Liquid Low-level Radioactive Waste Research Articles

Safety analysis and evaluation of transport and storage container for very Low-Level liquid radioactive waste

Safe temporary storage and transportation of the very low-level liquid radioactive waste generated during the Decommissioning and Decontamination (D&D) of nuclear power plants (NPPs) must be ensured. This study proposes a composite shielding transport container for very low-level liquid radioactive waste, which adheres to the industrial package (IP)-2 technical standards for packaging and transportation of radioactive materials. A shielding container based on barium sulfate (BaSO4) (a shielding material harmless to the human body) and a structurally reinforced frame were developed. Then, to confirm the structural safety of the container according to the regulations on the packaging and transportation of radioactive materials under drop weight and stacking tests, the Abaqus/Explicit program was used and on-site evaluations were performed. The maximum strains of about 8.8% and 2.2% were obtained in the drop-weight and stacking performance tests, respectively. Compared to the strain values of 40% at which high-density polyethylene (HDPE) could break, it was derived to be about 22% and 5.5%, respectively. The test satisfaction standard, that is, no loss or dispersion of radioactive contents and no shielding loss that could increase the radiation dose rate by more than 20% on the outer surface, were satisfied, confirming the safety of the container.

Composition of Chemical Elements and Ion Exchange Complex of Acid- and Alkali-Modified Natural Zeolites From the Sokyrnytsky Deposit

Natural zeolites are abundant and inexpensive resources. They are crystalline hydrated aluminosilicates with a framework structure that has pores and channels occupied by water, alkali, and alkaline earth cations. Having high cation exchange capacity, acting as a molecular sieve, natural zeolites have been widely utilized in recent decades as adsorbents in separation and purification processes. Modification of natural zeolite increases its adsorption capacity of environmental pollutants, in particular, radionuclides from low-level liquid radioactive waste. The article presents results obtained from a study of the chemical composition of the structural elements and ion exchange complexes of natural, acid-modified and alkali-modified zeolites from the Sokyrnytske deposit. The main rock-forming mineral of the Sokyrnytske zeolite is clinoptilolite. The zeolite was modified by a 5.5 M HCl solution for 2 hours at 100 oC using a backflow condenser. The ratio of solid to liquid phases was 1:2. For alkaline modification, 1.4 M NaOH solution was used. The exposure time was 2.75 hours. The conditions and phase ratio were similar to those in acidity modification. By composition of the ion exchange complex, natural zeolite belongs to potassium-calcium-sodium (K > Ca > Na) clinoptilolites. In the process of acidity and alkaline modification of the natural zeolite, redistribution of the exchangeable cations is observed and the content of structural cations in the clinoptilolite lattice changes. In alkali-modified zeolite, the content of exchangeable Na and Ca cations increases, and the content of K and structural Al cations decreases. In the acid-modified zeolite, the number of exchangeable Na, Mg, Ca, K cations decreases. At the same time, the content of Fe and Al decreases and the relative amount of Si in the lattice increases. The Si/Al ratio increases in the following succession: natural zeolite → alkali-modified zeolite → acid-modified zeolite. The specific surface area of the modified zeolites increases compared to the natural ones. The largest increase is observed for the acid-modified zeolite. The textural characteristics and mineral composition of the studied samples indicate that the natural, acid-modified and alkali-modified zeolites from the Sokyrnytske deposit may be used for removal of radionuclides from low-level liquid radioactive waste.

Biosorption kinetics of cerium(III) and cobalt(II) from liquid wastes using individual bacterial species isolated from low-level liquid radioactive wastes.

