Chernobyl accident

11.1.3 Environment contamination from the accident and its current state

The extent of surface contamination

The 1986 accident at the Chernobyl nuclear power plant, resulted in a sub­stantial release of radionuclides to the atmosphere and caused extensive contamination of the environment. According to the International Atomic Energy Agency (IAEA, 2006), a small part of the nuclear fuel (up to 3.5%) and a substantial fraction of volatile radionuclides were released from the damaged unit 4. The total activity amounted to approximately 12.5 x 1018Bq, and included 6.5 x 1018Bq of noble gases (IAEA, 2001).

A considerable territory of the former Soviet Union, particularly in Belarus, Russia, and Ukraine, as well of Western Europe, primarily the Scandinavian countries and the Alpine region, was severely contaminated. High levels of radioactive contamination in areas outside the Chernobyl Exclusion Zone arose for the following reasons: release of contaminated masses into the atmosphere to a height of 2,000 m and their intense move­ment at these altitudes; rainfall; and the presence of complex landscapes that dictated changes in directions and altitudes of the contaminated air masses movement.

The overall area of Western Europe countries where levels of 137Cs con­tamination exceeded 20 kBq m-2 (almost 10 times higher that global back­ground levels) due to the Chernobyl disaster amounted to approximately 280,000 km2 . Almost 75% of Ukraine’s territory suffered from radioactive contamination by 1 37Cs, which exceeded the pre-accident levels by more than double. The radionuclide decay, which has occurred in the 25 years since the Chernobyl accident, substantially corrected a pattern of radionu­clide distribution over Ukraine ’s territory. Over this period, the area of localities where 137Cs contamination levels exceeded 10 kBq m-2 has reduced to almost half what it was immediately after the accident. The area of sites where 90Sr contamination exceeded 4 kBq m-2 is now less than one third, i. e. practically 90% of Ukraine’s territory is characterized by the pre-accident levels of 90Sr contamination.

However, the level and extent of Ukraine ’ s territory contamination by Pu isotopes have not changed. 241Am activity is gradually increasing due to MPu decay; and the area of its distribution where levels exceed 0.2 kBq m-2 shall be 30% wider than the area of plutonium isotope fallout having the same density. The area of Ukraine contaminated by ’Sr, 241 Am, and Pu isotopes is substantially smaller than that contaminated by 137Cs.

Severely contaminated (over 1.5 MBq m-2 of 137Cs) localities (almost 300 km2) within the boundaries of ChEZ will remain uninhabitable for hundreds of years. These water-producing areas shall remain a long-term source of surface water and groundwater contamination due to surface washout and vertical migration.

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