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A Uranium Nitride Doped with Chromium, Nickel or Aluminum as an Accident Tolerant Fuel

Aneta Herman and Christian Ekberg

Uranium nitride (UN) is a possible accident tolerant fuel candidate for light water reactors. Apart from advantages in high metal density and high thermal conductivity, it suffers from low stability in water. We have suggested exploiting metal inclusions to enhance its stability in water by forming a protective layer. A uranium nitride doped with chromium (Cr 2.7 wt%), nickel (Ni 2.8 wt%) or aluminum (Al 1.5 wt%) was prepared by internal sol gel and carbothermal reduction. An electron dispersive spectroscopy revealed a homogeneous distribution of metals in all sol-gel products. The carbothermal reduction was performed in the N2+5%H2 mixture at 1500°C for 6 hours. X-ray diffraction confirmed UN phase formation in the samples. Pellets were manufactured by sintering in argon at 1800°C for 6 hours. During the sintering, a majority of the chromium evaporated from a surface, nickel moved towards the grain boundaries and aluminum formed an agglomerate on the rim of a pellet. Finally, the pellets were boiled in water at normal pressure. A reference pellet of pure UN utterly collapsed after 2 hours of boiling. Both nickel and aluminum doped pellets disintegrated within a couple of minutes. The chromium doped pellet did not collapse during 5 hours of boiling. This indicated a clear improvement in corrosion resistance of the uranium nitride based material.