Experimental simulation of the Paks-2 cleaning tank incident through separate effect and integral tests

Following the ex-core cleaning of VVER type fuel assemblies, a severe fuel damage took place at the Paks NPP. Assemblies with high decay heat remained without cooling for 7 h. As a common result of high temperature oxidation and final water quenching the assemblies were broken and the fuel rods fragmented. er to improve the understanding of the phenomena that took place during the Paks-2 incident, several series of separate effect and integral tests have been carried out. The separate effect tests investigated the phenomena related to the upward shift of fuel assemblies, to the role of the spacer grid and the spring in the loss of cladding integrity, and to the importance of high hydrogen content in the vesselʹs atmosphere on the embrittlement of zirconium. Integral tests were carried out in the CODEX facility to simulate the whole scenario of the incident using electrically heated fuel rods.