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Conference Article: Fabrication of uranium-plutonium mixed nitride and thermally stable carbide fuels

Arai, Y.; Fukushima, S.; Shiozawa, K.; Handa, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan))

Abstract

Synthesis of uranium-plutonium mixed nitride, (U,Pu)N, by carbothermic reduction in a mixed 92%N2-8%H2 stream was studied on a laboratory scale. UO mixed in a molar ratio, PuO2 and graphite powders were mixed in a molar ratio, C/(0.8U02+0.2Pu02), of 2.2, 2.5, 2.8, 3.1 and 3.5, and carbothermic reduction was performed at 1773 K for 0.2, 0.5, 1, 3, 6, 10 and 20 h. In the early stages of the reduction, oxide, sesquinitride and graphite phases were present besides (U,Pu)N, but they disappeared in the final stage where the weight change obtained was in a good agreement with the calculated value. Present experimental results show that the increase of C/(0.8U02+0.2Pu02) ratio aids the rapid removal of oxygen, but results in taking a long time to obtain high purity (U,Pu)N. Thermally stable uranium carbide pellets with low densities were fabricated by using pore former. In the present study, 0.5, 1.0 and 1.5 wt% of the pore former particles with a diameter ranging lo-100 pm were added to UC besides 0.1 wt% of Ni as a sintering aid. The powders were compacted into green pellets without an organic binder under the pressure of 300 MPa, followed by sintering at1873 K for 3 h in a flow of Ar gas. Bulk density of sintered uranium carbide pellets decreased with an increase of addition of the pore former; i.e. 94, 90 and 87 %TD for 0.5, 1.0 and 1.5 wt% addition of pore former, respectively. Microstructure of the pellets showed that UC matrix phase was fully sintered and spherical pores, not interconnected, were uniformly distributed in the pellets. It was confirmed by the heat-treatment experiments that the present pellets were by far thermally stable compared with those prepared by a conventional method with similar densities.

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key words: density; fabrication; fuel pellets; microstructure; mixed carbide fuels; plutonium carbides; plutonium nitrides; uranium carbides; uranium nitrides
Reference:
Technical committee meeting on advanced fuel for fast breeder reactors: Fabrication and properties and their optimization. Vienna (Austria). 3-5 Nov 1987
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--466, pp:25-33