ABOUT MIDAS
Materials for more efficient, cost-effective, cleaner and greener nuclear power
The nuclear fuel in light-water fission reactors is in the form of small pellets of uranium dioxide. These are contained within tubes made from the metal zirconium, which is mixed, or alloyed, with a small fraction of atoms of other metals, such as iron, chromium, niobium, tin and nickel.
These zirconium alloy tubes, known as fuel rods, need to last for a usage life of around six years, during which time they must withstand the harsh conditions of the reactor without failing. In the event of any issues in this functionality, the reactor must be shut down at great expense, lessening the supply of power to the electricity grid.
This presents a tough challenge for materials scientists and the alloys making up the tubes must be carefully engineered, right down to the atomic scale. The tubes are put through a series of thermo-mechanical treatments, being heated and cooled, squashed and stretched, in carefully designed ways, to give the final metal the correct, optimised, properties. This method of processing lines up the many microscopic zirconium crystals (known as grains) that the tube is made of and ensures that the additional alloying ingredients, the other metals, are gathered together in microscopic particles (known as secondary phase particles, or SPPs), spread throughout the tube. This pattern of grains and SPPs, known as the microstructure, must be just right if the fuel tubes are to function as intended.
Gaining greater understanding of the performance and behavioural properties of these materials in the extreme environment of a reactor core will enable better, more efficient use of nuclear fuel, providing routes to cleaner, cheaper and safer nuclear power.
The MIDAS Programme…
…benefits from a unique set of industrially-relevant materials irradiated in a research reactor to very high fluence levels, which were contributed to the research team by Westinghouse and the international Nuclear Fuel Industry Research (NFIR) programme. Due to their unique nature these samples have significant worth, which, alongside core funding from the Engineering and Physical Sciences Research Council (EPSRC) industrial commitments, bring the total value of the programme to around £25 million.
The assembly materials studied are those used as protective cladding for the highly radioactive fuel used in a nuclear reactor. Due to the need to operate reactors as safely as possible, fuel is often removed well before it is spent (i.e. before all the energy is extracted) because not enough is currently known about these cladding materials, so plant operators must adopt a highly cautious, safety-first approach. This reduces the cost-efficiency of nuclear power as an energy option, as well as meaning that the fuel assembly prematurely becomes additional waste, which must be safely handled and stored over the long term.
Reactor safety, however, remains paramount, so MIDAS also has a dedicated work package, within Key Challenge 4, on better understanding fuel cladding behaviour in accident scenarios. The aim of this is to ensure that reactors remain safe in the event of an incident such as Fukushima, as well as including work on the development of accident-tolerant fuels.
A further key theme of MIDAS is to explore the use of zirconium alloys in critical components for future fusion reactors. The UK has a leading position in defining the materials that will be chosen for the ITER and DEMO international fusion projects, and this theme will contribute to maintaining the UK's reputation as a centre of excellence in fusion research.
Central to the programme is the use of UK facilities at which work on active samples may be undertaken. These include National Nuclear User Facility sites at the National Nuclear Laboratory, Materials Research Facility and The University of Manchester's Dalton Cumbrian Facility, as well as new capabilities made available through the Henry Royce Institute. These have received significant investment from the UK government, and MIDAS is a key beneficiary of this investment, as well as being a trailblazing project to showcase what research is possible at these new and enhanced facilities.
The ultimate goal of MIDAS is to help the UK, and other countries, meet carbon reduction targets, and achieve an energy mix that produces less CO2. The MIDAS team is therefore working closely with a range of UK and international industrial partners and stakeholders in addressing this challenge and translate fundamental research into real-world impact.