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As an alternative to wet processing, pyroprocessing shows promise in recycling transuranic elements with high proliferation resistance. The ceramic crucible used in the electrowinning process is a critical issue encountered in pyroprocessing. These ceramic crucibles are frequently damaged by thermal stress and chemical reaction, which results in significant volumes of crucible waste that must be properly disposed. The volume of generated radioactive waste is a concern when dealing with nuclear power plants and decontamination issues. In this study, a chemically stable Sc 2 O 3 crucible was developed, based on thermodynamic calculations, and sintered using a LiCl–KCl electrowinning system. Secondary ion mass spectroscopy was used to measure the intrusion depth of Li in the sintered ceramics. X-ray diffraction was used to measure the reactivity with ceramic and liquid Li. [ABSTRACT FROM AUTHOR]

Pyroprocessing has shown promise as an alternative to wet processing for the recycling of transuranics with a high proliferation resistance. However, a critical issue for pyroprocessing is the ceramic crucibles used in the electrowinning process. These ceramic crucibles are frequently damaged by thermal stress, which results in significant volumes of crucible waste that must be properly disposed. Transuranic waste (TRU) elements intrude throughout the pores of a damaged crucible. The volume of generated radioactive waste is a concern when dealing with nuclear power plants and decontamination issues. In this study, laser treatment and sintering were performed on the crucibles to minimize the TRU elements trapped within. Secondary ion mass spectroscopy was used to measure the intrusion depth of Li in the surface-treated ceramics. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the corrosion behavior of new Ni-based structural materials was studied for electrolytic reduction after exposure to LiCl–Li2O molten salt at 650°C for 24–216h under an oxidizing atmosphere. The new alloys with Ni, Cr, Al, Si, and Nb as the major components were melted at 1700°C under an inert atmosphere. The melt was poured into a preheated metallic mold to prepare an as-cast alloy. The corrosion products and fine structures of the corroded specimens were characterized by scanning electron microscope (SEM), Energy Dispersive X-ray Spectroscope (EDS), and X-ray diffraction (XRD). The corrosion products of as cast and heat treated low Si/high Ti alloys were Cr2O3, NiCr2O4, Ni, NiO, and (Al,Nb,Ti)O2; those of as cast and heat treated high Si/low Ti alloys were Cr2O3, NiCr2O4, Ni, and NiO. The corrosion layers of as cast and heat treated low Si/high Ti alloys were continuous and dense. However, those of as cast and heat treated high Si/low Ti alloys were discontinuous and cracked. Heat treated low Si/high Ti alloy showed the highest corrosion resistance among the examined alloys. The superior corrosion resistance of the heat treated low Si/high Ti alloy was attributed to the addition of an appropriate amount of Si, and the metallurgical evaluations were performed systematically. [Copyright &y& Elsevier]

The purification of a LiCl-KCl salt mixture was carried out by a zone-refining process. To improve the throughput of zone refining, three heaters were installed in the zone refiner. The zone-refining method was used to grow pure LiCl-KCl salt ingots from a LiCl-KCl-CsCl-SrCl 2 salt mixture. The main investigated parameters were the heater speed and the number of passes. From each zone-refined salt ingot, samples were collected axially along the salt ingot and the concentrations of Sr and Cs were determined. Experimental results show that the Sr and Cs concentrations at the initial region of the ingot were low and increased to a maximum at the final freezing region of the salt ingot. Concentration results of the zone-refined salt were compared with theoretical results furnished by the proposed model to validate its predictions. The k eff values for Sr and Cs were 0.55 and 0.47, respectively. The correlation between the salt composition and separation behavior was also investigated. The k eff values of the Sr in LiCl-KCl-SrCl 2 and the Cs in LiCl-KCl-CsCl were found to be 0.53 and 0.44, respectively, by fitting the experimental data into the proposed model. [ABSTRACT FROM AUTHOR]

The isothermal and cyclic corrosion behaviors of magnesia-stabilized zirconia in a LiCl-Li 2 O molten salt were investigated at 650 °C in an argon atmosphere. The weights of as-received and corroded specimens were measured and the microstructures, morphologies, and chemical compositions were analyzed by scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction. For processes where Li is formed at the cathode during electrolysis, the corrosion rate was about five times higher than those of isothermal and thermal cycling processes. During isothermal tests, the corrosion product Li 2 ZrO 3 was formed after 216 h. During thermal cycling, Li 2 ZrO 3 was not detected until after the completion of 14 cycles. There was no evidence of cracks, pores, or spallation on the corroded surfaces, except when Li was formed. We demonstrate that magnesia-stabilized zirconia is beneficial for increasing the hot corrosion resistance of structural materials subjected to high temperature molten salts containing Li 2 O. [ABSTRACT FROM AUTHOR]

