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29 July 2013

Nuclear plant decommissioning

Dave Lochbaum

Dave Lochbaum

Lochbaum is the director of the Nuclear Safety Project at the Union of Concerned Scientists. He monitors...

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In 2013, four nuclear power reactors permanently shut down in the United States, joining more than two dozen reactors already retired. The reasons behind retirements vary—from accidents to economics. And the decommissioning process that follows retirement is anything but simple, depending on the size of the reactor: It can take nearly a decade, and can cost more than $500 million.

Three options exist for decommissioning nuclear reactors: safe storage, decontamination, and entombment.

Safe Storage. Safe storage is more deferral than decommissioning. The approach is to contain the parts of the plant that have radioactive materials, and then wait, up to 60 years, as the radioactive components decay and decontaminate naturally. For example, the Unit 1 reactors at Indian Point (New York), Dresden (Illinois), Peach Bottom (Pennsylvania) and Millstone (Connecticut) have been placed in safe storage until two other operating reactors at each site are permanently shut down. After all reactors have ceased operating, their owners will elect to entomb or decontaminate all three reactors.

But plant owners do not always find safe storage. In 1994, the Nuclear Regulatory Commission fined the owner of Dresden Unit 1 $200,000 for turning off heat inside the containment building. Sub-zero temperatures in January of that year froze water that burst a pipe, allowing 55,000 gallons of water to flood the containment. The NRC noted that the situation created the potential for another pipe to burst and drain water from Unit 1’s spent fuel pool. While this uncovered fuel would not have overheated, it would have created a serious radiation exposure problem. And as the NRC was writing up the ticket for that violation, another pipe broke due to aging, allowing 50,000 gallons of radioactively contaminated water to drain from a storage tank.

Decontamination. A process that can take up to 10 years, decontamination involves surveying plant structures and grounds to identify radioactively contaminated items, which fall into two categories: those that can be decontaminated and handled like non-radioactive parts and those that must be packaged and shipped to disposal sites licensed to accept radioactive materials.

Safety and financial factors determine how items are binned. For example, the outer two inches of a 3-feet thick concrete wall may be contaminated. Scraping away this layer would enable the remainder of the wall to be treated as non-radioactive material. But the scraping process could cause “fixed” contamination to become small, airborne particles and pose a health risk to workers. While selective contamination removal is sometimes justified, other times it is safer and cheaper to dispose an entire item as radioactive trash even though only a portion of it is contaminated.

The Nuclear Information and Resource Service and a coalition of organizations, in fact, have fought to prevent the recycling of contaminated materials from nuclear facilities being decommissioned and dismantled.

Entombment. Whereas decontamination involves transporting radioactive materials from a plant site to a licensed nuclear waste dump, entombment brings the nuclear waste dump to the site. While entombment is an option, its election is confined to a few special cases. The Hallam (Nebraska) and Piqua (Ohio) reactors have been entombed, but they were relatively small reactors (generating 256 and 46 megawatts of electricity, respectively) that operated for less than five years. Entombment is essentially not an option for larger nuclear reactors that operated for decades and made larger messes.

As more reactors undergo decommissioning, nuclear reactor owners learn to eliminate bad practices and expand good practices. Unfortunately, the learning curve’s shadow is complacency. History repeatedly shows that as soon as reactor owners feel they have learned enough to guard against disaster, the associated complacency can allow that guard to drop. One form of this is in life extensions of reactors. For example, the US nuclear industry began replacing steam generators in the mid-1980s to add 20 years to a reactor’s lifetime. Two decades later, these replacements had become routine. Yet the “routine” replacements factored into the unplanned permanent shut downs this year of reactors at Crystal River (Florida) and San Onofre (California).

Decommissioning must never become a template process. There are ample safety and economic reasons to get it right every time.