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Abstract: This paper suggests the estimation algorithm for life time of structure, system and components (SSCs) for decommissioning safety of nuclear facilities using the performance data of linguistic languages and fuzzy theory. The fuzzy estimation algorithm of life time can be easily applicable but the estimated results depend on the relevant membership functions and performance characteristic functions. This method will be expected to be very useful for maintenance and decommissioning of nuclear facilities’ SSCs as a safety assessment tool. [Copyright &y& Elsevier]

Abstract: This paper proposes a model for the quantification and estimating the radiological risks of decommissioning processes in nuclear facilities. Based on fuzzy linguistic variables, the membership function and inference rules were developed for quantifying the radiological risks of nuclear decommissioning processes. Also, the fuzzy inference system was developed and the proposed method was applied to the process of concrete decommissioning. The proposed model and system is flexible in that it allows a fast-computation of the subjective expert opinion when one or several input factors change. It is believed that the suggested model and system can be applied to evaluate the safety of complex systems by only changing the variable and inputs. [Copyright &y& Elsevier]

Abstract: This paper proposes the estimation method on probability of decommissioning hazards for nuclear facilities. Evaluation method of decommissioning hazardous accidents is based on fuzzy and event tree method. Expert’s knowledge was considered as state of the basic variable with a normal distribution, which was considered to represent the membership function. The proposed method has been successfully applied to the removal of rotary specimen rack in KRR-2. [Copyright &y& Elsevier]

Abstract: A decommissioning plan should be followed by a qualitative and quantitative safety assessment of it. The safety assessment of a decommissioning plan is applied to identify the potential (radiological and non-radiological) hazards and risks. Radiological and non-radiological hazards arise during decommissioning activities. The non-radiological or industrial hazards to which workers are subjected during a decommissioning and dismantling process may be greater than those experienced during an operational lifetime of a facility. Workers need to be protected by eliminating or reducing the radiological and non-radiological hazards that may arise during routine decommissioning activities and as well as during accidents. The risk assessment method was developed by using risk matrix and fuzzy inference logic, on the basis of the radiological and non-radiological hazards for a decommissioning safety of a nuclear facility. Fuzzy inference of radiological and non-radiological hazards performs a mapping from radiological and non-radiological hazards to risk matrix. Defuzzification of radiological and non-radiological hazards is the conversion of risk matrix and priorities to the maximum criterion method and the mean criterion method. In the end, a composite risk assessment methodology, to rank the risk level on radiological and non-radiological hazards of the decommissioning tasks and to prioritize on the risk level of the decommissioning tasks, by simultaneously combining radiological and non-radiological hazards, was developed. [ABSTRACT FROM AUTHOR]

Polysulfone membranes were prepared via the diffusion-induced phase inversion process from casting solutions consisting of polysulfone, dimethyformamide, and polyvinyl pyrrolidone as a polymeric additive. The effect of PVP added in casting solutions was analyzed by measuring the prepared membranes'' morphology and water permeability. Variations in a casting solution''s thermodynamic and kinetic properties caused by PVP addition suggest that the thermodynamic variation works in favor of the enhancement of demixing in the casting solution, but the rheological variation induces the opposite trend, or the delay of demixing. When prepared by the immersion coagulation into a water bath, the solidified membranes'' structural and functional properties indicate that the coagulation of cast solutions was affected by the trade-offrelationship between thermodynamic enhancement and kinetic hindrance. With a small amount of PVP in the casting solution, the thermodynamic driving force played a major role on solution demixing, inducing the demixing enhancement, corresponding to the acceleration of phase separation due to the PVP''s nonsolvent effect. Consequently, the PVP acts as a phase separation enhancer, resulting in both macropore enlargement and permeate flux increase. With more addition of PVP, however, the macropore structure and the water permeability were suppressed rather than enlarged or increased. These phenomena reflect that the demixing of the cast solution was delayed, with the kinetic hindrance offsetting the thermodynamic effect for phase separation enhancement. [Copyright &y& Elsevier]

Double-layered polysulfone (PSF) membranes, containing cerium activated yttrium silicate (CAYS) as a fluor, were prepared from double casting of two polymeric solutions, and their morphology and radioactive capacity were compared with those of single-layered membranes. The backing, the bottom layer of double-layered membranes, was made of a binary casting solution of polysulfone and methylene chloride (MC), its cast film being solidified by vacuum evaporation. The second casting solution with dimethylformamide (DMF) as solvent was cast over the solidified backing film and coagulated by being immersed into a nonsolvent bath of water or methanol. The prepared membranes revealed two distinct, but tightly attached, double layers, their attachment being identified by the morphology of the interface between the two layers. Membranes prepared with CAYS in the casting solution have more developed macropores than those prepared without CAYS. In the radionuclide detection test of the CAYS-impregnated membranes, the membranes solidified by water precipitation showed better detection efficiency than those solidified by methanol precipitation. Its superior efficiency is not due to better holding of the radioisotopes, but due to greater density of CAYS in the membrane surface region. In the comparison with single-layered membranes, the double-layered membranes showed a greater ability in holding the radionuclides, spotted on the surface, as well as an improvement in physical strength because of the dense backing layer. [Copyright &y& Elsevier]

