Glossary

An obsolete unit of absorbed radiation dose: 1 rad (rd) = 0.01 J/kg. The unit used today in the International System of Units is the gray: 1 gray = 100 rad.

Factor that the absorbed dose needs to be multiplied by in order to take into account the different effects caused by the same absorbed doses of different types of radiation. The result is the equivalent dose.

Undesired presence of radioactive substances in living creatures, objects or the environment. There is surface contamination (when it affects the surface of objects), external contamination (the skin of human beings) or internal contamination (internal organs of human beings).

Liquid or gaseous radioactive materials that, once they have been treated and measured, are discharged in a controlled manner into the environment at a nuclear or radioactive site.

Radioactive fluid (liquid or gaseous) from a nuclear or radioactive site which is subjected to control and, where necessary, to treatment, prior to its discharge into the environment.

Condition where the relationship between the activities of two or more radionuclides in a decay chain remains constant.

Device that emits ionising radiation, either because it contains a radioactive material or because this radiation occurs during normal operation.

According to Spanish legislation, any material containing substances that emit ionising radiation. According to this definition, any substance, including the human being, is radioactive material, since all existing substances contain radioactive isotopes. This does not mean that the existence of this radioactivity requires the adoption of some type of radiological protection measures. When it is necessary to state that a radioactive material contains radioactivity in a proportion that may call for the implementation of some kind of precaution, the term used is "radioactive substance".

Chain of radionuclides in which each member turns into the next one by means of radioactive decay, until a stable nuclide is finally reached.

Material or equipment which for a long period of time can be considered invariable and serves as the ultimate term for comparison in measurements of a given magnitude.

Any material that contains one or more radionuclides whose activity should be taken into account for radiological protection purposes. (See "Radioactive material".)

Any waste material or product that displays traces of radioactivity and for which no use is planned. Contaminated residual liquids and gases are included. - High-activity waste: 1. Highly radioactive liquids containing most of the fission products and some actinides, which are separated in the first extraction cycle with solvents during chemical reprocessing of the irradiated fuel, as well as the effluents related to that process. 2. The irradiated nuclear fuel, if it has been declared waste. 3. Any other activity waste comparable to the above ones. - Medium-activity radioactive waste: Lower level of activity and heat generation than high-activity waste, but they still require shielding during transport and handling. The term is used generally to refer to all waste not defined as high or low level. - Low-activity radioactive waste: Waste which owing to its low radioactive content requires no shielding during handling and transport.

Property of some chemical elements that enables them to emit electromagnetic waves or particles. This property is due to the existence of an unbalance between the number of neutrons and protons in the atom's nucleus, which causes instability and a release of the energy accumulated in the form of particles or waves. Natural radioactivity is due to elements that emit radiation spontaneously, as in the case of uranium, thorium, radon, etc.

Radioactive isotope.

Collection of rules and practices used to prevent the risks of receiving radiation doses and, if applicable, to mitigate the effects. (See "Nuclear safety".)

Property that enables certain substances to absorb the energy from ionising radiation, and subsequently to emit part of that energy as light.

Radioactive nuclide.

Toxicity caused by the intake into the organism of a radionuclide emitting ionising radiation and by its resulting products. Radiotoxicity depends not only on the radioactive characteristics of the radionuclide, but also on its physical and chemical state, and on the metabolism of that element in the organism.

Gaseous chemical element whose isotopes, all of them radioactive, belong to the natural series of uranium and thorium. The radon isotope with the longest semi-decay period is Radon 222, a descendant of Uranium-238, which is the main cause of air pollution due to natural radioisotopes.

For each magnitude, the ratio between the increase it undergoes and the time interval during which such an increase has taken place. The decay rate is measured in decays per second (dps); the exposure rate in roentgen per hour (R/h); the absorbed dose rate in gray per hour; the equivalent and effective dose rate in sievert per hour (Sv/h) or sievert per year (Sv/y); etc.

Part of a nuclear reactor which houses the fuel and where the fission nuclear reaction and heat release take place.

Container that holds the nuclear reactor's core, the reflector, part of the coolant and other components.

Groups of people whose exposure is reasonably homogeneous and representative of that of the most exposed individuals of the population owing to a given practice.

Value, below the discharge limit, which is taken as the basis for determining whether the operation of the corresponding systems is appropriate.

Material placed around a nuclear reactor in order to return by diffusion part of the neutrons that would otherwise escape.

Obsolete unit of equivalent and effective radiation dose. 1 rem = 0.01 J/kg. In the International System of Units it has been replaced by the sievert: 1 Sv = 100 rem.

Process undergone by irradiated nuclear fuel to recover the fissionable, residual or newly-formed atoms contained in it.

Heat associated with the radioactivity of irradiated nuclear fuel, once the reactor has been shut down or the fuel element has been removed from the reactor core.