Low-level Radioactive Wastewater Research Articles

Comparative study of silica-based porous materials in the purification of radioactive wastewater

A significant challenge in the treatment of low-level radioactive wastewater is the effective purification of low-concentration radionuclides. Silica-based adsorbents are advantageous for the deep-purification of low-concentration metal ions. This study investigates three primary types of silica-based adsorbents: functionalized mesoporous silica, various modified zeolites, and mesoporous calcium silicate hydrate (C-S-H). These adsorbents were synthesized and their deep-purification effects on heavy metals and radionuclides were compared. The results indicated that mesoporous silica showed relatively poor adsorption for most metal ions. Zeolites outperformed mesoporous silica, with Zn framework-modified zeolites showing enhanced adsorption for several metal ions. Notably, C-S-H displayed superior adsorption performance, achieving high adsorption capacities for various metal ions and radionuclides. Specifically, at a dose of 0.5 g/L, the adsorption efficiency of C-S-H for numerous radionuclides in nuclear power plant wastewater exceeded 92–99 %, highlighting its potential for practical applications. An in-depth analysis of the physical and chemical structure and the adsorption mechanisms of C-S-H revealed its large mesoporous structure and electrostatic attraction to cations across a wide pH range. Multivalent cations were removed through exchange with Ca2+ in C-S-H, whereas monovalent cations were removed through exchange with Na+ in C-S-H. The cyclic structure of silica-oxygen tetrahedra in C-S-H, which promotes large pore formation and provides abundant ion exchange sites, underpins its excellent adsorption properties. This study offers valuable insights for the selection and application of silica-based materials in radioactive wastewater treatment.

Enhanced Photocatalytic Removal of U(VI) from Real Radioactive Wastewater by Modulating the Surface Charge Microenvironment in Porphyrin-Based Hydrogen-Bonded Organic Framework.

Reduction of soluble U(VI) to insoluble U(IV) based on photocatalysts is a simple, environmentally friendly, and efficient method for treating radioactive wastewater. The present study involved the systematic comparison of the photoelectric properties of three metalloporphyrins with different metal centers and the synthesis of a novel porphyrin-based hydrogen-bonded organic framework (Ni-pHOF) photocatalyst by modulating the surface charge microenvironment in porphyrin for enhanced photocatalytic removal of U(VI) from wastewater. Compared to the metal-free HOF, the surface charge microenvironment around the Ni atom in Ni-pHOF accelerated the reduction kinetics of U(VI) under visible light illumination at the initial moment, showing a high removal rate, even in air. The removal rate of U(VI) from aqueous solution by Ni-pHOF can achieve over 98% in the presence of coexisting nonoxidizing cations and only decreased by less than 8% after five cycles, exhibiting high selectivity and good reusability. Furthermore, Ni-pHOF can remove 86.74% of U(VI) from real low-level radioactive wastewater after 120 min of illumination, showcasing practical application potential. Density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) spectra indicated that modulating the surface charge microenvironment in Ni-pHOF through porphyrin metallization is conducive to improving the charge separation efficiency, prompting more e- and •O2- to participate in the reduction reaction of U(VI). This work provides new insights into the metallization of porphyrin-based HOFs and paves a new way for the tailoring of porphyrin-based HOFs/COFs by modulating the surface charge microenvironment to achieve efficient recovery of U(VI) from real radioactive wastewater.

The Application of Laser-Scanning 3D Model Reconstruction Technology for Visualizing a Decommissioning Model of the Heavy Water Research Reactor

