Michio Seya

Uncertainty assessment of neutron resonance transmission analysis using the linear absorption model

Neutron resonance densitometry (NRD) has been proposed to quantify nuclear materials in particle-like debris of melted spent nuclear fuel formed in severe nuclear reactor accidents. The NRD is a hybrid technique of the neutron resonance transmission analysis and the neutron resonance capture analysis. We have studied the statistical uncertainties of the neutron resonance transmission analysis by using the linear absorption model. Particularly, the effects of impurities and sample thickness on the uncertainties were examined.

Demonstration of gamma-ray pipe-monitoring capabilities for real-time process monitoring safeguards applications in reprocessing facilities

ABSTRACT Nuclear material in reprocessing facilities is safeguarded by random sample verification with additional process monitoring applied to solution masses and volumes within the tanks to maintain continuity-of-knowledge of the operational processes. Measuring the unique gamma rays of each solution as the material flows through pipes connecting all tanks and process apparatuses could potentially improve process monitoring by verifying the composition in real time. We tested this gamma-ray pipe-monitoring method using plutonium-nitrate solution transferred between tanks at the Plutonium Conversion Development Facility at the Tokai Reprocessing Plant of the Japan Atomic Energy Agency. The gamma rays were measured with a lanthanum-bromide detector and a list-mode data acquisition system to obtain both time and energy information to evaluate the solution nuclear material as well as process conditions. Developed offline, we demonstrate this method can determine isotopic composition, flow-rate, volume, and process timing of a solution batch, introducing a viable online, in-line, unattended capability for improved process monitoring safeguards verification. The process and measurement details are presented here along with a description of the analyses used and the results of the evaluation.

Design study on differential die-away technique in an integrated active neutron NDA system for non-nuclear proliferation

A specific Differential Die-away Analysis (DDA) system in an advanced non-destructive analysis (NDA) system using a compact pulsed neutron generator has been studied and designed for non-nuclear proliferation in the Japan Atomic Energy Agency (JAEA). The NDA system is composed mainly of combination of four active neutron analysis techniques, DDA, PGA (Prompt Gamma-ray Analysis), NRTA (Neutron Resonance Transmission Analysis) and DGS (Delayed Gamma Spectroscopy). The design study on the DDA section in the system has been performed with Monte Carlo simulation code (MCNP) to evaluate the performance of the DDA system. The simulation result shows that the 239Pu mass (contained in MOX fuel) of as low as 0.01 g is detectable. The dependence of the performance on the type of the inner wall material in the DDA section and the thickness of the cylindrical moderator placed to circumscribe the measurement sample are presented.

Recent Progress in Research and Development in Neutron Resonance Densitometry (NRD) for Quantification of Nuclear Materials in Particle-Like Debris

To quantify special nuclear materials (SNM) in particle-like debris, a technique named neutron resonance densitometry (NRD) has been proposed. This method is a combination of neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis (NRCA) or prompt gamma-ray analysis (PGA). In NRTA, neutron transmission rate is measured as a function of neutron energy with a short flight path time-of-flight (TOF) system. Characteristic neutron transmission dips of Pu and U isotopes are used for their quantification. Materials in the samples (H, B, Cl, Fe, etc.) are measured by the NRCA/PGA method. For the NRD measurements, a compact TOF facility is designed. The statistical uncertainties of the obtained quantities of the SNMs in a sample are estimated. A high-energy-resolution and high-S/N γ-ray spectrometer is under development for NRCA/PGA. Experimental studies of systematic uncertainties concerning the sample properties, such as thickness and uniformity, are in progress at the TOF facility GELINA of European Commission (EC), Joint Research Centre (JRC), Institute for Reference Materials and Measurements (IRMM).

Evaluation of light transport property in alternative He-3 neutron detectors using ceramic scintillators by a ray-tracing simulation

We have developed a He-3 alternative neutron detector using ceramic scintillator sheets for nuclear safeguards. The alternative detector tube consists of four components: an aluminum regular square envelop tube, a light reflecting tube put on the inner surface of the square tube, a rectangular scintillator sheet sintered on a glass plate, and two PMTs provided at both ends of the tube. It permits neutron counting by detecting scintillator light with the PMTs. The light transport property of scintillator light inside the tube strongly depends on the inner structure of the detector tube. The light output of the scintillator light from the surface of the scintillator and the glass plate to the end in several arrangements of the scintillator in the tubes was investigated by a ray-tracing simulation. The simulation results on the influence of the glass plate on the properties are discussed.