The Vermont Yankee Nuclear Power Plant entered its final shutdown Monday at 1:03 p.m. The 620-megawatt reactor has been generating electricity for more than 42 years.
The reactor started the day at about 70 percent power. It’s been losing power gradually since September because its fuel, which wasn’t replaced at the normal 18-month interval, has started to decay.
Bringing the power down to zero took only a few hours, as plant operators inserted each of the reactor’s 89 control rods into its 368 fuel assemblies.
“As you drive these control rods in between the fuel assemblies, it no longer allows these assemblies to react with each other," says Yankee Government Affairs Manager Joe Lynch. "So they actually act like little shields and you’ll have one of these between every single one when we’re all shut down.”
Members of the media monitored the activities in the plant’s control room in Vernon on a screen at Yankee’s Brattleboro offices. A diamond-shaped grid mapped the control rods in the reactor, showing a green light for each control rod that was inserted. Dan Jefferies, a company trainer, described the action on the screen.
“They’re now inserting four rods," Jeffries explained. “Previously we had five rods in. Since I’ve been talking we’ve inserted two more control rods, those two down there, bringing power down. We’re at 25 percent reactor power."
Jefferies also kept his eye on another indicator that showed the declining power in megawatts. At about 25 megawatts, control room operators opened two circuit breakers.
The circuit breakers divert any steam the plant is still generating away from the turbines. Instead the steam goes into a condenser and is released into the Connecticut River. At that point — a little after noon — Yankee stopped sending energy to the electric grid. Shortly after that, Jefferies explained, operators prepared to insert a scram that accelerates the shut down.
"Within a few minutes I would expect,” Jefferies said, “They’ll scram the reactor and we expect that the remaining control rods that go in should insert within one to three seconds and all these will go to zero. These will all light up to zero when the reactor is scrammed."
The end came with little fanfare. Yankee decommissioning spokesman Martin Cohn praised the Entergy Vermont Yankee staff for finishing strong under difficult circumstances. And Cohn noted that the shutdown is also a beginning — the beginning of a decommissioning process that could take up to 60 years.
Cohn says workers will begin moving fuel from the reactor into the plant’s spent fuel pool early in January. On January 19, when the job is expected to be complete, 234 Vermont Yankee employees will be laid off. The remaining 316 workers will mothball the plant’s non-essential buildings, and prepare the site for the transfer of the spent fuel from the plant’s spent fuel pool into dry cask storage on site. At that time — around 2020, Cohn says — another in an ongoing series of layoffs will occur, leaving 127 workers at the plant.