Advanced Materials For Generation IV Nuclear Reactor Fuel

Project title: Advanced Materials For Generation IV Nuclear Reactor Fuel
Main applicant: Sergei Butorin, Division of Molecular and Condensed Matter Physics
Grant amount: 3 600 000 SEK for the period 2017-2020
Funder: Project Grant within New Nuclear Technology from the Swedish Research Council

Abstract: The goal of the project is to improve scientific knowledge of processes important for optimizing the properties of fuel materials for fourth generation (GEN IV) nuclear reactors. We aim to establish the fundamental physical, chemical and structural properties of such materials to reach a predictive understanding of the behavior of Th, U and Pu carbides and (U,Pu) mixed oxides fuels for GEN IV fast neutron reactors. The latter would also include Am. For materials prepared with different procedures, this is planned to be achieved by employing, besides the standard methods of characterization, advanced experimental techniques, such as greatly improved in terms of sensitivity and chemical contrast x-ray spectroscopic methods. The experiments will be supported by first-principle calculations taking into account the features of the f-electron systems.

For simulation of irradiated fuel materials, the properties of nuclear fuel materials with defects will be studied to predict the structural behavior of the fuel. Furthermore, in-situ experiments at high temperatures and controlled atmosphere will be conducted by taking advantage of the newly designed high-temperature cell.

The project will be carried out in collaboration with Helmholtz-Zentrum Dresden-Rossendorf and CEA (The French Alternative Energies and Atomic Energy Commission), Marcoule, France by taking advantage of their dedicated facilities for actinide research. A new beamline at the Swedish synchrotron MAX IV will be also utilized.

The European energy consumption is currently covered from various energy sources, as mineral and fossil fuels, renewable energy sources, and nuclear energy. Fossil and mineral fuels (coal, gas, oil) that are the leading primary source of energy are responsible for substantial CO2 emission. Nuclear energy comes on a second place and produces 27% of the European Union's (EU) electricity. This clearly shows that the need for nuclear energy still remains. While nuclear power offers benefits in terms of reduced carbon emission, it has limitations in terms of safety and influence of radioactive waste on the environment. The majority of current nuclear power plants belong to the family of light-water reactors (LWR), a technology that was developed in the fifties and sixties of the previous century. Replacement of older reactors requires a renewal of nuclear technology, a process that is currently ongoing. In this, the generation-IV (Gen IV) reactor systems are presently being researched and developed and expected to be commercially deployed from 2030.

The six prototype reactors are currently being considered in Gen IV. Among these prototypes are the Super Critical Water-Cooled (SCWR) reactor, the Sodium Cooled Fast Reactor (SFR), Lead-Cooled Fast Reactor (LFR) and the Molten Salt Reactor (MSR). The reactor types are planned to utilize new nuclear fuel materials, as uranium-thorium fluorides (UF4, ThF4) in MSR, uranium and plutonium carbides in SFR, mixed uranium oxide-carbides (UO2-UC2) in SCWR, and uranium nitrides in LFR. However, there exists only a limited knowledge of the physical, chemical and mechanical properties of the targeted Gen IV fuel materials due to the restricted handling of the nuclear materials, and property measurements which can only take place in specialized, restricted-access facilities.

In the framework of the GEN IV nuclear reactors development, innovative fuel cycles are also studied. The two main goals of these fuel cycles are an efficient use of the energy resources by recycling together the major actinides such as U and Pu, and a decrease of the waste radiotoxicity by partitioning and transmutating the minor ones, such as Np, Am, or Cm. However, the challenge is to incorporate the large quantities (up to 5 at.%) of highly radioactive minor actinide into the mixed oxide (MOX) nuclear fuel. Only a fluorite type solid solution, as in case of pure (U,Pu)O2, has to be achieved for the final product. One of the most concerned minor actinides is 241Am because of its high radioactivity and significant amount. Therefore, research efforts are focused on this actinide and its dilution in (U,Pu)O2 to produce uranium-plutonium-americium mixed oxides as transmutation targets.

The purpose of the project is to improve scientific knowledge of processes important for sintering and tuning the properties of materials for the GEN IV nuclear reactor fuel. We aim to establish the fundamental physical, chemical and structural properties of such materials to reach a predictive understanding of the behaviour of Th, U and Pu carbides and mixed oxides (MOX) of the U-Pu-O system which will also include Am. For materials prepared with different procedures, this is planned to be achieved by employing, besides the standard methods of characterization, advanced experimental techniques, such as greatly improved in terms of sensitivity and chemical contrast x-ray spectroscopic methods. These methods provide accurate information about the chemical states, homogeneity of compounds, (non)stoichiometry, carbon/metal and oxygen/metal ratio, local symmetry and environment and charge distribution. The experiments will be supported by model calculations taking into account the features of the f-electron systems.

For simulation of irradiation-damaged fuel materials, the properties of nuclear fuel materials with defects will be studied to predict behaviour of the materials under reactor operation. Furthermore, experiments at high temperatures and controlled atmosphere will be conducted by taking advantage of the newly designed high-temperature cell.

Part of the experiments foreseen in the proposal will be carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and CEA (Commissariat à l'Energie Atomique), Marcoule, France, where specialized laboratories exist for the synthesis of nuclear materials and their characterization through a variety of chemistry and physics techniques. A newly-constructed beamline at the Swedish synchrotron MAX IV will be also utilized.