Post-test analysis of the CMMR-4 test bundle

Madokoro, Hiroshi  ; Yamashita, Takuya  ; Sato, Ikken 

The test bundle of the latest test CMMR-4, Core-Material Melting and Relocation experiment, consists of 48 fuel rods filled with ZrO simulant pellets with Zircaloy claddings, a control blade with BC particles in SS tube and sheath, two Zircaloy channel box walls, and lower support structures. The height of the test bundle was 80 cm and the heating system of the test was the plasma heating, which enabled melting of the oxide simulant fuel pellets. The test confirmed that macroscopic gas permeability existed until the ceramic-fuel melted and that the hot fuel rods tended to remain as columns in the core region, which suggests the heating of the support structure in earlier phase is unlikely. This information is useful not only for 1F decommissioning but also for further understanding of a BWR severe accident progression. The test bundle was cut by using the abrasive waterjet (AWJ) technique that uses abrasive garnet of 150-300 micro m with feed rate of approximately 1.5 kg/min. In order to cut off about 30 mm of ZrB spot contained in the relocated melts, 750 liters of water, 84 kg of garnet and one nozzle replacement were necessary. The EPMA and XRD analyses of the cross-section showed that the place where repelled the garnet-contained waterjet contained ZrB. Since the cutting by AWJ technique has the property of selectively abrading the soft spots of the material, it must be noted that, in case of utilizing the technique in 1F decommissioning, garnet might be repelled by a hard boride and abrades places which were not expected.