Excursion-Limiting Fuse for the Mixed Spectrum Critical Assembly

An excursion-limiting fuse has been incorporated into the design of the Mixed Spectrum Critical Assembly. This fuse provides an ultimate shutdown mechanism, backing up the safety system and preventing clad perforation by removing fuel from the uncooled fast core during all credible accidents even with the safety system inoperative. The unique and important features of this fuse are:

1. The load-carrying fissile material is supported in a simple manner that provides excellent thermal isolation from the surroundings and adequate space to deform without interference with the decoupling action.
2. The portion of the coupling device where the mechanical separation takes place is located away from the load-carrying fissile material which triggers the action.

Tests show that this fuse does not release the fuel elements during normal operation, but that it will actuate in the event of an excursion.