Materials Reports  2022, Vol. 36 Issue (Z1): 21110113-4 |
| INORGANIC MATERIALS AND CERAMIC MATRIX COMPOSITES |
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| Study on Mechanism of Substoichiometric UO2-x Fuel for Special Nuclear Power Reactor |
| WU Xuezhi, YIN Bangyue
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| Reactor Engineering Technology Research Institute, China Institute of Atomic Energy, Beijing 102413, China |
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Abstract Substoichiometric uranium dioxide (UO2-x) was a special U-O fuel, compared with traditional UO2 fuel, due to its extremely low high temperature oxygen potential and high temperature volatilization, substoichiometric UO2-x fuel had become one of the candidate fuels for some special nuclear power reactors with high service temperature and long service time.In this work, the main line is the preparation process of substoi-chiometric uranium dioxide fuel (UO2-x), study on the formation mechanism of substoichiometric (n(O)/n(U)<2) . It mainly includes: the O/U ratio, oxygen potential (ΔGO2) and oxygen partial pressure (PO2) of substoichiometric fuel are calculated; the effects of process parameters such as adding uranium and sintering time on the O/U ratio and ΔGO2 of fuel are investigated.
As an oxide fuel with O/U ratio < 2.0, substoichiometric UO2-x is low in high temperature oxygen potential. In this study, the substoichiometric UO2-x fuel was prepared by UO2+x doped with uranium through a metallurgical process of powder, including mixing, pressing and sintering, so as to explore the change law of substoichiometric UO2-x fuel O/U ratio as well as relevant mechanism.
The results showed that O/U ratio of substoichiometric UO2-x fuel decreased with sintering oxygen potential (ΔGO2), O/U ratio < 1.995 only when ΔGO2<-642.89 kJ/mol. The substoichiometric UO2-x cannot be prepared by sintering with ordinary hydrogen at 2 023 K. Uranium reduces the O/U ratio of the fuel synergistically through participating in the reduction reaction and regulating sintering ΔGO2. Uranium is added to the fuel for liquid phase sintering, thus promoting the grain growth. The grain size of substoichiometric UO1.974 fuel ranges from 15 μm to 40 μm, and of stoichiometric UO1.974 fuel from 5 μm to 15 μm. Large grains are low in fission gas release rate. Raman spectra have shown that compared with conventional UO2 fuel, substoichiometric UO1.974 fuel has shifted spectral peak, which is the characteristic peak of the substoichiometric fuel.
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Published: 05 June 2022
Online: 2022-06-08
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