The Japan Maritime Self Defense Force (JMSDF) quickly began disaster relief operations from the sea at the coast of Sanriku after the Great East Japan Earthquake. We observed in situ situation of our activity area because we had to estimate the impact of the advection and diffusion of the radioactive substance in the sea. Two survey ships ”Wakasa” and ”Nichinan” of JMSDF observed the temperature, salinity and current in detail at the wide area of offshore Sanriku and 30 NM distant from Fukushima No.1 Nuclear Power Plant (NPP), Tokyo Electric Power Company in April and May 2011. No strong current exist in the area near Fukushima No.1 NPP. Southward current with tidal component dominate during the observation. The upwelling current is also observed along the continental slope off the coast of Sanriku. These data will be provided as the initial value of the simulation study on the diffusion of the radioactive substance and the spatiotemporal reference value that simulation model should resolve.
We have developed an advanced environmental transfer and dose assessment model 1.0 (AdvETDAM 1.0) for radionuclides (3H, 129I, 14C etc.) discharged from the first Japanese commercial nuclear fuel reprocessing plant located in Rokkasho. The computer code system was developed on a PC to describe atmospheric dispersion, terrestrial and aquatic transfers, and dose calculations of the radionuclides. The aquatic transfer model of the radionuclides targeted Lake Obuchi. which is a brackish lake neighboring the reprocessing plant. Futamata River flows into the lake, and provides most of fresh water to the lake. The lake is also connected through Obuchi Fishing Port at the mouth of the lake to the Pacific Ocean. The radionuclides are introduced into the lake through three routes: atmospheric deposition on the lake surface, inflow from the catchment area through Futamata River, and inflow from the Pacific Ocean. The radionuclide concentration in Futamata River water was simulated by a radionuclides transfer model for the catchment area of the river. Since the radioactive waste water is discharged to the coast of Rokkasho. the concentration of the radionuclides in seawater at the Obuchi Fishing Port was estimated by a radionuclide transfer model for the Rokkasho Coast. The Lake Obuchi model consists of a water current model and an ecosystem model including aquatic organisms. This paper introduces an overview of the Lake Obuchi model and the handling methods of parameters related to the radioiodine (129I) in the ecosystem model. Concentrations of 129I in lake water and biological samples collected from Lake Obuchi in 2008, which were higher than the background level, were simulated by using AdvETDAM 1.0 to confirm its function.
In order to develop a bioaccumulation model which predict the levels of hazardous chemicals in food chain of sea area, we carried out the surveys in Tokyo Bay to examine concentrations of coplanar-PCB (Co-PCB). crude fat levels and so on in fish (conger-eel : Conger myriaster and Japanese whiting : Sillago japonica).
From these research data, we could discuss about bioaccumulation profiles of Co-PCB of living fish in Tokyo Bay. As the results of discussion, the profiles were presumed as follows.
• The bioaccumulation levels of Co-PCB in conger-eel and Japanese whiting are risen with their age. but the level of fat does not affect to the increase of accumulation of age-related Co-PCB.
• In ihe conger-eel inhabiting Tokyo Bay. the Co-PCB is mainly distributed in that fat.
• The lower fat fish inhabiting Tokyo Bay has higher concentration of Co-PCB in crude fat unit.
• In the conger-eel and Japanese whiting inhabiting Tokyo Bay. the accumulation rates of Co-PCB congenr which have 5 or 6 chlorine atoms are higher than that of Co-PCB congeners which have 4 or 7 chlorine atoms.
• Non-ortho PCBs have lower accumulation rate than mono-ortho Co-PCBs.
• In the Co-PCB congeners which have same number of chlorine atoms, a Co-PCB congener which has higher water solubility has higher accumulation rate.