High-level Liquid Waste Research Articles

Highly efficient removal of radioactive 90Sr based on sulfonic acid-functionalized α-zirconium phosphate nanosheets

Excellent column packing is a precondition for efficient separation of radioactive 90Sr from high level liquid waste (HLLW). α-ZrP particles are traditionally used as column packing for capturing radioactive nuclides from HLLW due to their excellent stability and adsorption ability. However, there remains room for improvement in terms of capacity and selectivity. Here, the traditional α-ZrP column packing was exfoliated and further modified by anchoring sulfonic groups on its surface to improve its adsorption capacity for 90Sr. The resulting ZrP-SO3H not only retained the excellent properties of α-ZrP but also possessed a larger surface area and much more adsorption sites. Adsorption experiments indicated that ZrP-SO3H exhibited excellent adsorption ability for separating of Sr2+ from acidic condition, and the maximum adsorption capacity of Sr2+ fitted by a Langmuir model is 183.21 mg g−1, which is higher than that of traditional α-ZrP and other similar column packings. In addition, kinetic studies indicated that Sr2+ adsorption on ZrP-SO3H is fast, and surface chemical adsorption is the main interaction between Sr2+ and ZrP-SO3H. Remarkably, radioactive experiment proved that ZrP-SO3H is an excellent adsorbent, and shows good stability for high efficiency for selective removal of 90Sr under complicate radioactive environment. Our present results implied that the novel ZrP-SO3H is potential column packing and could be suggested as promising column packing for separation of 90Sr from HLLW.

Rapid solidification of Highly Loaded High‐Level Liquid Wastes with magnesium phosphate cement

Rapid solidification of radioactive wastes is one of the most effective methods to prevent the spreading of radioactive contamination after a nuclear emergency. In this study, magnesium phosphate cement (MPC) was used as matrix to rapidly solidify denitrated high-level liquid wastes (HLLW). The compressive strengths and leaching rates of the samples were studied to evaluate the performance of the solidification forms. Further, XRD, SEM, and EDS were used to measure phase compositions, microstructures, and microscopic chemical compositions, respectively, of the as-prepared samples. Moreover, the solidification mechanism of simulated radioactive ions in phosphate cement is discussed in this paper. According to the results, the compressive strength of the solidified forms was affected by the actual mass ratio of dead-burned magnesia (MgO) powders to potassium dihydrogen phosphate (KH2PO4) (M/P) and unreacted KH2PO4; with up to 50 wt% HLLW content, 4.2 MPa and 13.2 MPa can be achieved for an M/P ratio of 1 after 3 h and one day, respectively. The leaching rates of Sr2+ and Cs+ for the solidified forms were below 10−7 g/m2/d and 10−4 g/m2/d, respectively. The immobilization of radioactive ions via an MPC paste is not only due to chemical immobilization, but also due to the physical encapsulation offered by the dense structure of the MPC. The cement offers sufficient strength in a short time for the temporary storage and transportation of the solidified forms.

Study on Separation of Platinum Group Metals from High-level Liquid Waste Using Sulfur-containing Amic Acid-functionalized Silica

Study on Separation of Platinum Group Metals from High-level Liquid Waste Using Sulfur-containing Amic Acid-functionalized Silica

Study on complexation of palladium with thiourea-based ligands and its determination in simulated high-level liquid waste using solid phase extraction-electrospray mass spectrometry

ESI–MS was used to investigate the complexation of Pd(II) with thiourea based ligands such as thiourea (TU), N-benzoylthiourea (BTU), N,N-diethyl N′-benzoylthiourea (DEBT) in gas phase. Experimental parameters like quadrupole ion energy and collision energy were optimized for acquiring the spectra of Pd complexes with TU, BTU, and DEBT. Tandem mass spectrometric (ms/ms) studies were carried out to investigate the relative stability of various Pd species in the gas phase. Studies showed that DEBT forms a predominately ML2 type complex and hence is a better chelating agent for ESI–MS determination of Pd compared to TU and BTU. Based on these studies, an automated solid phase extraction method was developed for separation of Pd using DEBT, followed by its determination using ESI–MS. Developed method was used for determination of Pd in simulated high level liquid waste.

