Radiation shielding design studies of the accelerator-driven system demonstrator SAD

The radiation fields and the effective dose at the Sub-critical Assembly in Dubna (SAD) have been studied with the Monte Carlo code MCNPX. The effective dose above the shielding, i.e., in the direction of the incident proton beam of 3.0 μA, was found to be 190 μSv/h. This value meets the dose limits according to Russian radiation protection regulations, provided that access to the rooms in this area is not allowed for working personnel during operation. It was also shown that the attenuation of the effective dose in the shielding, after some adjustment distance, is determined entirely by the high-energy neutrons and can be described by two exponential functions, one in the inner part of the shielding consisting of heavy concrete and one in the outer part consisting of standard concrete. The tenth-valued attenuation lengths were found to be 58 cm in the heavy concrete and 93 cm in the standard concrete. In order to optimise the shielding design, the heavy concrete in the biological shielding was in the simulations replaced by iron. By varying the thickness of the iron section, it was found that a minimal effective dose, of about 0.13 μSv/h, is obtained for a combination of 250 cm of iron followed by 190 cm of standard concrete. (author)