Behavior of Th-20 wt% U Fast-Reactor Fuel Under Transient Heating to Failure

Sodium-bonded Th-20wt%U fast-reactor-type fuel elements have been studied in transient meltdown experiments ranging up to complete sample meltdown, conducted in the TREAT reactor. The high melting thorium matrix supported the fuel during transient heating at temperatures significantly beyond the solidus. Because the fuel was still relatively intact at the temperatures of cladding failure, internal pressure was not effective in ejecting fuel upon failure. The dominant mechanism of fuel movement was gravity.