Continuous separation of molybdenum and zirconium from simulated high-level liquid waste with a Taylor–Couette contactor

ABSTRACT Reprocessing of spent nuclear fuels generates high-level liquid waste (HLLW) which undergoes vitrification into borosilicate glass before final geological disposal. To ensure the quality of the glass, control of the concentration of chemical species such as molybdenum (Mo), which has an adverse impact on the vitrification process, is critical. Also, zirconium (Zr) can cause crud in washing process and Zr-93 is a long-lived fission product needed to be separated. In this study, a liquid–liquid countercurrent centrifugal contactor with Taylor–Couette flow (TC contactor) was applied to practical multi-species cases. Continuous separation of Mo and Zr from a simulated HLLW with bis(2-ethylhexyl) phosphoric acid (HDEHP) as extractant has been performed. Among a variety of metals in simulated HLLW, Mo, Zr, Y, and Fe are extractable, Mo and Zr were separated from HLLW by equilibrium, and Fe/Y separation was achieved by the effect of non-equilibrium state in TC contactor. Addition of tributyl phosphate could improve extraction of Mo. This study has expanded the scope of the TC contactor to multi-species separation processes.

Non-isothermal kinetics of the thermal decomposition of gadolinium nitrate

ABSTRACT High-level liquid waste (HLLW) contains more than 30 kinds of nitrates which consist of fission products. A series of such phenomena as evaporation, melting and thermal decomposition of HLLW takes place within the ‘cold cap’, which is floating on top of the molten glass pool. An understanding of the varied thermal decomposition behavior of various nitrates constituting HLLW is necessary to elucidate a series of phenomena occurring within the cold cap. In this study, gadolinium nitrate, which is one of main compositions of HLLW, was chosen as an example of the nitrate salt and its thermal decomposition was investigated using non-isothermal thermogravitmetry-differential thermal analysis-mass spectrometry and X-ray powder diffraction. Ozawa method was applied for gaining kinetic parameters for the consecutive reaction of gadolinium nitrate. Reaction rate equation of the decomposition under non-isothermal condition was described.

A modular process for the treatment of high level liquid waste (HLLW) using solvent-impregnated graphene aerogel

Graphene aerogel (GA) is a kind of superhydrophobic material with low density, high specific surface area and porosity. It can be used as modular matrix material to be impregnated with extractant due to its excellent organic solvent immobilization performance. In this paper, the modular GA based solvent impregnated adsorbents (GA-SIA) with various extractants were prepared. The adsorption performance of these adsorbents for typical fission products in high level liquid waste (HLLW) was investigated, and it is found that the adsorption performance is strongly dependent on the impregnated extractants. Based on the batch adsorption experiments, a modular process for the treatment of HLLW was proposed and tested. The results demonstrate that the modular process based GA-SIA possesses advantages of high selectivity, simple operation and low cost.

Separation of Palladium along with Minor Actinides byisoBu-BTP/SiO2-P Adsorbent from High-Level Liquid Waste

Aiming at the separation of Pd(II) along with MA(III) from high-level liquid waste, a porous silica based adsorbent isoBu-BTP/SiO2-P was prepared. The adsorption properties of isoBu-BTP/SiO2-P toward Pd(II) were investigated. It was found that with the increase of HNO3 concentration, Pd(II) adsorption ability increased initially as HNO3 concentration increased until 1 M, then remained unchanged as HNO3 concentration further increased. The adsorption kinetics and isotherm of Pd(II) onto isoBu-BTP/SiO2-P fit well with the pseudo-second-order rate law and Langmuir adsorption model, respectively. The adsorption thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. A hot test utilizing isoBu-BTP/SiO2-P packed column was conducted and the simultaneous separation of Pd(II) and MA(III) was achieved from solution by using 0.01 M HNO3-0.1 M TU and 0.01 M HNO3-0.01 M DTPA as eluents, respectively. The Pd(II) with isoBu-BTP/SiO2-P complex was illustrated to be 1:1 type by HRMS...

