Entergy’s Pilgrim Nuclear Power Station returned to full power early Monday morning, after a nearly two-week shutdown brought on by excessive water levels in the plant’s reactor vessel.
The Massachusetts facility, which is scheduled for closure by 2019, was reconnected to the electrical grid Saturday and returned to 100 percent power at about 3 a.m. Monday, according to a press release from the utility.
The plant was first shut down on Sept. 6 because of complications with a fluctuating feedwater regulating valve, which caused the high water levels. Water is pumped into the reactor vessel where it is boiled, converted to steam, and then piped to the turbine to generate electricity.
Pilgrim then experienced a 2,600-cubic-foot hydrogen release over a 24-hour period on Sept. 9, which Entergy reported to the Massachusetts Department of Environmental Protection and the Nuclear Regulatory Commission. NRC spokesman Neil Sheehan said by email Monday the hydrogen release posed no safety concern given how quickly the material dissipates and vents in this particular environment. Hydrogen would have to reach a concentration of at least 4 percent to become a fire or explosion threat, which was unachievable in this case, Sheehan said. The NRC is unaware of the exact reading, just that it was below the threshold of 4 percent, Sheehan added.
Sheehan said shut-down plants are susceptible to such releases because the hydrogen seal on the generator cooling systems cools and contracts. Once the plant starts up again, the hydrogen seal warms and expands, blocking any leakage, Sheehan said.
Entergy failed to restart the reactor on Sept. 13, bringing the reactor to 9 percent power before discovering an issue with the facility’s turbine turning gear. During the shutdown, Entergy repaired the feedwater regulating valve, evaluated a second valve, replaced a safety-relief-valve pilot valve, and replaced a turning gear in the main turbine, according to the company’s press release.
“Our priority focus at Pilgrim Station is always safety,” Pilgrim Vice President John Dent said in the statement. “Our operators followed detailed procedures to shut the plant down safely, and we used conservative decision-making to complete the work needed for future safe and reliable operation.”
The NRC in September 2015 downgraded Pilgrim to column 4 of its Action Matrix, the lowest safety rating a plant can have while remaining in operation. The decision followed a series of unplanned shutdowns and issues with safety relief valves at the plant. A month later Entergy, citing economic reasons, announced that Pilgrim would shut down by 2019, but concerned locals and lawmakers have been calling for the utility to shutter the facility as soon as possible.
The NRC has conducted two increased oversight inspections this year as a result of the plant’s poor performance, both times recording findings of “very low safety significance.” The first concerned water leakage from the core spray system, and the second a maintenance procedure failure for a salt service water pump. The agency expects to conduct its third and potentially final increased-oversight inspection at Pilgrim later this year or early 2017.