Radiocesium in the forest and forest industry, Studies on the flow, occurrence and technological enhancement of radionuclides in the forest industry with emphasis on radiocesium
Sammanfattning: In the aftermath of the nuclear weapons testing and as compared with agriculture, the forest industry has received relatively little attention in spite of its large-scale use of radiocesium- contaminated wood and water. After the Chernobyl nuclear power plant accident in 1986, numerous studies of the forest environment have been conducted with respect to radionuclide transfer through the forest ecosystem or its many components. Still, the impact from radioactive fallout on the forest industries that receive the bulk fraction of biomass removed from the forest has scarcely been investigated. Recycling process elements is a necessity in chemical pulping to be competitive. The chemical pulping process is primarily designed to extract, separate and recover the digesting agent carriers such as sodium and complementary carriers such as calcium needed for the production of fresh cooking liquors. Besides these chemical elements, unwanted elements in the process such as K and many other chemical elements are also retained as a consequence of their chemical similarity to sodium and calcium. Notably, two such elements are the long-lived fallout fission products radiocesium and radiostrontium which build-up to substantial activities in parts of the pulp mill recovery cycle and in ash and sludge deposits. Improvements of the pulp recovery processes and the striving towards completely closed systems are estimated to yield around 30 GBq Cs-137 per Bq/kg of Cs-137 in wood as an upper limit of the radiocesium activity inventory within an average Nordic pulp mill site. In the perspective of new emerging practices for industrial resource management of by-products, radionuclides will not only be transferred from the forest to the industries, but may be returned to the forest with by-products rich in valuable plant nutrients. The radionuclides in the forest soil and trees constitute a source of radiation and the consequences thereof can be evaluated in terms of the resulting absorbed dose rate in the environment.
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