Feasibility studies and development of NDA technologies for nuclear materials in the melted fuels formed in severe accidents

This paper presents feasibility (selection) study of NDA techniques, NRD (Neutron Resonance Densitometry) and LCSγ-NRF (LCS gamma-rays interrogation Nuclear Resonance Fluorescence), to measure nuclear material (NM) in debris of melted fuel with high precision. The melted fuel under consideration here is the one formed by the severe loss of coolant accidents of such as Units 1 - 3 of Fukushima-Daiichi NPP. NRD based on NRTA (Neutron Resonance Transmission Analysis) and NRCA (Neutron Resonance Capture Analysis) utilizing the TOF (Time of Flight) method is intended for measurement of NM (all isotopes of U/Pu) in particle-like debris. LCSγ-NRF using intense LCS (Laser Compton Scattered) gamma-rays (mono-energetic gamma-rays) is to measure NM (all isotopes of U/Pu) in small rock-like debris and cut-shape debris (cylindrical, slab-shpape). In this paper we also summarize advantages of two techniques compared with other NDA techniques. (author)