R2SUNED is a code system implementing the mesh-based Rigorous-two-step method for shutdown dose rates calculations, making use of MCNP and ACAB codes. In addition to the most relevant features of state-of-the-art R2S systems, novel and unique features have been implemented in R2SUNED to overcome limitations common to the current mesh-based R2S implementations. One of particular interest is the cell-under-voxel approach intended to address most of the issues associated with the conventional averaging technique used in the neutron flux determination. The underlying idea is to identify the cells enclosed in each voxel and calculate the average value of the neutron flux within each cell fraction. Subsequently, the activation of each material, filling the cell delimited by the voxel, is calculated using the neutron flux evaluated in the corresponding cell. This capability enables to properly resolve the strong spatial gradients of the neutron flux independently of geometrical considerations. Another relevant feature is that a flexible decay gamma source sampling has been incorporated to assure an efficient decay gamma transport in a vast diversity of problems. A verification of R2SUNED has been addressed on the ITER computational shutdown dose rate benchmark. It is highlighted both the limitations of voxel averaged neutron flux standard approach, and the ability of R2SUNED to overcome this issue. The excellent agreement of the results with those obtained using a mesh matching perfectly the geometry tells that R2SUNED performs correctly. Finally, a description of the most representative applications carried out with R2SUNED is provided for fusion relevant facilities.

Development of the R2SUNED Code System for Shutdown Dose Rate Calculations

D1SUNED system for the determination of decay photon related quantities

The ITER Tokamak Complex is the civil structure that will host the ITER Tokamak and the largest part of the associated systems. The dimensions are 120 m × 80 m × 60 m, built mostly of concrete, with over one thousand penetrations. During ITER operation, a radiation field will spread throughout the complex from diverse radiation sources. It must be characterized to check the compliance with the limits for electronics allocation and human intervention. However, the production of radiation maps in the ITER Tokamak Complex is a task of paramount sophistication due to challenges to adequately model in MCNP the radiation sources involved. In this work, two important methodological upgrades are presented. First, a new MCNP model of the Tokamak Complex, conceived to be computationally stable while capturing a conservative representation of the baseline. Second, a novel approach to model the plasma source, called a mosaic source, allows an unprecedented degree of realism and accuracy in terms of capturing the port specificities. Both represent a step change in the capacity to produce ITER radiation maps with increased reliability, augmenting previous versions. Examples of partial radiation maps are provided considering both methodological upgrades.

Lucia Perez

Papers

Shutdown dose rate analysis of European test blanket modules shields in ITER Equatorial Port #16

Nuclear analysis of the ITER Cryopump Ports