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Introduction
Published in G. Vaidyanathan, Dynamic Simulation of Sodium Cooled Fast Reactors, 2023
Natural uranium contains about 0.7% U235 and 99.3% U238. In any reactor some of the U238 component is turned into several isotopes of plutonium during its operation. Two of these, Pu239 and Pu241, then undergo fission in the same way as U235 to produce heat. In a fast neutron reactor (FNR) this process can be optimized so that it “breeds” fuel. Some U238 is also burned directly with neutron energies above 1 MeV (fast fission).
Nuclear and Hydro Power
Published in Anco S. Blazev, Energy Security for The 21st Century, 2021
All current fast neutron reactor designs use liquid metal as the primary coolant, to transfer heat from the core to steam used to power the electricity generating turbines. FBRs have been built cooled by liquid metals other than sodium—some early FBRs used mercury, other experimental reactors have used a sodium-potassium alloy (NaK).
The Other Energy Sources
Published in Anco S. Blazev, Power Generation and the Environment, 2021
All current fast neutron reactor designs use liquid metal as the primary coolant to transfer heat from the core to steam used to power the electricity generating turbines. FBRs have been built cooled by liquid metals other than sodium. Some early FBRs used mercury, other experimental reactors have used a sodium-potassium alloy (NaK.)
Experimental analysis of small sample reactivity measured in the SEG experiment by a deterministic reactor physics code system CBZ
Published in Journal of Nuclear Science and Technology, 2022
The abbreviation SEG stands for Schnelles Einsatz-Gitter in Germany, and it means a rapid (or fast) deployment lattice. The SEG lattice is composed of a cylindrical matrix of aluminium with a diameter of about 50 cm. It had cylindrical holes in the matrix, and these holes were filled with cylindrical pellets in defined order. The cylindrical hole configuration and the pellets arrangement are dependent on the lattices. The SEG lattice was introduced to the Rossendorf Research Reactor (RRR) in Germany, which was originally the Argonaut-type reactor having annular light water-moderated nuclear fuels surrounded by a graphite reflector. It also contained a removable internal graphite reflector, and this internal reflector was replaced by the SEG lattice. Since the SEG lattices included a small amount of neutron moderator and a large amount of thermal neutron absorbers such as boron and cadmium, neutron flux energy spectrum of a fast neutron reactor was formed in the SEG lattice. In the SEG lattice-introduced RRR cores (the SEG cores), the outer water-moderated nuclear fuel worked as a driver, and these cores were fast-thermal coupled systems. Between the internal SEG lattice and the outer driver region, a converter material, graphite or uranium, was placed.
Dimerization of 2-Ethylhexylphosphonic Acid Mono-2-ethylhexyl Ester (HEH[EHP]) as Determined by NMR Spectrometry
Published in Solvent Extraction and Ion Exchange, 2021
Ashleigh Kimberlin, Kenneth L. Nash
Phosphorus-based organic extractants have found many uses in the separations of metals. For example, the solvent extraction process TALSPEAK (Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes) was developed in the 1960s as a means of separating the trivalent minor actinides (Am and Cm) from fission-product lanthanides so that actinides found in used nuclear fuel could be more efficiently transmuted in a fast neutron reactor.[1,2] Traditionally, TALSPEAK utilizes the extractant di-(2-ethylhexyl)phosphoric acid (HDEHP), aqueous actinide holdback reagent diethylenetriamine-N,N,N’,N”,N”-pentaacetic acid (DTPA), and a concentrated lactic acid buffer.[2] Recent advances in TALSPEAK chemistry have included replacing these reagents with weaker ligands like the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexl ester (HEH[EHP]), the aqueous complexant N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), and malonic acid buffer in order to improve process predictability, extend the workable pH range of the process, and increase phase transfer kinetics.[3–6] Phosphorus-based acidic extractants also have been used industrially to isolate lanthanides and other precious metals from ores and waste streams. Lanthanide separation techniques have critical applications in medical isotope production as well.[7,8]
Americium Recovery from Highly Active PUREX Raffinate by Solvent Extraction: The EXAm Process. A Review of 10 Years of R&D
Published in Solvent Extraction and Ion Exchange, 2020
Manuel Miguirditchian, Vincent Vanel, Cécile Marie, Vincent Pacary, Marie-Christine Charbonnel, Laurence Berthon, Xavier Hérès, Marc Montuir, Christian Sorel, Marie-Jordane Bollesteros, Sylvain Costenoble, Christine Rostaing, Michel Masson, Christophe Poinssot
An ambitious R&D program was then launched to assess the performances of the process from the perspective of a future industrial implementation of the EXAm process. The synthesis of the extractants able to decrease the costs of the fabrication, the feasibility of the process implementation in industrial liquid-liquid contactors (pulsed columns, mixers settlers), the process monitoring, the clean-up, and the regeneration of the solvent and the treatment of aqueous wastes have been studied in great detail and did not show any major issues for up-scaling the process. Another objective was to adapt the process to treat concentrated PUREX raffinates in order to improve the compactness of the future workshop/facility. The flowsheet was thus optimized to handle higher concentrations of minor actinides and fission products. A concentration factor of a PUREX UOX3-type raffinate up to 3.5 could be reached after modifications (increase in HDEHP and TEDGA concentrations, addition of a TEDGA scrub). This new flowsheet was tested on a genuine PUREX HAC in laboratory-scale mixer-settlers in 2015 in the framework of an integral experiment. About 82% of americium was recovered with a decontamination factor of 50 versus curium. These values were lower than expected by calculations. The difference was attributed to an inaccurate modelling of curium complexation by TEGDA potentially explained by a different chemistry occurring at higher concentrations of curium. Americium was nevertheless purified enough from curium and fission products to be transmuted in a fast neutron reactor in the next coming years in order to demonstrate the closing of the americium fuel cycle. Meanwhile, R&D is also in progress in the frame of European projects to improve and simplify the EXAm process. New alternative processes based on TODGA-octanol mixture in the organic phase and either TPAEN (N,N,N′,N′-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine)[60–65] or SO3-Ph-BTBP (6,6ʹ-bis(5,6-di(3-sulphophenyl)-1,2,4-triazin-3-yl)-2,2ʹ-bipyridine tetrasodium salt)[65–67] as selective Am-stripping agent in aqueous phase have been recently assessed and seem to be promising routes for the separation of americium from PUREX raffinates by solvent extraction.