BEAM STOP OF SPIRAL2 FACILITY: ACTIVATION AND RESIDUAL DOSE RATE CALCULATIONS

SPIRAL2 facility will produce 5mA of deuterons at 40 MeV. A beam dump device has been designed to stop the beam. The residual dose rates in the beam dump room during beam-off phases at cooling times up to one year have been computed using the following methodology: i) ISABEL built-in MCNPX nuclear model to deal with deuterons transport and production and transport of secondary neutrons, ii) deuteron and neutron induced activation were simulated using ACAB code and EAF2007 library, iii) decay gammas were transported using MCNPX to compute residual dose rate. The ambient dose equivalent rate is mainly due to the activated copper pieces of the beam stop. Uncertainties in the results are mainly due to d-Cu activation cross sections and due to the determination of the neutron source. Correction factors to improve the activation cross section are proposed and residual dose rate range depending nuclear data used to compute the neutron source (nuclear model or library) will be evaluated.