State-of-the-art 3-D neutronics analysis methods for fusion energy systems

Recent advances in radiation transport simulation tools enable an increased fidelity and accuracy in modeling complex geometries in fusion systems. Future neutronics calculations for design and analysis will increasingly be based directly on 3-D CAD-based geometries, allowing enhanced model complexity, reduced human effort and improved quality assurance. Improvements have been made in both stochastic and deterministic radiation transport methodologies. To adapt the MCNP stochastic transport software, the translator approach allows CAD geometries to be converted from their native formats into standard input files, while the direct geometry approach uses computer graphics algorithms to perform the radiation transport on the CAD geometry itself. The former takes advantage of the efficiency of the native MCNP software without modifications while the latter permits the modeling of more complex surfaces. The ATTILA radiation transport package uses a finite-element formulation of the discrete-ordinate methodology to provide a deterministic solution on a tetrahedral mesh derived automatically from a CAD-based geometry. All of these tools are being applied to a dedicated benchmark problem consisting of a 40 degree sector of the ITER machine defined only in a CAD-based solid model. The specific benchmark problems exercise the ability to use a CAD-based geometry to solve a range of fusion neutronics problems including neutron wall loading, deep penetration and narrow duct streaming. The results of this exercise will be used to validate/qualify these tools for use on ITER. At the same time, many of these tools are being used to support the design of ITER components and other related fusion systems. UW has provided high-fidelity nuclear analysis of ITER first wall and shield modules identifying local effects of geometric features. ASIPP has used the MCAM tool to update and extend the existing ITER basic model and used it for neutronics analysis of the proposed Chinese ITER-TBM. FZK has used the McCAD interface programme to generate models of the Electron Cyclotron Resonance Heating (ECRH) launcher for integration into the standard ITER MCNP model. UKAEA have carried out design analysis of the RF antenna systems using both Attila and MCNP to determine a number of nuclear responses. Other systems being studied include the ARIES Compact Stellarator, IFMIF, and EAST. The widespread use of these tools in the design and analysis of ITER and other fusion energy systems will enable a more accurate assessment of the nuclear response of individual components, leading to a reduction in design margins, improved overall performance, and new level of quality assurance (QA) since these new tools ensure that engineering and analysis models are consistent. (orig.)