Long-term assessment model of radionuclides in the oceans (LAMER). Development and validation of the diffusion model in global ocean

To quantify the risk from nuclear cycle facilities, a Long-term Assessment ModEl of Radionuclides in the Oceans (LAMER) has been developed. A part of LAMER, an advection-diffusion model with a plutonium scavenging process has been developed for calculating the distribution of 137Cs and 239,240Pu in the Ocean. Calculations of 137Cs and 239,240Pu in seawater profiles and sediments were carried out using global fallout data from past atmospheric nuclear tests. The results were then compared with experimental data obtained from the 1960's to the 1990's at over 100 sites, mainly in the Pacific and Atlantic Oceans, in order to verify the model and to find optimum horizontal and vertical diffusion coefficients. The reasonable agreement between the calculated and measured 137Cs water profiles was found using the values of 1.3x108 cm2 s-1 and 0.3 cm2 s-1 for the horizontal and vertical diffusion coefficients, respectively. Calculated water profile concentrations and inventories 239,240Pu in water and sediment of the ocean have also showed a reasonable agreement with the experimental results. As for 137Cs, 82% and 93% out of 650 measured data, and as for 239,240Pu, 63% and 84% out of 734 measured data were included with factor 2 and 5, respectively. (author)