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Journal of Chinese Society for Corrosion and protection  2026, Vol. 46 Issue (2): 352-364    DOI: 10.11902/1005.4537.2025.158
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Research Progress on Corrosion Resistance of UN Fuel and Its Doping Modification
WANG Mingjiang, WANG Xiaomin(), XIAO Hongxing
Key Laboratory of Nuclear Reactor Technology, Nuclear Fuel Element and Material Sub-institute of NPIC, Chengdu 610213, China
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WANG Mingjiang, WANG Xiaomin, XIAO Hongxing. Research Progress on Corrosion Resistance of UN Fuel and Its Doping Modification. Journal of Chinese Society for Corrosion and protection, 2026, 46(2): 352-364.

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Abstract  

The UN fuel, characterized by its high melting point, high uranium density, and high thermal conductivity, demonstrates significant advantages over UO2 fuel in enhancing the safety and economy of reactors, making it one of the promising new high-performance fuels with great potential in the Accident Tolerant Fuel (ATF) program. However, the UN fuel exhibits poor resistance to hydrothermal corrosion. Previous studies have indicated that doping can improve the corrosion resistance of UN fuel to some extent. The doping substances that have been investigated include UO2, U3Si2, UB2, Zr, Cr, Al and Ni etc., which have achieved certain success in raising the initiation temperature of corrosion and reducing the corrosion rate of UN materials. This paper provides a comprehensive summary of the corrosion behavior of UN fuel and the research progress on improving the corrosion resistance of UN fuel through doping. Additionally, it analyzes the deficiencies in the present research and feasible directions for improvement, offering references for further research and enhancement of the corrosion resistance of UN fuel.
Key words:  UN fuel      corrosion resistance      preparation process      doping     
Received:  25 May 2025      32134.14.1005.4537.2025.158
ZTFLH:  TL352  
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WANG Mingjiang
WANG Xiaomin
XIAO Hongxing

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.158     OR     https://www.jcscp.org/EN/Y2026/V46/I2/352

Fig.1  Microstructure of the corroded UN pellet[11], there are obvious intergranular corrosion and grain separation
Fig.2  Changes in thickness of UN, U2N3 and UO2 samples vs exposure time to H2O2[12], the slope reflects its corrosion rate
Fig.3  Potential energy changes of the H2O dissociation reaction on the UN (110) surface[15] (a) and migration path of oxygen atoms[17] (b)
Fig.4  Influence of density, impurity content and H2 on the corrosion weight gain of UN[20]: (a) thermal ramp, (b) isothermal exposure at 400 ℃
Preparation processPurityDensityGrain sizeCorrosion resistance
HDNHigh--Higher purity is beneficial for enhancing corrosion resistance
CTR-NHigh carbon and oxygen content--Both carbon and oxygen impurities will reduce the corrosion resistance
HP-A higher sintering temperature may cause the UN to decom-pose and result in a decrease in densityRelated to the ball-milling method and the ball-mill-ing time; relatively smallerAffected by density and grain size, the influence of other microstructures still needs to be studied
SPS-It is conducive to increasing densityRelated to the ball-milling method and the ball-mill-ing time; relatively largerHigher density and smaller grain size are conducive to enhancing corrosion resistance. the influence of other microstructures still needs to be explored
Table 1  Influence of preparation process on the characteristics of UN fuel pellets
Fig.5  Relationship between the relative density of the pellet using SPS and temperature and pressure[31]
Preparation parametersGrain size / μmOnset temperature / ℃Oxidation rate / %·min-1
1500-80-298.60.35
1700-410-60377.60.44
1600-8010378.60.45
1550-1000.6381.80.14
1550-808401.30.35
1600-4428420.30.43
Table 2  Oxidation onset temperature of UN fuel samples with different preparation parameters[32]
Fig.6  Morphology of UN and UN-UO2 after 30 min of corrosion in water at different temperatures[36], there is obvious intergranular corrosion on the surface
Fig.7  Dependence of the fraction reacted (α) on temperature for the corrosion of UN and UN-UO2[13], doping with UO2 reduces the onset temperature of corrosion
Fig.8  Oxidation mass gain curves of UN and UN-U3Si2[44] (a) and icrostructure of UN-U3Si2 after 30 min corrosion (300 ℃, 9 MPa)[11] (b)
Fig.9  Morphology of UN-UB2 after corrosion, red arrows are included to show connections between oxidised grains (a), and Morphology of UN after corrosion[47] (b)
Fig.10  Microstructure of UN-ZrN[49] (a), oxidation mass gain curves of UN and UN-ZrN[49] (b), corrosion rates of UN and U0.77Zr0.23N in steam[50] (c), and Arrhenius plot[50] (d)
Fig.11  Segregation energy and strengthening energy of metals and oxygen elements on the grain boundary[53], O/N indicates that O occupies the N position
Fig.12  Mass gain curves of UN and composite pellets[56], (a) air, (b) steam
AdditiveFormInfluenceConclusion
UO2Dual-phaseThe onset temperature decreases and the corrosion rate acceleratesThe doping of UO2 will cause corrosion to occur throughout the entire core block, providing more diffusion channels and intensifying the corrosion of the fuel
U3Si2Dual-phaseThe onset temperature rises, and the corrosion rate accelerates in the later stage. The weight gain decreases within a short period of timeThe doping of U3Si2 transforms the corrosion mechanism into intergranular corrosion, thereby inhibiting crack propagation
UB2Partial solid solutionThe onset temperature increased while the corrosion rate remained basically the same, and the integrity after corrosion was betterThe UB2 at the grain boundaries may have inhibited the occurrence of corrosion through the grain boundary modification method, and enhanced the integrity after corrosion
ZrComplete solid solutionThe onset temperature and corrosion rate vary depending on the experimental methodThe sensitivity of solid solutions to air and steam may vary
Al、NiDual-phaseThe sintering process is difficult. The addition of Al will lower the initial temperatureThe differences between the UN and Al in terms of density and thermal expansion coefficient result in significant internal stress, which further aggravates the corrosion
CrPartial solid solutionThe initial temperature rises, and it further increases after annealingSolid solutions play a significant role in enhancing corrosion resistance. The effects of suppressing segregation and increasing the strength of grain boundaryneed to be further verified
Table 3  Summary of the influence of additives on the corrosion resistance of UN fuel
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