Graphical abstract Highlights • Self-propelled micromotor adsorbent was developed for selective adsorption of radioactive Cs. • The random movement of the micromotor adsorbent significantly reduced the Cs cleanup time. • The micromotor adsorbent was remotely steerable and collectable using a magnetic field. • More than 98% of the radioactive 137Cs ions were removed from solution containing competing ions. Abstract We report the development of magnetically steerable self-propelled micromotors that selectively remove radioactive Cs from contaminated water. Mesoporous silica microspheres were functionalized with the highly Cs-selective copper ferrocyanide, and half of the adsorptive particle surface was then coated with ferromagnetic Ni and catalytic Pt layers to fabricate Janus micromotors. The micromotor adsorbent displayed random propulsion in an H 2 O 2 solution via catalytic bubble evolution from the Pt surface, and the micromotor adsorbent self-propulsion resulted in an 8-fold higher Cs removal compared to the stationary adsorbent within one hour. The ferromagnetism of the Ni layer allowed the micromotor adsorbent to be magnetically and remotely steerable, and the propulsion speed under a magnetic field was ˜11-fold greater than it was in the absence of the magnetophoretic force. The adsorption of Cs by the self-propelling micromotor adsorbent and the subsequent magnetic recovery of the adsorbent enabled the successful removal of radioactive 137Cs from aqueous solutions. More than 98% of the radioactive 137Cs ions were removed from solution, even in the presence of competing ions, such as Na+ (1000 ppm). [ABSTRACT FROM AUTHOR]

Abstract Sodium dodecylbenzenesulfonate (SDBS) is widely used as an efficient detergent in various fields. It is also used to remove radioactive atoms including Cs ions, and as a result, Cs-bound SDBS are generated during a nuclear decontamination process. A silica-based adsorbent with mesopores was prepared and surface-functionalized with amine groups to have a positively-charged pocket for SDBS with electrostatic attraction. The removal of SDBS using such an adsorbent was investigated under various conditions. The removal of high SDBS concentration (more than 2000 ppm) was successfully carried out using both a mesoporous structure and electrostatic attraction. The effects of the initial SDBS concentration, the concentration of adsorbent, the SDBS adsorption time, and the pH in the adsorption of SDBS with the mesoporous silica-based adsorbent were investigated in detail. In addition, the adsorption of Cs ion-bound SDBS was investigated for a practical decontamination process, implying that the adsorbent did not remove Cs ions together with SDBS. Graphical abstract Image 1 Highlights • Mesoporous silica-based adsorbents were prepared to remove SDBS more than 2000 ppm. • Amine-functionalized porous silica (MSN-NH 2) showed high removal efficiency of SDBS. • MSN-NH 2 was found to be stable for adsorption of SDBS at pH 2–10. • The adsorbent could selectively adsorb SDBS from Cs ion-bound SDBS. [ABSTRACT FROM AUTHOR]

Highlights • A self-generated, strippable hydrogel containing adsorbents was developed for surface decontamination. • The hydrogel is composed of polyvinyl alcohol and phenylboronic acid grafted alignate. • The strippable hydrogel effectively removed 137Cs from the various surfaces including a porous cement surface. • A new eco-friendly volume-reduction method for radioactive waste was suggested. Abstract A self-generated, strippable hydrogel containing adsorbents was developed to remove the radioactive cesium from surfaces by adsorption for wide-area surface decontamination. Two aqueous polymeric solutions of polyvinyl alcohol (PVA) and phenylboronic-acid-grafted alginate (PBA-Alg) were easily applied to surfaces and subsequently self-generated a hydrogel based on the PBA-diol ester bond. Compared to the strippable coating and chemical gels, the PBA-diol ester bond-based hydrogel was easily peeled off the surfaces without a drying step due to its high elasticity, which is more practical and time saving. The resulting hydrogel displayed high 137Cs removal efficiencies of 91.61% for painted cement, 97.505% for aluminum, 94.05% for stainless steel, and 53.5% for cement, which was 2.3 times higher than that of Decongel due to the presence of the adsorbent in the hydrogel having an excellent Cs distribution coefficient (3.34 × 104 mL/g). Moreover, the volume of radioactive waste generated after the surface decontamination could be reduced by a simple magnetic separation of the adsorbent from the used hydrogel, which can reduce the waste disposal cost. Therefore, our hydrogel system has great potential as a new, cost-effective surface decontaminant in various nuclear industry fields including wide-area environmental remediation after a nuclear accident or terrorist attack. [ABSTRACT FROM AUTHOR]

A polyvinyl alcohol (PVA)-borate hydrogel-based strippable surface decontaminant containing an ammonium salt and Prussian blue (PB) was developed for the removal of 137Cs from various surfaces. This surface decontaminant can be easily prepared by the simple mixing of commercially available materials, such as PVA, borax, NH4Cl and PB, in water, and the decontaminant can be peeled off surfaces due to its high elastic property after surface decontamination. The hydrogel displayed an effective removal performance for Cs from painted cement, aluminum, stainless steel, and cement surfaces and a potential for reusability. Therefore, the PB/PVA-borate hydrogel has good potential as a new surface decontaminant. [ABSTRACT FROM AUTHOR]

A magnet-sensitive and strippable polymeric coating that consists of a magnetic adsorbent with 137 Cs adsorption properties using a polyacrylamide (PAAm)/alginate(Alg)-based hydrogel with highly elastic properties was developed for surface decontamination. The aqueous polymeric solution of PAAm and Alg containing adsorbent could be easily applied to 137 Cs-contaminated surfaces via the brush method. The simple addition of calcium ions on the surface induced the formation of an adsorbent/PAAm-Alg hydrogel film that could easily peel away from decontaminated surfaces due to its high elasticity. This polymeric coating displayed a good removal efficiency of 96.53% and a decontamination factor (DF) of 28.85 for 137 Cs-contaminated surfaces due to the presence of the adsorbent, which had a large distribution coefficient for Cs (3.34 × 10 4 mL/g), and the large amount of Cs chelating groups in the Alg and PAAm, such as carboxyl and amine groups. The generated volume of the radioactive wastes after surface decontamination was simply reduced due to the magnetic separation of the adsorbent from the used polymeric coating. Furthermore, this new ecofriendly volume reduction method for radioactive waste demonstrated the reusability of PAAm and Alg for further surface decontamination because almost all of the 137 Cs (99.838%) captured in the used polymeric coating was removed by magnetic separation of the adsorbent. Therefore, the adsorbent/PAAm-Alg-based polymeric coating system has excellent potential as a new cost-effective surface decontaminant. [ABSTRACT FROM AUTHOR]

