High density UO
Embodiments of the invention are directed to a method for production of a nuclear fuel pellet by spark plasma sintering (SPS), wherein a fuel pellet with more than 80% TD or more than 90% TD is formed. The SPS can be performed with the imposition of a controlled uniaxial pressure applied at the maximum temperature of the processing to achieve a very high density, in excess of 95% TD, at temperatures of 850 to 1600° C. The formation of a fuel pellet can be carried out in one hour or less. In an embodiment of the invention, a nuclear fuel pellet comprises UO 2 and a highly thermally conductive material, such as SiC or diamond.
1. A method for preparing a nuclear fuel pellet, comprising:
providing a homogeneous dispersion of powders as a nuclear fuel powder, the homogeneous dispersion of powders comprising uranium dioxide (UO 2 ) and a thermally conductive material selected from a metal or metal alloy, where the homogeneous dispersion of powders comprises 90 to 99 vol % of the UO 2 and the thermally conductive material has a thermal conductivity that is greater than 10 W/mK at 100° C.;
treating an inner surface of a die assembly with graphite;
loading said die assembly with said nuclear fuel powder;
placing said die assembly in a sintering chamber of a spark plasma sintering (SPS) apparatus;
applying a pulsed current, a vacuum, and heat, wherein temperature is increased to a maximum temperature of 850 to 1600° C. and a rate of increase after achieving a temperature of 600° C. is at least 50° C./minute;
maintaining said maximum temperature for a period of 0.5 to 20 minutes; and
applying a controlled pressure of 25 to 100 MPa to said die assembly during said period for said maintaining of said maximum temperature, wherein a nuclear fuel pellet is formed, and wherein during the maintaining said period, holding said maximum temperature and said controlled pressure until a density of more than 95% TD (theoretical density) of the UO 2 , an average grain size of at least 4 μm with little or no inter-granular pores, and a thermal conductivity of at least 8 W/mK at 100° C. is attained.
2. The method according to claim 1 , wherein said nuclear fuel powder further comprises other oxidation states of uranium oxide, uranium nitride, thorium oxide, plutonium oxide, or any combination thereof.
3. The method according to claim 1 , wherein said controlled pressure is a uniaxial pressure of 30 to 45 MPa.
4. The method according to claim 3 , wherein said nuclear fuel powder comprising a nuclear fuel comprises a mixture of oxides with a stoichiometry UO 2+x where x is 0 to 0.25, and wherein said maximum temperature is 1050° C. to 1600° C.
5. The method according to claim 1 , wherein said nuclear fuel powder consists of UO 2 and said thermally conductive material, and said thermally conductive material is uranium or a uranium alloy.
6. The method according to claim 1 , further comprising reducing said fuel pellet by exposure to a reducing gas.