The numerical simulation of caesium-137 transportation in ocean and the assessment of its radioactive impacts after Fukushima NPP release

After the damage of Fukushima Daiichi Nuclear Power Plant, a great number of radioactive materials were released into the Pacific Ocean. Therefore, it is necessary to research on the temporal and spatial distribution of these radionuclides. We use Princeton Ocean Model to simulate the circulation of the coast water of Fukushima NPP and obtain the concentration of cae- sium-137 by solving the diffusion equations. We employ the Monte Carlo N-particle （MCNP） code to assess the external doses caused by these contaminated sea water. To improve the efficiency and effectiveness of volume source in MCNP code, we es- tablish a transformation method between spot source and volume source, and determine an appropriate range of volume source. Finally, we calculate the absorbed doses of every organ/tissue and the effective dose of a human body.