Sodium-copper hexacyanoferrate-modified magnetic nanoparticles were fabricated for the highly efficient removal of radioactive cesium followed by the rapid magnetic separation of the absorbent from water. The Fe 3 O 4 nanoparticles, synthesized using a hydrothermal method, were coated with polyethyleneimine to immobilize Cu ions through metal coordination to amine groups in the PEI. Sodium-copper hexacyanoferrate (NaCuHCF) was subsequently formed on the surfaces of the magnetic nanoparticles as Cu ions coordinated the hexacyanoferrate ions. The resulting NaCuHCF-modified magnetic nanoparticles displayed an excellent saturation magnetization value (45.2 emu/g). Batch experiments revealed that cesium adsorption equilibrium was rapidly achieved within 10 min, and the maximum adsorption capacity of the adsorbent was 125 mg/g. The adsorption kinetics and isotherms fit well to a pseudo-second order model and Langmuir isotherm, respectively. The NaCuHCF-MNPs provided a high removal efficiency exceeding 99.428% of the radioactive cesium present. The adsorbent selectively adsorbed 137 Cs, even in the presence of competing cations. [ABSTRACT FROM AUTHOR]

Abstract: Tritium concentration analysis in temporary storage, where large numbers of containers store tritiated metallic waste temporarily, is performed numerically using a time dependent tritium concentration model under an atmosphere detritiation system (ADS) and vent detritiation system (VDS). The tritium concentrations in the temporary storage for both after tritium removal (T-removal) and without T-removal cases are estimated with respect to the capacity of ADS and VDS to find the influence of the tritium removal process. And also a numerical model for estimating tritium behavior in the concrete wall in the temporary storage is developed by using a one-dimensional diffusion model and tritium concentration model. The tritium permeated depths in the wall under the worst conditions are estimated for both after T-removal and without T-removal, respectively. [Copyright &y& Elsevier]

Abstract: As part of a fundamental research for the volume reduction of dismantled concrete, an investigation was carried out addressing the separation of the aggregates and the distribution of the radioactivity into the aggregates of contaminated concrete generated from dismantled nuclear facilities. Radioisotope 60Co was artificially used as a model contaminant for non-radioactive crushed heavy weight concrete taken from the Korea Research Reactor 2 (KRR-2) and light weight concrete from the uranium conversion plant (UCP) by thermal and mechanical treatment. The results showed that most of the 60Co nuclide was easily separated from the gravel and aggregate, and concentrated mainly into the porous fine cement paste. By thermal and mechanical separation treatment, the clean aggregate can be recovered up to 80% from radioactively contaminated concrete waste. The final wastes of formed cement paste were produced by thermal and mechanical treatment. Heavy and light cement pastes were vitrified. Volume reductions of the cement pastes were achieved at about 1/3 and 1/2.5, respectively. [Copyright &y& Elsevier]

Abstract: The purpose of this paper is to provide a basis for an optimization of a dismantling process of a research reactor and nuclear facility. An optimization of a dismantling process should be at the beginning of a study for an evaluation of the radioactivity inventory and the safety of the workers. Many countries have conducted an optimization to achieve a shortened dismantling schedule, a reduction of the amount of waste, and cut down on the decommissioning by using computer graphics such as animation, simulation, and virtual reality. In the present study, we propose methods for identifying the existence of radioactivity which is contained in the dismantled objects and for evaluating a worker’s dose through a simulation. To evaluate a worker’s external dose under a virtual dismantling environment generated by computer graphics, the shape of the thermal column horizontal door was created by 3D CAD and the radiation dose surrounding the door was calculated by using MCNP-4C. An animation that can demonstrate a dismantling procedure according to a dismantling scenario was produced. For matching the radiation dose, which was calculated by MCNP-4C with an area where workers are dismantling a door, a simulation module was developed which could show a worker’s external dose in real-time. The result from the distribution of the radioactivity enables us to specify where the most contaminated part of the dismantling objects is. In the animation, a virtual worker demonstrated a dismantling activity procedure as a chosen scenario. In the simulation, a worker’s exposure dose rate in real-time has been evaluated. [Copyright &y& Elsevier]

Abstract: The evaluation of decommissioning scenarios is critical to the successful development and execution of a decommissioning project. In the past, many experts have used a physical mock-up system to find the exact work processes and the working positions. Nowadays, these jobs are being done by a Digital Mock-Up (DMU) system. The DMU, which is a technology to realize an effective work process by using virtual environments through representing the physical and logical schema and the behavior of a real decommissioning work, can save on the cost and time, reduce the risk of making later changes, and develop various decommissioning scenarios. In this research, a decommissioning DMU system was developed for simulating the relevant dismantling processes. Decommissioning data-computing modules which can calculate a dismantling schedule, quantify a radioactive waste, visualize a radioactive inventory, estimate a decommissioning cost, and estimate a worker’s exposure were also developed to qualitatively assess the decommissioning information. And an analytic hierarchy process (AHP) model was developed to evaluate the decommissioning scenarios which reflected the quantitative and qualitative considerations. To establish the proper scenario for the thermal column in KRR-1, the developed decommissioning DMU system was applied to evaluate the two candidate scenarios of it. [Copyright &y& Elsevier]

