Electrochemical behavior of americium in NaCl-2CsCl melt

Hayashi, Hirokazu; Akabori, Mitsuo; Minato, Kazuo

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1331 - 1334, 2015/02

https://doi.org/10.1007/s10967-014-3471-9

Electrochemical behavior of Am in NaCl-2CsCl melt at 823 K was investigated by transient electrochemical techniques such as cyclic voltammetry and differential pulse voltammetry. The results show that Am(III) ion is reduced to Am metal by a two-step mechanism via Am(II) ion. Formal standard potential of Am(III)/Am(II) and that of Am(II)/Am(0) redox couples have been determined to be -2.73 and -2.97 V vs Cl/Cl, respectively.

Study to improve recriticality evaluation methodology after severe accident (Joint research)

Kugo, Teruhiko; Ishikawa, Makoto; Nagaya, Yasunobu; Yokoyama, Kenji; Fukaya, Yuji; Maruyama, Hiromi*; Ishii, Yoshihiko*; Fujimura, Koji*; Kondo, Takao*; Minato, Hirokazu*; et al.

JAEA-Research 2013-046, 53 Pages, 2014/03

JAEA-Research-2013-046.pdf:4.42MB

The present report summarizes the results of a 2-year cooperative study between JAEA and Hitachi-GE in order to contribute to the settlement of the Fukushima-Daiichi Nuclear Power Plants which suffered from the severe accident on March 2011. In the present study, the possible scenarios to reach the recriticality events in Fukushima-Daiichi were investigated first. Then, the analytical methodology to evaluate the time-dependent recriticality events has been developed by modelling the reactivity insertion rate and the possible feedback according to the recriticality scenarios identified in the first step. The methodology developed here has been equipped as a transient simulation tool, PORCAS, which is operated on a multi-purpose platform for reactor analysis, MARBLE. Finally, the radiation exposure rates by the postulated recriticality events in Fukushima-Daiichi were approximately evaluated to estimate the impact to the public environment.

Separation and recovery of Cm from Cm-Pu mixed oxide samples containing Am impurity

Hayashi, Hirokazu; Hagiya, Hiromichi; Kim, S.-Y.*; Morita, Yasuji; Akabori, Mitsuo; Minato, Kazuo

Journal of Radioanalytical and Nuclear Chemistry, 296(3), p.1275 - 1286, 2013/06

https://doi.org/10.1007/s10967-012-2304-y

Cm was separated and recovered as an oxalate from Cm-Pu mixed oxide which had been Cm oxide sample prepared 40 years ago. Plutonium ions were removed from the solution prepared by dissolution of Cm-Pu mixed oxide in nitric acid, by using an anion exchange resin column. Curium oxalate, a precursor compound of curium oxide, was prepared from the purified curium solution and supplied for the syntheses and measurements of the thermochemical properties of curium compounds.

Coordination characteristics of trivalent lanthanides and actinides in molten hydrate salts of Ca(NO) and CaCl

Fujii, Toshiyuki*; Okude, Genki*; Uehara, Akihiro*; Sekimoto, Shun*; Hayashi, Hirokazu; Akabori, Mitsuo; Minato, Kazuo; Yamana, Hajimu*

Journal of Radioanalytical and Nuclear Chemistry, 288(1), p.181 - 187, 2011/04

https://doi.org/10.1007/s10967-010-0907-8

Distribution behavior of Ce(III), Am(III), and Cm(III) between tri-n-butyl phosphate solution and molten calcium nitrate hydrate Ca(NO)HO or molten calcium chloride hydrate CaClHO was studied radiochemically. In Ca(NO)HO systems, maximum separation factors of Ce and Cm to Am were observed to be 12 (Ce/Am) and 1.7 (Cm/Am). The distribution ratios of these elements increased with the decrease of water activity in the hydrates, and the extractabilities at the water deficient region was less sensitive compared to those at the water abundant region. This trend was similar to the coordination circumstance change observed in electronic absorption spectra of Nd(III) in the hydrates.

Experimental study on the behavior of americium in pyrochemical process of spent nitride fuels

Hayashi, Hirokazu; Shibata, Hiroki; Akabori, Mitsuo; Arai, Yasuo; Minato, Kazuo

Proceedings of International Conference on Advanced Nuclear Fuel Cycle; Sustainable Options & Industrial Perspectives (Global 2009) (CD-ROM), p.1166 - 1173, 2009/09

R&D on the transmutation of long-lived minor actinides (MA) by the accelerator-driven system (ADS) using nitride fuels is underway at JAEA. In regard to reprocessing technology, pyrochemical process has several advantages in case of treating spent fuel with large decay heat and fast neutron emission, and recovering highly enriched N. In the pyrochemical reprocessing, plutonium and MA are dissolved in LiCl-KCl eutectic melts and selectively recovered into liquid cadmium (Cd) cathode by molten salt electrorefining. The electrochemical behavior in LiCl-KCl eutectic melts and the subsequent nitride formation behavior of plutonium and MA recovered in liquid Cd cathode are investigated. Electrochemical study of americium (Am) on electrolyses of AmN in LiCl-KCl eutectic melts and nitride formation of Am recovered in the liquid Cd cathode are presented. Electrochemical behavior of Am on anodic dissolution of AmN and recovery of Am into a liquid Cd cathode by electrolyses in LiCl-KCl eutectic melts was investigated by transient electrochemical techniques. Am was recovered as Am-Cd alloy in the liquid Cd cathode, in which AmCd type phase was identified besides Cd phase. The recovered Am was converted to AmN by the nitridation-distillation combined method. These results suggest that the pyrochemical process developed for the nitride fuel cycle is applicable for the nitride fuels containing Am, which is to be used for the transmutation of MA.

