Experimental Simulation of the Behavior of E110 Claddings under Accident Conditions Using Electrically Heated Bundles

Abstract

The integral behavior of zirconium cladding materials was tested under design basis and beyond design basis accident conditions in the CODEX (COre Degradation EXperiment) facility. The test series included five experiments and covered the typical loss-of-coolant accident conditions for normal reactor operation, shutdown conditions, and wet storage in the spent fuel pool. The electrically heated experimental bundles were composed of seven rods with a hexagonal arrangement. Traditional and sponge-based E110 claddings were used in the same bundle in order to carry out parallel testing of the two materials. The fuel rods were filled with alumina pellets and were pressurized with inert gas. Detailed posttest examination of the experimental bundles was carried out in order to collect information on the degradation process and on the final state of the rods. Four-point bending-type mechanical tests were carried out with the cladding tubes. Prompt gamma-ray neutron activation imaging driven by neutron radiography and hot extraction methods was applied to characterize the axial hydrogen profile. The eddy current technique and laser profilometry were used to investigate the deformation of ballooned rods. The microstructure of the claddings was examined by metallography. The experiments provided new information on ballooning, burst, high-temperature steam oxidation, and load-bearing capability during water quench of oxidized E110 claddings. The observed differences between traditional and sponge-based E110 alloys were in good agreement with the results from small-scale separate effect tests regarding burst and oxide layer formation.