Novel approach for efficient mesh based Monte Carlo shutdown dose rate calculations

A novel approach for the Monte Carlo based calculation of high resolution shutdown dose rate distributions was elaborated at KIT developing the previous R2Smesh technique. The method utilizes the MCNP code for particle transport calculations and the FISPACT code for the activity calculations providing the decay photon source distribution. The spatial distributions both of neutrons and decay photons are obtained by making use of the mesh tally technique available with MCNP5. This procedure has no limitation for the complexity of the geometry used for particle transport simulations. As a unique novelty, the present approach does not need a particle track output (PTRAC) file for the determination of the material composition in a mesh element. Instead a newly developed subroutine, linked to the MCNP code, takes care about the geometry cells, materials and their volume fractions in the mesh cell passing this information directly to the MCNP's mesh tally output file. The new approach is verified by means of benchmark calculations for JET and compared to the cell based rigorous 2 step (R2S) method. The results obtained fit very well experimental data. The successful application of the new interface to JET has demonstrated that this approach can be applied with confidence for shutdown dose rate assessments in ITER. © 2013 Elsevier B.V.