Currently, over 100 nuclear power units globally have been in operation for more than 40 years. Hindered by the limitations of computer technology at the time, these nuclear facilities lack detailed electronic drawings. Activities such as equipment replacement and process circuit system modifications during operation result in discrepancies between paper drawings and actual conditions. Given the complexity and irreversibility of nuclear facility decommissioning activities, virtual simulation technology is often employed before the decommissioning process begins to assist in designing and validating decommissioning plans. Consequently, the creation of high-precision 3D models is crucial for subsequent decommissioning designs. Through innovatively utilizing laser-scanning 3D model reconstruction technology in the reconstruction of the model of China’s first heavy water research reactor undergoing decommissioning, this paper provides an overview of the process of laser-scanning 3D model reconstruction and its application in reconstructing the heavy water research reactor model. Using a 3D laser scanner, four decommissioning areas of the heavy water research reactor, including the reactor building, secondary water pump room, ventilation center, and low-level radioactive wastewater storage tank area, were subjected to 3D laser scanning. The acquired point cloud data from 572 scanning stations were processed using point cloud processing software for denoising, stitching, and triangulation. The triangulated model was then imported into modeling software for 3D reconstruction, ultimately establishing a digitalized model of the heavy water research reactor suitable for subsequent decommissioning simulation and design.

Kapok fiber composites minimizing secondary waste and disposal costs for large-scale radioactive liquid treatment

Conventional liquid treatments for large-scale, low-level radioactive wastewater, such as ion exchange and waste solidification, face challenges due to the large amounts of secondary waste and high disposal costs. A new large-scale decontamination method is proposed that uses kapok fiber composites for rapid radionuclide adsorption and high volume reduction to minimize secondary waste. The composite consists of natural zeolite and kapok holocellulose, which has high water-soaking ability and low-temperature pyrolysis. The kapok composites, fabricated using a commercial wet-laid nonwoven manufacturing process, absorbs 99% of low-level radioactive cesium in 20 min, reducing the volume by 98% and the weight by 47% at 300 °C. The low-temperature pyrolysis process below 300 °C prevents cesium desorption and gasification by avoiding zeolite destruction. The mass-producible kapok composites can be used for adsorbing various radionuclides in large-scale wastewater by attaching specific adsorbents for target isotopes to the composites.

Construction of novel phytic acid-based lignin for highly efficient treatment of low-level radioactive wastewater: Synthesis, performance, and mechanistic insights

Low-level radioactive wastewater exhibits a serious jeopardize to the ecology, natural environment, and human health. Hence, this study constructed a novel adsorbent (PA-EHL) via a simple grafting reaction by using enzymatic hydrolysis lignin waste (EHL) and phytic acid (PA) as raw materials. The adsorption capacity of PA-EHL was evaluated using Ce(III) and La(III) as the representative nuclides. PA grafting significantly promoted the formation of good textural properties, high crystalline stability, and abundant phosphorous/oxygen-containing functional groups on lignin surface, thus appreciably strengthening the adsorption performance. The PA-EHL exhibited high adsorption capacity for Ce(III) with 743.16 and for La(III) with 735.60 mg/g within 240 min. In addition, the efficient ability of PA-EHL for adsorbing Ce(III) and La(III) displayed superior anti-ions interference abilities, excellent reusability, and extremely low operational fees. The P-O on PA-EHL surface as the main active site, displayed strong binding affinity for Ce(III) and La(III) via electrostatic attraction-dominated physisorption and complexation-dominated chemisorption, respectively. In summary, the constructed PA-EHL addresses the drawback of conventional adsorbents in view of complicated fabrication process, low adsorption capacity, inferior anti-ions interference abilities, and expensive cost, which makes it as a potential adsorbent in industrial application for the highly efficient treatment of low-level radioactive wastewater.

Application of vacuum membrane distillation-Fenton oxidation process for deep purification of low-level radioactive organic wastewater

During the production of UO2 kernel for the high temperature gas-cooled nuclear reactor, a large amount of low-level radioactive organic wastewater (LLROW) containing ammonia, uranium and organic compounds are generated. The current treatment process is suffered from the production of radioactive solid wastes, low adsorption efficiency of organic matters and the frequent membrane fouling during RO process. In this study, vacuum membrane distillation (VMD)-Fenton oxidation process was developed for the deep purification of the LLROW. The process parameters were optimized and the system performance was evaluated. As a result, all major contaminates such as uranium, NH3-N, TN and COD could meet the GB8978-1996 (secondary standard) and GB/T31962-2015 (B standard) for direct discharge. The membrane fouling was also studied by membrane autopsy as well as the quantum calculation. It was found that weak hydrogen bonds were formed between PTFE membrane and contaminants while the membrane fouling could be recovered by 0.1 M HCl cleaning.

