VERNON — About 2,700 gallons of water from the spent fuel pool at Vermont Yankee Nuclear Power Plant drained into a wastewater system on July 22.
The 300,000 gallon pool contains 2,500 spent fuel assemblies removed from the reactor core. The spent fuel assemblies are submerged below more than 20 feet of water.
The water drained about six inches over the course of about 30 minutes when employees who were working on the fuel pool cleanup system left drain valves open. Operators in the control room discovered the problem after an alarm system went off, according to Rob Williams, spokesman for the plant.
The radioactive water drained into a wastewater collection tank.
Employees didn't follow proper procedures, Williams said. Entergy Corp., which owns the plant, will be reviewing maintenance protocols.
Vermont Yankee did not send out a press release about the incident. Williams said notifying the public was not necessary because safety wasn't at issue.
Neil Sheehan, spokesman for the Region 1 District office for the Nuclear Regulatory Commission, said the plant has clear-cut reporting criteria. If a fire at the plant lasts for more than 15 minutes or if offsite firefighting assistance is called in, for example, the plant is required to report.
This incident, he said, “fell in the category of not having to be reported because it was a very low level risk and it was caught quickly.” Employees were not at risk of exposure to radiation because the amount of water over the assemblies provides ample shielding, he said.
The NRC's resident inspector is reviewing the incident, he said.
“There's no good reason for this to happen at any point,” Sheehan said. “It speaks to human error and attention to detail, no question about that.”
Arnie Gundersen, a nuclear engineer and former member of a Vermont Yankee oversight panel, said several steps in a procedure were skipped by employees. He is concerned about oversight and employee training at the plant as older workers retire. Procedures, he said, must be much more specific.
“It's a big deal, it's a safety-related system, we're not talking about mowing the lawn at VY,” Gundersen said. “There's 300,000 gallons in the pool, and it lost 1 percent of the water in 30 minutes. It is radioactive water, it's not like what you put in a water cooler.”
Gundersen said last year employees worked on the wrong diesel engine. One was shut down and they inadvertently shut the other one down, he said. “These kinds of mistakes shouldn't be happening,” Gundersen said.
The NRC treated the incident as “business as usual,” Gundersen said.