The existence of toxic heavy metals in the aquatic environment has emphasized a considerable exigency to develop several multifunctional biosorbents for their removal. Herein, three individual bacterial species of Cellulosimicrobium cellulans, Bacillus coagulans, and Microbacterium testaceum were successfully isolated from low-level liquid radioactive wastes. Their loading capacities towards cerium and cobalt metal ions were inclusivity inspected under variable operational parameters of pH, primary pollutant concentration, interaction time, temperature, stirring speed, and biosorbent dosage. By analyzing the influence of solution pH, concentration, temperature, biosorbent mass, and agitation speed on the biosorption kinetics, the biosorption process confirms pseudo-second-order kinetic, intraparticle diffusion, and Elovich equation. Remarkably, the isolated Microbacterium testaceum exhibited high loading capacities reaching 68.1mgg-1, and 49.6mgg-1 towards Ce(III), and Co(II) ions, respectively, at the initial concentration of 2.8mM, pH 4.5, and 25°C. Overall, the isolated bacterial species can potentially be offered up as a promising scavenger for Ce(III) and Co(II) from liquid waste effluents.

An Approach to the Localization of Technology for a Transport and Storage Container for Very Low-Level Radioactive Liquid Waste

An Approach to the Localization of Technology for a Transport and Storage Container for Very Low-Level Radioactive Liquid Waste

Comprehending the stability of Sr2+ immobilization in chemically bonded phosphate ceramic system: A mechanism study

Chemically bonded phosphate ceramics (CBPC) are a promising matrix for the immobilization of Sr2+ in medium -and low-level liquid radioactive waste. Understanding the stability of immobilization is crucial, especially when distinguishing the mechanism of chemical immobilization from that of physical encapsulation. However, the mechanisms underlying these processes remain unclear. In this study, ΔEaq, ΔE, and ΔE′ were calculated to study the stability of the immobilization. CBPC samples were synthesized to confirm the calculated results. A negative ΔEaq value accounts for the dominant mechanism of chemical immobilization. Negative ΔE and ΔE’ values indicate that physical encapsulation also contributes to the stability of immobilization, because Sr2+ could induce brucite to cover the K-struvite matrix. Corresponding experiments confirmed the mechanism of immobilization.

Efficient adsorption of strontium by in situ electrochemical synthesis of monohydric phosphate intercalated layered double hydroxides

The synthesized precipitate is a monohydric phosphate intercalated zinc–aluminum layered double hydroxide, which can effectively adsorb Sr2+ in low-level liquid radioactive wastes.

Correction to: Removal of 99Tc from low level radioactive liquid waste using di‑tert‑butyldibenzo‑18‑crown‑6 impregnated sorbent

The original article was published without an acknowledgment section. The complete acknowledgment section is given in this correction.

Recent Progress in the Membrane Distillation and Impact of Track-Etched Membranes.

Membrane distillation (MD) is a rapidly developing field of research and finds applications in desalination of water, purification from nonvolatile substances, and concentration of various solutions. This review presents data from recent studies on the MD process, MD configuration, the type of membranes and membrane hydrophobization. Particular importance has been placed on the methods of hydrophobization and the use of track-etched membranes (TeMs) in the MD process. Hydrophobic TeMs based on poly(ethylene terephthalate) (PET), poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) have been applied in the purification of water from salts and pesticides, as well as in the concentration of low-level liquid radioactive waste (LLLRW). Such membranes are characterized by a narrow pore size distribution, precise values of the number of pores per unit area and narrow thickness. These properties of membranes allow them to be used for more accurate water purification and as model membranes used to test theoretical models (for instance LEP prediction).

Radiological analysis of transport and storage container for very low-level liquid radioactive waste

As NPPs continue to operate, liquid waste continues to be generated, and containers are needed to store and transport them at low cost and high capacity. To transport and store liquid phase very low-level radioactive waste (VLLW), a container is designed by considering related regulations. The design was constructed based on the existing container design, which easily transports and stores liquid waste. The radiation shielding calculation was performed according to the composition change of barium sulfate (BaSO4) using the Monte Carlo N-Particle (MCNP) code. High-density polyethylene (HDPE) without mixing the additional BaSO4, represented the maximum dose of 1.03 mSv/hr (<2 mSv/hr) and 0.048 mSv/hr (<0.1 mSv/hr) at the surface of the inner container and at 2 m away from the surface, respectively, for a 10 Bq/g of 60Co source. It was confirmed that the dose from the inner container with the VLLW content satisfied the domestic dose standard both on the surface of the container and 2 m from the surface. Although it satisfies the dose standard without adding BaSO4, a shielding material, the inner container was designed with BaSO4 added to increase radiation safety.

