The federal agency that regulates nuclear power plants released more information on Monday about a leak over the summer at the Palisades plant near South Haven. The plant has one of the worst safety ratings in the US after a number of problems last year.
There have been at least three water leaks at Palisades in the past several months.
This one is arguably the most important because water was leaking from the actual vessel that holds the nuclear reactor. It’s important that water covers the reactor completely. The Nuclear Regulatory Commission doesn’t allow any leakage like this so the plant shut down in August to fix it.
The leak has been fixed and Palisades is operating. The leak was coming from a tiny hole in one of the reactor’s 45 control rod drive mechanisms. Plant operators can move these control rods in or out of the reactor vessel to control the rate of the reaction.
Regulators still don’t know what the root cause of the hole was. During a briefing Monday afternoon NRC Branch Chief Jack Giessner noted that there was a similar leak from the control rod drive mechanisms, CRDMs, in the past.
“All the CRDMs were replaced in 2001. That was one of the drivers for why we did a special inspection. We said ‘hey it’s only been 11 years and we have another through wall leak’ albeit in a different location,” Giessner said. The CRDM leak in 2001 was in a weld, where this leak is through a solid piece of pipe in the mechanism.
It’s not clear how quickly the hole formed. Giessner said Palisades operators believe it formed slowly over eight years. He admits that’s possible but believes it could have been only two years. In that case the NRC would want more closer inspections of the CRDMs more quickly.
Giessner estimates up 10,000 gallons of water leaked from the primary system that includes the reactor vessel over 33 days. That system hold 80,000 gallons total.
He says the radioactive water was contained in the building and then processed like normal radioactive liquid. There were no safety concerns for the public.
I asked Giessner how well he thought Palisades responded to the leak, because an independent safety assessment done last spring said there was a “repeated emphasis of production over safety”.
“I think they were prompt to shut down. I think the NRC’s assessment when they were getting ready to start up we weren’t happy with their performance in that case and we took specific action,” Giessner said. Giessner says the NRC had to prompt Palisades to do a more thorough inspection before restarting the plant.
Palisade is under more scrutiny because of the recent safety problems. The NRC wants to be more transparent about what’s going on there. So that’s why the agency took this unusual step of releasing preliminary results of its special inspection.
We’ll get the final results of that inspection in a few months. In the meantime, the NRC is in the middle of a different, even bigger inspection. This one is to follow up on the poor safety culture among workers at the plant that helped lead to Palisades downgraded safety rating.
The results of both of these inspections will impact the safety rating. But we won’t know the final results for a while.