Joining of Tungsten Cermet Nuclear Fuel

Nuclear Thermal Propulsion (NTP) has been identified as a critical technology needed for human missions to Mars due to its increased specific impulse (Isp) as compared to traditional chemical propulsion systems. A critical aspect of the program is to develop a robust, stable nuclear fuel. One of the nuclear fuel configurations currently being evaluated is a cermet-based material comprised of uranium dioxide (UO2) particles encased in a tungsten matrix (W). Recently, hot isostatic pressure (HIP) and spark plasma sintering (SPS) processing techniques have been evaluated for producing W cermet-based fuel elements from powder feedstocks. Although both techniques have been used successfully to produce W cermet fuel segments, the fabrication of full-size W cermet elements (>20) has proven to be difficult. As a result, the use of W cermet segments to produce a full-size W cermet fuel element is of interest. However, techniques for joining the segments are needed that will not lower the use temperature, damage the UO2 particles, or compromise the nuclear performance of the fuel. For these reasons, joining of the segments using braze or weld techniques is not desired. Therefore, diffusion bonding techniques will be developed during this investigation for producing full-size nuclear fuel rods from W cermet segments. To promote diffusion during solid state bonding, different refractory metal interfacial coatings will be evaluated.

NASA applications that would directly benefit from this technology include Nuclear Thermal Propulsion (NTP) and Nuclear Electric Propulsion (NEP). Initial NTP systems will have specific impulses roughly twice that of the best chemical systems, i.e., reduced propellant requirements and/or reduced trip time. The proposed Phase I and Phase II efforts would greatly assist NASA with achieving the promise of NTP and NEP. Potential NASA missions include rapid robotic exploration missions throughout the solar system and piloted missions to Mars and other destinations such as near earth asteroids.

Commercial sectors that will benefit from this technology include medical, power generation, electronics, defense, aerospace, chemicals, and corrosion protection. Specific applications include protective coatings, x-ray targets, valves, non-eroding throats and thrusters for propulsion, and crucible/furnace components.

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