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Kato, Masato; Hirooka, Shun; Ikusawa, Yoshihisa; Takeuchi, Kentaro; Akashi, Masatoshi; Maeda, Koji; Watanabe, Masashi; Komeno, Akira; Morimoto, Kyoichi
Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 12 Pages, 2014/08
Uranium and plutonium mixed oxide (MOX) fuel has been developed for Japan sodium-cooled fast reactors. Science based fuel technologies have been developed to analyse behaviours of MOX pellets in the sintering process and irradiation conditions. The technologies can provide appropriate sintering conditions, irradiation behaviour analysis results and so on using mechanistic models which are derived based on theoretical equations to represent various properties.
Hirooka, Shun; Kato, Masato; Morimoto, Kyoichi; Washiya, Tadahiro
Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 8 Pages, 2014/08
Since the severe accident at Fukushima Daiichi Nuclear Power Station, technologies to remove fuel debris from the damaged core have been developed. However, many subjects such as how to access to the core, cut the fuel debris, control criticality safety, estimate fissile materials, store removed debris and so on are still in existence. Purpose of this work is to evaluate the fuel debris properties by using analysis of simulated fuel debris and to estimate the inner state such as temperature profile and density profile which depend on elapsed time after the accident. The reported properties such as melting temperature, thermal conductivity and thermal expansion were obtained by the simulated fuel debris manufactured from UO
and zircaloy.
Kawamura, Hideyuki; Kobayashi, Takuya; Furuno, Akiko; Usui, Norihisa*; Kamachi, Masafumi*; Nishikawa, Shiro*; Ishikawa, Yoichi*
Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 7 Pages, 2014/08
Numerical simulations on oceanic dispersion of the radioactive cesium in the North Pacific from March 2011 to September 2013 were conducted to clarify the concentration of the radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant. We implemented the oceanic dispersion simulations with two independent ocean reanalysis dataset. It was suggested that the 
Cs concentration in the North Pacific was lower than the pre-Fukushima background level about two years after the Fukushima disaster. The intercomparison revealed that meso-scale eddies in the Kuroshio Extension region may have efficiently diluted the radioactive cesium concentration at the sea surface. In addition, it was suggested that the enhanced downward current accompanied by the meso-scale eddies played an important role in transporting the radioactive cesium into the intermediate layer.
Yokota, Hideharu; Tanaka, Shingo
Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 10 Pages, 2014/08
For understanding mass transport mechanism in the rock as natural barrier, 
dipole tracer migration experiments were implemented for a fracture in mudstone of Wakkanai Formation at the G.L.-250m gallery of the Horonobe URL, northern Hokkaido, Japan. Results of its preliminary analysis by the analytical solution retrieved from one-dimensional advection-dispersion equation indicate that a fracture surface in mudstone has both reversible and irreversible sorption characteristics for Cs
and Sr
but only irreversible that for Co and Eu
.
Saito, Tatsuo; Yamaguchi, Masaaki; Kato, Tomoko; Oda, Yoshihiro; Kitamura, Akihiro
no journal, ,
It has already passed nearly three years since the accident of a Fukushima Dai-ichi Nuclear Power Plant (FDNPP). Now, the main nuclide which is contributing to radiation dose rate is radioactive caesium (
Cs and Cs, hereafter, radioactive Cs). Predicting the distribution of radioactive Cs deposited in the soil surface of Fukushima Prefecture after the accident and understanding the adsorption/desorption mechanism between soil and radioactive Cs in the environment are indispensable for evaluating the impact of radiological exposure dose. Primary transportation mechanism of radioactive Cs is considered to be in the form of soil erosion on the land surface and sediment-sorbed contaminants transport in the water system. In our project entitled "Long-term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima" (F-TRACE project), we have been simulating radioactive Cs transport by watershed models. Based on these predictions, we evaluate a 1-cm dose equivalent rate with PHITS (Particle and Heavy Ion Transport code System) in a selected environment and present the results attained thus far.
Kitamura, Akihiro; Yamaguchi, Masaaki; Kurikami, Hiroshi; Sato, Haruo; Yui, Mikazu
no journal, ,
The major earthquake and tsunami on 11 March 2011 resulted in a nuclear accident at the FDNPP and the accident resulted in contamination of a wide range of terrestrial. Predicting distributions and fate of radioactive materials released from the FDNPP and deposited on the environment is one of the important subjects to be treated. The radionuclide of most concern in the Fukushima in now days is considered to be radioactive cesium which tends to adsorb with clay rich soils. We therefore developed a simple and fast simulation model utilizing the universal soil loss equation and the geographical information system. Relatively high contaminated areas exceeding 1.0
10
Bq/m
were observed within approximately 100 km radius of the FDNPP and there are 14 river basins exist in this area. We applied our model to predict the amount of soil and cesium losses from each river basin and annual discharge rates of radioactive cesium into the ocean are estimated for several years since the FDNPP accident.