DISTRIBUTION AND BEHAVIOR OF TC-99, NP-237, PU-239, PU-240, AND AM-241 IN THE COASTAL AND ESTUARINE SEDIMENTS OF THE IRISH SEA

Intertidal coastal and estuarine sediments from 24 sites in the Irish Sea have been analyzed for Tc-99, Np-237, Pu-238, Pu-239, Pu-240 and Am-241. The Np-237 activity and Pu-239/Pu-240 ratio were measured simultaneously by ICP-MS, and Tc-99 was determined by HR-ICP-MS which is ten times more sensitive than Q-ICP-MS. The activities of Tc-99, Np-237, Pu-239, Pu-240 and Am-241 were distributed over a wide range of 1.5-70.5, 0.01-13.3, 2.3-1589, 2.6-1894 Bq/kg, respectively. Activities of these radionuclides decreased exponentially with distance from the Sellafield source. The Am-241/Pu-239, Pu-240 and Np-237/Pu-239, Pu-240 ratios were almost constant with distance from the Sellafield. This result suggests that the distribution and behavior of Np and Pu are controlled by complicated factors such as the influence of transport, the variation with time of Np/Pu ratio in the Sellafield discharges and sedimentary mixing processes in the Irish Sea.