To accurately detect the composition and buried position of a combustible toxic substance by non-destructive inspection by using zirconium alloy as a base material in a channel box, by burying the combustible toxic substance with ferromagnetism or paramagnetism without touching furnace water, and by specifying depth from the surface of the zirconium alloy base material to the combustible toxic substance.
When a combustible toxic substance 12 is buried to a fuel channel box 11 made of zirconium alloy to control reactivity, it is required that thickness (t) of the toxic substance 12 and the amount of eccentricity (a) to a base material in a thickness direction should be within a design tolerance to properly guarantee the reactivity control property and the stability of the dimensions of the box 11. Then, in the box 11, the toxic substance 12 with ferromagnetism or paramagnetism is buried without touching furnace water, and depth from the surface of the zirconium alloy base material to the toxic substance 12 should be set to approximately 2 mm or less. Also, the toxic substance 12 should be gadolinium or a gadolinium alloy or a gadolinium compound with a gadolinium content of 30 wt.% or higher.
NAKAJIMA JUNJIRO
FUJIEDA TADASHI
SUZUKI KAZUHIRO
HITACHI ENG CO LTD