05000321/LER-2014-002
| Edwin I. Hatch Nuclear Plant Unit 1 | |
| Event date: | 05-01-2014 |
|---|---|
| Report date: | 06-27-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3212014002R00 - NRC Website | |
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send 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 intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes are for the High-Pressure Coolant Injection System (EIIS Code BJ), unless otherwise stated.
DESCRIPTION OF EVENT
On 5/1/2014 at 3:40 PM, with Unit 1 operating at 100 percent rated thermal power (RTP), condensation was found leaking out of the governor end gland seal and the coupling end of the High Pressure Coolant Injection (HPCI) turbine. By taking a temperature reading of the turbine casing, the steam supply isolation valve was shown to be leaking by to the HPCI Turbine Exhaust Drain Pot.
Even though the discovery of the condition occurred on 5/1/2014, further investigation revealed that certain conditions occurred prior to this date that contributed to this condition. On 3/4/2014 at 9:40 PM it was discovered that the HPCI Inlet Bypass air operated valve (AOV) was cycling. This valve will open and allow flow directly to the main condenser when the HPCI Inlet Drain Pot High Level setpoint is reached. The cycling of the valve was not accompanied with an annunciation "HPCI Turbine Inlet Drain Pot Level High" to the affected main control room (MCR) annunciator panel as expected with the HPCI Steam Supply valve (1E41-F001, EIIS Code BJ) confirmed closed. This anomaly was thought to be an annunciation problem, and the appropriate work orders were generated to determine the cause and correct the condition(s) present. However, the investigation was not properly prioritized and delayed the identification of the condition(s) that prevented the annunciation.
On 4/24/2014 the HPCI operability surveillance test was successfully performed. On 5/1/2014 it was identified that leakage past the steam supply valve was occurring based on input from the system engineer who had been monitoring the operation of the steam supply valve following the work performed on it in the recent Unit 1 2014 refueling outage. This is further supported by the fact that the system engineer specifically performs monthly HPCI system walkdowns and touches the turbine to confirm that the steam supply valve is not leaking. Prior to 5/1/2014 the most recent system walkdown by the system engineer was performed on 4/19/2014 at which time the HPCI turbine shell was cool to the touch. It is the engineer's judgment that following the HPCI surveillance on 4/24/2014 the steam supply valve did not completely seat resulting in leakage past the valve at that time which explains why this condition was not identified earlier during observations made in daily operator rounds. The leakage was sufficiently small to require approximately one week for condensation to build up to the point that it flowed from the HPCI turbine gland seals on 5/1/2014 at which time the HPCI turbine shell was too hot to touch.
On several occasions throughout the day on 4/30/2014 and 5/1/2014, annunciator "HPCI Room Instr Sump Lvl High" alarmed in the MCR. The associated annunciator response procedure allows operators to clear the alarm by cycling the HPCI room sump isolation valve. On 5/1/2014 condensation was observed leaking out of the governor end gland seal and the coupling end of the HPCI turbine. By taking a temperature reading of the turbine casing, the steam supply isolation valve (1E41-F001) was confirmed to be leaking by the valve to the HPCI turbine.
The HPCI system is designed to handle condensation that may result from leakage from the steam supply isolation valve and diverts residual condensate from the steam directly to the HPCI turbine exhaust drain pot. This is performed via a three-quarter inch gravity drain line upstream of the turbine stop valve. The turbine stop valve is normally closed when the system is not in operation.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send 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 intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.
Normal operation of the HPCI turbine exhaust drain pot is to drain to the HPCI Barometric Condenser on high level via the exhaust pot drain valve. This signal is given by the exhaust pot high level switch, which receives its power from a fuse that also provides power to the Exhaust Drain Pot Alarm Level Switch, and the Exhaust Drain Pot Low Level Switch. As a result it affects annunciation to the control room for Inlet Drain Pot High Level and Exhaust Drain Pot High Level. Unknown to Operations, at the time of the event, was the fact that the affected fuse was blown.
