Nondestructive measurement method of nuclear materials for sorting nuclear fuel debris

燃料デブリ仕分けのための核物質非破壊測定法

前田 亮  ; 米田 政夫   ; 藤 暢輔   

Maeda, Makoto; Komeda, Masao; Toh, Yosuke

In the decommissioning of the Fukushima Daiichi Nuclear Power Plant (1F), since objects removed from the Primary Containment Vessel (PCV) include not only fuel debris containing nuclear materials but also structural materials, it is not necessarily reasonable to treat all of them as fuel debris. Hence, it is important to establish a method for sorting of 1F fuel debris according to the quantity of nuclear materials present. However, the fuel debris may melt and mix with the control rods, which are neutron absorbers, making it difficult to apply conventional nondestructive measurement methods using neutrons. This study evaluates the performance of the Fast Fission neutron Coincidence Counting (FFCC) method, a nondestructive measurement method of nuclear materials that is less affected by neutron absorbers utilizing fast fission and fast coincidence on the order of nano second. Experimental results with a simple measurement system indicate that the FFCC method can detect significantly lower amounts of uranium than the sorting criteria, even in the presence of a substantial amount of neutron absorber, demonstrating high quantitativity. Optimization of the measurement system can lead to a dramatic enhancement of its capabilities. Therefore, the FFCC method is considered a promising technique for the sorting of 1F fuel debris.