Ammonium phosphomolybdate-modified UiO-66 as an efficient adsorbent for the selective removal of 137Cs from radioactive wastewater

137Cs is a radioactive pollutant in the production of wastewater from nuclear power plants. In this study, a rapid and simple in-situ synthesis new method was employed to prepare a novel AMP-functionalized UiO-66 composite material for the selective capture of 137Cs from low-level radioactive wastewater. Characterization techniques such as SEM-EDS, FTIR, XRD, TG, and BET were used to confirm the successful loading of AMP on the surface of UiO-66. UiO-66/AMP showed a good removal effect in pH4-11. At pH7, the effects of different parameters, such as the initial Cs concentration, the ratio of the amount of adsorbent to the volume of solution, and the adsorption time were investigated. The adsorption efficiency is 96.7%, the maximum adsorption capacity is 94.9 mg/g and has fast adsorption kinetics (90% Cs+ removal within 5 min). The adsorption data conformed to the pseudo-second-order kinetic model and Langmuir isotherm model, suggesting a monolayer homogeneous adsorption process. XPS helps confirm that the adsorption mechanism is the ion exchange between Cs+ and NH4+ ions. Particularly, in the adsorption experiments of 137Cs, UiO-66/AMP demonstrated good selectivity (KdCs: 5.8 × 103 ∼ 1.26 × 104 mL/g) towards trace Cs+ in a mixed ion solution with a molar ratio of 1 (Cs): 2.18 × 1015 (Na): 4.6 × 1014 (K): 2 × 1014 (Mg): 2 × 1014 (Ca), indicating its potential for selective capture of 137Cs from low-level liquid waste (LLLW).

Porphyrin-based hydrogen-bonded organic framework for visible light driven photocatalytic removal of U(VI) from real low-level radioactive wastewater

The reduction of soluble U(VI) to insoluble U(IV) precipitates by visible light is an environmentally friendly and highly effective strategy to remove uranium from uranium-containing radioactive wastewater. Herein, a porous hydrogen-bonded organic framework (HOF) of UPC-H4a was self-assembled by intermolecular hydrogen bonds of 5,10,15,20-tetra(4-(2,4-diaminotriazine)phenyl) porphyrin to remove U(VI) from aqueous solution. UPC-H4a has high crystallinity with permanent porosity, excellent photocatalytic property, good chemical stability, and strong photocatalytic reducibility. The experiments showed that UPC-H4a removed 98.18% of U(VI) after illumination for 120 min, with high selectivity, strong ion interference resistance, and good reusability. A real low-level radioactive wastewater was employed to estimate the potential of UPC-H4a for practical application and its removal rate can reach 66.14% in the presence of redox competing metal ions, exhibiting great potential for practical application. The DFT calculations and EPR spectra revealed that a more negative electrostatic potential of DAT-porphyrin and the formed intermolecular hydrogen bonds in UPC-H4a can facilitate the participation of photogenerated electrons in the O2/∙O2– reaction, and the radical of ∙O2– was proved to be the critical participant in U(VI) photoreduction. The discovery of UPC-H4a in this work will help to develop more potential applications of HOFs as photocatalysts in radioactive wastewater treatment.

Cesium ion removal from low-level radioactive wastewater utilizing synthesized cobalt hexacyanoferrate-sand composite

Abstract Here, a novel method of synthesis of a sand-based adsorbent for radioactive Cs+ ion removal is reported. Natural sand has been modified with cobalt hexacyanoferrate (CoHCF) using a simple and effective approach. The detailed physical–chemical characterization of the synthesized adsorbent is carried out using XRD, XPS, UV-visible, FT-IR, ICP-AES and Raman spectroscopy. Cs+ ion batch adsorption studies were conducted radio-analytically, and the sorbent’s adsorption capability was observed to be ∼5 mg g−1. The batch studies revealed that Cs+ ion was selectively adsorbed throughout a broad pH range of 1–10. The rate-controlling steps in the adsorption process, according to kinetic studies, are film diffusion and intraparticular diffusion and the adsorption process follows a second-order kinetics.

