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Due to a lapse in appropriations, the NRC has ceased normal operations. However, excepted and exempted activities necessary to maintain critical health and safety functions—as well as essential progress on designated critical activities, including those specified in Executive Order 14300—will continue, consistent with the OMB-Approved NRC Lapse Plan.

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Effective half-life

Effective half-life … The time required for the activity of a particular radioisotope deposited in a living organism, such as a human or an animal, to be reduced by 50 percent as a result of the combined action of radioactive decay and biological …

Dose rate

Dose rate … The dose of ionizing radiation delivered per unit time. For example, rems or sieverts (Sv) per hour. … Dose rate …

Radioisotope (Radionuclide)

Radioisotope (Radionuclide) … An unstable isotope of an element that decays or disintegrates spontaneously, thereby emitting radiation . Approximately 5,000 natural and artificial radioisotopes have been identified. … Radioisotope …

Auxiliary feedwater

Auxiliary feedwater … Backup water supply used during nuclear plant startup and shutdown to supply water to the steam generators during accident conditions for removing decay heat from the reactor . … Auxiliary …

Fuel temperature coefficient of reactivity

Fuel temperature coefficient of reactivity … The change in reactivity per degree of change in the temperature of nuclear fuel . The physical property of fuel pellet material (uranium-238) that causes the uranium to absorb more neutrons away from the …

Fertile material

Fertile material … A material, which is not itself fissile (fissionable by thermal neutrons), that can be converted into a fissile material by irradiation in a reactor . There are two basic fertile materials: uranium-238 and thorium-232. When these …

Chain reaction

Chain reaction … A reaction that initiates its own repetition. In a fission chain reaction, a fissionable nucleus absorbs a neutron and fissions spontaneously, releasing additional neutrons. These, in turn, can be absorbed by other fissionable nuclei, …

Monitoring of radiation

Monitoring of radiation … Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination in a region. Radiation monitoring is a safety measure to protect the health and safety of the public and the environment …

Dose, absorbed

Dose, absorbed … The amount of energy absorbed by an object or person per unit mass. Known as the “ absorbed dose ,” this reflects the amount of energy that ionizing radiation sources deposit in materials through which they pass, and is measured in units …

Pressurized-water reactor (PWR)

Pressurized-water reactor (PWR) … A common nuclear power reactor design in which very pure water is heated to a very high temperature by fission , kept under high pressure (to prevent it from boiling), and converted to steam by a steam generator (rather …