In this paper we describe a progressive two-step process that allows zirconium fluoride (ZrF 4 ) contained in spent baths for etched zirconium alloys to be effectively recycled on a pilot scale and produce a high purity regenerated pickling acid. In the first step, a spent pickling liquor is treated by a BaF 2 suspension to produce water insoluble Ba 2 ZrF 8 . After filtration of Ba 2 ZrF 8 more than 99.9 wt % purity pickling acid is regenerated. The precipitation mechanism of Ba 2 ZrF 8 is discussed and the role of BaF 2 particles size on the precipitation process is demonstrated. In the second step the as-precipitated Ba 2 ZrF 8 is mixed with Mg and Cu metal powders and heat-treated at 1200 °C (or above) to produce CuZr alloy ingot. The characteristics of the ingot are discussed in regard to Cu concentration and the heating temperature. [ABSTRACT FROM AUTHOR]

The purification of LiCl salt mixture has traditionally been carried out by a melt crystallization process. To improve the throughput of zone refining, three heaters were installed in the zone refiner. The zone refining method was used to grow pure LiCl salt ingots from LiCl-CsCl-SrCl 2 salt mixture. The main investigated parameters were the heater speed and the number of passes. A change in the LiCl crystal grain size was observed according to the horizontal direction. From each zone refined salt ingot, samples were collected horizontally. To analyze the concentrations of Sr and Cs, an inductively coupled plasma optical emission spectrometer and inductively coupled plasma mass spectrometer were used, respectively. The experimental results show that Sr and Cs concentrations at the initial region of the ingot were low and reached their peak at the final freezing region of the salt ingot. Concentration results of zone refined salt were compared with theoretical results yielded by the proposed model to validate its predictions. The k eff of Sr and Cs were 0.13 and 0.11, respectively. The decontamination factors of Sr and Cs were 450 and 1650, respectively. [ABSTRACT FROM AUTHOR]

The intergranular carbide precipitation behavior and its effect on the tensile properties were investigated in alloy 690. The precipitation of intergranular carbides, identified as Cr-rich M 23 C 6 , was retarded on the low-angle grain boundaries and the coincidence-site lattice boundaries. The M 23 C 6 carbides have a cube-cube orientation relationship with the matrix. The ultimate tensile strength, yield strength, and elongation of the solution annealed alloy 690 are 648.2 ± 8.2 MPa, 242.8 ± 10.5 MPa and 44.9 ± 2.3%, respectively. The ultimate tensile strength and the yield strength increased to 764.8 ± 7.8 MPa and 364.8 ± 10.2 MPa until the aging time reached 16 h. This increase is ascribed to the M 23 C 6 carbide acting as reinforcements. However, when the aging time exceed 16 h, these properties gradually decreased with increasing aging time. The decrease in ultimate tensile strength, yield strength, and elongation were mainly caused by the intergranular cracking due to the low bond strength between the carbide and the matrix. [ABSTRACT FROM AUTHOR]

Abstract: Zirconium (Zr) has commonly been used as a cladding material of nuclear fuel. Moreover, it is regarded as the only material that can be used for nuclear fuel cladding because it has the lowest neutron capture cross section of any metal element and because it has high corrosion resistance and size stability. In this study, Hf-free Zr tubes (Zr–1Nb–1Sn–0.1Fe) were used as anode materials and electrorefining was performed in a LiF–KF eutectic 6wt.% ZrF4 molten fluoride salt system. As a result of electrolysis, Zr scrap metal was recycled into pure Zr with low levels of impurities, and the size and density of the Zr deposit was controlled using applied current density. [Copyright &y& Elsevier]

Abstract: Zirconium has a low absorption cross-section for neutrons, which makes it an ideal material for use in nuclear reactor applications. However, hafnium typically contained in zirconium causes it to be far less useful for nuclear reactor materials because of its high neutron-absorbing properties. In the present study, a novel effective method has been developed for the production of hafnium-free zirconium. The process includes two main stages: magnesio-thermic reduction of ZrSiO4 under a combustion mode, to produce zirconium silicide (ZrSi), and recovery of hafnium-free zirconium by molten-salt electrorefining. It was found that, depending on the electrorefining procedure, it is possible to produce zirconium powder with a low hafnium content: 70ppm, determined by ICP-AES analysis. [Copyright &y& Elsevier]