Abstract
Effect of surrounding environment on neutron skyshine propagation was evaluated by the Monte Carlo code MCNPX using a fast neutron source reactor YAYOI of the University of Tokyo. The validity of using the MCNPX for evaluation of neutron skyshine dose was verified at first by comparison with the measurement. Then, MCNPX calculation was carried out using different environmental parameters-different ground conditions and different atmospheric conditions -to see the effect of each parameter. This paper succeeded in evaluating the quantitative effect of these parameters, and concluded that the condition of the ground gives as high as 30 % discrepancy in skyshine neutron dose, where the condition of atmosphere such as temperature, atmospheric pressure or relative humidity may lead to few tens of percent overestimation or underestimation.
