Dispersion (radiation protection)

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In radiation protection, dispersion describes the spread of radioactivity in the context of the respective meteorological situation .

Dispersion situations arise both in normal operation (e.g. in the case of occasional revision duties) and in certain incidents - or then accident situations of nuclear facilities and other facilities using radioactive substances. On the one hand, they are recorded in the current state using measurement technology (e.g. using the ODL measuring network in Germany or MADUK and NADAM in Switzerland); a. Accident situations are created based on forecasted source term data and current meteorological data, dispersion forecasts that are used to alert the affected population and for disaster control .

The models for dispersion calculation are provided by science. A Spanish study for an accident at the Almaraz nuclear power plant is an example . It assumes a real in the prevailing weather conditions of 10 May 2007 core damage in the reactor or an accident in the spent fuel pools for fuel, leading to a rather small containment leads Leaks. 10 16 Becquerel cesium are released (in the model example) in a westerly wind situation during 2 hours . The dispersion graphic over around 80 kilometers shows an almost hemispherical, relatively low-level activity plume. There is a short and narrow corridor of the highest radiation intensity from the source in the direction of the wind. As the distance increases, this merges into a wider corridor of medium radiation, which is flanked by areas of lower radiation. The soil deposits that the cloud leaves behind show a similar picture.

The spatial extent of such a release cloud or its fission product concentration are primarily dependent on the release duration or the size of the leak that has occurred. These determinants can to a certain extent be influenced by emergency measures. In this way, it may be possible over time - but only in the best case - to close a valve and thus eliminate the containment leak or at least reduce it. Or it can e.g. B. by repairing a pump or an emergency diesel generator set, the melting core can be flooded, which - but with a longer time window - the release would also be stopped prematurely. Should the fission products be retained in the containment of the nuclear power plant for a longer period of time before a leak occurs, this would lead to a lower source term on the one hand due to deposition processes on the containment structures and on the other hand due to radioactive decay of some nuclides .

In general, the cloud thins as the distance from the exit point increases. However, it is conceivable that at a distance of a few dozen kilometers it will find itself in a front of cooler air masses. This would partially condense again and more intense radiation effects would have to be expected again even at greater distances. It should be added that the above remarks only partially apply to light water reactors and that e.g. For example, the Chernobyl type that crashed in 1986, other laws also play a role.

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