Liquid Low-Level Radioactive Waste Treatment Using an Electrodialysis Process.

In this work, the possibility of using electrodialysis for the treatment of liquid low-level radioactive waste was investigated. The first aim of the research was to evaluate the influence of the process parameters on the treatment of model solutions with different compositions. Subsequent experimental tests were conducted using solutions containing selected radionuclides (60Co and 137Cs), which are potential contaminants of effluents from nuclear power plants, as well as components often found in waste generated from industrial and medical radioisotope applications. The results of the experiments performed on real radioactive waste confirmed that electrodialysis was a suitable method for the treatment of such effluents because it ensured high levels of desalination and rates of decontamination. The most important parameters impacting the process were the applied voltage and electrical current. Moreover, this research shows that the application of the ED process enables the separation of non-ionic organic contaminants of LLW, which are unfavorable in further stages of waste predisposal.

HYDROPHOBIZATION OF PET TRACK-ETCHED MEMBRANES FOR DIRECT CONTACT MEMBRANE DISTILLATION OF LIQUID RADIOACTIVE WASTES

This article provides the results of liquid low-level radioactive wastes treatment by direct contact membrane distillation using polyethylene terephthalate hydrophobic track-etched membranes. The hydrophobization of track-etched membranes was carried out by UV-induced graft polymerization of triethoxyvinylsilane with styrene and coating with fluorine-containing silanes. Hydrophobic membranes were investigated by scanning electron microscope, Fourier-transform infrared spectroscopy, contact anglemeasurements, and liquid entry pressure analysis. Prepared membranes were tested in treatment of liquid low-level radioactive wastes by membrane distillation. The influence of pore sizes on water flux and rejection degree was studied. Rejection degree was evaluated by conductometry and atomic emission method. Decontamination factors evaluated by gamma-ray spectroscopy for 60Co, 137Cs, and 241Am are 85.4, 1900 and 5.4 for membranes modified with polystyrene and triethoxyvinylsilanewith pore diameters of 142 nm; 85.0, 1462 and 4 for membranes modified with perfluorododecyltrichlorosilanewith pore diameters of 150 nm respectively.

Liquid low-level radioactive wastes treatment by using hydrophobized track-etched membranes

In this paper, we present the results of liquid low-level radioactive wastes (LLLRW) treatment by direct contact membrane distillation (DCMD) using polyethylene terephthalate (PET) track-etched membranes (TeMs). PET TeMs were modified by styrene and triethoxyvinylsilane (TEVS) using UV-induced grafting. Modification led to increase in the contact angle to 99° of PET TeMs (pore size from 150 to 300 nm). Hydrophobic PET TeMs were investigated by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), goniometric analysis, gas permeability test, liquid entry presser (LEP) analysis and scanning electron microscope (SEM). Prepared membranes were tested in treatment of LLLRW by DCMD. The influence of pore size on water flux and rejection degree was studied. Rejection degree was evaluated by conductometry and atomic emission methods. Decontamination factors (evaluated by gamma-ray spectroscopy) for 60Co, 137Cs, and 241Am were found to be 85, 1900 and 5 respectively. In most cases degree of rejection of Cs, Mo, Sr, Sb, Al, Ca, Fe, K, Mg and Na ions were more than 90% and close to 100%. The use of TeMs with a narrow pores size distribution and without tortuous channels allowed us to achieve better purification from radioactive wastes in comparison with hollow-fiber membranes.

