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Resuspension and atmospheric transport of radionuclides due to wildfires near the Chernobyl Nuclear Power Plant in 2015: An impact assessment

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In April and August 2015, two major fires in the Chernobyl Exclusion Zone (CEZ) caused concerns about the secondary radioactive contamination that might have spread over Europe. The present paper assessed, for the first time, the impact of these fires over Europe. About 10.9 TBq of 137Cs, 1.5 TBq of 90Sr, 7.8 GBq of 238Pu, 6.3 GBq of 239Pu, 9.4 GBq of 240Pu and 29.7 GBq of 241Am were released from both fire events corresponding to a serious event. The more labile elements escaped easier from the CEZ, whereas the larger refractory particles were removed more efficiently from the atmosphere mainly affecting the CEZ and its vicinity. During the spring 2015 fires, about 93% of the labile and 97% of the refractory particles ended in Eastern European countries. Similarly, during the summer 2015 fires, about 75% of the labile and 59% of the refractory radionuclides were exported from the CEZ with the majority depositing in Belarus and Russia. Effective doses were above 1 mSv y−1 in the CEZ, but much lower in the rest of Europe contributing an additional dose to the Eastern European population, which is far below a dose from a medical X-ray.

On Sunday 26th April 2015 at 23.30 (local time), exactly 29 years after the Chernobyl Nuclear Power Plant (CNPP) accident, a massive fire started in the Chernobyl Exclusion Zone (CEZ). The next morning (April 27th) at 07.30 the fire was partially stabilised and the fire-fighters focused on only two areas of 4.2 and 4.0 hectares. However, the fire spread to neighbouring areas due to the prevailing strong winds. During the night of April 27th to 28th, 2015, the fire spread to areas close to the Radioactive Waste Disposal Point (RWDP), and burned around 10% of the grassland area at the western of the RWDP1. On April 29th and 30th, 2015, the attempts to stop the fires in the CEZ did not succeed. Fire brigades from Chernobyl and Kiev region supported extinguishing attempts and the last 70 ha were suppressed on May 2nd, 2015. The radiation background is continuously monitored in the CEZ by an automated radiation monitoring system (ARMS) at 39 points1. Given the importance of this fire, background radiation and radionuclide content in the air near the fire were also analysed online.

Another less intensive fire episode took place in August 2015. About 32 hectares were initially burned in the CEZ on August 8th2. The fires started at three locations in the Ivankovsky area. As of 07.00 on August 9th, the fires had been reportedly localized and fire-fighters continued to extinguish the burning of dry grass and forest. The same fire affected another forested area, known as Chernobylskaya Pushcha. The fire spread through several abandoned villages located in the unconditional (mandatory) resettlement zones of the CEZ and ended on August 11th.

Forest fires can cause resuspension of radionuclides in contaminated areas3. This has caused concern about possible fires in heavily contaminated areas such as the CEZ4. While concerns were initially limited to the vicinity of the fires, Wotawa et al.5 have shown that radionuclides resuspended by forest fires can be transported even over intercontinental distances. Earlier in 2015, Evangeliou et al.6, based on a detailed analysis of the current state of the radioactive forests in Ukraine and Belarus, reported that forest cover in the CEZ has increased from about 50% in 1986 to more than 70% today. Precipitation has declined and temperature has increased substantially making the ecosystem vulnerable to extensive drought. Analysis of future climate using IPCC’s (Intergovernmental Panel on Climate Change) REMO (REgional MOdel) A1B climatic scenario7 showed that the risk of fire in the CEZ is expected to increase further as a result of drought accompanied by lack of forest management (e.g. thinning) and deteriorating fire extinguishing services due to restricted funding. The same group8 considered different scenarios of wildfires burning 10%, 50% and 100% of the contaminated forests. They found that the associated releases of radioactivity would be of such a magnitude that it would be identical to an accident with local and wider consequences9. The additional expected lifetime mortalities due to all solid cancers could reach at least 100 individuals in the worst-case scenario.

This paper aims at defining the extent of the radioactive contamination after fires that started in the CEZ on April 26th (ended 7 days after) and August 8th (ended 4 days after) 2015. We study the emission of the labile long-lived radionuclides 137Cs (t½ = 30.2 y) and 90Sr (t½ = 28.8 y) and the refractory 238Pu (t½ = 87.7 y), 239Pu (t½ = 24,100 y), 240Pu (t½ = 6,563 y) and 241Am (t½  = 432.2 y). These species constitute the radionuclides remaining in significant amounts since the Chernobyl accident about 30 years ago, and their deposition has been monitored continuously by the Ukrainian authorities. The respective deposition measurements have been adopted from Kashparov et al.10,11 and are stored in NILU’s repository website (http://radio.nilu.no). Using an atmospheric dispersion model, we simulate the atmospheric transport and deposition of the radioactive plume released by the forest fires. We also estimate the internal and external exposure of the population living in the path of the radioactive smoke. We assess the significance of the emissions with respect to the INES scale and define the regions over Europe, which were the most severely affected.

See more at: http://www.nature.com/articles/srep26062

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May 19, 2016 Posted by | Nuclear | , , , , , | Leave a comment