Immobilization of radioactive waste material in concrete matrix–A study of leachability aspects

The biomass, Ganoderma Lucidum, is a naturally growing macro-fungus that grows in rubber plantations, and has been found to remove uranium from low level radioactive wastewaters. Subsequent to the sorption of uranium, the loaded biomass needs to be safely and scientifically disposed. This is done by first immobilizing the waste biomass material in a solid matrix such as concrete or resin, and then disposing it in deep sea or geological repositories after due enclosures for safety. Despite immobilization there remains a risk of leaching of radioactivity from the loaded biomass material. This requires to be verified by testing leachability in lab under varying pH conditions that mimic sea water and geological repository environments. Short terms desorption and leachability experiments were conducted at the materials lab at MANIT, Bhopal to determine the leachability of radioactivity from the concrete matrix enclosing the loaded biomass. It was found that leaching was rapid in acidic conditions (0.2 N HCl), with 27.2 % uranium leaching out within 8 days. This indicated the suitability of alkaline sea-waters for safer disposal of uranium laden immobilized biomass. Mathematical models were subsequently developed based on the laboratory data to predict the long-term leachability for assessing the safety of disposal mechanism, and indicated the prominence of diffusion as the leachability mechanism. This paper details the experiments conducted, the materials used, the lab observation results, and the mathematical models developed to determine safety aspects related to possible leaching from immobilized concrete matrix in which radioactive biomass has been loaded.

Adsorption of Sr(II) in aqueous solution by multilayer titanium carbon nitrogen (Ti3CNTx) MXene: Box-Behnken modeling design and experimental study

The discharge of low-level radioactive wastewater from nuclear power accidents is an important source of radionuclides that enter and pollute the environment, such as 90Sr, which has a long half-life and is harmful. The effectiveness of multilayer Ti3CNTx MXene as a novel adsorbent for the removal of wastewater containing Sr2+ was explored. The synthesized multilayer Ti3CNTx MXene was characterized by XPS, FTIR, SEM, BET, and XRD. The influence of basic process parameters, such as time, pH, coexisting ion concentration, and initial concentration, on strontium adsorption efficiency, was determined. Ti3CNTx showed rapid kinetics (nearly 90% strontium removal after 15 min) and a broad active pH range of 3–12. The adsorption capacity of Ti3CNTx was better than that of Ti3C2Tx under the same reaction conditions. The maximum adsorption capacity of Ti3CNTx was 26.53 mg∙g−1 at 313 K according to the Langmuir isotherm. And the adsorption was consistent with the pseudo-second-order kinetic. The experiments of initial concentration and coexisting ions showed that the Ti3CNTx has a high affinity for strontium at low concentration, and the inhibition of Ca2+ is the largest. Ti3CNTx adsorbed Sr2+ via complex formation, electrostatic attraction, and encapsulation as revealed by various instrument characterization and analysis. The reusability of Ti3CNTx was good, after four cycles, the removal efficiency was 73%. Finally, the RSM model was applied to explore the optimal conditions of adsorbent to provide a reference for practical application. In conclusion, the results showed that the multilayer Ti3CNTx MXene has a good adsorption performance for strontium.

