Jun Takamine

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.

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).

Feasibility study on visualization of transient phenomena using high resolution on-line neutron imaging system at J-PARC

A neutron energy resolved imaging system with a time-of-flight technique has been newly installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously spatial distribution of several elements and crystals including various kinds of materials or substances on transient phenomena. A camera (CMOS, 48 frame/sec) equipped the system allows to obtain one TOF image resolved into narrow energy ranges with an each single pulsed neutron consecutively in the energy region from 0.01 to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 1.8 at En∼ 0.01 eV), neutron energy selectivity of the system, and capability for visualization of transient phenomena, were examined experimentally. The results obtained in the experiments show that the system can visualize the real-time neutron energy resolved images with a good spatial resolution even at transient phenomena.