Abstract:
This study focuses on reactor-core heat exchanger designs for nuclear thermal propulsion (NTP) systems, critical for reducing transit times to Mars (3–6 months vs. 8–9 months for chemical propulsion). We compare sodium-cooled fast reactors (SFRs) with lithium-cooled variants, analyzing neutron flux effects on material degradation and thermal efficiency.
Technical Depth:
Material Selection: Tungsten-rhenium alloys withstand 2,500°C temperatures but exhibit neutron embrittlement at >1022 n/cm2. Molybdenum-based ceramics show promise with 80% less swelling but require complex joining techniques.
Heat Exchanger Geometry: Plate-fin designs achieve 85% heat transfer efficiency but suffer from thermal stress cracks. Pebble-bed configurations reduce stress by 35% but lower efficiency to 72%.
Neutron Shielding: Hybrid shields combining boron carbide (thermal neutrons) and polyethylene (fast neutrons) reduce crew exposure to <0.1 mSv/day, meeting NASA standards.
Innovation:
A pebble-bed reactor with molybdenum-ceramic fuel particles and a layered shield reduces mass by 22% while maintaining 90% of SFR efficiency. Computational fluid dynamics (CFD) simulations show optimal propellant (LH₂) heating to 2,200°C with <5% temperature non-uniformity.
