Abstract: A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting for fuel decay during reactor shutdown, or heat produced during a mishap. The reactor system is enhanced with sealing means for excluding external air from contact with the liquid metal coolant leaking from the reactor vessel during an accident. The invention also includes a silo structure which resists attack by leaking liquid metal coolant, and an added unique cooling means.

Abstract: Both gadolinia nuclear fuel rods and urania fuel rods are non-destructively tested to determine the enrichment concentration of the fuel pellets therein by serially conveying the gadolinia rods and the urania rod along separate test channels through an active scanner where they are irradiated from a common neutron souce, and the neutron-induced gamma ray emissions are counted as a measure of the enrichment concentrations at a multiplicity of points distributed along the rod length. The enrichment counts are corrected for background radiation, variations in fuel density, and, in the case of gadolinia rods, for gadolinia content by passing these rods through a magnetometer.