Study of Failure Mechanisms of Hexcan-Wall in Severe Accident Condition in Fast Reactors

In the frame work of liquid metal fast breeder reactor safety,the failure location and time of stainless steel hexcan wall is an important issue,because it may greatly influence the courses and consequences of many severe accidents.For severe local accidents,the possibility of hexcan-wall failure is almost the same as the possibility of propagation of the accidents to neighboring subassemblies.According to the SCARABEE-N and SIMBATH experiments,a new failure mechanism was proposed.The melt-through of a well-cooled hexcan-wall could be caused by the burn out of sodium resulting from the local thermal erosion on the steel wall.Accordingly,for the Chinese experimental fast reactor,under the total instantaneous single subassembly blockage accident,the failure of the neighboring hexcan-wall was predicted to occur at 7.2~8 s after blockage formation.Subsequently,the molten mixture in the boiling pool begins to penetrate into the neighboring bundles,and then the accident propagates to the neighboring subassemblies.