Modification of PET ion track membranes for membrane distillation of low-level liquid radioactive wastes and salt solutions

The work concerns the purification of saline solutions and concentration of low-level liquid radioactive wastes (LLLRW) produced from nuclear research reactor (WWR-K) by membrane distillation in direct contact configuration (DCMD) using track-etched membranes (TeMs). Poly(ethylene terephthalate (PET) TeMs were hydrophobized by UV-induced grafting of styrene. Modification of PET TeMs (pore sizes from 135 to 268 nm) at optimal conditions led to increasing of contact angle to 104°. Hydrophobic PET TeMs were investigated by XPS, FTIR, SEM, liquid entry pressure (LEP) and goniometric. Prepared membranes were tested in DCMD of saline solutions and LLLRW. The effect of membrane pore diameter, temperature, concentration on fluxes and rejection degree was studied. Salt rejection was evaluated by conductimetry and atomic emission method (for Cs, Mo, Sr, Sb, Al, Ca, Fe, K, Mg and Na). Decontamination factors of radioisotopes (for 60Co, 137Cs, and 241Am) were evaluated by gamma-ray spectroscopy. Salt rejection and decontamination factors were found to depend on pore diameter and conditions of DCMD. In most cases the degree of rejection was between 90 and 100%. Decontamination factor of 137Cs reached to 1727.

Using porous iron composite (PIC) material to immobilize rhenium as an analogue for technetium

Technetium (99Tc), a uranium-235 (235U) and plutonium-239 (239Pu) fission product, is a primary risk driver in low level radioactive liquid waste at U.S. Department of Energy sites. Previous studies have shown success in using Zero Valent Iron (ZVI) to chemically reduce and immobilize redox sensitive groundwater contaminants. Batch and column experiments were performed to assess the ability of a novel porous iron composite material (PIC) to immobilize Tc(VII) in comparison with two commercial Fe oxide sorbents and reagent grade ZVI in the presence and absence of NO3−, a competing oxidized species that is often found in high concentrations in liquid nuclear waste. Perrhenate (ReO4−) was used as a non-radioactive chemical analogue for pertechnetate (TcO4−) under both oxic and anoxic test conditions. The PIC powder was the most effective at immobilizing Re(VII) under all batch test conditions. The presence of nitrate (NO3−) slowed the removal of ReO4− from solution, presumably through chemical reduction and precipitation. Even so, the PIC and ZVI were effective at removing both Re(VII) and NO3− completely from solution. Nitrate was reduced to NH3 with very little nitrite (NO2−) buildup during equilibration. Significant Re immobilization was observed in the column tests containing PIC sorbent, even though inlet solutions were in equilibrium with O2. The presence of NO3− hastened Re breakthrough, while NO3− reduction to NH3 was observed. The results suggest that PIC and ZVI would be the most effective at the removal of TcO4− from contaminated groundwater sites.

USING AEROBIC SYNTROPHIC ASSOCIATIONS OF MICROORGANISMS FOR THE DECONTAMINATION OF LIQUID RADIOACTIVE WASTE

The primary objective of the study was to test the possibility of cesium-137 transmutation into a stable barium isotope in contact with an aerobic syntrophic association (SA - a conglomerate of several thousands of different species of bacteria, protozoa and fungi living in symbiosis with each other) together with a set of macro- and microelements. The study was performed sequentially on two different SA. In the course of the work, the transmutation of cesium-137 into stable barium with the use of SA was not experimentally revealed, but the phenomenon of cesium-137 biosorption by both SA was detected to different degrees. In the course of the experiment the possibility of cesium-137 sorption by SA from the solution in the pH range of 7.7 - 8.6 was shown. In the process of the work, the time dependence of cesium-137 distribution in the liquid phase and the phase of SA was determined. The time dependence of the sorption capacity of the syntrophic association was revealed. With further continuation of the study, it is possible to obtain a mixture of SA capable of selectively extracting and concentrating prescribed radionuclides from the liquid phase.The result of this work may be the development of a technology for processing and conditioning low-level liquid radioactive waste (RW) by transferring the bulk of radioisotopes in the phase of SA (the so-called "nanosorbent of biological origin"), with multiple volume reduction.The cost of such a technology compared to existing technologies using synthetic sorbents should be several times less due to the cheapness of the SA and the reagents required for it. Besides, the new technology is more environmentally friendly. The process of biotechnologyoxidation of sulfide ores and concentrates based on the activity of chemolitotrophic bacteria that translate insoluble metal sulfides into soluble metal sulfates can serve as analogue for hardware design of RW purification technology using nanosorbent of biological origin.

