Historical research guide · 0010 · 2023
Accessing Icy Worlds Using Lattice Confinement Fusion (LCF) Fast Fission
Theresa L. Benyo
In one minute
In February 2023 Theresa Benyo and Lawrence Forsley took a NASA Glenn NIAC project to JPL’s Cryobot Workshop with a direct pitch: give an ice-melting probe its own small nuclear engine. NASA wants to reach the oceans under Europa, Enceladus, Ceres and Pluto, which means boring through as much as forty kilometres of ice, at pressures running to ten kilobar, on a power source that is small, long-lived and throttleable. Their answer is lattice confinement fusion — the reaction NASA Glenn published in Physical Review C in 2020, in which deuterium packed into a metal lattice reaches close to solid fuel density and fuses because the metal’s own electrons screen the charge, so only a few atoms need heating at a time. Benyo and Forsley pair it with fast fission: fusion neutrons of up to 14.1 MeV are energetic enough to split thorium-232 and natural uranium-238, so no enriched uranium is needed. Waste heat melts the ice, the electricity runs the probe, and the same system could drive nuclear electric propulsion on the way out.
Connection
This is chapter 12’s programme stated as a mission: the NASA Glenn lattice fusion result turned into a power plant small enough to ride inside a probe, with the enriched-uranium problem engineered out.
From the source
Lattice confinement fusion sidesteps the pressure, temperature and containment problem of ordinary fusion. Deuterium loaded into a metal lattice sits at close to solid fuel density, and the lattice’s electron cloud screens the deuteron’s charge so that only a few atoms need to be heated at a time.slide 8, How LCF Works; Pines et al., Phys. Rev. C 101, 044609 (2020)
The fusion reactions supply neutrons energetic enough to fission material that is not fissile on its own — about 2 MeV is the requirement, and D(t,n)α delivers 14.1 MeV — so thorium-232 and natural uranium-238 can carry the fission half of the cycle and no enriched uranium is needed.slide 9, Hybrid Fusion-Fast Fission, reaction tables
The result is a variable-output power source smaller than existing fissile reactors, free of the plutonium-238 supply problem and of high-enriched or high-assay low-enriched uranium, with the reactor’s thermal waste heat used directly to melt or ultrasonically vibrate a path through the ice.slide 10, Potential Impact; slide 11, Takeaways
Icy-world conditions set the requirement and they are severe: crusts up to 40 km thick, pressure from vacuum to over 10 kbar, temperature from cryogenic to above 270 K, and several ice phases that change how fast a probe can travel — which is why the power source has to be throttleable.slides 3 and 5, citing Journaux et al., PNAS (2023) and Culbert et al., Nature Communications 13:2007 (2022)
The same LCF-driven fast-fission unit could serve as high specific-impulse nuclear electric propulsion, shortening the cruise to the outer planets. What to watch: a thrust-and-power figure from a built unit rather than a design estimate.slide 4, Mission Context; slide 7, Innovation
Scaling is the open item, and the team names it as their own next step: raising the technology readiness level of LCF fast fission. What to watch: a demonstrated throttleable unit meeting the cryobot reference numbers of 8–12 kW thermal at better than 1 W per cubic centimetre.slide 3, Cryobot reference; slides 11 and 12
The way in
https://ntrs.nasa.gov/citations/20230002343How to cite it
Theresa L. Benyo (2023) Accessing Icy Worlds Using Lattice Confinement Fusion (LCF) Fast Fission https://ntrs.nasa.gov/citations/20230002343