Experimental investigation of role of burn-up for local fault propagation in lmr fuel assemblies

The main objective of the experiments Mol 7C/3 to 6 was to investigate the role of burn-up in the propagation of local faults in LMR fuel subassemblies. The test sections contained bundles of 30 fuel pins with burn-ups between 0.3 and 10 at% and porous blockages as local fault initiators. The main result of the experiments is that with rising burn-up there is an increasing potential for damage progression from the blockage to the surrounding bundle and structures. Only at low burn-up, faults of the kind and type investigated are self-limiting. At medium and high burn-ups, active protection systems, in particular the delayed neutron detection system, are required to prevent whole core involvement.