|Quad Cities Nuclear Power Station Unit 1|
|2542017004R00 - NRC Website|
|Person / Time|
Exelon Generation Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML18005A276 (5)|
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
004 2017 00
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Unit 1 HPCI Did Not Trip Due to Wear Debris in the Turbine Stop Valve Oil Resetting Solenoid
A. CONDITION PRIOR TO EVENT
Unit: 1 Reactor Mode: 1 Event Date: November 7, 2017 Event Time: 18:10 hours Mode Name: Power Operation Power Level: 100%
B. DESCRIPTION OF EVENT
On November 7, 2017 at1810 hours
, during performance of the quarterly High Pressure Coolant Injection (HPCI) [BJ] Pump Operability test, the Unit 1 HPCI turbine [TRB] failed to trip when the remote HPCI Turbine Trip pushbutton [HS] was depressed. Operations directed the shutdown of the Unit 1 HPCI system by isolating the HPCI steam supply valves [ISV], causing HPCI flow to reduce to 0 GPM. After the isolation was completed, Unit 1 HPCI was declared inoperable but available. There were no other structures, systems or components (SSC) inoperable during this event time period that could have contributed to this event. After troubleshooting, the internal HPCI stop valve oil resetting solenoid [PSV] was replaced. Following the replacement of the solenoid valve, the HPCI system was declared operable on November 8, 2017 at2335 hours
C. CAUSE OF EVENT
The cause of the HPCI turbine failure to trip was determined to be accumulation of wear debris within the HPCI stop valve oil resetting solenoid valve causing the solenoid valve to stick in the energized position. The wear debris was caused by a manufacturing deficiency.
D. SAFETY ANALYSIS
System Design According to the Quad Cities Nuclear Power Station (QCNPS), Units 1 and 2 Updated Final Safety Analysis Report (UFSAR) Section 126.96.36.199, the HPCI subsystem is designed to pump water into the reactor vessel under Loss of Coolant Accident (LOCA) conditions which do not result in rapid depressurization of the pressure vessel. The loss of coolant might be due to a loss of reactor feedwater or to a small line break which does not cause immediate depressurization of the reactor vessel. The sizing of the HPCI subsystem is based upon providing adequate core cooling during the time that the pressure in the reactor vessel decreases to a value that the Core Spray [BM] subsystem and/or the Low Pressure Coolant Injection (LPCI) [BO] subsystem become effective. The HPCI subsystem is designed to pump 5600 gallons per minute into the reactor vessel within a reactor pressure range of comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resourcenrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may rot conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
004 2017 00 about 1120 pounds per square inch gage (psig) to 150 psig. Initiation of the HPCI subsystem occurs automatically on signals indicating reactor low-low water level or high drywell pressure. HPCI injection into the reactor vessel may be accomplished manually by the operator or without operator action by the HPCI automatic initiation circuitry. HPCI can also operate in a pressure control mode of consuming steam from the reactor vessel without providing full injection into the vessel (down to and including zero injection).
Safety Impact The safety significance of this event is minimal. The HPCI Turbine Stop Valve would not trip, however this did not impact the injection function of HPCI, until the system was isolated via the steam supply valves. The HPCI steam supply valves would have to be manually opened to allow HPCI to function as an injection system. The HPCI system was declared inoperable but available once the steam supply valves were closed.
Since HPCI is a single train safety system, this notification is being made in accordance with 10 CFR 50.73 (a)(2)(v)(D), Event or Condition that Could Have Prevented Fulfillment of a Safety Function.
Risk Insights Automatic HPCI trip failure is represented in the Quad Cities Full Power Internal Events (FPIE) PRA model, which includes the HPCI turbine steam stop valve and others to manually control HPCI and prevent level overfill. The accident sequences involved are Automatic Transit without a Scram (ATWS) sequences, for which a HPCI trip failure leads to Boron dilution. ATWS sequences contribute about 3.7% to Core Damage Frequency (CDF). This assessment looks at the oil resetting solenoid valve trip failure. The PRA assessment found that there is minimal risk impact since the changes in CDF and LERF due to the HPCI (mechanical) trip failure are very small.
E. CORRECTIVE ACTIONS
1. Replaced solenoid valve internal to HPCI Turbine Stop Valve and verified proper operation.
1. Evaluate PM frequency change for Turbine Stop Valve internal solenoid valve replacements. Also evaluate current design for improvement by changing solenoid valve model or manufacturer.
F. PREVIOUS OCCURRENCES
The Station events database, LERs, and INPO Consolidated Event System (ICES) were reviewed for similar events at Quad Cities Nuclear Power Station. This event was attributed to wear debris in the HPCI Turbine Stop Valve oil resetting solenoid valve.
No previous occurrences applicable to the circumstances of this event were identified in this search.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to infocollects.Resource:'y nrc.gov. and to the Desk Officer, Office cf Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may riot conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
004 2017 00
G. COMPONENT FAILURE DATA
Failed Equipment: Solenoid Valve Component Manufacturer: Barksdale Component Model Number: Q165A322BBG-1 Component Part Number: N/A This event has been reported to ICES as Report No. 426159