COVERT — Whether Palisades nuclear power plant closes in 2018 or in 2022, the process of decommissioning the plant could take up to 60 years, per Nuclear Regulatory Commission (NRC) guidelines.
Late last year Palisades owner, Entergy Corp., announced it would shutter Palisades in October 2018. To do this The Michigan Public Service Commission (MPSC) has to sign off on the request by Consumers Energy to terminate it’s power purchase agreement with Entergy early.
If the MPSC rules the contract can’t be terminated, when it releases it’s decision in late September 2017, then Entergy will continue to operate Palisades under the current contract terms (which goes until 2022), Palisades spokeswoman Val Gent said.
Once the plant closes, Entergy will have two years to release a Post Shutdown Decommissioning Activities Report (PSDAR).
The PSDAR will include timelines on decommissioning the plant, a permanent fuel removal plan and what the plans are for the land the plant is on.
When Entergy closed it’s Vermont Yankee nuclear power plant in December 2014, it submitted the PSDAR to the NRC prior to shut down.
“It is possible that we could do so for Palisades as well. Regardless, Entergy will submit the PSDAR to the NRC per the required timeline,” Gent said.
Until the PSDAR is released, exactly how the plant will be decommissioned can only be guessed by looking at what other plants that have closed have done and what the NRC’s requirements are for decommissioning.
“Three words can sum up the process – safety, compliance and transparency. Safety of our employees, contractors and surrounding community will remain our top priority,” Gent said.
The initial decommissioning activities involve extensive planning to safely and efficiently move the station to post shutdown status and to develop plans to decommission the Nuclear Power Station and terminate the station license within 60 years, Gent said.
In simple terms, decommissioning is getting a site’s radioactivity down to acceptable levels: 25 millirem a year. A millirem is the measure of radiation the body absorbs as it’s exposed to radioactive material.
In the environment humans are exposed to about 620 millirem a year. Half of that is from natural radiation sources, like radon and uranium in the soil and the other half is from x-rays and other medical technology.
Plants are given 60 years to decommission based on a calculation involving cobalt 60. Cobalt 60 is an isotope used in the steel around the reactor because of its hardening abilities.
The isotope has a half life of 5.2 years. Lots of decay occurs in about 10 half-lifes. So 10 half-lifes is 52 years, and another 8 years is given for the clean-up, said Rhex Edwards, senior health physicist and decommissioning expert at the NRC.
Radioactivity is always present even if most of the material has decayed, Edwards said. So there’s also a requirement that the level is as low as reasonably achievable. For example, Palisades wouldn’t be allowed to leave a chunk of rock on the ground, even if it’s 23 millirem.
“The burden is on the site to do the clean-up. They have to demonstrate to us that it’s done and then as an added level of assurance we go do our own inspection, survey and sampling,” Edwards said.
Palisades can choose to get the radiation levels down several different ways: either letting the radioactive material decay over a chosen number of years, or cleaning and removing radioactive parts of the plant.
The site itself is going to remain owned by Entergy throughout the entire process, and the NRC doesn’t have regulatory authority to say what the end state of the property has to be. Entergy could decide to keep some buildings or it could tear them all down.
When the NRC surveys a closed nuclear power plant site, it considers a worst-case scenario. The “resident farmer scenario” is used because it’s impossible to know the future land use.
The scenario assumes that the property is cleaned up, a farmer moves in, plants crops, has livestock, puts in a well, raises a family and lives off the crops and livestock.
“All of those food sources and water sources would all be subject to the worst-case material that was left behind on site that the site told us about and that we confirmed with our surveys. All of that would be taken in by the farmer and we would see what dose in millirem that individual would receive and it would have to be below 25 millirem and as low as reasonably achievable,” Edwards said.
Storage and disposal
The nuclear fuel rods are removed from the nuclear reactor as soon as a nuclear power plant is closed.
The fuel is then placed into the spent fuel pool for at least a year for cooling, according to NRC regulations. Then it is transferred to dry casks.
The majority of sites load the used fuel into the casks in about 3-5 years after it shuts down, Edwards said.
Palisades has a dry cask storage program for it’s used fuel because the U.S. doesn’t have a permanent storage facility for these casks.
The used fuel will remain secured on site, under guard, monitored during shutdown and decommissioning activities, and subject to the NRC’s oversight until it is removed by the federal Department of Energy, which it’s contracted to do eventually.
The casks are stored on a concrete pad, 2-3 feet thick, designed to support the weight of the casks through all sorts of scenarios like earthquakes, tornadoes and other natural occurrences.
Palisades has one of the most analyzed dry cast storage pads in the country, Edwards said. There’s several reports where the NRC has independently documented and reviewed the engineering that has gone into those designs to determine that they are safe and will stay in place. They are not going to move, tip over, slid toward the lake or anything, he said.
The casks are large concrete and steel tubes The fuel itself is encased in a steel liner with a coating around it and sealed in the canister through redundant confinement barriers.
Casks use a passive system with the fuel being cooled by natural air flow. Air enters the cask through vents near the bottom, and removes heat as it travels through the cask, eventually exiting through vents at the top. The fuel is low enough in heat that it can be safely cooled that way forever, Edwards said.
There are options to choose from on how to dispose of and clean other radioactive material from the site, like the water, trash bags, rags and concrete, but this material is being disposed of all the time from hospitals, Edwards said.
The water is filtered through several different processes, then is sampled multiple times. It is then discharcharged if it falls within the discharge permits. All of those discharges are reported to NRC and the reports are made public.
If the buildings are taken down, or cleaning is done, when most of the radioactive material has decayed, then the materials can go to a regular landfill. If it’s done earlier then it goes to a nuclear landfill licensed by the NRC.
Those materials have to get from the site to one of those facilities in a public way, as well. While it’s done safely, there’s always an increased risk when moving radioactive material from one point to another. NRC regulations ensure the safety for that, Edwards said.
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