Alex Valentine

Several international leading efforts are focused on the improvement of evaluations for nuclear data. This data captures all of the physics of nuclear interactions for which the applications are far ranging from medical fields to criticality simulations. Nuclear analysis in the field of fusion, commonly referred to as neutronics, is one such application, typically employing Monte Carlo methods that rely on continuous-energy, pointwise cross-section data. Historically, the most widely adopted and complete radiation transport code in this field is MCNP, however in recent years there has been an evident trend in exploration of alternatives, most notably OpenMC. Nuclear analysis is a critical driver of the design, operation, safety and decommissioning of future fusion power plants stressing the importance of confidence in the transport codes and underlying nuclear data used in prediction of the radiation environment. Here we present recent developments to the JADE tool—a framework originally conceived for verification and validation of nuclear data within MCNP, now extended to performing cross-code comparisons. In particular, the developments required for the complete integration of OpenMC are detailed. A demonstration of this capability is presented for several of the currently implemented computational and experimental OpenMC benchmarks, with results compared against MCNP with the Fusion ENDF-3.2c and Evaluated Nuclear Data Library/B-VIII.0 nuclear data libraries.

Global research programs seeking to achieve a commercially viable model of a fusion power plant are being accelerated at an unprecedented rate. One critical element to the design and licensing is an accurate understanding of the radiation environment throughout the plant lifetime and subsequent decommissioning phase. The radiation field, which results from the nuclear fusion reaction, gives rise to highly complex phenomena such as flux leakage, materials activation, and decay gamma fields. Demonstration of compliance with limits, the integrity of components, and the permissibility of operations are all fundamental to regulatory approval and the overall safety of a nuclear device. As such, neutronics, which is used in the general sense to refer to the mapping of radiation fields in nuclear devices, is a critical design driver. The Applied Radiation Technology group at the United Kingdom Atomic Energy Authority is a world leader in this field, developing new methods and deploying state-of-the-art codes to conduct nuclear analysis. As well as applied neutronics in areas spanning fusion reactors, medical applications, spallation neutron sources, and nuclear fission, there is an extensive parallel experimental program undertaking critical radiation field characterization and conducting measurements using an array of bespoke particle detection systems. This paper highlights recent technical developments made by this group in the context of outstanding challenges in this field, as well as providing an overview of current methods and capabilities for the broader interest of the community.

Analyses of radiation fields resulting from a deuterium-tritium (DT) plasma in fusion devices is a critical input to the design and validation of many aspects of the reactor design, including, shielding, material lifetime and remote maintenance requirements/scheduling. Neutronics studies, which perform in-depth analysis are typically performed using radiation transport codes such as MCNP, TRIPOLI, Serpent, FLUKA and OpenMC. The Serpent 2 Monte-Carlo code, developed by VTT in Finland, is the focus of this work which seeks to benchmark the code for fusion applications. The application of Serpent 2 in fusion specific analysis requires validation of the codes performance in an energy range, and a geometrical description, which significantly differs to conventional nuclear fission analysis, for which the code was originally developed. A Serpent model of the Frascati Neutron Generator (FNG) Helium Cooled Pebble Bed (HCPB) mock up experiment has been prepared and the calculated results compared against experimental data, as well as the reference Monte Carlo code MCNP. The analysis is extended to a model of DEMO with HCPB blanket concept. For this model, the flux, nuclear heating, tritium production and DPA are calculated, all of which are integral nuclear responses in fusion reactor analysis. In general, a very good agreement is demonstrated for both of the benchmarks, with any discrepancies pinpointed to different physics models implemented.