A glossary of radioactivity

Le Monde, a French newspaper, invited the reader to a glossary of radioactivity last month, and the following is a translation from French into English (mechanical translation, which was human-amended)

Becquerel: International unit of measurement of radioactivity. The Becquerel (Bq) measures the activity of a radioactive source, that is to say, the number of transformations or disintegrations of atoms which occur in one second. For example, a body whose activity is 12 000 becquerels means that 12,000 atoms disintegrate every second there.

Bore: Present in the primary circuit water as boric acid dissolved, it allows, through its ability to absorb neutrons, to moderate chain reaction.

Cesium: Rare and toxic metal. One of its isotopes, cesium 137, is a radioactive fission product found in the different circuits of the nuclear zone.

Contamination: Surface deposition of dust or radioactive liquids. Human infection may be external (skin) or internal (through ingestion or respiration).

Containment: Also called the reactor building, the containment building is a concrete building inside the tank which is the heart of the reactor and steam generators. It is the third of the barriers that isolates the radioactive materials contained in the heart of the reactor environment, after the fuel cladding and primary circuit. It must be sealed to retain the radioactive material which would be released during a break in the primary circuit after an accident.

Nuclear fission: Splitting of a heavy nucleus, eg uranium or plutonium, into two parts under the effect of neutron bombardment. This fission is accompanied by a large release of energy and the emission of other radiations, including neutrons that can sustain the reaction. This reaction is the basis for the production of nuclear energy.

Nuclear Fusion: Formation of a heavy nucleus from two lighter nuclei, eg, deuterium and tritium, which are isotopes of hydrogen. The value of fusion is that it could potentially produce much more energy to fuel mass equal to fission.

But in spite of research conducted worldwide for 50 years, outside the military field with the H-bomb, no effective implementation of the fusion energy production has yet emerged. It is the purpose of international research project ITER.

Nuclear fusion reactor: When nuclear reactor ceases to be properly cooled, the nuclear fuel rods (which contain uranium or plutonium and the highly radioactive fission products) are beginning to overheat and melt inside reactor. They move from solid to liquid state.

The fusion of the heart is considered a serious nuclear accident due to the likelihood that radioactive materials can pass through the containment. Not to be confused with nuclear fusion.

Gray: A unit of measurement (Gy) of the amount of radiation absorbed by a body or an object. For example, a dental X-ray corresponds to an absorbed dose of 0.2 mGy, a chest radiograph, 1 mGy, a session of radiotherapy, 2 Gy

INES: International Nuclear Event Scale, and radiological. The logarithmic scale has eight levels, rated from 0 to 7, to measure the severity of a nuclear accident. Designed by the International Atomic Energy Agency (IAEA), has been adopted by some fifty countries in 1991.

Iodine: An element where radioactive isotopes, such as iodine 131, are massively present in the fission products of the nuclear industry. In an accident, emission-131 is a factor for cancer and serious disorders of the thyroid. Thyroid fixes in fact much of the iodine absorbed through food, water or inhalation.

The distribution of stable iodine can saturate the thyroid to prevent its radioactive isotopes from being fixed.

Mox: Nuclear fuel mixture that depletes uranium oxide and plutonium oxide from the reprocessing. It is used in the current generation of reactors (light water, boiling or pressurized).

Pool: The pool of fuel storage has two functions: it receives all the assemblies of the heart of the reactor during refueling outages and serves as the storage of spent fuel assemblies awaiting - often several years - they are sent to a reprocessing plant. The pool cooling is necessary to evacuate the power emitted by the fuel.

Radioactivity: Emission of alpha, beta and gamma radiation accompanying the decay of an unstable element or fission. Radioactivity is naturally and artificially. In the latter case, the nuclei are emitters produced in the laboratory or in nuclear reactors. The radioactivity is measured in becquerels.

Reactor nuclear installation capable of initiating and maintain a fission chain reaction. In a nuclear power plant, it is he who provides the heat for producing steam. Different types of reactors in operation worldwide: pressurized water reactor (PWR), as in France, boiling water reactors, as in Japan, or fast neutron reactors.

Nuclear reaction: Conversion of one or more atomic nuclei. The two main ones are the fusion and fission.

Sievert: Unit of measurement (Sv) of the effects of radiation on living organisms exposed. It is calculated by multiplying the absorbed dose of radioactivity per unit mass by a correction factor unit that takes into account the dangers of radiation. The normal dose received by the organism is an mSv per year. It is considered that from 100 millisieverts (mSv) is likely to develop cancer.




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