Energy From Thorium Discussion Forum

Just out of curiousity, does anyone know the extent to which the Uranium Hydride based HPM could be modified to use Thorium or Mixed Thorium/Uranium fuel?

[0085] Thorium hydride has physical-chemical properties similar to uranium hydride, but only for part of the hydrogens per molecule. The first two hydrogens bound to a thorium atom (ThH.sub.2) are more tightly bound than the others, up to Th.sub.4H.sub.15. This results in a dissociation pressure for hydrogen compositions above ThH.sub.2 that is similar to UH.sub.3 but only a fraction of the hydrogens are mobile. Use of thorium hydride would result in greater physical disruption of the powdered fuel as hydrogen escapes to stabilize periods of positive reactivity and slow the return of hydrogen during periods of negative reactivity by increasing the thickness of the powder barrier through which the gas must be forcefully transported. Thorium could be used as the fertile diluent for either fissile uranium or plutonium. Because the transient calculations predict that less than one percent of the stored hydrogen need be exchanged to maintain criticality stability, the limit on the fraction of hydrogens in thorium hydride that are mobile should not present a significant difficulty. Thorium hydride may ultimately be even more attractive than uranium hydride because separating the fissile components from the fertile components would be a chemical separation instead of an isotopic separation. Furthermore, the fissile product of thorium absorption of a neutron is U.sup.233, which is a very attractive fissile fuel for reactors.

[0086] Thorium also permits higher temperature operation of the reactor because of its high melting temperature of 1755.degree. C. The higher temperature operation offers the possibility of higher efficiency conversion of the thermal power generated by the reactor to electrical power. The high melting temperature would complicate the zone refining processing of the spent fuel; however, alloys of thorium and uranium would reduce the melting temperature. For a wide range of compositions on the uranium rich side of the phase diagram the melting point of the alloy is a fixed value of 1375.degree. C. On the thorium rich side of the phase diagram, the melting temperature is approximately linear with thorium content from the 1375 to the 1755.degree. C. point for compositions from 50 to 100% thorium.