Low-level Radioactive Effluents Research Articles

Highly selective adsorption and lattice process of cesium by cubic cyanide-based functional materials

Cesium (Cs) is a byproduct of nuclear bombs, nuclear weapons testing, and nuclear fission in nuclear reactors. Cs can enter the human body through food or air and cause lasting damage. Highly efficient and selective removal of 137Cs from low-level radioactive effluents (LLREs), which contain many radionuclides and dissolved heavy metal species, is imperative for minimizing LLRE volume, and facilitating their final disposal. Prussian blue analogs (PBAs) have received much attention as materials for the removal of radioactive Cs because of their affinity for adsorbing Cs+. In this study, an inexpensive and readily available cyanide-based functional material (PBACu) exhibiting high efficiency and excellent selectivity toward Cs capture was designed through a facile low-temperature co-precipitation process. Nano-PBACu, crystallizing in the cubic space group (Fm-3m (225)), has an average pore size of 6.53 nm; consequently, PBACu can offer abundant atomic occupation sites for capturing and incorporating Cs. Here, the pseudo-second-order kinetic model and Langmuir model fitted well with the adsorption of Cs + on PBACu, with a maximum capture capacity of 95.75 mg/g within 5 min, confirming that PBACu could rapidly capture Cs ions. PBACu strongly and selectively interacted with Cs even in a simulant containing large Na+, NH4+, Ca2+, and Mg2+ ion concentrations in an aqueous solution. The process of Cs + adsorption by cyanide-based functional crystals was confirmed to involve the entry of Cs+ into cyanide-based functional crystals to replace K+ and finally achieve the lattice incorporation of Cs. The current results broaden the lattice theory of radionuclide Cs removal and provide a promising alternative for the immobilization of Cs from radioactive wastewater.

Two-Dimensional Ion-Imprinted Silica for Selective Uranium Extraction from Low-Level Radioactive Effluents

Two-Dimensional Ion-Imprinted Silica for Selective Uranium Extraction from Low-Level Radioactive Effluents

Biogene-derived aerogels for simultaneously selective adsorption of uranium(VI) and strontium(II) by co-imprinting method

• The concept of simultaneously selective adsorption is proposed for the first time. • The adsorbent is synthesized by co-imprinting method from biogenic materials. • The adsorbent shows excellent selectivity towards both U(VI) and Sr(II) ions. • The adsorption capacity can reach 317 mg U/g and 160 mg Sr/g simultaneously. Recovery of multiple radionuclides from radioactive effluents is extremely important for either environmental protection or sustainable development of nuclear energy. In this work, we report a strategy of simultaneously selective removal of uranium(VI) and strontium(II) from simulative highly saline low level radioactive effluents employing co-imprinting method. Specifically, a novel aerogel (U/Sr-IP) is imprinted with uranium(VI) and strontium(II) from biogenic dopamine and sodium alginate. The aerogel shows better selectivity for uranium(VI) and strontium(II) against other cations compared with non-imprinted polymer. The maximum adsorption capacities are calculated from Langmuir models to be 317 and 160 mg/g for uranium(VI) and strontium(II), respectively. Simultaneously selective adsorption of uranium(VI) and strontium(II) saves the time and space in dealing with complex radioactive wastewater. Noteworthily, when the concentration of sodium chloride (1 mol/L) is five times than that of radioactive effluents, 83% of the adsorption capacity is maintained even after 5 recycles. After the adsorption, uranium(VI) and strontium(II) are eluted by Ca(NO 3 ) 2 and Na 2 CO 3 successively, which makes the aerogel more practical by sequential elution. The prepared U/Sr-IP is an efficient and competitive adsorbent in harsh environment, displaying a promising application in removal of radionuclides from highly saline low level radioactive effluents. This work demonstrates a concept of simultaneously selective adsorption of two or more radionuclides for the first time.

Dual Ion-Imprinted Mesoporous Silica for Selective Adsorption of U(VI) and Cs(I) through Multiple Interactions.

Separation of uranium and cesium from low-level radioactive effluents (LLRE) is of great significance for sustainable development of the nuclear industry and for the environment. However, high salinity and massive coexisting ions of LLRE are giant challenges for the separation. To address the challenges, we report a strategy for efficient and simultaneous separation of uranium and cesium from a high-salt environment by dual ion-imprinted mesoporous silica based on multiple interactions. The as-prepared adsorbents can reach equilibrium for uranium and cesium within 1 h with a maximum capacity of 221.7 mg U g-1 and 34.5 mg Cs g-1. The sorption mechanism demonstrates that the highly active phenolic hydroxyl groups of imprinted cavities can extract uranium and cesium effectively through multiple interactions, including coulomb attraction, redox, ion exchange, and complexation. The synergism of multiple interactions and imprinted cavity endows the sorbent with good selectivity for uranium and cesium over other cations and with excellent salt tolerance. This work demonstrates a new strategy of selective extraction of nuclides by multifunction adsorbent through multiple interactions.

