and the NCP may have been capable of injecting into the RCS when in the mode of applicability of TS 3.4.12.
Dates — one CCP and the NCP capable of Injecting into RCS 3/23/12 to 3/25/12 1/14/12 to 3/19/12 6/2/11 to 6/20/11 5/6/11 to 5/30/11 3/19/11 to 3/25/11 10/5/10 to 10/15/10 3/4/10 to 3/5/10 10/10/09 to 10/15/09 11/9/09 to 11/18/09 A request for interpretation of TS 3.4.12 was submitted to the NRC as WCNOC considers the LCO to be met when both safety injection pumps and one CCP are not capable of injecting into the RCS with the second CCP and the NCP capable of injecting into the RCS.
ROOT CAUSE:
The apparent cause for this potential violation is the failure to specifically define in the TS LCO that the centrifugal charging pump is an Emergency Core Cooling System (ECCS) centrifugal charging pump.
The TS 3.4.12 Bases specifies that the term CCP refers to the safety related ECCS pumps only.
CORRECTIVE ACTIONS:
A request for interpretation of TS 3.4.12 was submitted to the NRC on May 31, 2012.
The affected Operations procedures will be revised to apply a conservative understanding of LCO 3.4.12 by specifying that the NCP is rendered incapable of injecting into the RCS in the mode or other specified condition in the Applicability of TS 3.4.12 since a CCP is required for a functional boration injection flow path.
The TS 3.4.12 Bases will be revised to apply a conservative understanding of LCO 3.4.12 by specifying that the NCP is rendered incapable of injecting into the RCS in the mode or other specified condition in the Applicability of TS 3.4.12.
SAFETY SIGNIFICANCE:
The safety significance of this event is low. The LTOP PORV setpoint limit curve (Pressure and Temperature Limits Report Figure 2.2-1) is determined based on the updated heatup and cooldown limit curves, and the analysis results of limiting LTOP transients. The methodology for this determination is given in WCAP-14040-A, "Methodology Used to Develop Cold Overpressure Mitigation System Setpoints and RCS Heatup and Cooldown Limit Curves," Revision 4. The limiting LTOP mechanisms analyzed for WCGS under water solid conditions were:
a. FOR LIMITING MASS ADDITION LTOP MECHANISM Operation of one CCP and the NCP with instrument air failure resulting in the flow control valve in the letdown line failing closed (letdown isolation) and the flow control valve in the charging line failing open (maximum charging flow), and b. FOR LIMITING HEAT ADDITION LTOP MECHANISM Inadvertent start-up of a reactor coolant pump with a maximum 50 degrees F temperature mismatch between the RCS and the hotter steam generators.
These analyses, using the LOFTRAN computer code, take into consideration pressure overshoot and undershoot beyond the PORV open and close setpoints, which can occur as a result of time delays in signal processing and valve stroke times. The maximum expected pressure overshoot and undershoot calculated from the limiting mass input and heat input transients, in conjunction with the 10 CFR 50, Appendix G, pressure limits and reactor coolant pump No. 1 seal pressure limit, are utilized in the selection of the pressure setpoints for the PORV. The mass injection rate assumed in the design basis mass input transient is based on 100% flow capacity of the NCP and one CCP. The maximum combined pump flow has been assumed in order to envelop the maximum flow possible by the operational configuration that uses the NCP for charging with one CCP remaining operable, or the use of one CCP for charging with the NCP remaining operable, during shutdown modes.
OPERATING EXPERIENCE/PREVIOUS SIMILAR OCCURRENCES:
None