Understanding failed LMR oxide fuel element performance

The occurrence of fuel element failures in liquid-metal fast breeder reactors and the issues for continued operation of failed fuel pins have been studied intensively. Exploratory experiments with ceramic fuel in sodium were already performed in 1963. In order to investigate in detail the behavior of defective mixed-oxide fuel pins during continued power operation, a program in the sodium loop devices at Siloe was initiated as a French-German endeavor. The conclusions reached from 11 experiments where oxide pins were operated beyond cladding breach under well-controlled conditions are as follows: 1. Small pinhole defects develop rather slowly; after some weeks at power cycling conditions, sodium enters the pin. 2. Even with large defects of initially 30 mm, highly embrittled end-of-life pins caused limited fuel loss. After a temporary shutdown of the Siloe reactor, the program was continued to investigate the performance of fertile (Breeder) oxide pins with special emphasis on in-core storage conditions.