05000373/LER-2017-001

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LER-2017-001, Reactor Core Isolation Cooling System Inoperable Longer than Allowed by the Technical Specifications due to Low Suction Pressure Trips
Lasalle County Station, Unit 1
Event date: 12-16-2016
Report date: 02-08-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
LER closed by
IR 05000373/2017002 (3 August 2017)
3732017001R00 - NRC Website
LER 17-001-00 for LaSalle County, Unit 1, Regarding Reactor Core Isolation Cooling System Inoperable Longer than Allowed by the Technical Specifications due to Low Suction Pressure Trips
ML17039A744
Person / Time
Site: LaSalle, Lasalle Exelon icon.png
Issue date: 02/08/2017
From: Vinyard H T
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RA17-014
Download: ML17039A744 (4)


comments regarding burden estimate to the FO A Pnvacy and Information Collections Branch (T-5 F53), U.S Nuclear Regulatory Commssion, Washngton DC 20555-0001, or by e-mail to Infocollects.Resource@nrc.gov and to the Desk Officer, Off ce of :nformation 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 2. DOCKET NUMBER - 00

PLANT AND SYSTEM IDENTIFICATION

LaSalle County Station Unit 1 is a General Electric Boiling Water Reactor with 3546 Megawatts Thermal Rated Core Power. The affected system was Unit 1 Reactor Core Isolation Cooling System (RCIC).

CONDITION PRIOR TO EVENT

2017 001

DESCRIPTION OF EVENT

On October 18, 2016, while Unit 1 was in Mode 1 at 100% power, the Unit 1 RCIC system tripped on low suction pressure during a normal start that was being performed in accordance with the RCIC system pump operability valve test procedure, following completion of scheduled maintenance activities. Repairs were performed that restored the system to operability on October 20, 2016. A second event involving a Unit 1 RCIC system trip on low suction pressure occurred on November 17, 2016, revealing a related cause. Previously, the last successful RCIC operability test had been performed on August 27, 2016.

Background:

The RCIC system is provided to assure adequate core cooling in the event the reactor is isolated from its primary heat sink in conjunction with a loss of normal feed-water flow to the reactor vessel. The normal water flow path is from the Cycled Condensate Storage Tank through the RCIC pump and into the discharge line. Steam enters the turbine, where most of the energy is removed driving the turbine, and is then exhausted to the Suppression Pool through a check valve and motor operated exhaust isolation valve. The design of the RCIC system has various instrumentation monitoring performance parameters. Various RCIC turbine trip functions are provided, including low pump suction trip to protect against cavitation and lack of cooling that could cause damage to the pump. The RCIC turbine steam admission valve uses a logic in which the turbine speed demand is compared with the actual turbine speed and generates an error signal that is passed to the Electronic Governor Remote (EG-R). The EG-R interprets the signal to hydraulically position the governor valve to control steam admission to the RCIC turbine.

Event 1:

On October 18, 2016, at 22:23 CST, during start of the Unit 1 RCIC system post-maintenance test (PMT) surveillance following planned maintenance activities, the system tripped on low suction pressure. Troubleshooting identified the potential causes were related to the low-pressure switch out of calibration and the flow controller ribbon cable not seated correctly. Corrective actions included replacement of the pressure switch and the flow controller. Further troubleshooting was not performed due to successful RCIC startup following these initial troubleshooting actions. The RCIC system was declared operable and associated Technical Specifications (TS) timeclocks were exited on October 20, 2016, at 03:00 CST.

Event 2:

On November 17, 2016, at 11:00 CST, during start of the Unit 1 RCIC system for its quarterly surveillance, RCIC tripped on low suction pressure following fluctuations in suction pressure. All other parameters, including those in the field, were verified to be normal, and Unit 1 RCIC was placed in a safe configuration and declared inoperable. Troubleshooting determined the cause was degradation of the EG-R. In addition, rust was found on the oil port face, potentially restricting oil flow to the EG-R. The degraded EG-R was replaced with a new EG-R, and the degraded EG-R was sent off-site for component failure analysis. The PMT and a detailed review of historical performance data indicated improved EG-R governor positioning. The RCIC system was declared operable on November 20, 2016, at 19:05 CST.

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.

001 2017 - 00

CAUSE OF EVENT

The component that caused both of the low suction pressure trips was the EG-R hydraulic actuator for the RCIC governor valve. The EG-R component failure analysis (report dated December 16, 2016) determined the failure mechanism was due to the presence of internal iron oxide deposits on the control lands and on the inside of the bore. These deposits resulted in binding between precision internal components which caused intermittent operation of the EG-R. Rust deposits and wear was also noted on several actuator components, which suggested there had been moisture entrained in the oil.

The root cause for both of the Unit 1 RCIC low suction pressure trips was inadequate management of the EG-R hydraulic actuator PM strategy. The site did not perform preventative maintenance on Unit 1 RCIC EG-R on an interval that would prevent internal fouling from adversely affecting RCIC governor performance.

REPORTABILITY AND SAFETY ANALYSIS

This event is reportable in accordance with 10 CFR 50.73(a)(2)(0(8) as a condition prohibited by TS due to the failure to complete TS 3.5.3, Required Action A.2 within the specified Completion Time of 14 days. The Unit 1 RCIC inoperable period was from the first system trip on October 18, 2016, to when full restoration of the system was completed on November 20, 2016. The EG-R was determined by failure analysis completed on December 16, 2016, to be the failure mechanism that caused Unit 1 RCIC inoperability to be longer than the allowed 14-day Completion Time. The events for the October 2016 and November 2016 RCIC trips did not meet the reporting threshold in accordance with 10 CFR 50.72.

There were no safety consequences associated with the events since there was no loss of safety function. RCIC system is not an Engineered Safety Feature (ESF) system, and no credit is taken in the safety analyses for the RCIC system operation. RCIC does not meet the threshold for failure of a single train non-safety system since it is not included in the safety analysis. In addition, the Unit 1 High Pressure Core Spray (HPCS) system remained available during the period that the Unit 1 RCIC system was inoperable. There were no actual demands for either Unit 1 RCIC or Unit 1 HPCS during this period.

CORRECTIVE ACTIONS

The degraded EG-R was replaced. The degraded EG-R was sent off-site for component failure analysis. Post-maintenance testing and a detailed review of historical performance data indicated improved EG-R governor positioning. The Unit 1 RCIC system was declared operable on November 20, 2016, at 19:05 CST. A root cause investigation identified additional corrective actions, including actions to improve RCIC system trending and to develop and implement an appropriate PM strategy that includes EG-R device-specific replacement frequency and EG-R oil reservoir clean-flush frequency. The EG-R on the Unit 2 RCIC system was also successfully replaced as part of the extent of condition review.

PREVIOUS OCCURRENCES

A review of Licensee Event Reports for the past three years identified no previous similar occurrences at LaSalle Station.

COMPONENT FAILURE DATA

Part Description: Actuator, Hydraulic, Governor Manufacturer: Woodward Model No.: A9903-026

3. LER NUMBER