Sodium dodecylbenzenesulfonate (SDBS) is commonly used to remove radioactive nuclides such as Cs ions during decontamination of shut-down nuclear power plants. Potential environmental problems still remain because of the incomplete removal of large amounts of SDBS from radioactive liquid waste. For the first time, mesoporous silica nanofibers (MSFs) were fabricated for an efficient SDBS separation. MSFs were prepared by electrospinning using tetraethyl orthosilicate, a surfactant, and a template polymer; the product had a large surface area, a high pore volume, and a uniform pore size distribution. The internal pores or external surface were modified with quaternary ammonium salt, providing affinity to water and an electrostatic interaction with SDBS. The MSF-based adsorbent had excellent adsorption ability for SDBS (158.98 mg/g) over conventional adsorbents. In addition, the MSF-based adsorbent could selectively adsorb SDBS from a mixed solution of SDBS and Cs ions. Judging from the Freundlich pseuso second-order kinetic adsorption, the adsorption isotherm indicated that the SDBS adsorption was a kind of multilayer physisorption. • Mesoporous silica nanofibers (MSF) were prepared by electrospinning. • Ammonium salt was introduced on the MSF surface. • The modified MSF improved selective removal of SDBS in mixture of SDBS and Cs ions. [ABSTRACT FROM AUTHOR]

A new fabrication method of nanofibrous metal oxide electrode comprising Pt nanofiber (Pt–NF) covered with PbO 2 on a Ti substrate was proposed. Pt–NF was obtained by performing sputtering deposition of Pt on the surface of electrospun poly(vinyl alcohol) (PVA) nanofiber on a Ti substrate, in which PVA was then removed by calcination (Ti/Pt–NF). Subsequently, by introducing PbO 2 to the Ti/Pt–NF using the electrodeposition method, a nanofibrous Ti/Pt–NF/PbO 2 electrode was finally obtained. Because the Ti substrate was covered by nanofibrous Pt, it had no environmental exposure and thus, was not oxidized during calcination. The crystal structure of the PbO 2 mainly consisted of β -form rather than α -form; the β -form was suitable for electrochemical decomposition and remained stable even after 20 h of use. The nanofibrous Ti/Pt–NF/PbO 2 electrodes showed 10% lower anode potential, 1.6 times higher current density at water decomposition potential, lower electrical resistance in the ion charge transfer resistance, and 2.27 times higher electrochemically active surface area than those of a planar-type Ti/Pt/PbO 2 electrode, and demonstrated excellent electrochemical performance. As a result, compared with the planar electrode, the Ti/Pt–NF/PbO 2 electrode showed more effective electrochemical decomposition toward nitrilotriacetic acid (80%) and ethylenediaminetetraacetic acid (83%), which are commonly used as chelating agents in nuclear decontamination. [Display omitted] • Electrospun PVA nanofibers were used as template for Ti/Pt–NF. • Pt nanofibers were obtained through a sputtering and calcination method. • Nanofibrous PbO 2 electrode was prepared using electrodeposition method. • The electrochemical property of nanofibrous PbO 2 were enhanced compared with that of flat PbO 2. [ABSTRACT FROM AUTHOR]

Because of its excellent chelating property, ethylenediaminetetraacetic acid (EDTA) is used as a complex agent, not only for heavy metals, but also for radioactive isotopes during the decontamination of nuclear facilities. The removal of EDTA was investigated by adsorption with commercially available, gel-type, anion-exchange resins (AERs), which are based on cross-linked polystyrene with positive tertiary amine groups. Because of the positive charge on AERs, they could adsorb EDTA effectively even in a solution mixed with ions of cesium (Cs) via electrostatic attraction. Because EDTA adsorption by cation-exchange resins (CERs) was not possible, it was concluded that the negative charges on CERs do not contribute to the interaction with EDTA. The maximum adsorption capacity (qmax) of AER (2 g/L) for EDTA removal, calculated by the Langmuir isotherm model was 0.47 mmol/g for initial EDTA concentrations in the range of 0.01–1 mM in the EDTA/Cs mixed solution. The Langmuir isotherm model was found to be suitable for EDTA adsorption on AERs, indicative of monolayer adsorption. The results clearly suggested that the AERs could efficiently remove EDTA, regardless of the presence of nuclides, such as Cs ions in the aqueous solution. [ABSTRACT FROM AUTHOR]

Based on a conventional cation-exchange polymer resin, Cs ion exchange resins were fabricated for the removal of radioactive Cs via two preparation methods. Prussian blue (PB), which have been commonly used to remove radioactive 137Cs, was synthesized on the surface of resins. To provide a strong interaction between the polymer resin and PB, polydopamine (PDA) was used as a linker, present on the surface of the polymer resins. Based on the same principle, two types of Cs ion exchange resins were prepared via different orders of fabrication sequence. From the removal test of Cs ions, it was found that the two types of the resins did not show noticeable difference in adsorption of Cs ions, in which adsorption of Cs ions took place heterogeneously and chemically with multilayer adsorption. [ABSTRACT FROM AUTHOR]

Highlights • Sodium alginate beads containing chemically bound PB beads were prepared. • The beads showed improved adsorption of Cs ions compared to conventional sodium alginate beads containing PB. • The beads showed efficient adsorption in a fixed bed column as well as in a batch with good stability. • The beads exhibited high removal efficiency toward radioactive 137Cs. Abstract A new approach for efficient removal of radioactive 137Cs was developed using a sodium alginate hydrogel beads-based adsorbent containing chemically bound Prussian blue (PB). Sodium alginate was crosslinked with Fe (III) ions to form hydrogel beads, in which Fe (III) had a dual function; it served as a crosslinking agent and also led to PB formation via reaction with hexacyanoferrate. Fe (III) ions, an unusual crosslinking agent for sodium alginate gel, led to stable, homogeneous distribution of PB inside the beads. The amount of embedded PB in the composite beads was more than two times larger than in the conventional sodium alginate-PB composite beads, resulting in an adsorption capacity for Cs ions that was two to five times higher, mainly because of a higher PB contents and because of the microporosity of the sodium alginate hydrogel. [ABSTRACT FROM AUTHOR]