Behavior of americium in pyrochemical process of the nitride fuel cycle

Hayashi, Hirokazu; Shibata, Hiroki; Akabori, Mitsuo; Arai, Yasuo; Minato, Kazuo

Proceedings of 2008 Joint Symposium on Molten Salts (USB Flash Drive), p.910 - 915, 2008/10

R&D of the nitride fuel cycle technology is underway at JAEA. Behavior of americium (Am) in the pyrochemical process, which include anodic dissolution of AmN and recovery of Am into liquid Cd cathode by electrorefining in LiCl-KCl eutectic melts, and nitride formation of Am recovered in liquid Cd cathode, are presented.

Cyclic voltammetry behavior of americium at a liquid cadmium electrode in LiCl-KCl eutectic melts

Hayashi, Hirokazu; Akabori, Mitsuo; Minato, Kazuo

Nuclear Technology, 162(2), p.129 - 134, 2008/05

https://doi.org/10.13182/NT08-A3939

The electrode reactions of americium at a liquid cadmium electrode were investigated by cyclic voltammetry (CV) of AmCl-(LiCl-KCl) at both 723K and 773K in comparison with those at a molybdenum electrode. The redox peaks assigned to Am(III)/Am(0) (in Cd) were observed with the liquid Cd electrode while the redox reactions of Am(III)/Am(II) and Am(II)/Am(0) were observed with the Mo electrode. The formal standard potential of Am(III)/Am(0) obtained with the liquid Cd electrode is more positive than those calculated for the Mo electrode at both 723K and 773K. The potential shifts were attributed to the lowering of the activity of Am by the formation of the intermetallic compound at the interface between Cd and the molten salt. The Gibbs free energies of formation of the Am-Cd intermetallic compound, which could be AmCd, are estimated to be -119 and -113 kJ/mol at 723K and 773K, respectively.

Preparation of gadolinium chloride without using corrosive gases

Shibata, Hiroki; Hayashi, Hirokazu; Minato, Kazuo

JAEA-Research 2007-027, 17 Pages, 2007/03

JAEA-Research-2007-027.pdf:1.4MB

For application to the preparation of MA chlorides with high-purity, a preparation method, in which corrosive gas like chlorine or hydrogen chloride and so on was not used, of the chloride from the oxide was developed. The preparation conditions of this method were optimized by carrying out preliminary examinations in which gadolinium was used as surrogate for MA. An anhydrous complex chloride ((NH)GdCl) was obtained by heating an HCl solution dissolving gadolinium sesquioxide (GdO) and ammonium chloride (NHCl) under a nitrogen gas flow. An anhydrous GdCl with high-purity was obtained by heating (NH)GdCl at 350 degrees under a dynamic vacuum.

Experiments on the behavior of americium in pyrochemical process

Hayashi, Hirokazu; Akabori, Mitsuo; Minato, Kazuo

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 3 Pages, 2005/10

For a basis of the future nuclear cycle, it is very important to understand and control the behavior of TRU (Np, Pu, Am, Cm) in the nuclear fuel cycle. Experimental study of pyrochemical process of fuels containing TRU requires the facility having not only shielding for -ray and neutron but also ability to keep a high purity inert gas atmosphere; because minor actinide chlorides can easily react with oxygen or water vapor in an atmosphere. The module for TRU high temperature chemistry (TRU-HITEC) had been installed to study the basic properties of TRU in the pyrochemical processes. In the present work, the behavior of Am in pyrochemical process was investigated by electrochemical methods.

Determination of uranium and rare-earth metals separation coefficients in LiCl-KCl melt by electrochemical transient techniques

Kuznetsov, S. A.*; Hayashi, Hirokazu; Minato, Kazuo; Gaune-Escard, M.*

Journal of Nuclear Materials, 344(1-3), p.169 - 172, 2005/09

https://doi.org/10.1016/j.jnucmat.2005.04.037

The knowledge of separation coefficients of actinides and rare-earth metals is important for developing pyrometallurgical process of spent nuclear fuel. Electrochemical experiments were carried out at 723-823 K to estimate separation coefficients in LiCl-KCl eutectic melt containing uranium and lanthanum trichlorides. Uranium and lanthanum separation coefficients is calcurated with the voltammetric peak potentials of U (III) and La (III), their concentration in the melt and kinetic parameters for U(III) discharge such as diffusion coefficients, and standard rate constants of charge transfer. The diffusion coefficients of U (III) were determined by some electrochemical measurements. The standard rate constants of charge transfer for electroreduction of uranium U(III) +3e =U were calculated by impedance spectroscopy method.