Nuclear Thermal Propulsion Reactor Materials

Abstract

Nuclear thermal propulsion (NTP) systems have been studied in both the USA and the former Soviet Union since the 1950s for use in space science and exploration missions. NTP uses nuclear fission to heat hydrogen to very high temperatures in a short amount of time so that the hydrogen can provide thrust as it accelerates through an engine nozzle. Benefits of NTP systems compared to conventional chemical and solar electric powered propulsion systems include higher fuel efficiency, greater mission range, shorter transit times, and a greater ability to abort missions and return to Earth in the event of system failure. As a result of these benefits, the US National Aeronautics and Space Administration (NASA) is evaluating NTP for use in crewed missions to Mars, and plans for a possible mid-2020s flight demonstration of a NTP engine are under development. The extremely harsh conditions that NTP systems must operate in present a number of significant engine design and operational challenges. The objective of this chapter will be to describe the history of NTP material development, describe current NTP material fabrication and design practices, and discuss possible future advances in space propulsion material technologies.

Nuclear Thermal Propulsion

“…The technology was too new and not well understood in the early 1960s, but was being investigated in parallel to the NERVA experiments. CERMET compacts consist of ceramic fuel particles embedded in a refractory metal matrix [19,20]. The choice of matrix and fuel material influences thermal stability, thermal conductivity, structural integrity, and neutronics performance of the CERMET compact.…”

“…In a simplistic sense, CERMET fuels are particles of ceramic fuel (i.e., UO 2 or UN) encapsulated in a metal matrix, typically, but not limited to, tungsten, rhenium, or molybdenum. The research conducted by ANL and GE included the development and testing of the CERMET fuel and the design of the ANL-200, ANL-2000 [20,21], and the GE 710 reactors [21,23]. These CERMET programs focused entirely on HEU fuel kernels and fast reactor concepts.…”

“…The matrix material of a CERMET usually makes up about 30-60% of the compact volume [23], so its properties are both neutronically and structurally important. The ANL and GE programs focused mostly on natural tungsten as matrix material [20]. Among the available matrix materials, tungsten provides the largest fracture strength and temperature stability [6].…”

Thermal Barrier Coatings Overview: Design, Manufacturing, and Applications in High-Temperature Industries

“…In this technology, Mo 2 C acts a diffusion barrier to minimize the amount of carbon reacting with the Mo. The biggest challenges in the NTP research field relate to minimizing three things: high-temperature hydrogen corrosion, fracture caused by temperature gradients, and radiation damage that would impede reactor performance during operation . In general, reduced hydrogen ingress into carbon fuel elements, along with reduced property mismatching in the materials, could improve component lifetime and overall performance.…”

“…The biggest challenges in the NTP research field relate to minimizing three things: high-temperature hydrogen corrosion, fracture caused by temperature gradients, and radiation damage that would impede reactor performance during operation. 141 In general, reduced hydrogen ingress into carbon fuel elements, along with reduced property mismatching in the materials, could improve component lifetime and overall performance. Another fuel option being studied for use in NTP systems is W/UO 2 and Mo/UO 2 ceramic metal (CERMET) fuel, which must be able to operate in excess of 2700 K while remaining compatible with the H 2 propellant.…”