Sodium-copper hexacyanoferrate (NaCuHCF)-functionalized magnetic nanoadsorbents were fabricated for the highly efficient magnetic removal of radioactive caesium from seawater. The magnetic nanoclusters (MNCs), composed of many individual Fe 3 O 4 nanoparticles, were covalently coated with polyethyleneimine (PEI) to functionalize the MNC surfaces with NaCuHCF. After simple immobilization of Cu and Na ferrocyanide on the NC surface, the resulting NaCuHCF-functionalized MNCs showed good magnetic properties and a significant adsorption capacity for Cs + with a high content of NaCuHCF (36.04%). The adsorption kinetics and isotherms were well fit to a pseudo-second-order model and Langmuir isotherm, respectively. The sorption of 97.35% Cs by the NaCuHCF-PEI-MNCs completed in less than 5 min, and the maximum adsorption capacity of the adsorbent was 166.67 mg/g. The NaCuHCF-PEI-MNCs selectively adsorbed Cs even in the presence of various competing ions, such as Na, K, Mg, and Ca, and the Cs removal mechanism was revealed as ion exchange between Cs in solution and Na in the NaCuHCF-PEI-MNCs. In radioactive tests, our adsorbent displayed excellent removal performance in real seawater with a high removal efficiency exceeding 99.73%, a decontamination factor exceeding 372, and a high stability in water over a wide pH range from 4 to 10 with negligible leaching of Fe. [ABSTRACT FROM AUTHOR]

A stimuli-sensitive, strippable coating material that consisted of a magnetic field-sensitive adsorbent with excellent 137 Cs adsorption and a temperature-sensitive, elastic Poly vinyl alcohol (PVA)-borate hydrogel was developed for the decontamination of 137 Cs-contaminated surfaces. The viscous solution of adsorbent/PVA-borate complex can easily be applied to a surface at 50 °C, subsequently forming an adsorbent/PVA-borate hydrogel film that is strippable from the surface at room temperature. The film displayed a good removal efficiency of 83.46% and the decontamination factor (DF) of 6.05 from the 137 Cs-contaminated surface due to the presence of the adsorbent, which had a large distribution coefficient for Cs (3.34 × 10 4 mL/g). Moreover, the PVA-borate complex can be reused following a simple addition of water via the magnetic separation of the adsorbent, which can capture 99.071% of the 137 Cs in the used hydrogel film. These findings suggest a new eco-friendly volume-reduction method for radioactive waste after surface decontamination. [ABSTRACT FROM AUTHOR]

We report the Cs desorption behavior of cationic molecules, including a cationic surfactant, cationic polyelectrolyte, and ammonium ion, against hydrobiotite, which is composed of slightly expandable vermiculite and non-expandable biotite. The degree of ionization of polyethyleneimine (PEI) increased with decreasing pH, and the increased cationic charge under acidic conditions enhanced the desorption of Cs from hydrobiotite by ion exchange. Even though the cationic surfactant with a permanently charged quaternary ammonium head group showed less pH-dependent Cs desorption compared to PEI, the maximum Cs desorption of the cationic surfactant was lower than that of PEI. PEI showed the highest Cs desorption efficiency among the tested cationic ion exchangers, suggesting that the high cationic charge of the polyelectrolyte originating from its large number of ionizable units is effective at Cs desorption from mixed-layer clay minerals. [ABSTRACT FROM AUTHOR]

We report on a new approach to increase the removal of cesium from contaminated clays based on the intercalation of a cationic polyelectrolyte into the clay interlayers. A highly charged cationic polyelectrolyte, polyethyleneimine (PEI), was shown to intercalate into the negatively charged interlayers and readily replaced Cs ions adsorbed on the interlayers of montmorillonite. The polycation desorbed significantly more Cs strongly bound to the clay than did single cations. Moreover, additional NH 4 + treatment following the PEI treatment enhanced desorption of Cs ions that were less accessible by the bulky polyelectrolyte. This synergistic effect of PEI with NH 4 + yielded efficient desorption (95%) of an extremely low concentration of radioactive 137 Cs in the clay, which is very difficult to remove by simple cation-exchange methods due to the increased stability of the binding of Cs to the clay at low Cs concentrations. [ABSTRACT FROM AUTHOR]

We demonstrate a simple method for the visual determination and removal of Co ions using a bead-shaped, capturing probe based on hybridized sodium alginate. For Co ions, the designed protocol consisted of three main constituents: an azopyridine-based Co ion-probe for visual detection; sodium alginate as an adsorbent for the Co ion and a bead construct for removal and structure; silica as a linker for the probe and the alginate, leading to a robust structure. When the composite beads were exposed to Co ions, the yellow color of the beads turned to intensive violet and the color intensity was associated with the Co ion concentration. The color variation was quantified using red-green-blue (RGB) color values that were obtained with a scanner and evaluated with Photoshop. The technique achieved both visual recognition with obvious color change of the beads and efficient removal of the radioactive 60 Co ion. The sensing and removal of any radioactive isotope could be achieved with an appropriate sensing probe, to provide a simple and universal platform for remediation. [ABSTRACT FROM AUTHOR]

