After a nuclear power plant is permanently shut down, it must be decommissioned. This entails two steps. First, the company that operates the plant either decontaminates or removes contaminated equipment and materials. It also places the used nuclear fuel in dry storage until its final disposal. These materials and equipment account for more than 99 percent of the plant’s radioactivity. Their removal lowers the level of radiation and thus reduces the exposure of workers during subsequent decommissioning operations.

In the second step, the company deals with the small amount of radioactivity remaining in the plant, which must be reduced to harmless levels through a cleanup phase—decontamination.

In decontamination, workers remove surface radioactive material that has accumulated inside pipes and heat exchangers or on floors and walls, and was not decontaminated during normal plant operations because of inaccessibility or operational considerations. They are aided in decontamination activities by the records that plants are required to keep during operation. Workers use chemical, physical, electrical and ultrasonic processes to decontaminate equipment and surfaces. The removed radioactive material is concentrated, packaged and transported for disposal at a designated site. Concentration cuts the volume of low-level radioactive waste, thus reducing the expense of disposal.

A wide range of decontamination techniques is available, including those developed by the Department of Energy, the Electric Power Research Institute and the decommissioning industry. Many are in use now at operating plants as part of standard preventive maintenance programs or general repair efforts.

Companies have three primary decommissioning options:

DECON (Decontamination)
In DECON, all components and structures that are radioactive are cleaned or dismantled, packaged, and shipped to a low-level waste disposal site, or they are stored temporarily on site. Once this task—which takes five or more years—is completed and the NRC terminates the plant’s license, that portion of the site can be reused for other purposes.

SAFSTOR (Safe Storage)
In SAFSTOR, the nuclear plant is kept intact and placed in protective storage for up to 60 years. This method, which involves locking that part of the plant containing radioactive materials and monitoring it with an on-site security force, uses time as a decontaminating agent—the radioactive atoms “decay” by emitting their extra energy to become nonradioactive or stable atoms. If a plant is allowed to sit idle for 30 years, for example, the radioactivity from cobalt-60 will be reduced to 1/50th of its original level; after 50 years, the radioactivity will be just 1/1,000th of its original level. Once radioactivity has decayed to lower levels, the unit is taken apart, similar to DECON.

ENTOMB
This option involves encasing radioactive structures, systems and components in a long-lived substance, such as concrete. The encased plant would be appropriately maintained, and surveillance would continue until the radioactivity decays to a level that permits termination of the plant’s license. In 1999, the NRC found that entombment may be a viable decommissioning option and held a public workshop to explore the issue. In late 2001, the NRC published an advanced notice of proposed rulemaking to solicit additional public input. The industry commented that some form of this option should be established in regulation.

In addition to the nuclear energy industry’s demonstrated ability to amass the funds and expertise needed for safe and timely decommissioning, the public and plant workers are further protected by a strict and comprehensive set of federal regulations.