Recent progress in research and development on the neutron resonance densitometry for particle-like debris of melted fuel

摘要

Neutron resonance densitometry (NRD) has been proposed to quantify nuclear materials accurately in particle-like debris of melted fuel formed in severe accidents of nuclear reactors such as Fukushima Daiichi nuclear power plants. NRD is a method combining NRTA (neutron resonance transmission analysis) and NRCA (neutron resonance capture analysis). It relies on the neutron TOF (time of flight) technique using a pulsed white neutron source. In this contribution, progress made in the development of the NRD for the characterization of nuclear materials mixed with highly radioactive nuclides is presented, together with the basic concept and principles. Development of a specially designed gamma-ray spectrometer for NRCA and an evaluation of the performance are presented. The applicability of NRD as a non-destructive analysis method has been studied using Monte Carlo simulations and neutron TOF experiments at the GELINA facility of the EC-JRC-IRMM. We conclude that NRD has a potential to determine the quantities of Pu and U isotopes in particle-like debris of melted fuel with counting statistics uncertainties less than 1% with 20 min measurement period, even in the presence of 2.5 w% ~(nat)B and 9 w% ~(56)Fe.