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The Chernobyl Accident: Model calculations of Concentrations and Deposition of Radioactive Releases (1986)

Author	RIVM
Date	June 1986
Classification	2.34.8.30/27 (CHERNOBYL ACCIDENT - CONSEQUENCES EUROPE - GENERAL)
Front

1. Introduction

On 26 April 1986, 1.23 local time a reactor unit of 1000 MW of the RBMH type in 
the Chernobyl power station ignited following an explosion. An unknown amount 
of radioactive material was released in the atmosphere. According to Soviet 
authorities the reactor fire had ended on May 5, although the situation was still 
called "complicated".
The contaminated air masses were transported over Europe and resulted in 
significantly increased radiation levels in the major parts of Europe. During the first 
phase of the accident the weather in Europe was dominated by a high pressure area 
over the western part of the USSR and a low pressure area over Iceland and north-
western Europe. In the Chernobyl area the wind at the 850 mbar level was south-east 
to south with a speed of 8-10 m/s. Initially the radioactive cloud was transported to 
Scandinavia. Later a more easterly flow transported freshly released material to 
central and western Europe. During the last phase of the accident the wind in the
Chernobyl area came from a westerly and northerly direction. In the beginning of 
May the heavy rainfall resulted in a abrupt decrease of air concentrations but also 
in a sharp increase in soil contamination in Europe.
On May 6, a WHO-expert group presented a report (1) which provided a description 
of the course of events in the first 12 days after the accident occurred. However, 
the preparation-time of this report was too short to give more than a qualitative 
interpretation of air mass trajectories and the, at that time still scarcely 
available, measurements.

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