We propose a new approach to remediate cesium-contaminated clays based on intercalation of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) into clay interlayers. Intercalation of DTAB was found to occur very rapidly and involved exchanging interlayer cations. The reaction yielded efficient cesium desorption (∼97%), including of a large amount of otherwise non-desorbable cesium ions by cation exchange with ammonium ions. In addition, the intercalation of DTAB afforded an expansion of the interlayers, and an enhanced desorption of Cs by cation exchange with ammonium ions even at low concentrations of DTAB. Finally, the residual intercalated surfactants were easily removed by a decomposition reaction with hydrogen peroxide in the presence of Cu 2+ /Fe 2+ catalysts. [ABSTRACT FROM AUTHOR]

Prussian blue-functionalized magnetic nanoclusters were fabricated for the highly efficient removal of radioactive cesium (such as 137 Cs) and rapid magnetic separation of absorbent from 137 Cs-contaminated water. The magnetic nanoclusters, synthesized via the hydrothermal method, were coated with Prussian blue (PB) via a simple reaction with potassium hexacyanoferrate under acidic conditions. The resulting Prussian blue-functionalized magnetic nanoclusters had a large distribution coefficient, even in the presence of 3000 ppm competing ions such as K + , Na + , Ca 2+ and Mg 2+ , and excellent removal efficiency (>99.7%) of radioactive cesium from contaminated water. Furthermore, they possess good saturation magnetization values (27.5 emu/g), allowing for rapid separation from an aqueous solution using an external magnetic field. Therefore, these magnetic adsorbents have promising applications for the treatment of radioactive cesium-contaminated water. [ABSTRACT FROM AUTHOR]

Abstract: A mixed polydiacetylenes (PDAs) vesicle with a phospholipid unit is functionalized by entrapping fluorescent benzoxazole (BZ) molecules inside the PDA vesicles. Upon photo-polymerization and heat-treatment of the self-assembled vesicles, a weak red fluorescence can be observed. Excitation of BZ molecules enables the amplification of PDA vesicle fluorescence resonance energy transfer (FRET) to more than four times that of the direct excitation of red-phase PDA vesicles. The backbone of the PDA vesicles act as energy acceptors, which absorb energy from embedded BZ donor molecules inside the PDA vesicle, which emit blue fluorescence. The amplified red emission from the PDA vesicle can be altered by pH changes in the aqueous solution and thus the PDA vesicle mixed with a phospholipid and entrapped molecules inside can be a promising candidate as a pH sensor. [Copyright &y& Elsevier]

Abstract: The purpose of the present study was to apply thermal treatments to reduce the volume of HEPA filter media and to investigate the volatility and leachability of heavy metals and radionuclides during thermal treatment. HEPA filter media were transformed to glassy bulk material by thermal treatment at 900°C for 2h. The most abundant heavy metal in the HEPA filter media was Zn, followed by Sr, Pb and Cr, and the main radionuclide was Cs-137. The volatility tests showed that the heavy metals and radionuclides in radioactive HEPA filter media were not volatilized during the thermal treatment. PCT tests indicated that the leachability of heavy metals and radionuclides was relatively low compared to those of other glasses. XRD results showed that Zn and Cs reacted with HEPA filter media and were transformed into crystalline willemite (ZnO·SiO2) and pollucite (Cs2OAl2O34SiO2), which are not volatile or leachable. The proposed technique for the volume reduction and transformation of radioactive HEPA filter media into glassy bulk material is a simple and energy efficient procedure without additives that can be performed at relatively low temperature compared with conventional vitrification process. [Copyright &y& Elsevier]

This work studied a way to reclaim uranium from contaminated UO oxide scraps as a sinterable UO powder for UO fuel pellet fabrication, which included a dissolution of the uranium oxide scraps in a carbonate solution with hydrogen peroxide and a UO precipitation step. Dissolution characteristics of reduced and oxidized uranium oxides were evaluated in a carbonate solution with hydrogen peroxide, and the UO precipitation were confirmed by acidification of uranyl peroxo-carbonate complex solution. An agglomerated UO powder obtained by the dissolution and precipitation of uranium in the carbonate solution could not be pulverized into fine UO powder by the OREOX process, because of submicron-sized individual UO particles forming the agglomerated UO precipitate. The UO powder prepared from the UO precipitate could meet the UO powder specifications for UO fuel pellet fabrication by a series of steps such as dehydration of UO precipitate, reduction, and milling. The sinterability of the reclaimed UO powder for fuel pellet fabrication was improved by adding virgin UO powder in the reclaimed UO powder. A process to reclaim the contaminated uranium scraps as UO fuel powder using a carbonate solution was finally suggested. [ABSTRACT FROM AUTHOR]

Abstract: This work studied a process to recover uranium from contaminated (U,Gd)O2 scraps generated from nuclear fuel fabrication processes by using the dissolution of (U,Gd)O2 scraps in a carbonate with H2O2 and the precipitation of the dissolved uranium as UO4. The dissolution characteristics of uranium, Gd, and impurity metal oxides were tested, and the behaviors of UO4 precipitation and Gd solubility were evaluated with changes of the pH of the solution. A little Gd was entrained in the UO4 precipitate to contaminate the uranium precipitate. Below a pH of 3, the uranium dissolved in the form of uranyl peroxo-carbonato complex ions in the carbonate solution was precipitated as UO4 with a high precipitation yield, and the Gd had a very high solubility. Using these characteristics, the Gd-contaminated UO4 could be purified using dissolution in a 1-M HNO3 solution with heating and re-precipitation upon addition of H2O2 to the solution. Finally, an environmentally friendly and economical process to recover pure uranium from contaminated (U,Gd)O2 scraps was suggested. [Copyright &y& Elsevier]