Treatment of Simulated Radioactive Wastewater Using Reverse Osmosis and Membrane Distillation

With the rapid development of nuclear power, increasing attention has been paid to the treatment of low-level radioactive wastewater (LLRW). In this study, reverse osmosis (RO) and membrane distillation (MD) are used to treat LLRW containing Ce(III), U(VI), and Co(II). RO was used for the purification of LLRW. MD was used for further concentration of RO concentrate. The effect of the operating parameters, including operating pressure (0.6 to 1.4 MPa), feed pH (7 to 9), feed concentration (2 to 10 mg/L), feed temperature (50°C to 90°C), and feed flow rate (80 to 160 L/h) on the permeate flux and the rejection rate of the RO process and MD process was studied. The results demonstrate that it is very effective to use the RO process to treat LLRW containing Ce(III), U(VI), and Co(II), with the rejection rates of Ce(III), U(VI), and Co(II) higher than 99.97%, 99.98%, and 99.35%, respectively. The operating pressure has a significant effect on the permeate flux in the RO process. The permeate flux increases from 9.84 to 23.03 L/m2·h when the operating pressure increases from 0.6 to 1.4 MPa. The feed pH has an apparent influence on nuclide rejection. At the feed pH = 9, the rejection rates of Ce(III), U(VI), and Co(II) by the RO process can reach 99.99%, 99.99%, and 99.79%, respectively. MD can reject almost all the nuclides in the RO concentrate, with rejection rates consistently higher than 99.98%. Increasing the feed temperature and feed flow rate can result in a significant increase in the permeate flux, but has almost no effect on nuclide rejection in the MD process.

Preparation of chitosan-based asymmetric electrodes by co-imprinting technology for simultaneous electro-adsorption of multi-radionuclides

The operation of the nuclear industry generates a great deal of radionuclides-containing low-level radioactive wastewater (LLRW). The development of new adsorbents and techniques for radionuclides separation from LLRW will be of great significance for environmental safety and sustainable development of nuclear energy. Electro-adsorption is a potential technique for the separation of radionuclides, but the simultaneous recovery of multiple radionuclides by electro-adsorption have not been reported before. Here, a novel approach was reported for the simultaneous electro-adsorption of strontium (Sr2+), cesium (Cs+), uranium (UO2(CO3)22–) and rhenium (ReO4−) (the non-radioactive surrogate of technetium) from LLRW by chitosan-based asymmetric electrodes. The UO2(CO3)22–/ReO4− co-imprinted chitosan hydrochloride (URIC) and Sr2+/Cs+ co-imprinted chitosan (SCIC) prepared by co-imprinting technique were loaded on the surface of carbon clothes and used as asymmetric electrodes. The maximum electro-adsorption capacities of URIC for U(VI) and Re(VII) were 427.4 mg and 531.9 mg/g and the maximum adsorption capacities of SCIC for Sr(II) and Cs(I) were 254.5 mg and 231.5 mg/g at the potential of 1.2 V, which were at least 3.7 times higher than the values obtained without potential. The electro-adsorption for all these ions conformed to pseudo-second-order kinetics and the adsorption equilibrium can be reached within 30 min at pH 8.0 and 298.15 K, which were more than twice faster than physicochemical adsorption. The electrodes revealed better selectivity for these four target ions against other competing ions in comparison with non-imprinted chitosan functionalized electrodes. Furthermore, the electrodes showed conspicuous salt resistance in simulative LLRW with high ionic strength (1 mol/L NaCl) and high removal efficiencies can be retained after five adsorption and desorption cycles. XPS studies revealed that UO2(CO3)22– and ReO4− anions were bound to URIC mainly through electrostatic interaction, while Sr2+/Cs+ were bound to SCIC by complexation interaction between Sr2+/Cs+ and –NH2/–OH on the backbone of chitosan. This work reports an innovative approach for the simultaneously selective electro-adsorption of multiple radionuclides from LLRW assisted by co-imprinting technology, which can be popularized to the simultaneous separation of other charged contaminants efficiently, thus achieving deep purification of wastewater.

