Glossary of key nuclear power terms

Control rods: Metal rods containing neutron-absorbing material that are used to stop fission from taking place in a nuclear reactor.

Decommissioning: Safe removal of a nuclear facility from service. Nineteen reactors are currently undergoing decommissioning. There are three allowed methods:

1). Decon (Decontamination): Structures, systems and components containing radioactivity are dismantled, removed and disposed of off-site. Plant property is decontaminated so it may be released for unrestricted use.

2). SAFSTOR: Systems are drained and buildings and components left on-site, losing some of their radiation over time. They must be dismantled and the site decontaminated within 60 years of reactor shutdown.

3). Entomb: Radioactive contaminants are encased in structurally strong and long-lived substances such as concrete. Material stays encased until radioactive waste decays.

Dry cask: A heavily shielded container used to store or transport radioactive material such as spent fuel. Spent fuel rods must cool for at least five years in a pool before being moved into casks.

Fission: Splitting of an atom, which releases large amounts of heat.

Nuclear Waste Policy Act: 1982 law under which federal government would identify a site and develop a geological repository to store radioactive spent fuel from the nation’s reactors

Reactor types in U.S.:

1). Boiling water reactor: Water is boiled using the heat released from fission. Steam drives the turbine, which activates generators to produce electricity.

 2.) Pressurized water reactor: Operates like a pressure cooker. Water heated to very high temperature through fission but kept under pressure to prevent it from boiling. Resulting steam drives turbine, which activates generators and produces power.

Scram: The sudden shutting down of a reactor, usually by rapid insertion of control rods, either automatically or manually.

Spent fuel: Radioactive fuel rods in a nuclear reactor that are no longer usable. They are removed from the reactor core and replaced with fresh fuel rods. The spent fuel rods are still highly radioactive and continue to generate heat for decades. They are stored in pools or dry casks.

Spent fuel pool: Large pools, at least 20 feet deep, where highly radioactive spent fuel rods are kept once they are removed from the nuclear reactor. Circulating water cools the rods.

Yucca Mountain: Federally owned desert land in Nevada identified in 1987 as the best location for a long-term geological repository for radioactive waste. Public resistance has kept the plan on hold. Meanwhile the industry already has produced more than 70,000 metric tons of waste, which exceeds the maximum that would have been stored at Yucca.