Development of a practical decontamination procedure for uranium-contaminated concrete waste

Practical decontamination procedure and equipments have been developed to decontaminate uranium-contaminated concrete waste generated from a uranium conversion plant. The direct burning of mortar block coated with epoxy and then the mechanical removal of the burned surface reduces the amount of sludge by preventing the dissolution of whole cement paste in concrete block. And the removal of calcium from the concrete washing solution for the use of electrokinetic equipment decreases the volume of waste by a recycling of the solution. This improved decontamination procedure makes more than 70 % of concrete waste be self-disposed and remarkably reduces secondary radioactive waste.     

Fast concentration of dissolved forms of cesium radioisotopes from large seawater samples

The method developed for cesium concentration from large freshwater samples was tested and adapted for analysis of cesium radionuclides in seawater. Concentration of dissolved forms of cesium in large seawater samples (about 100 L) was performed using composite absorbers AMP-PAN and KNiFC-PAN with ammonium molybdophosphate and potassium–nickel hexacyanoferrate(II) as active components, respectively, and polyacrylonitrile as a binding polymer. A specially designed chromatography column with bed volume (BV) 25 mL allowed fast flow rates of seawater (up to 1,200 BV h^?1). The recovery yields were determined by ICP-MS analysis of stable cesium added to seawater sample. Both absorbers proved usability for cesium concentration from large seawater samples. KNiFC-PAN material was slightly more effective in cesium concentration from acidified seawater (recovery yield around 93 % for 700 BV h^?1). This material showed similar efficiency in cesium concentration also from natural seawater. The activity concentrations of ¹³⁷Cs determined in seawater from the central Pacific Ocean were 1.5 ± 0.1 and 1.4 ± 0.1 Bq m^?3 for an offshore (January 2012) and a coastal (February 2012) locality, respectively, ¹³⁴Cs activities were below detection limit (<0.2 Bq m^?3).     

Polyvinyl alcohol-borate hydrogel containing Prussian blue for surface decontamination

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.     

Decontamination of uranium-contaminated concrete

This study examined the decontamination method by washing with nitric acid for uranium contaminated concrete pieces produced from the decommissioning of a uranium conversion plant and evaluated the amount of waste sludge generated from the treatment. In addition, carbonate solution, nitric acid and sulfuric acid were used as the extraction reagents for the uranium, and their efficiencies were also compared. For concrete pieces coated with and without epoxy, the separation method of cement paste from aggregates was preferable to the leaching of uranium from concrete because of its simpler decontamination process. When concrete pieces with epoxy were heated for 2 h at 400 °C, pulverized and sequentially washed with 0.1, 2.0 and 1.0 M of nitric acid, their radioactivity reached below the limit value of uranium for self-disposal. Unlike previous results, uranium dissolved in 1 and 2 M sulfuric acid solutions was not removed by strong anion exchange resins such as IRA 910 and Ag1×8.     

Determination of 41Ca with LSC and AMS: method development, modifications and applications

Despite the emission of only low energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certified standard, Liquid scintillation counting (LSC) determinations are still reasonable options for a radioanalytical laboratory involved in nuclear installation decommission. Besides, accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for ⁴¹Ca, is gaining increasingly broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for ⁴¹Ca determination with LSC and AMS in varying materials (i.e. water, concrete, sediment, soil, and biota). The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, interfering radionuclides as ⁵⁵Fe, ⁶⁰Co, ¹⁵²Eu, U or actinides are removed with decontamination factors of 10²–10⁴. Quench curves for determining the measurement efficiency is generated with a ⁴¹Ca solution gained from the ⁴¹Ca/⁴⁰Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 67–86 %, measurement efficiencies of 1–10 % and detection limits of 0.05 Bq g^?1 and 0.3 Bq L^?1. Aliquots of the digestion solutions of LSC can be easily converted into CaF₂–AMS targets by successive oxsalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on ⁴¹Ca results from LSC and AMS for the same material.     

Development of an ion-exchange method for separation of radioiodine from tellurium and antimony and its application to the production of 124I via the 121Sb(α,n)-process

A novel anion-exchange chromatographic method for separation of radioiodine from an antimony target irradiated with ³He- or α-particles was developed, with separation yield of radioiodine amounting to 90 ± 5 % and its decontamination factor from the Te and Sb radionuclides to ~10⁴. The optimized separation method developed was then applied to the production of ¹²⁴I via the ¹²¹Sb(α,n)¹²⁴I process using a highly enriched ¹²¹Sb target. Quality control tests showed that the separated ¹²⁴I occurred >99 % as iodide and the longer lived impurities ¹²⁶I and ¹²⁵I amounted to 0.16 % and <0.05 %, respectively. The trace level of inactive Sb impurity was determined by ICP–OES.     

