[en] It was found out from the experiences that sodium removal from small crevices by conventional method was difficult. And, in order to improve the operation, a saturation boiling process was applied and experiments using test pieces have started. Since the purpose of this process is to remove final remaining deposits, bulk sodium removal must be done before. The saturation boiling process is a modification of the water charging process. When water is charged into the process cell or tank, the pressure inside is adjusted so that boiling of the water is initiated. The formation of hydro-oxide membranes at the surface of the sodium prevents further reaction between sodium and water. Results have been obtained from test pieces of bolts and crevices of flat plates and cylinders. (author)