Feasibility study on passive neutron technique applied to fuel debris measurement at Fukushima Daiichi Nuclear Power Plants

Nagatani, Taketeru ; Nakajima, Shinji; Asano, Takashi 

Fukushima Daiichi Nuclear Power Plants (1F) were struck by the earthquake and tsunami on March 11, 2011 and meltdown of the reactor cores of Units 1-3 occurred. Japan decided decommissioning of them. For decommissioning of 1F, Japan plans to recover fuel debris safely and to account nuclear material in it adequately. Survey of applicable technologies for nuclear material quantification of fuel debris, currently, is being conducted by Japan Atomic Energy Agency (JAEA) and United States Department of Energy (DOE) under the collaborative agreement. This survey will identify technologies with the most promising capability to meet IAEA safeguards needs. As one of candidate technologies of plutonium quantification in fuel debris, we, Plutonium Fuel Development Center of JAEA, consider the application of the passive neutron technique which is wildly applied to the field of material accountancy and safeguards in plutonium handing facilities. Fuel debris contains minor actinides and fission products which are intense neutron and ray emitter due to burn-up of fuel in the reactor. It also contains neutron absorber such as gadolinium included in fuel to moderate burn-up and boron added after accident to avoid re-criticality. These materials make it difficult to quantify plutonium by the current passive neutron technique. Therefore, R&D activities regarding selective counting for neutron derived from plutonium, reduction of ray influence and estimation of neutron absorber influence are required in order to overcome above difficulties. This paper provides a concept for application of passive neutron technique to fuel debris measurement.