Disassembly of the steam generator safety test facility (SWAT-3)

Shimoyama, Kazuhito ; not registered

The Steam Generator Safety Test Facmty, SWAT-3, was constructed in order to confirm the safety of the steam generator of a fast reactor against a water leakage from a heat transfer tube. And to clarify the range of the part in which the repair is required before restart by grasping the damage of the steam generator. This report describes the technical experience of extraction of sodium and removal of sodium-water reaction products from the SWAT-3, which was disassembled in 1996 through 1999. It was the first experience in Japan to disassemble the large-scale sodium facilities containing reaction products. The disassembly work was performed safely and efficiently as planned procedures. Especially, through the disassembly of the dump tank that contained a large amount of reaction product deposits, numerous knowledge and experience were obtained and some special disassembly techniques were developed. Main results are introduced in the following (1)To prevent the blockage of the piping by sodium-water reaction products in the cover gas space division in the tank, it was clarified that the double piping with the electric heater was effective. (2)Welding Technique between a pipe and a sodium tank surface was established. (3)It was verified that the fusion cutting of tank main body was possible by covering sodium-water reaction products with dry sand. No significant corrosion was observed in the structural material of the dump tank whose internal surfaces had been contacted with the reaction products for a long time. Even small scratches or marks during manufacturing procedure were observed to remain in the inspection. The obtained knowledge and experience will provide useful information for planning and actual works of the similar procedures and safety management relating to future disassembly of the present sodium-water reaction test facilities and sodium loops containing certain impurities, also for planning of post accident procedures of FBR plants.