Neutron skyshine from nuclear facilities

The advance in neutron skyshine research and the significance are first described. Then, skyshine calculation methods in 1980s particularly and the skyshine experiment in Japan with various nuclear facilities (reactors, D-T neutron sources, accelerators) are reviewed. In comparison with such experiment usable as bench mark, the skyshine calculation methods (Monte Carlo method, transport calculation method) are evaluated for their accuracy and merits and demerits. The values by Monte Carlo calculation were in agreement within about 30 % with the experimental values. Those by DOT 3.5 calculation were twice as large as the experimental values. Those by PALLAS calculation were in good agreement in dose with the experimental values, but the spectra were considerably different. The values by SKYSHINE-2 were in good agreement with the experimental values, but since the ground effect was ignored, the values may deviate from the experimental ones if it is taken into account. (Mori, K.)