05000293/LER-2013-006
| Pilgrim Nuclear Power Station | |
| Event date: | |
|---|---|
| Report date: | |
| 2932013006R00 - NRC Website | |
BACKGROUND:
The Pilgrim Station Core Standby Cooling systems (CSCS) consist of the High Pressure Coolant Injection (HPCI) system, Automatic Depressurization system (ADS), Residual Heat Removal (RHR) System Low Pressure Injection (LPCI) mode, and Core Spray (CS) system. The HPCI system is designed to pump water into the reactor vessel for high pressure core cooling. Although not part of the CSCS, the reactor core isolation cooling (RCIC) system is also designed to pump water into the reactor vessel for high pressure core cooling, The HPCI System flow indicating controller (FIC-2340-1) installed in the Main Control Room functions to maintain a process flow at a desired set-point. The controller provides for both manual and automatic process control and has an internal set-point control circuit. The controller compares a process variable (HPCI flow from FT-2358) with a control set-point (normally set at 4250 gpm).
Engineering Change EC12967 was issued to replace obsolete GMAC HPCI flow controllers with NUS Instrument Corporation Model PID901-540 flow controllers. These NUS flow controllers were reverse engineered and intended to be equivalent replacements. On 2/24/13 the NUS HPCI System flow controller was installed in the Main Control Room and successfully tested to verify operability.
On May 23, 2013, the plant was starting up from a Refueling Outage (RFO-19). In accordance with Technical Specification (TS) 3.5.C.1, the HPCI System is required to be tested at a reactor pressure of 150 psig to verify system operability. Procedure 8.5.4.3 provides test criteria for system operability and ensures that the system automatically starts and can control flow at or above 4250 gpm. The HPCI system was operated on May 23, 2013 at 0034 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> and met test criteria. Subsequent HPCI system runs were planned to address post maintenance test requirements.
EVENT DESCRIPTION:
On May 23, 2013, at 1050 hours0.0122 days <br />0.292 hours <br />0.00174 weeks <br />3.99525e-4 months <br />, during plant start-up from RFO-19 with the reactor at 2% core thermal power, reactor pressure at - 525 psig, and the mode switch in the Startup/ Hot Standby position, PNPS declared the HPCI system inoperable due to failure of the HPCI flow indicating controller to maintain system discharge flow rate above 4250 gpm while in the automatic mode from the Main Control Room during planned post maintenance testing. Limiting Condition for Operation (LCO) actions for Technical Specification 3.5.C.2 were entered.
CAUSE OF THE EVENT:
The apparent cause evaluation identified that the direct cause of the HPCI system failure was flow controller FIC-2340-1 out of calibration by 550 gpm due to degradation of the flow controller automatic (null) control/output circuit.
The apparent cause evaluation was based on removal of the flow controller, bench testing, and implementing a detailed troubleshooting plan.
PID901-540 flow controllers are installed in the HPCI system, RCIC system, and Control Rod Drive (CRD) system. Based on system testing, the condition was only identified in the HPCI flow controller located in the Main Control Room.
CORRECTIVE ACTIONS:
Corrective actions completed included troubleshooting, bench testing, and successful recalibration and adjustment of the HPCI flow controller. Post calibration testing confirmed stable operation of the flow controller during HPCI System Operability test runs.
Corrective actions planned include:
- Replace the installed Main Control Room HPCI flow controller.
- Send the replaced flow controller to the vendormanufacturer for evaluation.
- Revise flow controller calibration procedures as necessary to address adequate guidance/steps to check for the degradation that caused this event.
- After vendor evaluation, incorporate appropriate revisions into applicable procedures and document actions in the Corrective Action Program (CAP).
These corrective actions will be tracked in the Corrective Action Program via CR-PNP-2012-4286.
ASSESSMENT OF SAFETY CONSEQUENCES:
The event occurred during power ascension from RFO-19. Core Thermal Power was at approximately 2% and reactor pressure was approximately 525 psig.
CSCS systems include HPCI, ADS, CS, and RHR - LPCI mode. Although not part of the CSCS systems, the RCIC system is capable of providing water to the reactor vessel for high pressure core cooling, similar to the HPCI system.
During the time period that HPCI flow controller was out of service, the ADS, CS, RHR, and RCIC systems were either operable or available. These systems provided capability to supply makeup water to the vessel and ensured adequate core cooling while the HPCI system was not operable. During the event, the HPCI system automatically started and controlled flow at slightly less than 4250 gpm. HPCI system was restored to operable status and there was no long term safety significance associated with the event.
The bounding case of risk assessment was failure of the HPCI pump to operate. This would result in an increase in core damage frequency (CDF) of 3.66E-6/reactor year. The exposure time is estimated from when the last successful run of the HPCI Pump was performed on 5/23/13 at 0034 hrs until the HPCI System and flow controller was tested satisfactorily on 5/24/13 at 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />. This results in approximately 26 hours3.009259e-4 days <br />0.00722 hours <br />4.298942e-5 weeks <br />9.893e-6 months <br /> of exposure time and the incremental core damage probability (ICDP) is 5.43E-9, which is non-risk significant.
REPORTABILITY
This event was reported to the USNRC via Event Report #49064 on 5/23/2013 pursuant to 10 CFR 50.72(b)(3)(v)(B) and (D) - Any event or condition that at the time of discovery could have prevented fulfillment of the safety function of structures or systems that are needed to: Remove residual heat and Mitigate the consequences of an accident.
A review of Pilgrim Station License Event Reports (LERs) issued since year 2000 was performed. The focus of the review was LERs that involved loss of HPCI system function or loss of system function due to flow controller malfunction. The following LERs were reviewed:
LER-2004-002 - HPCI System Inoperable Due to Fuse Failure in Gland Seal Condenser Circuit.
These LER events do not identify any similar failure mechanisms to that described in this LER.
In March 2012, Pilgrim Station identified defects in NUS Model PID901-540 flow controllers that were purchased to replace HPCI and RCIC System flow controllers (Condition Report CR-PNP-2012-1406). A manufacturer report was generated to document the 10 CFR Part 21 Evaluation (No. 21-12-09). The issue specifically addressed relates to flow controller setpoint thumbwheel manufacturing assembly defects. Pilgrim sent the all flow controllers back to the manufacturer for reconditioning.
The condition addressed in this LER event report differs from the manufacturing defects evaluated in the vendor's Part 21 evaluation.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES The EllS codes for Components and Systems referenced in this report are as follows:
COMPONENTS CODES
Flow Indicating Controller FIC
SYSTEMS
High Pressure Coolant Injection (HPCI) BJ
REFERENCES:
Condition Report CR-PNP-2013-4286 and the associated Apparent Cause Evaluation Report; HPCI Flow Controller Failure to Achieve Rated Flow While in Auto.
Condition Report CR-PNP-2012-1406, NUS Model 901-540 Flow controller defects.