Calculation of radiation hazard connected with the SAD spallation target replacement

The Subcritical Assembly in Dubna (SAD) is a device coupled with existing 660 MeV proton accelerator (max beam current 3.2 μA). The main characteristic parameters of the core are: MOX fuel, keff=0.95, fission power 27.6 kW, Pb reflector. The SAD target consists of one central and 18 hexagonal (36 mm pitch) Pb prisms in two concentric layers. The main goal of the calculations, is the evaluation of the radiation hazard connected with replacement of the target elements after planned six months working period. The total induced radioactivity and its spatial distributions in the target elements were presented elsewhere. Here the longitudinal distribution and the time evolution of the gamma/beta emmiters activity, their spectra in the most active central target element and adequate radiation exposure are shown. The attenuation factors for these gamma ray spectra for commonly used shielding materials (Pb, Fe) are calculated as well. The MCNPX code is used for radioisotope production calculations. Gamma and beta spectra are calculated using modified EvIzo program and TORI database. Methods and tools used for gamma spectra simulation are checked using the results obtained in the experiment with bare Pb cylindrical target.