Development of a method for the determination of plutonium in fuel debris by dual times neutron measurements

Nagatani, Taketeru ; Sagara, Hiroshi*; Kosuge, Yoshihiro*; Nakaguki, Sho; Nomi, Takayoshi ; Okumura, Keisuke 

Neutrons emitted from fuel debris are dominated by Cm-244, and plutonium cannot be quantified only by nondestructive measurements based on the neutron measurements. In this paper, focusing on the difference in half-lives of Cm-244 and plutonium, we devised a method to quantify the Pu-240 effective mass in fuel debris by measuring it two times and evaluated numerically its applicability. As the results, it was confirmed that long time interval, more than five years, will be required to evaluate the Pu-240 effective mass accurately. It was also confirmed that for fuel debris with high burnup, the Pu-240 effective mass will be overestimated by Cm-246, and we devised a method to correct for this.