Proposal of shutdown dose estimation method by Monte Carlo code

In the ITER project, the estimation of the dose equivalent rate levels after reactor shutdown for hands-on maintenance around the torus is a key point. The Sn transport and activation codes, because of their poor ability for modelling complex geometry (as in the ITER machine), yield a large uncertainty in radiation transport calculations where the geometry is not simple. In this paper, we propose a method that solves the above problem using a Monte Carlo code that allows a detailed geometry description. This new method requires modification of nuclear data library replacing a prompt gamma spectrum with a decay gamma spectrum and also a modest change in the computer program (MCNP). A simple geometry benchmark problem was conducted, comparing the new method and an existing method (THIDA-2). The agreement of the two methods is fairly good, suggesting that the new method is useful for very complex geometry devices. The slight difference observed in the results from both methods likely comes from the difference in the nuclear data library used in both methods.