Pyrogenic carbon for decontamination of low-level radioactive effluents: Simultaneous separation of 137Cs and 60Co

Radiocesium (137Cs) and radiocobalt (60Co) represent main dose-significant radionuclides in low-level radioactive liquid effluents released from commercial nuclear power plants (NPPs). Although pyrogenic carbon-based adsorbents (biochars, BC) have been studied for toxic metal removal, the reports of their use in the adsorption of radionuclides are rare. This article focuses on the competitive removal of Cs+ and Co2+ ions from radioactive solutions to waste biomass derived biochar and the multi-component isotherms. BC exhibited a good affinity to both Cs and Co, and in single-component systems the maximal adsorption capacity Qmaxexp reached 97.4 ± 5.0 (Cs+) and 74.5 ± 0.4 μmol g−1 (Co2+). 3D adsorption surfaces obtained by Sheindorf-Rebuhn-Steintuch (SRS) and extended Freundlich models indicate that the sorption of Cs+ ions from the Cs–Co binary system is significantly affected by Co2+ ions and during the adsorption competitive and interaction effects between Cs+ and Co2+ ions occur. Moreover, mono- and divalent cations present in the solution acted as competing ions, decreasing the Kd values. SEM-EDX maps, FTIR and XPS spectra confirmed that both biochar mineral and carbon fraction participated in Cs and Co immobilization. Beside interactions of Cs+ and Co2+ ions with O-containing moieties on the biochar surface (chemisorption), mineral components and porosity of BC (physisorption) were involved in both Cs and Co removal. Finally, the adsorption loading and fast kinetics for both Cs and Co indicate suitability of biochar to decontaminate low-level radioactive effluents contaminated by 137Cs and 60Co.

Removal of radiocesium from low level radioactive effluents by hexacyanoferrate loaded synthetic zeolite: laboratory to pilot plant scale demonstration

Abstract Present paper reports removal of radiocesium from low level waste using a modified sorbent (13X-CFC) prepared by in-situ precipitation of potassium copper hexacyanoferrate(II) inside the macropores of a synthetic zeolite. The Cs exchange isotherm of the sorbent is established and it found to follow Fruendlich absorption isotherm equation. It is varified that presence of hexacyanoferrate on zeolite facilitates rapid Cs uptake performance. This is further confirmed in laboratory scale column tests, wherein excellent Cs removal performance from low level waste simulant was observed even at higher flow rates (40 bed volumes per hour). The utility of the sorbent is established through successful demonstration in a pilot scale (50 L) trial with almost complete removal of 137Cs from more than 14,000 bed volumes of actual low level waste. The sorbent, owing to its low cost and excellent 137Cs removal performance, is expected to find application in treatment of very low active waste streams.

Removal of 137Cs and 90Sr from low-level radioactive effluents by hexacyanoferrate loaded synthetic 4A type zeolite

Copper hexacyanoferrate was imbued on pores of synthetic zeolite and the formation of needle shaped copper hexacyanoferrate microcrystals was confirmed by XRD and SEM. Batch equilibrations showed that the sorbent has good affinity for Cs and Sr which was further confirmed from column studies. It is established that a substantial amount (>8000 bed volumes) of low level waste contaminated with 137Cs and 90Sr can be treated in fixed bed column. The sorbent, owing to its low cost, simple preparation process and excellent 137Cs and 90Sr removal performance, is expected to find wide spread application in nuclear industry.

The conceptual flowsheet of effluent treatment during preparing spherical fuel elements of HTR

High temperature gas-cooled reactor (HTR) is one of the advanced nuclear reactors owing to its inherent safety and broad applications. For HTR, one of the key components is the ceramic fuel element. During the preparation of spherical fuel elements, the radioactive effluent treatment is necessary. Referring to the current treatment technologies and methods, the conceptual flowsheet of low-level radioactive effluent treatment during preparing spherical fuel elements was established. According to the above treatment process, the uranium concentration was decreased from 200mg/l to the level of discharged standard.

Identification and characterisation of radioactive particles in salt marsh sediments

Radionuclides from authorized low level radioactive effluent discharges from the nuclear fuel reprocessing plant at Sellafield, UK, are present in the Irish Sea sediments. The distribution of radionuclides in salt marsh sediment profiles can be related to the discharge history from Sellafield. Radioactive particles, from the intertidal salt marsh sediments in the Esk estuary (10 km from Sellafield), have been isolated and investigated. Autoradiography and heavy liquid density separation were used to find and isolate these particles. Scanning electron microscopy, combined with energy dispersive X-ray analysis (SEM-EDX), was used to obtain information on the morphology and elemental composition of the particles, and alpha spectrometry for radionuclide composition. Particles are typically 1 — 20 μm size. Elemental analysis suggests that they are composed mainly of uranium. Alpha spectrometry shows that they have been irradiated, and transuranium nuclides (Pu, Am, Cm) can be identified in them.