Efficient extraction of U(VI) from uranium enrichment process wastewater by amine-aminophosphonate-modified polyacrylonitrile fibers

The enrichment and recovery of U(VI) from low-level radioactive wastewater in the process of uranium enrichment is important for the sustainable development of nuclear energy and environmental protection. Herein, a novel amine-aminophosphonate bifunctionalized polyacrylonitrile fiber (AAP-PAN), was prepared for the extraction of U(VI) from simulated and real uranium-containing process wastewater. The AAP-PAN fiber demonstrated a maximum adsorption capacity of 313.6 mg g−1 at pH = 6.0 and 318 K in the batch experiments. During the dynamic column experiment, over 99.99% removal of U(VI) could be achieved by the fiber using multi-ion simulated solution and real wastewater with an excellent saturation adsorption capacity of 132.0 mg g−1 and 72.5 mg g−1, respectively. It also exhibited an outstanding reusability for at least 5 cycles of adsorption process. The mechanism for U(VI) removal was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis in the assist of simulation calculation. It suggested that the amine and aminophosphonate groups can easily bind uranyl ions due to U(VI) is more likely to combine with oxygen atoms of CO and PO, respectively.

Covalent organic frameworks functionalized electrodes for simultaneous removal of UO22+ and ReO4- with fast kinetics and high capacities by electro-adsorption

The recovery of radioactive ions from high salinity low-level radioactive wastewater (LLRW) is important for the sustainable utilization of nuclear energy. Previous work primarily focuses on developing adsorbents that remove individual types of ions via physicochemical adsorption. Here, we report a new strategy for the simultaneous recovery of uranium (UO22+) and rhenium (ReO4-) as a non-radioactive surrogate of technetium from LLRW via electro-adsorption. Carboxyl functionalized covalent organic frameworks (COF-1) and cationic covalent organic frameworks (COF-2) were prepared as cathode and anode materials, respectively. The adsorption capacities were 411 mg U/g for COF-1 and 984 mg Re/g for COF-2 under 1.2 direct-current (DC) volts, 2.5 and 2.1 times higher than the capacities of the same adsorbents obtained by physicochemical adsorption. We also found that the electro-adsorption of uranium and rhenium follows pseudo-second-order kinetics with the adsorption rates of 0.45 and 1.05 g/mg/h at pH 7.0 and 298.15 K, again two times faster than those measured in physicochemical adsorption. Therefore, electro-adsorption improves both adsorption capacity and kinetics by maximizing the utility of available active sites in adsorbents and facilitating ion migration towards the adsorbents. The adsorption efficiencies for uranium and rhenium reached 65.9% and 89.2%, respectively, after electro-adsorption for 2 h. The high efficiencies can be maintained after five adsorption-desorption cycles. Furthermore, the electrodes showed high selectivity for uranium(VI) and rhenium(VII) and excellent salt resistance even in 1 mol/L NaCl solution. XPS studies revealed that covalent bonds were formed between uranium(VI) and carboxyl groups on COF-1, and rhenium(VII) was bound to cationic COF-2 through electrostatic interaction. Our asymmetric electrodes design can be extended to simultaneously and efficiently remove other types of radioactive or heavy metal ions from wastewater.

Efficient adsorption of U(VI) using in low-level radioactive wastewater containing organic matter by amino groups modified polyacrylonitrile fibers

Efficient adsorption of U(VI) using in low-level radioactive wastewater containing organic matter by amino groups modified polyacrylonitrile fibers

Polyamine-modified polyacrylonitrile fibers for efficient removal of U(VI) from real fluorine-contained low-level radioactive wastewater

It is of great significance to develop an adsorbent with high adsorption capacity and excellent resistance to anion and cation interference toward the removal of U(VI). Herein, a novel polyamine-modified polyacrylonitrile-based fiber (PANPA) has been synthesized through hydrothermal method, which can validly remove U(VI) from solution. Combined with mesoscopic, spectral characterization and simulation method, the removal behavior and mechanism of U(VI) from high fluorine uranium-containing wastewater by PANPA are systematically investigated. The results show that, based on the strong coordination principle of polyamine group and UO22+, PANPA can selectively remove U(VI) from wastewater. In addition, the qmax of 459.27 mg g−1 was more than that of many other adsorbent materials. More importantly, PANPA is not affected by high concentration of F−, and exhibits higher distribution coefficient (559,900 mL g−1) and removal efficiency (99.5%) to U(VI) than other coexisting ions in real wastewater. Furthermore, the column experiment was also implemented to remove U(VI). The results indicate that PANPA is a promising material to effectively remove U(VI) from real wastewater produced during the fabrication of nuclear fuel elements.

