In the night 25/26 April1986 it all started. The radioactive releases from Chernobyl reached the Nordic countries late 27 April. At noon the following day all the world knew that an accident had occurred - two and a half days after it started.
In April.l986 there was, generally speaking, quite a high level of preparedness for nuclear accidents in the Nordic countries but still, as it was shown, quite insufficient for accidents abroad with such extensive countrywide consequences as the Chernobyl accident proved to have.
The total depo.sition over the Nordic countries was about 10 PBq Cs-137 and the major part was found in wet deposition areas. As a total of about 80-90 PBq Cs-137 is assumed to have been released from Chernobyl, more than 10% was deposited over the Nordic countries with the average Cs-137 concentration of 1.2 kBqm-2 in Denmark, 11 in Finland, 5.1 in Norway and 10 in Sweden.
The deposition from the Chernobyl accident added to the present fallout from the atmospheric tests in early 60's. The two depositions were of the same order of magnitude e.g in Sweden 4.25 PBq of Cs-137 from Chernoby1 and 1.25 PBq from the atmospheric tests. However the fallout during the 60's-was rather evenly distributed with an average of about 3 kBqm-2 while the Chemobyl deposition was extremely variable from almost zero up to about 200 kBqm-2