DARPA wants to bypass the thermal middleman in nuclear power systems
DARPA’s push to “bypass the thermal middleman” in nuclear power is prompting renewed interest in direct energy conversion, from radiovoltaics and thermophotovoltaics to exotic fusion schemes that aim to turn charged particle motion straight into electricity. Commenters contrast these ideas with today’s nuclear plants, which are essentially complex, expensive steam boilers, and argue that cutting out turbines and vast pipe networks is likely essential if nuclear is to become cheaper and more scalable. Others highlight the formidable physics, materials, and regulatory hurdles, noting that existing direct-conversion technologies like betavoltaic batteries and RTGs work only at tiny power levels and that neutron-heavy reactions, safety concerns, and cost-benefit trade‑offs remain major obstacles.
Direct nuclear-to-electric conversion ideas
- Discussion centers on bypassing the “thermal middleman” (steam cycles) via:
- Radiovoltaics / betavoltaics and thermo-photovoltaics that convert ionizing or IR radiation directly to electricity, but with low absorption and power density issues.
- Direct capture of charged fusion products (e.g., Helion-style coils where plasma expansion induces current).
- For fission, most energy is in fast, charged daughter nuclei; capturing that as electrical potential instead of heat is conceptually possible but technologically unclear.
Fusion approaches and skepticism
- Fusion is described as “infinitely harder” than fission, especially for net-positive energy and direct conversion.
- Helion’s pulsed D–D / D–He³ concept is debated:
- Proponents highlight low neutron fraction and direct electromagnetic capture.
- Critics argue schedules have slipped, material/energy-flux limits may be insurmountable, and many fusion startups resemble overhyped VC plays.
Nuclear batteries and betavoltaics
- Existing betavoltaic cells (e.g., Ni‑63 in diamond) offer ~100 µW in tiny volumes:
- Energy density over decades is huge, but instantaneous power is far below phone-level needs.
- Could suit low-duty, intermittent devices, potentially with supercapacitors.
- Safety and regulation:
- Beta emitters are relatively easy to shield but dangerous if inhaled/ingested as dust.
- Widespread consumer use conflicts with non-proliferation, tracking, and waste rules.
- Some argue they’d be easier to monitor than heavy metals; others stress regulatory and security burdens.
Economics, efficiency, and waste heat
- Conventional reactors convert ~1/3 of fission heat to electricity; everything is “a big nuclear boiler.”
- Main roadblock is cost and complexity (thousands of long-lived, high-spec welds; huge skilled labor needs), not thermodynamic efficiency alone.
- Direct conversion is framed as the kind of breakthrough needed to make nuclear economically competitive.
- District heating and hydrogen production from reactor heat are discussed:
- District heating faces infrastructure, siting, and perception barriers.
- High-temperature electrolysis/thermochemical H₂ could use heat more directly but demands extreme temperatures and still competes with cheap intermittent renewables.
Safety, regulation, and risk perception
- Radiation fatalities are rare under strict regulation; some see this as proof safety works, others as evidence of overregulation and excessive cost.
- Comparisons are made with untracked heavy-metal pollution, suggesting societal risk trade-offs are inconsistent.
Speculative and niche concepts
- Fission-fragment rockets as high-Isp drives (and possible direct power sources) are discussed, along with RTGs, plasma scintillator schemes, and even black-hole/Hawking-radiation thought experiments.