|Quad Cities Nuclear Power Station Unit 1|
|Reporting criterion:||10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident|
|2542017003R00 - NRC Website|
|Person / Time|
Exelon Generation Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17321A065 (5)|
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Ccmmission, Washington, CC 20555.0001, or by e-rna.: to Infocollects.Rescurce@nrc.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 not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
2017 - 00 003
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].
Control Room Emergency Ventilation Air Conditioning Compressor Discharge Pipe Fitting Refrigerant Leak
A. CONDITION PRIOR TO EVENT
Unit: 1 Reactor Mode: 1 Event Date: September 21, 2017 Event Time:1550 hours
Mode Name: Power Operation Power Level: 100%
B. DESCRIPTION OF EVENT
On 09/21/2017 at 1550, Operations started Control Room Emergency Ventilation (CREV) Air Conditioning (AC)[CMP] for Tracer Gas Testing. Per Operations instructions, Mechanical Maintenance went to inspect the Control Room Emergency Ventilation system for refrigerant leaks before Tracer Gas Testing was started. Mechanical Maintenance reported a refrigerant leak on the discharge piping [PSF] of the compressor, right above the inlet to the condenser [GOND]. The leak was at the expansion joint of a fitting. Operations declared the refrigeration condensing unit (RCU) of Train B of Control Room HVAC inoperable at 1730 and entered Technical Specification (TS) 3.7.5 Condition A.
The refrigerant leak was minimal, which allowed the Air Conditioning Compressor to run and maintain Control Room Temperature before it was secured. This event is a Maintenance Rule Functional Failure for the Control Room Emergency Ventilation system.
C. CAUSE OF EVENT
The cause of the refrigerant leak on the Control Room Emergency Ventilation Air Conditioning compressor discharge pipe fitting was due to a high cycle fatigue crack that initiated at the root of expansion joint transition on the outer surface. No material anomalies were associated with the crack origin. The compressor discharge piping is approximately five linear feet in length with two 90-degree bends and enters the condenser at a 45-degree angle.
Adding a support to the short length of pipe would not reduce the vibrations or stress acting on the pipe. A contributing factor to the high cycle fatigue was that the lifespan (20 yrs) of the fitting was reduced because of high vibration conditions it experienced during a portion of its installed life. Three previous compressor failures (2005, 2009 & 2011) caused the high vibration conditions.
D. SAFETY ANALYSIS
System Design The purpose of the Control Room Emergency Ventilation system is to maintain the proper air environment for instrumentation and personnel in the Control Room. The Train B CREV AC system is a single train safety-related system that is designed to maintain design temperature in the Control Room Envelope (CRE) under post-accident Estmated burden per response to comply with this mandatory cdlecton request:80 hours
. Reported comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currentty 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
2017 - 00 003 conditions. The loss of the CREV AC could impact the plant's ability to mitigate the consequences of an accident. The Train B CREV Refrigeration Condensing Unit (RCU) 0-9400-102 is a Carrier reciprocating compressor; Model 5H120, with a capacity of 90 tons. The backup to the Train B CREV system is the Train A Control Room HVAC system, which is a non-safety-related system.
Safety Impact The safety significance of this event was minimal. The CREV system filtration capability was not lost, and control room temperature was maintained during this event. In addition, the non-safety related Train A Control Room HVAC system was available throughout this event. Although the refrigerant leakage was small, CREV AC could not be relied upon to fully perform its safety function during an accident.
Risk Insights The CREV AC system is not explicitly modeled in the Plant Probabilistic Risk Assessment (PRA). Certain Operator Actions (OAs) are modeled in the PRA; however, the effect of this event on OA human error probabilities (HEPs) would have a negligible quantitative impact on the calculated Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) since loss of CREV AC events reduce temperature control of the Control Room temperature as slow progressing events. In the loss of CREV system event, station procedures direct the opening of doors and use of temporary fans, as necessary. Applicable operator training is performed on these actions, and the equipment is pre-staged as a part of the station blackout response requirements.
Although opening Control Room doors to support room cooling would introduce the increased potential for radiological or chemical events impacting the Main Control Room habitability, the probability of a loss of Control Room HVAC event coincident with a radiological or chemical event is small and therefore, would also have a negligible quantitative impact on CDF and LERF.
In conclusion, the degradation of the 0-9400-102 CREV AC compressor discharge pipe fitting was not risk significant.
E. CORRECTIVE ACTIONS
1. The failed Control Room Emergency Ventilation compressor discharge pipe fitting was replaced.
2. Since the three previous compressor failures (2005,2009 & 2011) that caused high vibration conditions were corrected via a compressor modification, the new compressor discharge pipe fitting is expected to function beyond the life of the plant.
F. PREVIOUS OCCURRENCES
The station events database, LERs, and INPO ICES were reviewed for similar events at Quad Cities Nuclear Power Station. This event was primarily attributed to high cycle fatigue on the Control Room Emergency Ventilation Air Conditioning compressor discharge pipe fitting.
No previous occurrences applicable to the circumstances of this event were identified in this search.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NEOB-10202, (3150-01041, Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currency 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
2017 - 00 003
G. COMPONENT FAILURE DATA
Failed Equipment: Control Room HVAC Compressor Discharge/Condenser Inlet Pipe Fitting Component Manufacturer: Mueller Brass Company Component Model Number: W-1381 This event has been reported to ICES under record #423784.