The O-Ring Fuel Channel: A Self-Circulating Toroidal Concept for Molten-Fuel Fast-Spectrum Reactors

This note introduces a nuclear fuel channel concept for fast-spectrum reactors, designated the O-Ring. The channel is a sealed tube forming a closed toroidal loop — not to be confused with annular fuel elements or annular cross-sections — containing molten fuel that circulates by natural convection: heated fuel rises through a central fission (core) zone and descends through a peripheral breeding (blanket) zone. Each channel thus constitutes a self-contained circulation circuit with no external piping. The channel cross-section varies along its length to independently optimize neutron economy in each zone. Multiple O-Ring channels are arranged in a lattice within a common vessel filled with liquid-metal or high-temperature gas coolant. The concept combines features of molten-salt reactors (liquid fuel, continuous fission-product redistribution) with those of conventional pin-type fast reactors (discrete fuel elements, standard lattice geometry, sealed fuel boundary). Because circulation is slow andinternal to each channel, the effective delayed-neutron fraction remains close to its static value — a key kinetic advantage over externally-pumped molten-fuel designs. Passive safety is provided by Doppler feedback, a fusible drain plug, and geometric subcriticality upon fuel drainage. This document establishes the concept for priority purposes; quantitative neutronics, thermohydraulics, and materials selection are identified as subjects for future work.