05000461/LER-2016-009
| Clinton Power Station, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 4612016009R00 - NRC Website | |
| ML16238A478 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 08/22/2016 |
| From: | Stoner T R Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-009-00 | |
| Download: ML16238A478 (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.
PLANT AND SYSTEM IDENTIFICATION
General Electric—Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX]
EVENT IDENTIFICATION
Trip of Fuel Building Fans Due to Damper Failure Results in Loss of Secondary Containment A. Plant Operating Conditions before the Event Unit: 1 Mode: 1 Event Date: 06/24/16 Mode Name: Power Operation Event Time:
Reactor Power:
1511 99 percent
B. DESCRIPTION OF EVENT
On June 24, 2016 at 1511-(CST) Clinton Power Station (CPS) was operating at 99 percent reactor power when the MCR received two unexpected annunciators associated with the Fuel Building ventilation system (VF), 5042-4D (Trouble VF system local panel 1PL44J) and 5042-5D (Hi Diff Press Fuel Bldg). Subsequent investigation determined that VF exhaust fan isolation damper 1VF11YA had failed closed as a result of a failure of solenoid 1FSVVF005. As a result, Secondary Containment (SC) vacuum degraded, eventually exceeding the Technical Specification (TS) limit of 0.25 inch vacuum water gauge (WG). Both the Fuel Building (FB) `B' supply and exhaust fans auto started as designed, to restore SC vacuum, however, the sequence was not timely enough to prevent the FB differential pressure from exceeding the TS requirement. TS Limiting Condition for Operation (LCO) 3.6.4.1, Secondary Containment, Required Action A.1 and Emergency Operating Procedure (EOP) — 08, Secondary Containment Control were entered. The momentary loss of the VF fans also resulted in no flow through the VF exhaust ductwork and; therefore, duct monitors 1RIX-PROO6A-D were declared inoperable. The lack of monitored VF exhaust flow associated with LCO 3.3.6.2, Secondary Containment Isolation Instrumentation, Fuel Building exhaust radiation resulted in a momentary loss of SC isolation capability and Standby Gas Treatment System (SGTS) initiation capability on VF exhaust high radiation. As a result of this condition, LCO 3.3.6.2 Required Actions A.1 and Action B.1 were entered. At 1512, SC vacuum was restored within TS limits following the auto start of supply fan 1VFO3CB and exhaust fan 1VFO4CB. TS LCO 3.6.4.1 Required Action A.1 and TS LCO 3.3.6.2 Required Actions A.1 and B.1 were subsequently exited.
At 1602, EOP-08 was exited.
CPS replaced failed solenoid valve 1FSVVF005. In addition, Exelon PowerLabs evaluated a similar failed ASCO solenoid valve in determining a cause of component failure. The failure conditions of this valve were similar based on observations by field technicians. CPS concluded the apparent cause of ASCO solenoid valve 1FSVVF005 failure was due to sticking as a result of a slightly deformed and worn core. The Powerlabs evaluation further attributed the most likely cause of the initiating event to a manufacturing defect in the solenoid valve due to its low inservice time (11 months).
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
2016 - 00 009
C. CAUSE OF EVENT
The apparent cause of this event is the failure of the ASCO solenoid valve, 1FSVVF005, due to sticking as a result of a slightly deformed and worn core. Due to its low inservice time (11 months), the most likely cause of the initiating event is a subtle manufacturing defect.
D. SAFETY ANALYSIS
There were no safety consequences associated with this event described in this report. The event is reportable in accordance with 10CFR50,73(a)(2)(v)(C) as a condition that could have prevented fulfillment of a safety function to control the release of radioactive material because SC was declared inoperable.
The SGTS system was fully operable at the time of the event and capable of performing the required safety function. Operations entered EOP-08 for SC vacuum less than minus 0.25 inch WG and entered TS LCO 3.6.4.1 Required Action A.1. SC vacuum was restored to within TS limits within the completion time requirement. The SC vacuum is kept slightly negative relative to the atmospheric pressure to prevent leakage to the atmosphere. The VF system is a non- safety ventilation system which is normally in service to maintain SC vacuum. The SGTS system is the safety-related system which is relied upon to perform this function following an accident. During the event both VF 'B' supply and exhaust fans auto started as designed and restored SC to operability consistent with its design function. In addition, the SGTS system remained available to respond to an accident condition throughout this event. Therefore, the ability of the station to maintain secondary containment in an accident scenario was never jeopardized or challenged by the VF system fan trip.
Because the SGTS remained available to restore SC vacuum in event of an accident, this event report does not constitute a safety system functional failure.
E. CORRECTIVE ACTIONS
The failed component, 1FSV-VF005, was replaced and the VF system was restored to normal operation. Additional maintenance activities are planned for the VF system including establishing preventative maintenance tasks for the replacement of solenoid operated valves and rebuilding a damper actuator on a periodic basis. Additional parts quality testing is being established for VF damper solenoids to identify manufacturing defects prior to placing them in service.
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
2016 - 00 009
F. PREVIOUS SIMILAR OCCURENCES
Fuel Building Ventilation System And Loss Of Secondary Containment Differential. Pressure The cause of this event was the VF system inboard exhaust isolation damper 1VFO7Y air supply solenoid was prematurely degraded and caused the damper to isolate the VF system flow-path during the Main Control Room Ventilation (VC) Train B startup, resulting in a VF system trip and a subsequent loss of SC. The troubleshooting team concluded that during the VC Train B startup, the air supply solenoid on the VF system inboard exhaust isolation damper 1VFO7Y responded to a minor perturbation of the supply voltage or a surge of current on the bus by repositioning (dropping out) because the solenoid was weak or degraded, resulting in isolation of the VF system inboard exhaust isolation damper. The VF system inboard exhaust isolation damper failed closed, thus fulfilling its safety function.
G. COMPONENT FAILURE DATA
Component Description: Solenoid Valve (ASCO Red Hat II) Model Number HB8320G001