Basic Study on Solvent Extraction Characteristics of [Hbet][Tf<sub>2</sub>N] for Advanced Removing Process of Mo(VI) and Zr(IV) from High Level Liquid Waste

Basic Study on Solvent Extraction Characteristics of [Hbet][Tf<sub>2</sub>N] for Advanced Removing Process of Mo(VI) and Zr(IV) from High Level Liquid Waste

Behavior of Host Materials with Surrogates of the Rare Earth–Actinide Fraction under Ion Irradiation

The behavior of rare earth titanate phases of monoclinic and orthorhombic symmetry under ion irradiation was studied. Three samples contain a set of rare earth elements (REE), and in one sample the high-level waste (HLW) is simulated by neodymium. The samples were prepared by sintering at 1400°С or cold crucible induction melting followed by melt crystallization. The samples were irradiated with 1-MeV Kr2+ ions at temperatures in the range 298–1023 K on a tandem installation consisting of an ion accelerator and a transmission electron microscope. The critical amorphization doses for the samples at 298 K were (1.5–2.5) × 1014 ion cm–2. These values correspond to those for monoclinic titanates Nd2Ti2O7 and La2Ti2O7, are close to those for REE–Ti pyrochlores and brannerite, and are lower by an order of magnitude than those for zirconolites at the same irradiation mode. The critical amorphization temperature of the phases studied (900 K) is comparable to that of Nd2Ti2O7 (920 K), but higher than that of La2Ti2O7 (840 K). Close radiation resistance of the REE2Ti2O7 and REE4Ti9O24 phases in which the rare earth elements are represented by a mixture of elements similar in composition to their set in spent nuclear fuel and liquid HLW from its reprocessing or solely by Nd confirms the assumption that Nd is a suitable surrogate for the whole rare earth–actinide fraction.

Selective extraction of Cs(I) using 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-calix[4]arene in ionic liquid solvents and its application to the treatment of high-level liquid waste

To separate heat-generating Cs from high-level liquid waste (HLLW), the extraction of Cs(I) using 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-calix[4]arene (calix[4]arene-R14) in combination with 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) ionic liquids ([C n mim][NTf2], where n = 2, 4, and 6) was investigated. Under moderately acidic conditions, the calix[4]arene-R14/[C n mim][NTf2] system showed a higher extraction efficiency (ECs) than that exhibited by the conventional calix[4]arene-R14/dichloromethane system. All extraction processes reached equilibrium within 5 min. Slope analysis revealed that the Cs:calix[4]arene-R14 inclusion complex has a 1:1 stoichiometry. The extraction was found to be exothermic and influenced by the presence of Na(I). These extraction systems exhibited high efficiency and selectivity for Cs(I) in simulated HLLW.

Biosorption of strontium ions from simulated high-level liquid waste by living Saccharomyces cerevisiae.

In this study, the Saccharomyces cerevisiae (S. cerevisiae) was modified by γ-ray. The RNA-seq results reflect that the high γ-ray energies could change some gene fragments, such as deletion, recombination, and mutation. The biosorption of strontium ions (Sr2+) to different types of S. cerevisiae (S. cerevisiae (K-0), modified S. cerevisiae (Y-7), and non-living S. cerevisiae (H-K)) from the simulated high-level liquid waste (S-HLLW) was assessed at different experimental conditions. The sorption experimental results show that, under an appropriate condition, γ-ray radiation can enhance its biosorption capacity slightly of Sr2+ to S. cerevisiae. The maximum metal uptake and efficiency of Y-7 under S-HLLW were 11.656mgg-1 and 37.91% at 32h (wet weight), respectively. They decreased to 9.46mgg-1 and 30.76% under radiation conditions. SEM-EDX and TEM analysis indicates that Sr2+ was adsorbed both on the cellular surface and the inner parts of the cells. Our experimental results fit well to the Langmuir and Freundlich model isotherms (r2 > 0.94), and the maximum biosorption capacity values reached qmax > 24.74mgg-1 at 32°C. Negative values ofΔG0 and positive values ofΔH0 were observed, indicating the spontaneous and endothermic nature of Sr2+ biosorption on modified S. cerevisiae. The biosorption kinetics follow a pseudo-second-order equation at 32°C (r2 > 0.94). The desorption efficiency of Sr2+ adsorbed onto Y-7 was 7.65 ± 0.52%, 76.51 ± 2.13%, and 65.62 ± 2.42% by deionized water, 1M HCl, and 0.1M EDTA-Na, respectively. However, they were lower than H-K (18.82, 83.32, and 73.32%). Our findings demonstrate that living S. cerevisiae (Y-7) is a promising sorbent material for the treatment of radioactive process streams.

