The Palisades nuclear power plant is returning to service after being shut down for the last four weeks to repair a leaking water tank.
The tank is a giant aluminum sphere that holds 300,000 gallons of water in case of emergencies or a planned refueling outage.
The tank is made up of a bunch of aluminum plates welded together. There are 26 plates on the bottom of the tank. Palisades spokesman Mark Savage says they found “several minor through wall leaks” in the aluminum walls and some flaws in the welds themselves and repaired them all.
“We examined every inch of those welds; 100-percent of the welds in the bottom of that tank," Savage said.
So is the tank fixed?
"Although we cannot see the bottom of the tank itself we can certainly monitor what comes from that tank. And the amount of water that we’ve collected thus far has steadily decreased over the last five day," Savage said.
Savage says on Saturday twenty gallons of water drained from the sand bed beneath the tank. Yesterday only a half of one gallon was collected. Savage wrote this in a written statement.
On July 6, while refilling the tank, workers observed water in the sand bed beneath the tank that provides support for the tank’s floor. This was expected since previous tank leakage had dampened the sand under the tank. No other leakage from the tank has been identified.
Savage says repairs were done on the tank in 1990. Back then the water draining from the sand bed eventually went to zero after the tank was repaired.
Savage said the leaks may have been caused by a number of factors. "Floor stress, metal flexing, etc. That's why we conducted so many different examinations," Savage said. Experienced welders inspected the tank through five different tests.
"A new tank is certainly one option, as is coating the floor of the tank with a polymer lining. We have a team assembled on site to look at long-term fixes. We continuously monitor tank operation, as it is critical to the plant's nuclear safety," Savage added.
The Nuclear Regulatory Commission issued a response this afternoon:
"Currently, there is a small leak coming from the area surrounding (the tank) that has being quantified at approximately 0.2 gallons per day. It is possible that this leakage is from the tank or from moisture surrounding areas, as a consequence of a previous leak and/or maintenance activities. The NRC has reviewed the licensee’s evaluation of the leak and determined that due to its size the leak does not pose a risk to the safe operation of the plant. If the leakage increases significantly, the licensee has guidance to shut down the plant. The NRC resident inspectors will continue to monitor the leakage from the tank and the licensee actions in response to the leakage. The leakage is not being released to the environment."
The nuclear plant near South Haven is under a special federal investigation over this leaking water tank. The agents with the Nuclear Regulatory Commission are looking into allegations of wrongdoing related to the tank. But specifics aren’t really available. Neither is the timeline for the investigation to conclude.
Earlier this year nuclear regulators downgraded Palisades’ safety rating to one of the worst in the country.