Preliminary Conceptual Design of Nuclear Thermal Rocket Reactor Cores Using Ceramic Fuels with Beryllium or Composite Neutron Moderators

Abstract

Several preliminary conceptual designs of nuclear thermal rocket reactor cores are presented that use tin-bonded monolithic ceramic [mononitride (UN), monocarbide (UC), and uranium dioxide (UO₂)] fuel plates or pins with molybdenum-tungsten alloy clad. Neutron moderation is provided by a block of Be metal or composite materials using metal hydrides such as ZrH_1.6 or YH_1.6 with different matrices (MgO or Be). Mainly high-assay low-enriched uranium is considered, but highly enriched uranium is also assessed for a few configurations. Nominal core thermal power is 300 MW corresponding to about 66 kN (15 klbf) of thrust, and with minimal modifications, 500 MW may be possible (25 klbf of thrust). Depending on the configurations, the amount of ²³⁵U needed for criticality is 30 to 90 kg, and reactor weight is 2.5 to 3.8 tonnes.

Keywords:

• Nuclear thermal propulsion
• ceramic fuels
• UN
• UC
• beryllium
• composite moderators

Acknowledgments

The authors gratefully acknowledge Douglas Burns from Idaho National Laboratory and Mike Houts from NASA for providing funding and encouragement as well as Lance Snead and Jason Trelewicz from the State University of New York at Stony Brook for sharing their insights regarding composite moderators.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Notes

^a The solubility of W in liquid Sn is very low (0.001 at. % at 2273 K).^[19] The solubility of Mo in liquid Sn is higher than that of W but is still acceptable (~1 at. % at 2500 K and at equilibrium, that is, after 1 to 3 days^[20]) especially given the short time at high temperature experienced by the NTR fuel system during normal operation.

^b Reference [33] indicates that “A positive hydrogen worth creates an inherent positive power coefficient via the turbopump. An increase in reactor power causes an increase in pump power input, which increases hydrogen flow/density, which increases reactivity, which in turn causes a further increase in power. There is a slight lag in this effect due to the travel time of the coolant from the reactor to the pump and from the pump to the reactor (the lag will effectively be the longer of these two times), which will be on the order of seconds.”

Additional information

Funding

This work was supported by NASA and by the U.S. Department of Energy, Office of Nuclear Energy, under U.S. Department of Energy Idaho Operations Office contract [DE-AC07-051D14517]. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.