The Steps to Closing a Nuclear Power Plant

How Do Nuclear Power Plants Work?
Nuclear reactors are designed to achieve one simple goal: heating water. The heated water turns into steam, which drives a turbine that turns a generator to produce electricity. TMI is a pressurized water reactor, meaning that the water heated by the reactor is kept under extremely high pressure. The essential working parts of the system are the reactor, water, steam generators, steam turbine, pumps that circulate water through the system, and the pressurizer.

Nuclear power is possible because of fission, the splitting apart of nuclei. All nuclear reactors in the U.S. that produce commercial electricity are powered with Uranium fuel. When free neutrons strike a Uranium nucleus, it splits apart, and most of that energy is directly converted into heat. As these free neutrons strike other Uranium atoms, it creates a chain reaction, and nuclear reactors are designed to sustain this reaction to continuously produce energy. Steam escapes as the only emission from the cooling towers, which is not only critical for producing electricity, but for removing the intense heat that the reactor water carries. 

To prevent the fission reaction from multiplying out of control, nuclear reactors are equipped with control rods made from materials that easily absorb neutrons. Control rods are withdrawn to initiate a chain reaction and are submerged to varying degrees and lengths in order to manage it. This is how operators control how much energy a power plant produces.

Decommissioning Options The biggest challenge in the decommissioning process is to manage the radioactive fuel safely and efficiently. The spent nuclear fuel must be removed from the reactor and transferred to a used fuel pool before finally containment in dry storage facilities. Power plant operators have three possible choices for decommissioning: DECON, SAFSTOR, and ENTOMB.

DECON is a process of immediate dismantling; the radioactive materials are decontaminated to levels such that they can be moved off-site and stored elsewhere. (In 1987, the Nuclear Waste Policy Act designated Yucca Mountain in the remote Nevada desert as the US national repository for spent nuclear fuel). SAFSTOR — the option chosen by TMI officials and is also known as “deferred dismantling” — means that the nuclear facility is maintained and monitored over a long period of time to allow the radioactivity to decay before the facility is dismantled. (Waiting 50 years allows the radiation to decay to 1% of the original contamination levels). Lastly, the ENTOMB process means that the radioactive contaminants are permanently encased on-site — “entombed.” No NRC-licensed facility has ever chosen this course of action.

TMI Unit 1 will be decommissioned according to the SAFSTOR plan of action.

Phases of Decommissioning
There are three main phases of decommissioning: transition, major decommissioning and storage, and the final license termination.

 The initial transition from operation to shutdown requires the licensee of the nuclear power plant to submit a post-shutdown decommissioning report to the NRC. The TMI report can be found here and includes descriptions of and plans for all aspects of the process, including the decommissioning operations, radioactive waste management, and potential environmental impacts of closing the plant.

The major decommissioning and storage activities can begin ninety days after the NRC receives this report; these include permanent removal of major components, such as the reactor vessel and steam generator. According to the SAFSTOR timeline, this stage involves maintaining the facility while waiting for more radioactive decay. This creates a much safer environment for the decommissioning workforce who will still be working on-site. Exelon — the company that owns and operates the facility — estimates that most of the spent fuel pool will be moved to dry cask storage by the end of 2022 (Exelon has plans to construct an Independent Spent Fuel Storage installation facility on-site), and the ultimate dismantling of the cooling towers is estimated for 2074.

A Changing Energy Landscape
The consequences of climate change are having more immediate and disastrous effects in our daily lives, making our aspirations for reliable and clean energy sources even more necessary and urgent. Although TMI and other nuclear power plants are closing, nuclear power remains a critical component of our country’s broad spectrum of energy capabilities. The 1979 accident indeed had a lasting effect on the nuclear power industry in the U.S. writ large, and the more recent expansion of fracking has also brought significant competition to the nuclear power industry. All these factors, intersecting with and influenced by political and economic forces over time, have accumulated in significant changes to our modern energy landscape. Only time will tell how these changes will shape the future of nuclear power.