Investigation of cesium uptake from aqueous solutions using new titanium phosphates ion-exchangers

The uptake of cesium from aqueous solutions (pH 5) using titanium phosphates was investigated in the absence and presence of background electrolyte (0.1 M NaNO₃) using a batch technique. The determination of cesium was performed by gamma spectroscopy using ¹³⁷Cs as tracer. The obtained sorption isotherms could be satisfactorily reproduced by a Langmuir sorption equation. The maximum uptake capacity values (q _max) calculated fitting the experimental data by this equation were 167 and 118 mg/g for solutions of initial pH 5 in the absence and presence of background electrolyte. Kinetics data obtained at 293, 308 and 323 K could satisfactorily reproduced by the pseudo-second order equation. It was demonstrated that the new synthesized materials can remove considerable amounts of cesium from aqueous solutions and ion exchange is considered to be the principal mechanism for cesium removal. Toxicity characteristic leaching procedure and desorption tests provided data about the application of the sorbents in environmental remediation.     

Levels and effects of natural radionuclides in soil samples of Garhwal Himalaya

Distribution of natural radionuclide gives significant parameter to assess the presence of gamma radioactivity and its radiological effect in our environment. Natural radionuclides are present in the form of ²²⁶Ra, ²³²Th and ⁴⁰K in soil, rocks, water, air, and building materials. Distribution of natural radionuclides depends on the type of minerals present in the soil and rocks. For this purpose gamma spectrometer is used as tool for finding the concentration of these radionuclides. The activity concentration of naturally occurring radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in these soil samples were found to vary from of 8 ± 1 Bq/kg to 50 ± 10 Bq/kg with an average 20 Bq/kg, 7 ± 1–88 ± 16 Bq/kg with an Average 26 Bq/kg and 115 ± 18–885 ± 132 Bq/kg with an average 329 Bq/kg, respectively. In this paper, we are presenting the radiological effect due to distribution of natural radionuclide present in soil of Garhwal Himalaya.     

Sorption of the long-lived radionuclides cesium-134, strontium-85 and cobalt-60 on bentonite

The sorption of long-lived radionuclides of cesium, strontium and cobalt (¹³⁴Cs, ⁸⁵Sr and ⁶⁰Co) on bentonite under various experimental conditions, such as contact time, pH, sorbent and sorbate concentrations have been studied. The uptake of Cs and Sr was rapid and equilibrium was reached almost instantaneously in both the cases, while Co sorption was time dependent. The sorption of these nuclides increased by increasing pH. The uptake of Cs, Sr and Co increased with increasing the amount of the bentonite clay. The percentage sorption for Cs, Sr and Co decreased with increasing metal concentrations. The desorption studies with 0.01M CaCl₂ and ground water at low-metal loadings on bentonite showed that about 95% of Cs, 85-90% of Sr and 97% of Co were irreversibly sorbed. These results could be helpful for nuclear waste management, for waste water effluents containing low concentrations of cesium, strontium and cobalt.     

Extraction of cesium in seawater off Japan using AMP-PAN resin and quantification via gamma spectroscopy and inductively coupled mass spectrometry

The March 2011 earthquake off the Japanese coast and subsequent tsunami that devastated the Fukushima Dai-Ichi nuclear power plant resulted in the largest accidental release of cesium 137 and 134 to the oceans. Seawater samples were collected in June 2011 from 30 to 600 km off the coast of Japan as part of initial mapping of the spread of contamination in the ocean. Cesium was extracted from unfiltered and filtered (<1.0 μm) seawater using an absorber based upon an organic polymer polyacrylonitrile (PAN) containing ammonium molybdophosphate (AMP) Sebesta and Stefula (J Radioanal Nucl Chem 140:15–21, 1990). The AMP-PAN resin can be counted directly using gamma spectroscopy for ¹³⁴Cs and ¹³⁷Cs. Stable ¹³³Cs was added to evaluate extraction efficiency and quantified by ICP-MS. Our 5 mL AMP-PAN resin column was on average 95 % efficient in the removal of cesium from 20 L samples at an average flow rate of 35 mL min^?1. Measured activities of ¹³⁴Cs and ¹³⁷Cs ranged from a few Bq m^?3 to >300 Bq m^?3. The extraction column can be adapted to different sample volumes and easily used in the field.     

A fast and very sensitive LSC procedure to determine Fe-55 in steel and concrete

This procedure for determining Fe-55 contributes to a safe and economically reasonable decommissioning of nuclear power plants. Co-60, Fe-55 and Ni-63 are the most abundant, long-lived radionuclides associated with contaminated piping, hardware, and concrete for several decades of years after shutdown. The analysis of Fe takes about three hours until the measurement with an anticoincidence shielded LSC Quantulus 1220 starts. The decontamination factors are ranging from greater than 10⁵ to 10⁹ for all important naturally and artificially occurring radionuclides except Sb. The chemical yield stays constant at a value of about 92% up to 0.1 g stable Fe in steel, concrete or other material. The detection limits (confidence level 95%) reach values of 8 mBq per sample or about 60 mBq/g steel and 1.5 mBq/g concrete at a counting time of 1000 minutes. Four to eight analyses are performed by one technician during eight hours.     