Highly Efficient Uptake of TcO4 - by Imidazolium-Functionalized Wood Sawdust.

99Tc is a radioactive fission product, mainly in the form of TcO4–, with good solubility and mobility in the environment. The development of effective and inexpensive materials to remove TcO4– from nuclear industry wastewater or contaminated water is significant. Wood sawdust is a byproduct of the wood processing industry and is an abundant, low-cost, and sustainable material. The mesostructure of wood consists of numerous hollow cells that are joined endwise to form an interconnected channel matrix capable of rapid transfer of ions. Imidazolium-functionalized wood sawdust (IM-WS) was synthesized using natural wood sawdust by a two-step reaction. It has excellent properties of TcO4–/ReO4– adsorption including rapid adsorption dynamics (30 s to equilibrium), good adsorption stability (pH 3–9), high selectivity (adsorption of 45.4 Re % in 1000 times excess of NO3– ions, 76.6 Re % in 6000 times excess of SO42– ions, and 92.2 Tc % in a simulated mixed solution; after adsorption, the concentration of TcO4– decreased to 0.056 ppb from the initial concentration of 12.09 ppb in 1000 times excess of SO42−), and in particular low production costs. These characteristics give it great prospects for low-level radioactive wastewater treatment and environmental remediation.

Decontamination of uranium contained low-level radioactive wastewater from UO2 fuel element industry with vacuum membrane distillation

The rapid development of nuclear industry has generated large quantities of low-level radioactive wastewater (LLRW) to pose a potential threat globally. In this study, the feasibility of vacuum membrane distillation (VMD) process for the decontamination of uranium contained LLRW from UO2 fuel element production has been studied using commercial PTFE hollow fiber membrane. The effects of operation conditions, such as feed temperature/pH, vacuum pressure and feed flow velocity were investigated and optimized with artificial UO2(NO3)2 solution. The real process wastewater from the UO2 fuel element factory were then treated by VMD process under the optimized conditions for 1400 min with the concentration factor up to 9. No clear evidence of membrane fouling or wetting were noticed during the VMD operation nor the membrane autopsy studies. With an average permeate flux of 7.3 L m−2 h−1, it exhibited excellent retention towards all major contaminates such as uranium, COD, and NH4+-N to meet the Integrated Wastewater Discharge Standard of China (GB 8978-1996) for direct discharge.

Technical Points of Water-Draw and Discharge Impact Analysis in Guidelines for Water Resource Assessment of Coastal Nuclear Power Plants

Nowadays, cleaner production is getting more and more attention, and nuclear power has been widely used due to its low energy consumption and lower pollution. Most nuclear power plants in China, including those under construction and constructed ones, are coastal. For a nuclear power plant, however, its large amount of water consumption and high guarantee rate of water quality will have impacts on the regional water-resource allocation in the site area. During the water-discharge process, low-level radioactive wastewater and warm water will be discharged, while medium or even highly radioactive wastewater will be generated in an accident, both of which will affect the environment of the receiving water. In 2016, the Chinese government began to work on the Guidelines for Water Resources Assessment of Coastal Nuclear Power Plant Projects. The compilation work, led mainly by the Ministry of Water Resources, focused on analyzing key technical points of the impacts of water intake, wastewater discharge, and their reduction measures, as well as water-protection measures. In this study, the technical requirements for impact analysis of water-draw, wastewater discharge, and their remedial measures for coastal nuclear power construction projects in different periods were put forward. Lastly, the measures for water conservation, protection, and management were given. All the technical requirements and measures gave a research basis and technical support for the formulation of the guidelines.