|Lasalle County Station, Unit 2|
|Reporting criterion:||10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident|
|LER closed by|
|IR 05000373/2017002 (3 August 2017)|
IR 05000373/2017004 (13 February 2018)
|3742017002R00 - NRC Website|
|Person / Time|
|From:||Vinyard H T|
Exelon Generation Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17089A657 (4)|
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 Infocolleets.Resource@nrc.goy, 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 2. DOCKET NUMBER - 00
PLANT AND SYSTEM IDENTIFICATION
LaSalle County Station Unit 2 is a General Electric Boiling Water Reactor with 3546 Megawatts Thermal Rated Core Power.
The affected system was the Division 3 Diesel Generator Cooling Water (DGCW) system, which is a support system for the High Pressure Core Spray (HPCS) system and associated Division 3 Emergency Diesel Generator.
CONDITION PRIOR TO EVENT
Unit(s): 2 Reactor Mode(s): 1
DESCRIPTION OF EVENT
Event Date: January 30, 2017 Event Time: 1908 CST Mode(s) Name: Power Operation Power Level: 98 percent On January 30, 2017, during monthly operability surveillance testing of the Unit 2 Division 3 DGCW system, the cooling water strainer backwash valve 2E22-F319 was unable to open when the strainer control switch was selected and during subsequent manual operation of the valve. The valve was eventually able to be closed; however, no flow was detected during the manual backwash operation. The Division 3 DGCW system was declared inoperable. Upon investigation, operators determined the cause of the valve malfunction was due to stem-disc separation.
The Division 3 DGCW system is a support system for the HPCS system and the associated Division 3 Emergency Diesel Generator. The required actions of Technical Specifications (TS) 3.7.2 were entered on January 30, 2017 at 1908 CST when the 2B DGCW system was declared inoperable. Required Action (RA) A.1 was immediately completed to declare the supported HPCS system inoperable. TS 3.5.1 RA B.1 to administratively verify the Reactor Core Isolation Cooling (RCIC) system operability was completed immediately, and RA B.2 was entered to restore HPCS to operable status within 14 days. TS 3.8.1 was not applicable since a note provides that Division 3 AC electrical power sources are not required to be operable when HPCS is inoperable. An Emergency Notification System (ENS) report 52519 was made on January 30, 2017 in accordance with 10 CFR 50.72(b)(3)(v)(D), for an event or condition that could have prevented fulfillment of the safety function of structures or system that are needed to mitigated the consequences of an accident.
CAUSE OF EVENT
The Division 3 DGCW strainer backwash valve 2E22-F319 was unable to open due to stem-disc separation within the valve body. The apparent cause of the stem-disc separation was erosion due to the carbon-steel valve internals in a raw water system environment. The use of carbon steel valves and components in raw water systems led to the valve component's accelerated corrosion and pitting.
Contributing causes include extension of preventative maintenance (PM) to replace the valve beyond the life of valve 2E22- F319, and T-gap measurement used to determine valve health requires optimization. The use of carbon steel valves in raw water systems was first evaluated in 1996 as an operational vulnerability at LaSalle Station. The valve failed prior to its scheduled replacement in November 2017.
REPORTABILITY AND SAFETY ANALYSIS
This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of the safety function of structures or system that are needed to mitigate the consequences of an accident. This condition could have prevented the HPCS system, a single train safety system, from performing its design function, to provide cooling to the required equipment, which rendered the cooling water system inoperable in accordance with TS 3.7.2, Diesel Generator Cooling Water (DGCW) System.
2017 002 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
2017 - 00 002 There were minimal safety consequences associated with the event since other emergency safety systems remained operable, including emergency core cooling system (ECCS) systems for Division 1 and Division 2 and their associated emergency diesel generators. The DGCW system remained functional as the system retained the ability to provide the required flow through the system. However, this event was considered a safety system functional failure, as defined in accordance with NEI 99-02, Regulatory Assessment Performance Indicator Guideline.
The station performed troubleshooting to identify the initial condition of the valve. The Division 3 DGCW strainer backwash valve 2E22-F319 was cut out and replaced by a new stainless steel type. The degraded valve was sent offsite for component failure diagnostics and analysis. An apparent cause investigation was performed which determined the cause of the valve's stem-disc separation was accelerated corrosion and pitting of the carbon-steel valve internals in a raw water system environment.
The extent of condition applies to the Unit 1 and Unit 2 DGCW and core standby cooling system (CSCS) valves that are exposed to a raw water environment. Some of these valves have been replaced with stainless-steel components, while other valves are scheduled for replacement in future refueling outages.
A review of LaSalle Station Licensee Event Reports for the past three years, related to stem-disc separation issues or HPCS system issues, identified the following similar instance at LaSalle Station.
On December 29, 2014, Unit 2 was in Mode 1 at 100 percent power with a operability test in progress on the 2B DG. During performance of the test, operators noticed a small leak of about one drop per second coming from the casing of the 2B HPCS DGCW pump. The 2B DG and supported HPCS system were declared inoperable. The station entered TS 3.5.1 Required Actions B.1 to verify the RCIC system was operable and B.2 to restore HPCS to operable status within 14 days. Examination of the pump casing determined the apparent cause of the leak was erosion from impeller flow impingement. The pump was replaced and returned to service on January 3, 2015. This event did not involve stem-disc separation in a valve; however, it was related to a failure affecting performance of the HPCS system.
COMPONENT FAILURE DATA
Manufacturer: Anchor Darling (A391) Device: Gate Valve, 4-inch, Carbon-Steel Component ID: Model 94-14040