Abstract: The dynamic precipitation characteristics of UO4 in different solution conditions (pH, ionic strength, uranium and H2O2 concentrations) were characterized by measuring changes in the absorbance of the precipitation solution and by monitoring the change of particle size in a circulating particle size analyzer. The precipitation solution conditions affected the precipitation characteristics such as the induction time, precipitation rate, overall precipitation time, and particle size in a complex manner. With increases in both pH and ionic strength, the induction time was prolonged, and the individual particle size decreased, but the individual particles tended to grow by aggregation to form larger precipitates. The uranium concentration and the ionic strength of the solution affected the induction time and precipitation rate to the greatest extent. [Copyright &y& Elsevier]

Abstract: A great volume of uranium electrokinetic leachate has been generated during the operation of the electrokinetic decontamination experiment to remove uranium from radioactive soil. Treatment technology for the reuse of the generated uranium leachate was developed. The concentration of uranium in the generated uranium leachate was 180ppm and concentrations of Mg(II), K(I), Fe(II), and Al(III) ions were high. When sodium hydroxide was put in the uranium leachate as a precipitant, the precipitation velocity was shorter and the precipitate particle size was larger than those of calcium hydroxide. The treatment process for uranium leachate consists mainly of mixing and cohesion, precipitation, concentration, and filtration. In order for the pH of a precipitate solution to reach 11, the amount of sodium hydroxide and calcium hydroxide needs to be 2.7–3.0g/100ml. In several respects, sodium hydroxide is more efficient as a precipitant than ammonium hydroxide and calcium hydroxide. The results of precipitation experiments show that a mixture of NaOH+0.2g alum+0.15g magnetite is an optimal precipitant for filtration. The average particle size of precipitate with NaOH+alum+0.15g magnetite was 600μm. Because a pH level of 9 provides the lowest total amount of metal concentrations in the supernatant, sodium hydroxide should be added to 0.2g alum and 0.15g magnetite for optimal filtration until the pH of the leachate reaches 9. [Copyright &y& Elsevier]

Type 304 stainless steel specimens artificially contaminated with CsCl solution were treated with KOH solution and KNO solution, respectively. Cs ion removal tests by a Q-switched Nd:YAG laser at 1064 nm at a given fluence of 57.3 J/cm were performed. The surface morphology and the relative atomic mole ratio of the specimen surface were investigated by SEM and EPMA. The order of Cs ion removal efficiency of laser was no-treatment < KOH < KNO during the 42 shots. From the investigation of XPS peaks around 532.7 and 292.9 eV, KNO on a surface of specimen was found to be fully decomposed during the laser irradiation. It was suggested that CsO particulates formed by the reaction between the reactive oxygen generated from the nitrate ion and Cs ion on the metal surface could be easily suspended. For the KOH system, FeOOH was formed during the laser irradiation and it changed into FeO. It was also suggested that CsO particulates were formed by the reaction between the reactive oxygen generated from the decomposition of KO and Cs ion on the metal surface.. [ABSTRACT FROM AUTHOR]

Abstract: This work studied anodic dissolution characteristics of a SIMFUEL electrode at several potentials in carbonate solutions of a high concentration at several pHs. The electrolytic uranium dissolution of SIMFUEL was much affected by a corrosion product of UO2CO3 generated at the electrode during the dissolution in carbonate solution. The corrosion product distorted the voltammogram of SIMFUEL in the potential region of oxygen evolution and increased the overpotential of oxygen evolution at the electrode. The effective dissolution of the SIMFUEL electrode in a carbonate solution could be obtained at an applied potential such as +4V (vs SSE) or more which had an overpotential of oxygen evolution high enough to rupture the corrosion product on the electrode surface. The corrosion potential of SIMFUEL decreased with pH in the carbonate solution, and the dissolution rate and current efficiency of the SIMFUEL increased with a decrease of pH in the carbonate solution. [ABSTRACT FROM AUTHOR]

Abstract: Vertical electrokinetic-flushing equipment suitable to the geological characteristics of Korean nuclear facility sites was developed for the decontamination of some real radioactive soil. The optimum reagent and electric current were chosen through vertical electrokinetic-flushing experiments. The effect of the particle size of some soil and the radioactive concentration of some soil on the removal efficiencies of the nuclides from said soil were analyzed. The experimental results are as follows. The removal efficiencies of 60Co and 137Cs by nitric acid were increased by 3.3% and 2.0% more than those by acetic acid. And, moreover, when nitric acid instead of acetic acid was used, it had the advantage of a reduction of the electricity consumption due to its higher electrolytic conductivity. The higher the radioactivity concentration of the soil was, the higher the removal efficiencies of 60Co and 137Cs were. Namely, the removal efficiencies of 60Co and 137Cs from the soil of a high concentration (2850Bq/kg) were increased by 13.7% and 3.9% more than those from the soil of a low concentration (135Bq/kg). The larger the particle size of the soil was, the higher the removal efficiency of 137Cs was. Namely, the removal efficiency of 137Cs from the soil of average 1.2mm particle size was increased by about 2% more than that from the soil of average 0.6mm particle size. Also, the removal efficiencies of 60Co and 137Cs by the application of an electric current of 20mA/cm2 were increased by 1.3% and 4.2% more than those by the application of 10mA/cm2. The removal efficiencies of 60Co and 137Cs from the radioactive soil of 1825Bq/kg were 99.9% and 94.3% by an electrokinetic-flushing decontamination by the application of an electric current of 20mA/cm2 for 50 days. [Copyright &y& Elsevier]

A three-dimensional graphic simulation has been carried out for the dismantling process of the Rotary Specimen Rack(RSR) in the Korea Research Reactor-1&2 (KRR-1&2). First of all, the general steps of the graphic simulation were established and reviewed for the dismantling process of the object. Four dismantling processes, which are the removal of RSR, reactor core region, beam tube, and thermal column and activated concrete, were selected for the graphic simulation on the virtual space by the consideration of the activation, worker training, work difficulty and so on. In the present study, the dismantling procedure of the RSR was divided into several steps and its visual simulation was performed by the 3D graphic software. Finally, the simulation result was converted to moving file with extension of AVI so that easy approach can be made on window OS system. [Copyright &y& Elsevier]

