海底堆積物における長寿命人工放射性核種の分布と挙動

アイリッシュ海の沿岸堆積物

抄録

Over the last four decades, the Irish Sea has received controlled discharges of radioactive effluents from the Sellafield (Windscale) nuclear fuel reprocessing plant in Cumbria, UK. Enhanced levels of a range of fission, activation and transuranic elements have been detected in a variety of environmental media. Most of Pu and ²⁴¹Am and about 10% of ¹³⁷Cs discharged have been retained in a deposit of the fine sediment near the discharge point. The quantities of radionuclides discharged annually from Sellafield decreased by two orders of magnitude from the mid-1970s to 1980, but estimated internal and external exposure for critical group decreased by only less than one order of magnitude over this period. Redistribution of the highly contaminated marine sediment is potentially of major significance.
In this paper, a review is presented of published work and our studies relating to the artificial long-lived radionuclides, ⁹⁹Tc, ¹³⁷Cs, ²³⁷Np, Pu isotopes and ²⁴¹Am, in sediments around the Irish Sea coast. The dominant mechanism (solution and/or particle transport) of supply of these radionuclides to coastal sediment is mainly discussed.