Adsorption and separation behaviors of molybdenum from high-level liquid waste using a silica-based hydroxyoxime impregnated adsorbent

To separate Mo(VI) from high-level liquid waste, a silica-based (anti-DEHDO + Dodec)/SiO2-P adsorbent was synthesized by impregnating an anti-isomer of 5,8-dietyl-7-hydroxy-6-dodecanonoxime (DEHDO) as a hydroxyoxime-type extractant and a molecule modifier of 1-dodecanol into a SiO2-P support, where “P” indicates the polymerized styrene–divinylbenzene inside macroporous SiO2 particles. Adsorption and separation behaviors of Mo(VI) in HNO3 solutions onto the adsorbent were investigated by batch and column methods, respectively. The adsorbent can effectively adsorb Mo(VI) in both methods. In addition, Pd(II) and Zr(IV) contained in the simulated high-level liquid waste were successfully isolated by the adsorbent packed column, respectively.

An industrial-scale annular centrifugal extractor for the TRPO process

Annular centrifugal extractors (ACEs) offer advantages including excellent hydraulic and mass-transfer performance, small hold-up volume, short residence time, and thus low solvent degradation, high nuclear criticality, easy start-up and shut-down, high compact structure. Therefore, ACEs have attracted increasing interest for future nuclear processing schemes, including the partitioning of high-level liquid waste (HLLW). Laboratory-scale and pilot-scale ACEs have been applied in demonstration tests of the trialkyl phosphine oxide (TRPO) process for HLLW partitioning. In this study, an industrial-scale ACE (260 mm in rotor diameter) with magnetic coupling and a “hanging” rotor structure was developed for the TRPO process. Moreover, a series of hydraulic and mass-transfer tests were carried out in the industrial-scale ACE. The maximum throughput can reach 10 m3/h under suitable operation parameters when kerosene is used as the organic phase, and water is used as the aqueous phase. The influence of the total flowrate, the flow ratio (aqueous/organic, A/O), and the rotor speed on the liquid hold-up volume was determined. The extraction stage efficiency is higher than 98% under test parameters for extraction of Nd3+ and HNO3, using 30% TRPO kerosene as the extractant from an HNO3 solution containing Nd. All results show good performance of the industrial-scale ACE for the TRPO process.

Investigation of Flow Behavior of Joule-Heating Flow in a 2-D Model of a Reprocessing Glass Melter Cavity

Flow behavior was observed in a simplified model cavity of a multiphase High Level Liquid Waste (HLLW) reprocessing glass melter. Electrodes were set to generate Joule-heating flow in the cavity. A chaotic flow occurred because the lower part of the cavity was heated while the top surface of the cavity was cooled. Downflow and upflow occurred alternately in cavities. The shape of the cavity was a sloping bottom cavity, which was similar in shape to the real glass melter. To know the flow behavior in the cavity, 1-D flow behavior and 2-D flow behavior were measured in an experiment and simulated by an original CFD code. In the sloping bottom cavity, chaotic flow occurred in the upper part of the cavity. In the case of the sloping bottom cavity which had the same set of electrodes as the glass melter, the effect of the downflow near the electrodes decreased. The same phenomena could be predicted in the melter. The experimental results were also used to validate the CFD code, which will be helpful for developing a multiphase Joule-heating flow predicting.

Conjugated microporous polymers bearing phosphonate ligands as an efficient sorbent for potential uranium extraction from high-level liquid wastes

Conjugated microporous polymers bearing phosphonate ligands are stable and efficient for uranium extraction under highly acidic and strong radioactive conditions.

Effects of γ-ray Irradiation on Thiodiglycolamide-type Extractant-impregnated Adsorbents for Separation of Platinum Group Metals from High-level Liquid Waste

To estimate the applicability of thiodiglycolamide-type extractant-impregnated adsorbents to separation of the platinum group metals (PGMs) from high-level liquid waste, radiation effects on the adsorption behavior of PGMs onto a macroporous silica-based (Crea-TOA)/SiO2-P absorbent and on the stability of the adsorbent were investigated by using γ-rays emitted from 60Co, and the results were compared with those obtained using (MOTDGA-TOA)/SiO2-P. A difference in adsorption behaviors of PGMs onto the two adsorbents was not observed with or without irradiation up to 100 kGy of the absorbed dose. Decomposition of the impregnated extractants and degradation of the adsorption capability increased with increasing absorbed dose, but the distribution coefficient of Pd remained >102 up to approximately 250 kGy. The retention ratio of loaded PGMs gradually decreased with increasing absorbed dose. From these results, the adsorbents were considered to be useful for the adsorption of PGMs irrespective of whether the adsorption system was irradiated, except for when the adsorbent was irradiated by a very large dose.

Extraction Behavior of Sr (II) from High-Level Liquid Waste using Ionic Liquid Extraction System with DtBuCH18C6

The extraction behavior of Sr(II) from high-level liquid waste (HLLW) has been investigated using 4’,4’(5")-di-(tert-butyl cyclohexano)-18-crown-6 (DtBuCH18C6) as an extractant in combination with three types of ionic liquids, [Cnmim][NTf2] (n = 2,4,6) as solvents, where [Cnmim]+ is 1-alkyl-3-methylimidazolium and [NTf2]- is bis(trifluoromethylsulfonyl)amide. DtBuCH18C6 in the [Cnmim][NTf2] system can be used as a good choice for matching, and a higher DSr can be achieved. Within the acidity range studied, the DSr follows the order of [C2mim][NTf2] > [C4mim][NTf2] > [C6mim][NTf2]. In their extraction systems, DSr decreases with increasing concentration of HNO3 in the aqueous phase. Thermodynamic parameters for the extraction of Sr(II) tested elements were calculated using the Van’t Hoff equation, showing that the reaction is spontaneous and exothermic. Existence of inorganic salts such as KNO3 usually reduces ESr for all systems, and the decreasing degree is much larger than that of NaNO3. The extraction systems exhibited high extraction efficiency and high selectivity for Sr(II) from simulated HLLW containing 25 typical elements and 2M HNO3. From the results, the DtBuCH18C6 in [Cnmim][NTf2] system may provide an alternative for extraction of Sr(II) under HLLW conditions.

Adsorption of platinum-group metals and molybdenum onto aluminum ferrocyanide in spent fuel solution

Separation of platinum-group metals (PGMs: Ru, Rh, Pd) and Mo from high-level liquid waste (HLLW) makes the vitrification process more stable. Aluminum ferrocyanide (AlHCF) has been synthesized, and it is suitable for the simultaneous recovery of PGMs and Mo from HLLW. In this study, an adsorption experiment onto AlHCF was conducted in a spent fuel solution prepared from an irradiated MOX fuel. An adsorption experiment in a simulated HLLW with 26 elements was also conducted as reference. As a result, both Pd and Mo have been successfully adsorbed on AlHCF in both the spent fuel solution and the simulated HLLW. Americium was not adsorbed onto AlHCF as tri-valent lanthanide ions were.

Adsorption Behavior of Sr(II) from High-level Liquid Waste using Crown Ether with Ionic Liquid Impregnated Silica Adsorbent

4’4’(5’)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) modified with 1-ethyl-3-methylimidazolium bis (trifluoro methylsulfonyl) imide ([C2mim][NTf2]) was loaded onto porous silica/polymer composite support (SiO2-P) particles with a mean diameter of 50 μm and used to extract Sr(II) from HNO3 solutions. The effect of HNO3 concentration on the equilibrium kinetics and thermodynamic properties of Sr(II) uptake were investigated by batch methods. The adsorbent exhibited excellent adsorption selectively for Sr(II) over a wide range of HNO3 concentrations. The adsorption of Sr(II) in the presence of 3 M HNO3 on (DtBuCH18C6+[C2mim][NTf2])/SiO2-P attained equilibrium within 1 h, and a relatively large distribution coefficient (Kd) of ca. 30 cm3·g−1 was obtained. Kinetic data were successfully modeled using pseudo-second-order kinetics. The adsorption of Sr(II) was a spontaneous and exothermic process. The uptake isotherm of Sr(II) for (DtBuCH18C6+[C2mim][NTf2])/SiO2-P followed a Langmuir-type adsorption equation.