• H 2 O 2 was used to enhance cation-exchange treatment for Cs+ desorption from clay mineral. • Hydrobiotite (HBT) exhibited the most favorable H 2 O 2 activation because of its high Fe content. • H 2 O 2 treatment with solvated Mg2+ enhanced Cs+ desorption from HBT by expansion of interlayer region. • ∼99% removal of radioactive Cs+ from HBT was achieved by three cycles of H 2 O 2 treatment. In this study, hydrogen peroxide (H 2 O 2) was used to enhance the cation-exchange treatment for Cs+ desorption from clay minerals. Among various investigated clay minerals, hydrobiotite (HBT), which has interstratified layers of vermiculite and biotite, exhibited the highest Cs+ sorption capacity and the most favorable H 2 O 2 activation because of its high Fe content. In X-ray diffraction analysis, HBT treated with H 2 O 2 and 0.1 M Mg2+ showed substantial changes in its basal spacing, indicating expansion of the interlayer region induced by treatment of H 2 O 2 and strongly hydrated divalent cations. In addition, more than 80% of the Cs+ was readily desorbed from HBT with 35% H 2 O 2 solution and 0.1 M Mg2+ at room temperature. After three cycles under the same treatment conditions (35% H 2 O 2 solution and 0.1 M Mg2+), approximately 99% removal of radioactive Cs+ was achieved. These results suggested that H 2 O 2 treatment with solvated Mg2+ enhanced Cs+ desorption from HBT by altering the interlayer region through intercalation of hydrated divalent cations in conjunction with the H 2 O 2 decomposition reaction. [ABSTRACT FROM AUTHOR]

Radioactive Cs ions are extremely harmful to the human body, causing cancers and other diseases. Treatments were performed on radioactive Cs present in wastewater after use in industrial or medical fields. Prussian blue (PB) has been widely used for the removal of Cs ions from water but its colloidal structure hinders reuse, making it problematic for practical use. To solve this problem, we used a commercial macroporous polymer resin as a PB matrix. To provide an efficient anchor for PB, the surface of the polymer resin was decorated with sodium dodecylbenzenesulfonate to produce a negatively charged surface. The successful chemical binding between the polymer resin and PB prevented leakage of the latter during adsorption and crosslinked structure of the matrix provided regeneration of the adsorbent. The adsorbent maintained its removal efficiency after five repeats of the regeneration process. The PB-based, Cs ion-exchange resin showed excellent selectivity toward Cs ions and good reusability, maintaining its high adsorption capacity. Image 1 • Cs ion-exchange resin was synthesized from polystyrene-based resin beads containing Prussian blue (PB). • Adsorption of SDBS by the polymer resin was efficiently carried out by the presence of PB. • The crosslinked adsorbent provided easy and stable reusability without any PB leakage. [ABSTRACT FROM AUTHOR]

Among the surfactants used for removal of radioactive nuclides generated from nuclear decontamination, sodium dodecylbenzenesulfonate (SDBS) is frequently used. A potential environmental problem of incomplete elimination of SDBS from radioactive liquid wastes (RLWs), which contain a high concentration of SDBS and radioactive nuclides, still remains. Removal of SDBS was evaluated by adsorption using commercially available, macroporous polymer-based adsorbents, HP20 and HP2MGL, which are styrene (St)- and methyl methacrylate (MMA)-based crosslinked resin beads, respectively. The effect of the macroporosity and chemical structure of the macroporous adsorbent resins (MARs) on the adsorption behavior was investigated. HP20 did not have any functionality for adsorbing SDBS, but it showed effective adsorption toward SDBS (less than 20 min to reach 90% adsorption), because of the hydrophobic interaction between the phenyl groups in the St unit in HP20 and in the SDBS. The removal of SDBS from a mixed solution of SDBS and Cs ions was investigated to elucidate the adsorption process in an imitation of the sort of RLWs. This investigation suggests that MARs can potentially be used for the removal of SDBS not only from a SDBS solution but also from a mixed solution of SDBS and Cs ions. [ABSTRACT FROM AUTHOR]

A simple one-step approach to fabricating Prussian blue-embedded magnetic hydrogel beads (PB-MHBs) was fabricated for the effective magnetic removal of radioactive cesium (137Cs) from water. Through the simple dropwise addition of a mixed aqueous solution of iron salts, commercial PB and polyvinyl alcohol (PVA) to an ammonium hydroxide (NH4OH) solution, the formation of hydrogel beads and the encapsulation of PB in beads were achieved in one pot through the gelation of PVA with in situ-formed iron oxide nanoparticles as the cross-linker. The obtained PB-MHBs, with 43.77 weight % of PB, were stable without releasing PB for up to 2 weeks and could be effectively separated from aqueous solutions by an external magnetic field, which is convenient for the large-scale treatment of Cs-contaminated water. Detailed Cs adsorption studies revealed that the adsorption isotherms and kinetics could be effectively described by the Langmuir isotherm model and the pseudo-second-order model, respectively. Most importantly, the PB-MHBs exhibited excellent selectivity for 137Cs in 137Cs-contaminated simulated groundwater (55 Bq/g) with a high removal efficiency (>99.5%), and the effective removal of 137Cs from real seawater by these PB-MHBs demonstrated the excellent potential of this material for practical application in the decontamination of 137Cs-contaminated seawater. [ABSTRACT FROM AUTHOR]