A molecular dynamics study of the thermal properties of thorium oxide

There is growing interest in the exploitation of the thorium nuclear fuel cycle as an alternative to that of uranium. As part of a wider study of the suitability of thorium dioxide (thoria) as a nuclear fuel, we have used molecular dynamics to investigate the thermal expansion, oxygen diffusion, and heat capacity of pure thoria and uranium doped (1-10%) thoria between 1500K and 3600 K. Our results indicate that the thermal performance of the thoria matrix, even when doped with 10%U, is comparable to, and possibly better than, that of UO2

GEANT4 Target Simulations for Low Energy Medical Applications

The GEANT4 code offers an extensive set of hadronic models for various projectiles and energy ranges. These models include theoretical, parameterized and, for low energy neutrons, data driven models. Theoretical or semi-empirical models sometimes cannot reproduce experimental data at low energies(<100MeV), especially for low Z elements, and therefore recent GEANT4 developments included a new particle\hp package which uses evaluated nuclear databases for proton interactions below 200 MeV. These recent developments have been used to study target designs for low energy proton accelerators, as replacements of research reactors, for medical applications. Presented in this paper are results of benchmarking of these new models for a range of targets, from lithium neutron production targets to molybdenum isotope production targets, with experimental data. Also included is a discussion of the most promising target designs that have currently been studied

5MW Power Upgrade Studies of the ISIS TS1 Target

The increasing demand for neutron production at the ISIS neutron spallation source has motivated a study of an upgrade of the production target TS1. This study focuses on a 5 MW power upgrade and complete redesign of the ISIS TS1 spallation target, reflector and neutron moderators. The optimisation of the target-moderator arrangement was done in order to obtain the maximum neutron output per unit input power. In addition, at each step of this optimisation study, the heat load and thermal stresses were calculated to ensure the target can sustain the increase in the beam power

GEANT4 Simulations of Proton-Induced Spallation for Applications in ADSR Systems

In order to assess the feasibility of spallation driven fission and transmutation, we have simulated proton induced neutron production using GEANT4, initially benchmarking our simulations against published experimental neutron spectra produced from a thick lead target bombarded with 0.5 and 1.5 GeV protons. The Bertini and INCL models available in GEANT4, coupled with the high precision (HP) neutron model, are found to adequately reproduce the published experimental data. Given the confidence in the GEANT4 simulations provided by this benchmarking, we have then proceeded to simulate neutron production as a function of target geometry and thence to some preliminary studies of neutron production in an ADSR with the geometry similar to that of the proposed Belgian MYRRHA project. This paper presents the results of our GEANT4 benchmarking and simulations

Au4V – Moment Stability and Spin Fluctuations in the Ordered Phase

Although neither gold nor vanadium generally possess a magnetic moment, the intermetallic compound Au4V is found to be ferromagnetic below 42K. In this paper we report the results of a muon spin relaxation study of the itinerant electron moment fluctuations in Au4V above the Curie temperature. The temperature dependence of the muon spin relaxation rate is found to be similar to that of the weak itinerant helimagnet, MnSi

Three Dimensional Mapping of Texture in Dental Enamel

We have used synchrotron x-ray diffraction to study the crystal orientation in human dental enamel as a function of position within intact tooth sections. Keeping tooth sections intact has allowed us to construct 2D and 3D spatial distribution maps of the magnitude and orientation of texture in dental enamel. We have found that the enamel crystallites are most highly aligned at the expected occlusal points for a maxillary first premolar, and that the texture direction varies spatially in a three dimensional curling arrangement. Our results provide a model for texture in enamel which can aid researchers in developing dental composite materials for fillings and crowns with optimal characteristics for longevity, and will guide clinicians to the best method for drilling into enamel, in order to minimize weakening of remaining tooth structure, during dental restoration procedure

GEANT4 Studies of Magnets Activation in the HEBT Line for the European Spallation Source

The High Energy Beam Transport (HEBT) line for the European Spallation Source is designed to transport the beam from the underground linac to the target at the surface level while keeping the beam losses small and providing the requested beam footprint and profile on the target. This paper presents activation studies of the magnets in the HEBT line due to backscattered neutrons from the target and beam interactions inside the collimators producing unstable isotopes

Thorium Energy Futures

The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options – liquid or solid, with or without an accelerator – can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice