Axially heterogeneous FBR core concept and its nuclear characteristics

This work consists of conceptual design and experimental studies on an axially heterogeneous core (AHC) for large LMFBRs. Trade-off studies were performed to optimize the AHC, from which it was found out that the AHC has the following advantages compared to the conventional homogeneous core (HOC); lower peak linear power, lower peak fast fluence in fuel cladding materials, lower burnup reactivity, lower potential of energetic consequences in hypothetical core disruptive accidents and so on. Aiming at further improvement of the core performance, the AHC core configuration was studied taking control rod operating into account. Critical experiments of the AHC were performed using the FCA facility at JAERI. The experiments demonstrated satisfactory fundamental nuclear characteristics, such as a flat power distribution. The calculational accuracies for the AHC were found to be nearly the same as those for the HOC. Through our studies, the AHC with improved safety and economic characteristics was proposed prior to designs in other countries, and the characteristics were demonstrated by experiments. These have provided a technical basis for development of future large LMFBR cores. (author)