129I/ 127I ratio measurements in bovine thyroids from the North Cotentin area (France)

Iodine-129 is routinely released in the gaseous and liquid low-level radioactive effluents of nuclear spent fuel reprocessing plants. Environmental impact assessment of these discharges are performed based on monitoring samples of different types of natural indicators. Thyroid is considered as a relevant organ to monitor radioactive iodine isotopes. In this study, bovine thyroids were collected in herds located in the Cotentin area under the influence of authorized low level gaseous effluents of the La Hague nuclear fuel-reprocessing plant. For low level 129I/ 127I ratios, characteristic of environmental samples (10 −12 to 10 −7), RNAA or SMA that includes important radiochemical preparation steps are used. This paper demonstrates the interest of direct γ-X spectrometry to measure 129I activities, associated to INAA to measure 127I to attain higher ratios levels (10 −6 to 10 −4). This study shows the interest of monitoring bovine thyroids considered as sentinel organs to characterize the dispersion in space and time of 129I discharged in low level radioactive gaseous effluents by the La Hague reprocessing plant.

Application of Ultrafiltration and Complexation to the Treatment of Low-Level Radioactive Effluents

Abstract This paper addresses certain aspects of the design and development process aiming at reducing the radioactivity of liquid low-level waste streams (LLLW) to a very low level. Two types of membrane processes are being examined: ultrafiltration (UF) and seeded ultrafiltration (SUF). The UF membrane enables the removal of very fine particles of solid material from liquid radioactive waste. Only the particles with molecular weight above the cut-off of the UF membrane are retained. Much greater radioactivity removal may be achieved if the effluent is treated with high-molecular-weight ligands that form complexes with radioactive ions or small-sized radioactive molecules. This paper presents results of experiments consisting of decontamination of model radioactive effluents, simulated waste, and original LLLW by using several ligands for binding the radioactive ions of Cr, Co and Cs.

Environmental Dose Assessment For Low-level Radioactive Effluents Discharged From Tokai Reprocessing Plant

In the normal operation of the Tokai reprocessing plant, low-level radioactive effluents are discharged to the atmosphere and the ocean under rigid control. Radiation exposures to the population around the plant have been estimated for potential pathways with site-specific parameters such as food consumption, concentration factors of marine organisms, and meteorological conditions. External exposures to a radioactive cloud and internal exposures from inhalation and oral intake of radionuclides are evaluated for airborne effluents. External exposures to a contaminated fishing net and fishing boat are considered pathways for fishermen. External exposure to a contaminated beach and internal exposure via oral intake of marine products are evaluated for liquid effluents. Since the plant began operation in 1977, estimated effective dose equivalents for the public have been less than the annual effective dose equivalent limit of 0.1% recommended by the International Commission on Radiological Protection (1977).

Implications of sedimentological and hydrological processes on the distribution of radionuclides: The example of a salt marsh near Ravenglass, Cumbria

This paper summarizes sedimentological and hydrological studies at a salt marsh site on the north bank of the River Esk near Ravenglass which have a bearing on the fate of the low-level radioactive effluent from the reprocessing facility at Sellafield, Cumbria. A range of techniques has been used including electromagnetic distance measurement (EDM) and pore water pressure studies. The results show that: 1. (a) Over a two-year period there were no significant net changes in salt marsh creek level, although shorter-term (probably seasonal) fluctuations, of the order of 2 cm, occurred. These were attributed to expansion of clay particles during the winter months. Nearby, however, there were vertical changes of the order of 1 m due to erosion. 2. (b) Pore water pressures indicated a dynamic situation with very rapid responses both to tidal fluctuations and to rainfall. During neap tides there was clear evidence for water seeping upwards from the underlying clay/sand interface. Shortlived radionuclides ( 95 Zr 95 Nb and 106Ru) were detected in this zone. 3. (c) Soil polygons, once initiated by desiccation, thereafter provide preferential routes for water (and radionuclides) to the sub-surface sediment. These, and other results, are discussed in the context of previous studies. It is concluded that the complexity of the estuarine environment results in most data being site specific.

Technetium-99 content in some marine organisms collected near La Hague, France

Analyses for 99Tc in some marine biological samples taken near the outlet of the low level radioactive effluent pipeline of the nuclear reprocessing plant of La Hague, France, gave positive results. From 500 to 3500 pCi kg −1 wet weight of 99Tc were observed in brown algae; Fucus sp. appeared to be a good indicator of this long-lived radionuclide in a marine environment.

Daily Feeding Rates of Bluegill (Lepomis macrochirus) Determined by a Refined Radioisotope Method

The daily values of 137Cs intake by bluegill (Lepomis macrochirus) from a small impoundment receiving low-level radioactive effluents were used to calculate the daily feeding rates of the fish. The calculations of 137Cs intake, for a nonequilibrium state, were based on fish growth, the seasonal fluctuation of 137Cs concentration in fish, and the temperature-elimination rate relationship. The feeding rates were obtained by dividing the daily intake of 137Cs by the concentration of 137Cs in the diet. The daily meal of bluegill varied from 0.8% of body weight in February to 3.2% in June with an annual mean of 1.75%. There was a positive correlation (r2 = 0.805) between the daily meal and the daily temperature. The ecological growth efficiency was 4.2% during the period from April to October.