Due to the blown fuse, the exhaust drain pot drain valve no longer opened automatically on a high exhaust drain pot signal. As a result the steam condensate from the gravity drain line filled the exhaust drain pot, the turbine exhaust line, and the turbine itself and was not accompanied by HPCI Turbine Exhaust Drain Pot Level High annunciation in the MCR. Once the steam condensate filled the turbine casing to the point of the gland seal, it started leaking into the HPCI room instrument sump. The annunciator alarm for high sump level in the HPCI instrument room was received in the MCR and the situation was investigated further. The HPCI system was declared inoperable due to the unknown outcome of operation of the turbine with this level of water in the casing.
CAUSE OF EVENT
The cause of the event is seat leakage from the HPCI steam supply valve (1E41-F001) in conjunction with the fuse failure. The valve is an Anchor/Darling double disc parallel seat valve and seats at a 0 degree angle. Without the leak-by from the steam supply valve, the turbine casing and the Turbine Exhaust Drain Pot could not have filled with steam condensate. The fuse failure resulted in a loss of power to three Exhaust Drain Pot switches and the MCR annunciation for Inlet and Exhaust Drain Pot high level. This prevented the HPCI Exhaust Drain Pot from draining through the automatic opening of the drain valve, and prevented the notification to the MCR that the drain pot was not draining as intended.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable in accordance with Title 10 of the Code of Federal Regulations (CFR), Part 50.73(a)(2)(v)(D) because an event, or a condition existed, that could have prevented the fulfilment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
Even though HPCI is not credited in Hatch's design basis accident, suction on recirculation break, in the Loss Of Coolant Accident (LOCA) analysis to mitigate the consequence of an accident, this condition is being reported under this section of the CFR. The HPCI system is designed to provide adequate cooling to limit fuel-clad temperature in the event of a small break in the nuclear steam supply system that does not result in rapid depressurization of the reactor vessel. The Automatic Depressurization System (ADS) is the redundant system for the HPCI system and is initiated on low reactor water level condition coincident with a Primary Containment high pressure condition and one of the Low Pressure Coolant Injection (LPCI) or Core Spray (CS) low pressure pumps in operation. Upon initiation of ADS, the reactor is depressurized to a point where either the LPCI system or the CS system can operate to maintain adequate core cooling. This capability was maintained during the time the HPCI turbine casing contained an unacceptable level of water present.
The CS system, the LPCI system, and ADS system were operable during the time the condition was present. In the event of an accident, these systems would have been capable of mitigating the consequences of an accident in the absence of the HPCI system. Based on this information, this event has very low safety significance.
CORRECTIVE ACTIONS
Maintenance manually cycled the HPCI Turbine Exhaust Drain Pot Isolation Valve in order to drain the HPCI turbine of condensation.
The blown fuse was replaced and the Exhaust Drain Pot Drain Valve opened as designed to allow flow to the barometric condenser. The fuse is being verified to be functional once per shift on an ongoing basis by confirming the Exhaust Drain Pot Level Switches have power. Additionally, administrative controls were put in place to ensure the Exhaust Drain Pot continues to be drained once per shift. These will be ongoing actions until the steam supply valve can be repaired during the next Unit 1 refueling outage or the valve is confirmed to be no longer leaking if better seating is established.
ADDITIONAL INFORMATION
Other Systems Affected: None.
Failed Component Information:
Master Parts List Number: 1E41-F001 EIIS System Code: BJ Manufacturer: Anchor/Darling Reportable to Epix: Yes Valve Co. (A391) Model Number: 19023 Root Cause Code: - EllS Component Code: ISV Commitment Information: This report does not create any new licensing commitments.
Previous Similar Events:
In 2000, on Hatch Unit 2, HPCI was being tested when water was found spraying from the area of the main pump outboard mechanical seal. When the pump was shutdown, maintenance personnel found the seal cavity full of water and its drain line clogged. Personnel unclogged the drain line and then discovered that the oil level was above the high water mark. Further tests found that water intrusion had happened in the oil system.