Vermiculite as a potential component of the engineered barriers in low- and medium-level radioactive waste repositories

Abstract Vermiculite (VMT) was tested as a low-cost, eco-friendly adsorbent for the removal of cesium(I), strontium(II), europium(III), americium(III), and technetium(VII) radionuclides from aqueous solutions. The raw material was characterized and checked as potential adsorbent. The removal efficiency (Er, %) was studied as a function of the main factors important for the management of radioactive liquid wastes. It was found that the uptake from the aqueous solutions simulating the radioactive liquid wastes was in the order: Cs(I) Sr(II) (both about 95%) > Am(III) (about 90%) > Eu(III) (about 80%). When a reducing agent is added to the solution technetium-99 may also be completely removed. The usefulness of VMT in liquid low level radioactive waste management has also been confirmed by checking its radiation stability. Vermiculite can be considered as a promising material for sorption of the radionuclides from radioactive waste solutions and as a potential additive to the engineered barriers in LLRW repositories.

A rapid method for decontamination of low and intermediate level liquid radioactive wastes by amalgamation

The objective of this study is to develop an integrated workstation for rapid decontamination of low and intermediate level liquid radioactive wastes. The workstation comprises of an electrochemical amalgamator that allows the reduction of different radio nuclides cations in the waste and eventually form amalgamates. The de-amalgamation results in purification of mercury and leftover of radioactive waste residue behind as secondary waste.

A rapid method for decontamination of low and intermediate level liquid radioactive wastes by amalgamation

A rapid method for decontamination of low and intermediate level liquid radioactive wastes by amalgamation

Decommissioning strategy for liquid low-level radioactive waste surface storage water reservoir

The Techa Cascade of water reservoirs (TCR) is one of the most environmentally challenging facilities resulted from FSUE “PA “Mayak” operations. Its reservoirs hold over 360 mln m3 of liquid radioactive waste with a total activity of some 5 × 1015 Bq.A set of actions implemented under a special State program involving the development of a strategic plan aimed at complete elimination of TCR challenges (Strategic Master-Plan for the Techa Cascade of water reservoirs) resulted in considerable reduction of potential hazards associated with this facility.The paper summarizes the key elements of this master-plan: defining TCR final state, feasibility study of the main strategies aimed at its attainment, evaluation of relevant long-term decommissioning strategy, development of computational tools enabling the long-term forecast of TCR behavior depending on various engineering solutions and different weather conditions.

Perrhenate sorption kinetics in zerovalent iron in high pH and nitrate media

Technetium(Tc)-99 is one of major risk drivers in low level radioactive liquid waste at the U.S. Department of Energy sites. Cementitious waste technology (CWT) has been considered immobilizing pertechnetate, Tc(VII)O4−, in brine and alkaline waste solutions, as Tc(IV) oxides and/or sulfides with the use of reducing agents like slag. In this study, zero valent iron (ZVI) was evaluated as a potential reducing agent in CWT as a function of pH and [nitrate] (0–0.1M) using perrhenate, Re(VII)O4−, as an analogue for Tc(VII)O4−. Batch Re(VII)O4− sorption experiments in conjunction with X-ray absorption spectroscopic analysis showed that the Re(VII) sorption occurred via the reductive precipitation of Re(IV)O2(s) and the extent of sorption decreased with increasing pH from 8 to 10. Interestingly, pseudo 2nd order kinetic rates increased with increasing [nitrate] which was attributed to co-adsorption of NH4+ (i.e., a reaction product of reduced nitrate by ZVI), facilitating electrostatic attraction towards ReO4− under alkaline conditions. Considering the thermodynamically favorable reduction of Tc(VII) over Re(VII), ZVI might have potential for improving the reduction capacity of the current CWT.