Engineered microstructure composites as means of improving the oxidation resistance of uranium nitride

QC 230910

Abstract

Owing to its high uranium density and good thermophysical properties,

uranium nitride (UN) fuel has been considered as a potential Accident Tolerant

Fuel (ATF) candidate for use in Light Water Reactors (LWRs). However,

the main disadvantage of UN is its low oxidation resistance in water/steam

containing atmospheres at the operating temperatures of LWRs.

The main objective of this thesis is to investigate a concept of engineered

microstructure composites as means of improving the response of UN to waterside

corrosion. The methodology for incorporating the corrosion resistant

additives in the form of metals, nitrides and oxides into the UN matrix has

been developed and tested. The additives were proposed to produce coated

(no interaction with UN) or doped (incorporation of the additive into the

UN bulk) grains, which will be able to shield the UN from the oxidising environment

and slow down the oxygen diffusion through the bulk. The UN

composite pellets containing the selected additives were sintered using the

Spark Plasma Sintering (SPS) technique. The resulting microstructures of

the composite pellets were well characterised prior to subjecting some of the

engineered microstructure representative samples to oxidation testing in air

and steam containing environments.

The obtained results indicate that the response to air and steam oxidation

of the composite samples differs from that of pure UN. Moreover, a delay in

the oxidation onset was observed for the composite samples UN-20CrN^premix

and UN-20ZrN^premix in steam and for UN-20CrN^premix pellet in air. The

improved response to oxidation was accompanied by the formation of the

ternary oxides, an observation that could be applied to the screening process

of the additive candidates for waterproofing of UN.

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