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Broken Valve in Emergency System at LaSalle Nuclear Plant via Union of Concerned Scientists

An NRC Special Inspection Team (SIT) conducted an inspection at the LaSalle Nuclear Plant this spring to investigate the cause of a valve’s failure and assess the effectiveness of the corrective actions taken.

The two units at Exelon Generation Company’s LaSalle County nuclear plant about 11 miles southeast of Ottawa, Illinois are boiling water reactors (BWRs) that began operating in the early 1980s. While most of the BWRs operating in the U.S. are BWR/4’s with Mark I containment designs, the “newer” LaSalle Units feature BWR/5’s with Mark II containment designs. The key distinction for this commentary is that while BWR/4’s employ steam-driven high pressure coolant injection (HPCI) systems to provide makeup cooling water to the reactor core in event that a small pipe connected to the reactor vessel breaks, the BWR/5’s use a motor-driven high pressure core spray (HPCS) system for this safety role.

The Event

Workers attempted to refill the Unit 2 high pressure core spray (HPCS) system with water on February 11, 2017, following maintenance and testing of the system. The Unit 2 reactor was shut down for a refueling outage at the time and this downtime was used to inspect emergency systems, like the HPCS system.

[…]

The NRC determined that the violation to be a Severity Level III Violation (out of a four-level system with Level I being most serious) based on the failure of the valves preventing the HPCS system from performing its safety function.

But the NRC exercised enforcement discretion per its Enforcement Policy and did not issue the violation. The NRC determined that the valve design defect was too subtle for Exelon to have reasonably foreseen and corrected before the Unit 2 valve’s failure.

[…]

The only blemish on Exelon’s handling of the matter was its weak justification for operating Unit 1 until its next scheduled refueling outage before checking whether its HPCS injection valve was damaged or broken. But the NRC’s SIT helped Exelon decide to hasten that plan with the result that Unit 1 was shut down in June 2017 to replace the susceptible Unit 1 valve.

Read more at Broken Valve in Emergency System at LaSalle Nuclear Plant 

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