The issue of Cs-137 in firewood and biomass combustion: a review

Abstract

In large parts of Europe, the Chernobyl accident of 1986 caused fallout of Cs-137. This led to the uptake of Cs-137 in trees or other materials used for bioenergy production or as firewood for domestic purposes. This Cs-137 may concentrate in the ashes of the combustion process in such a way that the clearance level of 100 Bq per kg, defined in Directive 2013/59/Euratom (EU BSS), may consequently be exceeded. There is currently no clear consensus in Europe regarding the regulatory approach to this issue: should the import and use of Cs-137 contaminated biomass and its ashes be considered as a planned exposure situation or rather as an existing exposure situation? If considered as an existing exposure situation, which reference level should be applied? We compare the approaches in various European countries, such as Finland, Norway, Sweden, Belgium and the Netherlands. Results of a recent measurement campaign performed in Belgium on firewood imported from Belarus, Ukraine and other countries show a quite large range of Cs-137 activity concentration in firewood. Analysis of samples from biomass combustion confirms that the clearance level of 100 Bq per kg Cs-137 may be exceeded even when the activity concentration in the initial pellet is trivial. A review of dose-assessment studies performed by STUK and from the literature is presented. The general context of biomass energy production is sketched: for instance, in the Netherlands, 40 large biomass firing plants (capacity > 10 MW) are operational and some 20 more are already planned. The fly ashes from the biomass combustion may be a valuable resource for the construction industry, and the issue of Cs-137 contamination is connected with the requirements of the EU BSS regarding the natural radioactivity of building materials. Assessing the impact of Cs-137 contamination and clarifying regulations in the frame of a graded approach are important elements in this context.

Radioactivity of residues from waste incineration facilities in Finland

“…Due to the presence of fallout Cs-137 in the Finnish environment [26] originating from the Chernobyl nuclear accident in 1986 and atmospheric nuclear weapons testing in the 1950s and 1960s, the general exemption and clearance level of 0.1 kBq kg −1 for Cs-137 from the EU-BSSD is not practical in Finland. For example, almost all ash from bioenergy production in Finland exceeds this level for Cs-137, often by a large margin [27,28]. In Finland, the exposure from fallout Cs-137 is considered as part of natural radiation and thus fallout Cs-137 is included in the regulations for natural radiation [25].…”