Methodology to address radioprotection and safety issues in the IFMIF/EVEDA accelerator prototype

摘要

In the IFMIF/EVEDA accelerator prototype, deuterons (with energies up to 9 MeV) interact with the materials of the accelerator components due to beam losses and in the beam dump, where the beam is stopped. The productions of neutrons/photons together with radioactive inventories due to deuteron-induced reactions are some major issues for radioprotection and safety assessment. Here, we will focus on the proposal of a computational approach able to simulate deuteron transport and evaluate deuteron interactions and production of secondary particles with acceptable precision. Current Monte Carlo codes, such as MCNPX or PHITS, when applied for deuteron transport calculation, use built-in semi-analytical models to describe deuteron interactions. These models are found unreliable in predicting neutron and photon generated by low energy deuterons, typically present in the IFMIF/EVEDA prototype accelerator. In this context, a new computational methodological approach is proposed based on the use of an extended version of current MC codes capable to use evaluated deuteron libraries for neutron (and gamma) production. The TALYS nuclear reaction code is found to be an interesting potential candidate to produce the evaluated data for double-differential neutron and photon emission cross sections for incident deuterons in the energy range of interest for IFMIF/EVEDA applications. The recently-released deuteron Talys-based Evaluated Nuclear Data Library, TENDL-2009, is considered a good starting point in the road to achieve deuteron data files of enough quality for deuteron transport problems in EVEDA. Unfortunately, current Monte Carlo transport codes are not able to handle light ion libraries except for protons. To overcome this drawback the MCNPX code has been extended to handle deuteron (also triton, helion and alpha) nuclear data libraries. In this new extended MCNPX version called MCUNED, a new variance reduction technique has also been implemented for the production of secondary particles induced by light ions nuclear reactions, which allow reducing drastically the computing time needed in transport and nuclear response function calculations. Verification of these new capabilities for Monte 2 Carlo simulation of deuteron transport and secondary products generation included in MCUNED is successfully achieved. The existence of the MCUNED code allows us for the first time testing the deuteron crosssection TENDL package by simulation of integral experiments. Some preliminary efforts are addressed to compare existing experimental data on thick target neutron yields for Copper with those computed by the MCUNED code using TENDL cross sections.