Atomistic Scale Study of Radiation Effects in ABO3 Perovskites

Summary
The development of nuclear power is at an important juncture, with two competing but in many ways complementary technologies: fusion and fission. However, while the nuclear methodology is different the engineering challenge is the same, that is, the need to remove the generated heat while structures are subject to high levels of radiation damage and residual nuclear products. In particular, radiation damage effects and gas bubble formation are problematic issues for the development of both fusion and GenIV fission reactors. For example in a GenIV fission core, the Xe and Kr gas comes from fission of the fissile nuclei, that is, Pu and U, while in a fusion core He is formed within the D-T plasma. This proposal aims to address these issues using tunable perovskites, as model materials, and focusing on the following issues:

1. Crystalline to amorphous transformation mechanisms in tunable ceramics instigated using non-radioactive ion beams.
2. Bubble nucleation at micro-structural traps in predominantly fission reactor materials, e.g. oxide based fuels, and ODS materials, but which can be formed by He implantation from fusion plasma He nucleation, and damage in materials for use in fusion cores, such as YBCO superconductors suggested as magnetic containment in for example, ITER and DEMO.

The research will be undertaken using the approach of experimental and simulation techniques combined holistically. The experimental study will utilise in-situ and bulk irradiation, primarily in combination with advanced electron microscopy and atom probe tomography. The complementary simulation programme will be based on irradiated materials, but focusing on recovery mechanisms, bubble evolution, and validation of current models.

The outcomes of the research will be used in the development of new materials for use as both fuels, for example Inert Matrix, or as magnetic containment devices in ITER/DEMO. The information from this research can also be utilised in other non-standard reactor technologies such as the travelling wave designs.

The information derived will also help the design of future waste forms for Pu/U, specifically into new phases capable of tolerating the effects of radiation damage, and He bubble formation.

For all nuclear materials the progress of radiation damage, whether the material is to be used as a waste form, or within a reactor, needs to be understood as it determins the useful life of the structure. Currently there are many models in the literature outlining the effects of radiation damage, and there are also many outlining the effects of gas bubble evolution. However, there are none that describe the effects of radiation damage, and gas bubble formation together. In combination these effects have dramatic impact on the long-term stability of materials, and greater understanding is demanded if their effects are to be alleviated.

The results from this work will help to overcome this knowledge gap, and will be used to nform the generation of new materials. For example, within a ceramic nuclear fuel, do gas bubbles form first around fission fragments or are the fission fragments attracted to the gas bubbles already formed? This is an important question and not easily answerable, but it is one of the issues that impacts future ceramic fuel development despite having been of concern for many years. This work will directly address this question, as the ability of ion irradiation to irradiate materials under a range of conditions allows the effect of a metal impurity to be studied directly. The results from this work will be used to drive new, and enhanced models for predicting this behaviour, while at the same time provide a mechanism by which current models can be validated, or improved.

During this work we also intend to drive further the effects of radiation damage and gas bubble formation in materials for use within a fusion core, primarily modelling the effects in materials proposed for use as magnetic containment, i.e. superconducting magnets based on the perovskite structure. This is an area of research we will make important contributions to, and provide information that is not only lacking but without which current research is being hampered.

The enhanced examination of ceramic materials using atom-probe tomography is an area where this work will have a large impact. There is currently a limited range of ceramics being investigated by this state of the art method, this work will help to increase its exposure, with methods being developed, and results being presented to wider community. The use of atom probe tomography in nuclear materials science is generally limited to metallic-based systems, this work will show the potential for atom probe tomography for use in ceramics.

During the course of our research, as a group, we must work collectively, with the results from the experimental programme being introduced into, and validating, the modelling programme and while the modelling provides insights and understanding not accessible experimentally. The results from this work will be shared in the traditional manner, that is, though publications and conference presentations. In addition we will build upon our collective collaborations with other groups worldwide studying similar effects: e.g. at Los Alamos National Laboratory (LANL), Australian Nuclear Science and Technology Organisation (ANSTO), the Institute for Transuranic research (ITU), the Universities of Tennessee (UT), Michigan (UMich) and the Commissariat à l'énergie atomique et aux énergies alternatives (CEA).

Finally one impact that is often overlooked is the provision of skilled researchers in the field, for example this work will, upon completion, have generated two post doctoral researchers in the fields of radiation damage and atom probe tomography of nuclear materials. Both of these fields are currently demanding more people to work within the UK and thus our project contributes to the UK being world leading in the generation of new nuclear technology.