Civil Engineering Reference
In-Depth Information
atmospheric dispersion and deposition conditions. From the emergency manage-
ment point of view, three situations can be distinguished.
• An accident is taking place, but no radioactive substances have been released yet
(pre-release phase)
• There are releases going on that influence the acute emergency management in
the affected area (acute release phase)
• A release takes or took place, but the atmospheric dispersion and deposition
processes are over or no longer significant or relevant (later phase)
Occasionally, the term “early phase” is used for designating the pre-release
phase and the acute release phase together.
The pre-release phase begins when the possibility of a relevant release is
recognized, and terminates either when the event is brought under control or with
the onset of a major release. By definition there have not yet been any releases, thus,
estimates of a potential future radiological situation can only base on forecasts of
the source term and the meteorological conditions. With respect to the latter, the
meteorological data measured at the facility can be used for the near future and the
nearby surroundings; otherwise, numerical weather prognosis data are to be
employed. In the pre-release phase, preventive measures against an expected
release can be carried out in order to exclude any subsequent radiation exposure.
In the acute release phase, the available information are meteorological data
measured on site and in the surroundings, prognoses from numerical weather
forecast models, and maybe measured source term data from the plant instrumen-
tation (mostly, however, only source term estimates). Moreover, increasingly
more measurements of the local
-dose rate and of soil and food contamination
levels will become available as time goes on. In the acute phase, preventive
measures should be carried out preferably in areas not situated in the current or
predicted transport directions or those not yet reached by the radioactive cloud.
Unforeseen changes in the release pattern or in the meteorological conditions can
necessitate changes in, or additions to, the measures already initiated. Also,
special attention must be given to the radiation protection of emergency crews
and auxiliary teams.
The later phase, when the external radiation and inhalation of radioactive
material from the cloud and also the deposition processes are over or no longer
relevant in the area under consideration, can be divided into a transitional phase and
a long-term phase.
At the beginning of the transitional phase, there will be still the necessity for
continuing the analyses of the radiological situation that were already started during
the release phase but likely not finished because this requires a sufficient number
and quality of measurements of the contamination levels in food, drinking water,
surfaces, soils, plants, and water bodies. At the end, the necessary data, resources
and time will be available for deciding upon the event-related justification and
optimization of measures for controlling the exposure of the general population, of
subgroups of the population with higher risks, and of the executing radiation
protection and rehabilitation workers. It is now the time to decide about changes
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