Uranium nitride-silicide advanced nuclear fuel: Higher efficiency and greater safety

The development of new nuclear fuel compositions is being driven by an interest in improving efficiency/lowering cost and increasing safety margins. Nuclear fuel efficiency is in large measure a function of the atomic density of the uranium, that is, the more fissionable uranium available per unit volume the less fuel volume that is required. Proliferation concerns limit the concentration of fissile 235U, and thus attention is directed to higher overall uranium content fuel. Among the options are the high temperature phases U3Si2 and composite UN- U3Si2 where the design would have the more water-stable U3Si2 surround the more soluble, but higher uranium density UN grains. (Uranium metal of course has the highest atomic density, however its low melting point, high degree of swelling under irradiation, and chemical reactivity eliminate it from consideration.) Another advantage of the nitride and silicide phases are their high thermal conductivity, greatly exceeding the current standard UO2 fuel, with the high conductivity potentially allowing the fuel to operate at a higher power density. Please click Additional Files below to see the full abstract

Synthesis, characterization, and phase stability of high temperature thermoelectric metal borides and silicides

Thermoelectric (TE) materials are used for converting waste heat into electricity. The TE technology is attractive because it uses solid-state devices that are immovable, highly reliable, and eco-friendly. Currently, the TE materials have low conversion efficiencies at higher temperatures and uses expensive elements (Te, Ge, etc.) for TE power generation. Investigation was made on selected alkaline earth metal borides (CaB6, and SrB 6,) and silicides (Mg2Si and CaSi) and transition metal borides and silicides of ABX-type (A = Ti/ Nb/ Mn; B = Co; X = B/Si). Screening of the alloys were done based on the available literature/calculations of energy band gaps, crystal structure, transport, and thermodynamic properties. Experiments were conducted on alkaline earth metal silicides (Mg 2Si and metal-doped Mg2Si), transition metal boride (TiB 2), and transition metal silicide (Mn4Si7). The selected alloys were synthesized and analyzed. Thermodynamic properties (specific heat, change in enthalpy, entropy, Gibbs energy, and activities) of the alloys were determined at higher temperatures using differential scanning calorimetry (DSC), differential thermal analyzer (DTA), and solid-state galvanic or EMF cell methods. Reaction kinetic studies on Mg2Si and metal-doped Mg2Si (Mg2Si: mX; X = Ti, Nb, Mn, Co; m = 0 - 0.08 mol) were conducted. Thermodynamic modelling tools were used to calculate the thermodynamic properties and phase equilibria of alloys. This research work provide the fundamental knowledge on thermodynamic and thermoelectric properties of metal borides and silicides