Experience at the CNA plant with underwater inspection and modification of fuel assemblies

The CNA new sipping unit designed by Belgonucleaire is an example of a wet sipping system which provides for leak indication either by water soluble fission products or by fission products. The demineralized water is used to reduce the activity background and thus to improve the leakage detection efficiency. A dry sipping possibility also exists in this unit. Reprocessing of the CNA fuel assemblies requires the withdrawal of the Sb-Be secondary neutron sources out of the fuel assemblies before this reprocessing. As the CNA fuel assemblies are not dismountable, a specific equipment has been designed, based on the utilization of the electro-erosion technique to perforate under water the adapter plate of the fuel assembly top nozzle right at the position of the secondary source rod. This equipment has been operated very effectively: high accuracy in the control of the perforation positioning and speed and in the control of the water contamination by nozzle material during perforation: the secondary source has been removed from more than 80 assemblies out of 10 reloads. The same equipment has been used for the extraction of about 15 fuel rods out of 2 demonstration MOX fuel assemblies for postirradiation examination and reprocessing tests on MOX rods. 16 figs