VERNON — The standout, 318-foot tall stack on the Vermont Yankee nuclear power plant site, once home to peregrine falcons, is no longer.
Demolition of the stack, which handled the release of radioactive gases from the plant, was all but completed this week, as part of the ongoing demolition and cleanup of the nuclear power plant. Demolition, which is on schedule, is expected to be completed by 2026, way ahead of Entergy Nuclear’s original timetable.
The plant is now owned by NorthStar, an industrial demolition company.
According to Neil Sheehan of the Nuclear Regulatory Commission, the stack’s debris will be treated as low-level radioactive waste and shipped out of state. He said the exterior of the stack was not radioactive, but out of an abundance of caution all the debris from the stack was considered as such.
He said the stack was part of the plant’s augmented off-gas system.
“The system was designed to reduce radioactive gaseous effluents by collecting primary coolant system off-gases from the primary system and providing for delay or holdup for the purpose of reducing the total radioactivity prior to release to the environment,” Sheehan said in an email. He said the stack was 318 feet tall.
“Continuous stack monitors checked on the gross noble gas radioactivity released from the plant stack. Because release rates were normally below the detection limit of these monitors, periodic grab samples were taken and analyzed for the gaseous isotopes present. Discharge was halted if the effluent concentrations exceeded predetermined levels,” he wrote.
The off-gas was passed through HEPA filters and vacuum pumps before it was routed to the stack for release to the environment, Sheehan added.
Krypton is an example of a noble gas that was released from the stack.
Sheehan noted that the main emissions stack at the Pilgrim nuclear power plant south of Boston was taken down late last year, as part of Pilgrim’s decommissioning.
NorthStar’s president Scott State said the ventilation stack demolition had started earlier this year.
“The project began earlier this year as members of our specialized team working on a bracketed scaffold system manually demolished the top 200’ of the stack using handheld pneumatic tools,” State said via a prepared statement.
“NorthStar’s team then demolished the remaining 100 feet of stack utilizing our high reach excavator equipped with a hydraulic pulverizer,” he said.
Demolition is now in the final phase as NorthStar collects and securely packages the stack debris for shipment to and disposal at WCS repository in Texas, he said.
State said to the best of NorthStar’s knowledge the stack was constructed between June and October of 1970 and was a stand-alone structure. The stack was constructed of reinforced concrete sloping in thickness from the base to the top.
According to Bob Spencer, chairman of the Vernon Planning Commission, the stack for years used to be home to a family of peregrine falcons, and local people knew to watch the once-endangered birds.
He said that during a recent tour for the planning commission of the Yankee site he learned that NorthStar had moved the nest to another location in Vernon.
“You could almost always see peregrine falcons,” Spencer said.