Fuel elements for nuclear reactors

TL;DR: In this paper, the outer and inner tubular sheaths of a nuclear core were modeled as a binary eutectic and the inner sheath was shown to collapse at a lower temperature than the outer sheath.

Abstract: Elements having a highly enriched fuel content may become dangerous because on melting they may cause the build up of a super-critical mass leading to a nuclear explosion. This may, e.g., occur by complete loss of coolant from the reactor core. This danger can be eliminated by an element composed of an outer and an inner tubular sheath of different materials between which the fuel is cortained in tubular form. The material of the inner sheath is so selected that it collapses at a lower temperature than the outer sheath. When such a collapse occurs some of the fuel content discharges under gravity along the inside of the outer sheath. Three examples are given: (1) fuel content and inner sheath after mutual solid diffusion form a molten alloy while no reaction occurs with the outer sheath; (2) an inner sheath of two-ply material forming a binary eutectic at a temperature higher than 50 deg C below the melting point of the fuel content and more than 200 deg C below that of the outer sheath; (3) a single material for the inner sheath (vanadium) that melts at a temperature higher than 50 deg C below the melting point of themore » fuel cortent (enriched uranium) and more than 200 deg C below the melting point of the outer sheath (of niobium). (auth)« less