Code development and design study on accelerator-driven transmutation research at JAERI

The calculation models in the cascade code NMTC/JAERI have been improved on bases of the new nuclear theory and new measured data. The intranuclear nucleon-nucleon scattering process calculation has been modified taking into accounts the effects of reflection and refraction of nucleon in nucleus and nucleon-nucleus scattering cross section. The preequilibrium process model was adopted to improve the prediction about nucleon back scattering. Adjustment was made for parameters in the high energy fission model and the adoption of total reaction cross section estimated systematically. Some benchmark calculations were carried out to verify the prediction capability of the modified cascade code. The ACCEL code system for designing an accelerator-driven system has recently been upgraded as the ATRAS system. The Sn transport code TWOTRAN2 and Monte Carlo transport code MORSE have been replaced by new codes TWODANT with faster computation time and MCNP4A with the continuous Monte Carlo method respectively. The 73 group-wise cross sections up to 20 MeV have newly been produced to be used with the TWODANT code. The burnup code BURNER linked with TWODANT was also prepared well. The conceptual design study on proton accelerator-driven transmutation systems with nitride fuel and new molten salt of minor actinides were carried out as another promising options. The solid fuel system consists of a sodium-cooled subcritical core with pin-bundle type assemblies of actinide nitride fuel and a multi-layer type spallation target of tungsten. It is expected to have the better thermal characteristics than metal fuel system. When the system is driven by several tens mA proton beam with an energy of 1 GeV, amounts of minor actinides transmuted per year and the power generation were given respectively. The burnup calculations up to 300 days and the preliminary dynamics analysis were performed to examine the transmutation capability and the nuclear safety in this system. The nuclear characteristics of the system with MA-PbCl3 type chloride molten salt fuel was examined and compared with MA-NaCl type one researched already. (authors)