The plume's immediate effect was on Nordic Countries to the North West of the Soviet Union. The plume initially swept past Northern Poland and across the Atlantic on April 26. The plume took an arced shape and was quite large, and although the cloud did not cover the whole country of Sweden it had a large enough sphere of influence from the radiation to affect the whole country.

When the plume first arrived it was not immediately detected because most of the radioactive detection centers that Sweden already had up were in the Northern Arctic parts of Sweden to keep an eye on the radiation levels of Soviet nuclear weapons testing. The first place where the plume arrived was in Southern Sweden between Utlangan and Lund at 5:00 GMT(Greenwich Mean Time). It was first noticed by the Forsmark Nuclear Power Plant at around 7:00 AM. The radiation in the air was noted to be at 20-150 counts per second (normal range is 5-10 counts per second), and the immediate reaction of the power plant was that there was a leak. Eventually other Nordic countries all noticed the radiation and calculated the Soviet Union as the source. 

Scientists at Studsvik identified 16 different radionuclides in the air as well as in the grass. Audioradiography and Electron Microscopy revealed the there were some dangerous hot particles which measured at about 1,000 counts per second. Some of the contamination revealed pure ruthenium which was definite evidence that there was a major meltdown because ruthenium melts at about 2,250 degrees Celsius. 

Another definite sign that there was a core meltdown was the proportion of the non-volatile elements, even though it was little compared to the proportions of volatile elements it still showed signs of a core meltdown. By 1:00 AM on April 29, 1986, it was clear to all researchers in the Nordic countries that there was an obvious core meltdown in the Ukraine area. At this same time the West was just being informed, hours before the Soviets admitted and made the accident public knowledge. 

Of all of the Nordic countries, Sweden was the most deeply affected. A major way that Sweden was affected was the contamination of meat and other produce such as lichen. The meat contained 4,000 Bq/kg of cesium-137 12 times more than the permissible amount. The lichen which is used as a food source during the winter contained 8,000, 16,000 and sometimes up to 30,000 Bq/kg. They were the most deeply affected because the lichen plant absorbs most of its nutrients from the air rather than from its roots. Also lichen, unlike other plants, does not shed tissue making it take about 9 years for the amount of cesium contaminant to reduce in half. Also reindeer was a major source of income that was affected. Meat from about 50,000 reindeer had to be thrown away. 

Altogether, the effects to Sweden totaled $100 Million US dollars in the first year alone. The fallout also caused around 100 more fatalities due to cancer derived from high doses of radiation. The people also changed their attitude towards nuclear power, now 65% of the population was against Nuclear power after seeing the effects to their country that will continue there and in many other Nordic countries for many years to come.