[en] In an experimental multi-purpose high temperature gas reactor (VHTR) being developed in Japan, because of the high temperature fuel, the quantity of fission product released from the coated fuel particles is considerable, which then deposits in the primary cooling system as plate-out. This plate-out phenomena were calculated by the use of the code PADLOC for the calculation of the distribution of fission-product deposition. The values were compared with those obtained with the in-pile gas loop OGL-1 installed to the JMTR (Japan Material Testing Reactor). Using the code PADLOC which assumes the material transfer in flow-paths and surface-layer adsorption equilibrium, the tendency of decrease in the concentration distribution from upstream to downstream was enhanced in comparison with that measured in the OGL-1. In this connection, a microscopic model of decreasing the material transfer rate was presented, so that the results by the calculation with the code PADLOC agreed with those measured in the gas loop OGL-1. (Mori, K.)

[en] Procedures of shielding analysis are described which were used for the shielding modification design of the Nuclear Ship 'MUTSU'. The calculations of the radiation distribution on board were made using Sn codes ANISN and TWOTRAN, a point kernel code QAD and a Monte Carlo code MORSE. The accuracies of these calculations were investigated through the analysis of various shielding experiments: the shield tank experiment of the Nuclear Ship ''Otto Hahn'', the shielding mock-up experiment for 'MUTSU' performed in JRR-4, the shielding benchmark experiment using the ¹⁶N radiation facility of AERE Harwell and the shielding effect experiment of the ship structure performed in the training ship 'Shintoku-Maru'. The values calculated by the ANISN agree with the data measured at 'Otto Hahn' within a factor of 2 for fast neutrons and within a factor of 3 for epithermal and thermal neutrons. The γ-ray dose rates calculated by the QAD agree with the measured values within 30% for the analysis of the experiment in JRR-4. The design values for 'MUTSU' were determined in consequence of these experimental analyses. (author)

[en] Experimental studies of neutron and gamma-radiation skyshine at nuclear reactor are proceeding in cooperation with Russia, Kazakhstan and Japan as a project of international science technology center (ISTC). Fast neutron streaming from the vertical experimental hole of IVG.1M reactor which has a cylindrical core are analyzed by a monte carlo n-particle transport code (MCNP) with variance reduction methods, in which a weight window method and a cell importance method can be selected. Calculation results on radial distribution of fast neutron flux at 100 cm above the reactor is compared with the experimental values. The calculated values of neutron flux by using the cell importance method, however, is very different from the experimental values at close distance of 10 cm from the center. Skyshine analysis of neutron radiation streaming from the reactor are also carried out by the equivalent source model in which a point source and the detectors are located at 10 cm and 1 m above the ground, respectively. The calculated values of total neutron flux distribution are very close to the experimental values. The effects of the air composition on neutron flux calculation are also investigated. (M. Suetake)