About the project
Accident tolerant fuel manufacture and characterisation
Uranium nitride fuel is considered for commercial use in light water reactors, but faces issues related to compatibility with water. Using spark plasma sintering for manufacture of UN pellets, our division has previously shown that the corrosion rate of UN pellets exposed to high temperature steam can be reduced by an order of magnitude. Within projects funded by SSF, further improvement of the water tolerance of uranium nitride is pursued.
Uranium nitride contains 40% more uranium atoms per volume unit than uranium dioxide. Moreover, the thermal conductivity of UN is on average seven times higher than that of UO2. Hence, the residence time of the fuel in a water cooled reactor could be increased substantially, in conjunction with an improved margin to fuel melting. Hence there is an interest for using UN as fuel in commercial water-cooled reactors. To this end, the water tolerance of UN pellets exposed to high temperature steam needs to be improved and the cost of UN manufacture related to the required use of nitrogen enriched in 15N must be reduced (14N is a strong neutron absorber in a thermal spectrum).
Our division has previously developed a method of UN pellet manufacture based on a combination of hydriding/nitriding of metallic uranium and spark plasma sintering. The outcome is highly dense UN pellets with fully closed porosity. Exposing such pellets to high temperature steam at pressures typical for LWR applications, it was found that corrosion rates could be reduced by an order of magnitude, as compared to UN pellets manufactured using conventional methods. Moreover, it was shown that the method applied for UN powder production reduced losses of 15N to acceptable levels.
The cost of converting enriched uranium hexafluoride to a metallic source material may be substantial. Hence methods for manufacturing UN directly from enriched UF6 should be developed and qualified. The tolerance to water exposure may be further enhanced by embedding UN-particles in a matrix of AlN or UO2, yielding composite UN-AlN and UN-UO2 fuels. In addition, a solid solution of UN and CrN may provide a defence in depth for water attack.
The current research focuses on the following activities
- Direct manufacture of UN using ammonolysis of UF4 andUF6.
- Manufacture of composite UN-UO2 fuels.
- Manufacture and characterisation of (U,Cr)N, (U,Cr)N-AlN and UN-AlN pellets using spark plasma sintering.
External funding for the project:
- SSF (10 MSEK)
Staff involved in the project:
- Mikael Jolkkonen (Researcher)
- Janne Wallenius (Professor)
- Diogo Costa (PhD student)
- Yulia Mischenko (PhD student)
Industrial and academic partners:
- Westinghouse
- Chalmers
- Bangor University
Peer reviewed journal publications resulting from the project:
Mikael Jolkkonen, Pertti Malkki, Kyle Johnson, Janne Wallenius
Uranium nitride fuels in superheated steam
Journal of Nuclear Science and Technology 54 (2017) 513.
Denise Adorno Lopes, Selim Uygur, Kyle Johnson
Degradation of UN and UN-U3Si2 pellets in steam
Journal of Nuclear Science and Technology 54 (2017) 405.
Kyle Johnson, Valter Ström, Janne Wallenius, Denise Adorno Lopes
Oxidation of accident tolerant fuel candidates
Journal of Nuclear Science and Technology 54 (2017) 280.
Kyle Johnson, Alicia M. Raftery, Denise Adorno Lopes, Janne Wallenius
Fabrication and microstructural analysis of UN-U3Si2 composites for accident tolerant fuel applications
Journal of Nuclear Materials, 477 (2016) 18.
Kyle Johnson, Janne Wallenius, Mikael Jolkkonen and Antoine Claisse
Spark plasma sintering and porosity studies of uranium nitride
Journal of Nuclear Materials, 473 (2016) 13.
Pertti Malkki, Mikael Jolkkonen, Tobias Hollmer and Janne Wallenius
Manufacture of fully dense uranium nitride pellets using hydride derived powders with spark plasma sintering
Journal of Nuclear Materials 452 (2014) 548