05000354/LER-2013-009
| Hope Creek Generating Station | |
| Event date: | 12-05-2013 |
|---|---|
| Report date: | 04-04-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 49608 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3542013009R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric— Boiling Water Reactor {BWR/4} Main Turbine— EIIS Identifier {TNTRB}* Moisture Separator— EllS Identifier (SB/MSR)* Moisture Separator Dump Valve {SB/LCV} Reactor Protection System — EDS Identifier {JC}* Reactor Recirculation Pumps— EDS Identifier {AD/P} Safety Relief Valves - EDS Identifier {SB/RV} * Energy Industry Identification System (EDS) codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF EVENT
Event Date: December 5, 2013 Discovery Date: December 5, 2013
CONDITIONS PRIOR TO EVENT
Hope Creek was in Operational Condition (OPCON) 1 operating at approximately 75 percent rated thermal power.
No other structures, systems or components were inoperable at the time of the event.
DESCRIPTION OF EVENT
On December 5, 2013, at 03:25 EST Hope Creek Unit 1 was operating at approximately 75 percent rated thermal power with the 'A' moisture separator (MS) {SB/MSR} high level control loop in the process of being tuned. The high level control loop consists of the MS dump valve (SB/LCV), the valve controller, and the level transmitter.
During tuning, the MS drain valves were closed so that the MS level could be controlled by the MS dump valve. The dump valve cycled open and closed. Technicians were unable to open the MS drain or dump valves for approximately two minutes. With the dump and drain valves closed, the MS level increased to the setpoint for a turbine trip signal.
The main turbine {TA/TRB} trip caused an actuation of the reactor protection system {JC} resulting in an automatic reactor scram. The recirculation pumps {AD/P} tripped as expected. All control rods inserted as required and no automatic emergency core cooling system (ECCS) or reactor core isolation cooling (RCIC) system initiations occurred. The plant was stabilized in hot shutdown (OPCON 3).
During the recovery of the recirculation pumps, the digital electro-hydraulic control (DEHC) system was mis-operated which caused the turbine bypass valves to cycle. This caused reactor level to swell above Level 8 then shrink below Level 3 resulting in a second actuation of the reactor protection system.
A four-hour NRC Emergency Notification System (ENS) notification was required by 10 CFR 50.72(b)(2)(1v)(B) for an actuation of RPS when the reactor was critical. The ENS notification (#49608) was completed on December 5, 2013, at 05:40. An eight-hour NRC ENS notification was required by 10 CFR 50.72 (b)(3)(iv)(A) for an event that results in a valid actuation of RPS. This event involved two automatic actuations of RPS; the second RPS actuation was reported at 10:00 via an update to ENS # 49608. This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A).
CAUSE OF EVENT
A causal evaluation determined the failure of the MS dump valve was due to thermal binding. The valve dimensional clearances were based on analysis performed at thermal equilibrium; however, the assumption of thermal equilibrium is not valid for all thermal events when temperature rise is not uniform throughout the valve.
Organizational and programmatic issues associated with risk recognition contributed to the scram during power ascension activities. Existing station procedures lacked sufficient detail to ensure startup exceptions or constraints were tracked to completion. In addition, all unrefuted or non-conclusive causes identified during troubleshooting were not adequately dispositioned.
The second actuation of the reactor protection system was caused by mis-operation of the digital electro-hydraulic control (DEHC) system, due to crew knowledge deficiencies, poor communication, and failure to adhere to procedures.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event. The high moisture level in the 'A' MS resulted in a main turbine trip and subsequent automatic reactor scram. All control rods inserted. All reactor protection systems functioned as designed. All systems responded as expected. There were no consequences from the second RPS actuation since the reactor was already in hot shutdown (OPCON 3). No ECCS or RCIC initiation setpoints were reached in either the first scram or the second RPS actuation. The plant was stabilized in hot shutdown after the reactor was depressurized to allow the start of a reactor recirculation pump.
SAFETY SYSTEM FUNCTIONAL FAILURE
A review of this event determined that a Safety System Functional Failure (SSFF) did not occur as defined in Nuclear Energy Institute (NEI) 99-02, "Regulatory Assessment Performance Indicator Guideline." This event did not prevent the ability of a system to fulfill its safety function to either shutdown the reactor, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
PREVIOUS EVENTS
A review of events for the past three years at Hope Creek was performed to determine if a similar event had occurred. A similar event occurred on December 1, 2013, and is documented in LER 2013-008-00.
CORRECTIVE ACTIONS
1. A design change was implemented modifying control of the MS dump valve from a modulating function to a full open function on high level.
2. During the next refueling outage, the MS dump valves will be modified to prevent thermal binding.
3. The integrated operating procedures for plant startup will be revised to incorporate requirements for complete documentation of operational constraints and full disposition of each constraint by Operations or Senior Station management.
4. The troubleshooting procedure will be revised to require entering the operational decision making process for any unrefuted or non-conclusive causes identified.
5. Other corrective actions are tracked in the corrective action program.
COMMITMENTS
This LER contains no commitments.