Naoki Surugaya

Evaluation of plutonium(IV) extraction rate between nitric acid and tri‐n‐butylphosphate solution using a glass chip microchannel

Extraction of Pu(IV) with tri-n-butylphosphate is performed using a glass chip microchannel to evaluate the extraction rate. Two-phase flow forms in the microchannel by introducing a solution of Pu(IV) and tri-n-butylphosphate with flow rates above 5 μL/min. The Pu(IV) extraction reaction proceeds at the interface between the two phases. To evaluate the extraction rate, the contact time between the two phases is varied from 0.48 to 4.8 s by changing the confluent length of the microchannel and the flow rate. The Pu concentration of each phase collected from the microchannel is measured with an alpha liquid scintillation counter, and the contact time dependence of Pu(IV) extraction is obtained. An extraction model based on diffusion in the microchannel and the reaction at the interface is proposed and applied to determine the extraction rate. The extraction process is assumed to follow pseudo-first-order kinetics, and the extraction rate constant of Pu(IV) is determined to be 1.5 × 10(-2) cm/s. The investigation demonstrates that a microfluidic device can be a new tool to determine Pu(IV) extraction rates.

Selective recovery of minor trivalent actinides from high level liquid waste by R-BTP/SiO2-P adsorbents

Concerning the selective recovery of minor trivalent actinides (MA(III) = Am(III) and Cm(III)) from high level liquid waste (HLLW) by extraction chromatography, adsorption and elution behaviours of MA(III) and fission products (FP) in a nitric acid media were studied using iHex-BTP/SiO2-P adsorbents, which is expected to show high adsorption affinity for MA(III) even in concentrated HNO3 solution, such as HLLW. In the batch experiments, Pd showed strong adsorption on iHex-BTP/SiO2-P adsorbents under any concentration of HNO3. The MA(III) and heavy Ln(III) (Sm(III), Eu(III) and Gd(III)) were also adsorbed at the condition of high HNO3 concentration, but they showed no adsorption under low HNO3concentration. The separation factor for MA(III)/heavy Ln(III) took the maximum value (over 100) at around 1mol/dm3 HNO3. It was difficult to elute MA(III) or heavy Ln(III) selectively by HNO3 from the iHex-BTP/SiO2-P adsorbents degradated by γ-ray irradiation. The chromatographic separation of real HLLW by an iHex-BTP/SiO2-P column showed that MA(III) could be recovered selectively by adjusting the acidity of the feed solution, i.e. HLLW, to 1mol/dm3 and using H2O as eluant. The adsorption of Pd(II) can be decreased by the addition of appropriate complexing reagents, e.g. DTPA, into HLLW without any effects on the MA(III) adsorption.

Quantitative determination of total cesium in highly active liquid waste by using liquid electrode plasma optical emission spectrometry

A sensitive analytical method for determination of total cesium (Cs) in highly active liquid waste (HALW) by using modified liquid electrode plasma optical emission spectrometry (LEP-OES) is developed in this study. The instrument is modified to measure radioactive samples in a glove box. The effects of important factors, including pulsed voltage sequence and nitric acid concentration, on the emission of Cs are investigated. The limit of detection (LOD) and limit of quantification (LOQ) are 0.005 mg/L and 0.02 mg/L, respectively. The achieved LOD is one order lower than that of recently developed spectroscopic methods using liquid discharge plasma. The developed method is validated by subjecting a simulated HALW sample to inductively coupled plasma mass spectrometry (ICP-MS). The recoveries obtained from a spike-and-recovery test are 96-102%, implying good accuracy. The method is successfully applied to the quantification of Cs in a real HALW sample at the Tokai reprocessing plant in Japan. Apart from dilution and filtration of the HALW sample, no other pre-treatment process is required. The results agree well with the values obtained using gamma spectrometry. The developed method offers a reliable technique for rapid analysis of total Cs in HALW samples.

Study on the Behavior of Radiolytically Produced Hydrogen in a High-Level Liquid Waste Tank of a Reprocessing Plant: Comparison Between Actual and Simulated Solutions

Abstract Experiments using a small-scale apparatus with 30 ml of actual high-level liquid waste from the Tokai Reprocessing Plant were carried out to show that the hydrogen concentration in the gas phase reaches a steady-state value of much less than 4% (lower explosive limit) in the absence of sweeping air. The H2 concentration reached a steady-state value as was expected, and it was compared with a value predicted from an equation with parameters that had been obtained using the simulated solution. Satisfactory agreement showed that the Pd-ion catalytic H2 consumption reaction previously found in the simulated solution proceeded equally well in the actual solution.