A study of the factors affecting the adsorption of cobalt ions onto Pakistani coal powder from solutions

Large deposits of coal are abundantly available in Pakistan. An attempt has been made to check its efficacy for the cobalt ions from aqueous solutions in order to exploit the locally available naturally occurring cheaper material for the decontamination/removal of metal ions from nuclear and industrial effluents. The adsorption behavior of cobalt ions on coal powder has been studied as a function of various physicochemical parameters i.e., stirring speed, shaking time, pH, concentration of cobalt ions, temperature, etc. Conditions for the uptake of cobalt ions were established. Adsorption dynamics models such as intra-particle diffusion model, pseudo-first order kinetic model (Lagergren’s equation) and pseudo-second order kinetic model were applied to the adsorption data to elucidate the adsorption process and its mechanism. Results reveal that the adsorption mechanism is predominantly diffusion and both intra-particle and boundary layer diffusion seem significant in the rate controlling step. The adsorption process is best accounted for using pseudo second order kinetic model and the overall rate of adsorption process appears to be controlled by more than one step, namely the external mass transfer and intra-particle diffusion mechanism. The existence of two slopes in the Freundlich plot also confirms the surface diffusion and intra-particle diffusion modes of adsorption. The Langmuir isotherm equation was obeyed well in the whole range of cobalt ions concentration with high value of correlation coefficient (r ²  = 0.999). The adsorption energy (E _a) calculated from D–R isotherm was 6.756 kJ/mol indicating physical nature of adsorption. The adsorption of cobalt ions increased with the increase of temperature and thermodynamic parameters such as ΔH, ΔS and ΔG were calculated. Results suggested that the cobalt ions adsorption on coal powder is endothermic (ΔH 33.90 kJ/mol) and spontaneous (negative ΔG values) process. The adsorption of other metal ions on coal powder was studied at optimized condition for cobalt ions to check its selectivity. Consequently, cobalt ions can be removed from Zr, Ru Eu, Er, Sm, Gd, Dy, Ce, U, and Th ions, where as Cs, Cr and Sr ions reduces the adsorption of cobalt ions by co-adsorption and their reducing affect is in the order of Sr > Cr > Cs.     

Utilization of low-cost sorbent for removal and separation of 134Cs, 60Co and 152+154Eu radionuclides from aqueous solution

Eggshell material was used as low-cost and eco-friendly biosorbent for removal of ¹³⁴Cs, ⁶⁰Co and ^152+154Eu radionuclides from aqueous solution. The eggshell material was calcined at 500 and 800 °C, and then characterized. Comparative studies on the natural and calcined eggshell for sorption of the three radionuclides were carried out. It was found that, the uptake is in the order: Eu(III) > Co(II) > Cs(I). Further, column chromatography was used in separation of ¹³⁴Cs, ⁶⁰Co and ^152+154Eu using 0.15, 0.2 and 0.5 mol/l nitric acid, respectively. Eggshell material can be considered as a promising material for separation of radionuclides from radioactive waste solution.     

Radiological hazard and radiogenic heat production in some building materials in upper Egypt</p> </p>

Summary Samples of limestone, sand, marble, clay brick, red brick, gypsum, Portland cement and white cement collected from upper Egypt used in building manufacturing have been analyzed for the natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K usingg-ray spectrometry. The specific concentrations for ²²⁶Ra, ²³²Th and ⁴⁰K, ranged from 20-88, 13-115 and 54-304 Bq/kg, respectively. The average specific activities of these radionuclides were compared. Higher values of ²²⁶Ra and ²³²Th could be noticed in marble while that of ⁴⁰K was in red bricks. Radium equivalent activities, dose rate and the annual gonadal dose equivalents AGDE were calculated for the measured samples to assess the radiation hazard arising from using those materials in the construction of dwellings. The radioactive heat production values of the selected materials have also been determined. They vary from a minimum of 0.41 for white cement to a maximum of 5.52mW/m³ for marble samples. The calculated heat-production values are quite similar to those estimated in Corsica.</p> </p>     

Studies on removal of cobalt from an alkaline waste using synthetic calcium hydroxyapatite

The removal of cobalt from an alkaline waste solutions containing sodium was carried out using a radiotracer in a batch method using synthetic calcium hydroxyapatite (HAP). The influence of different parameters such as solution pH, contact time, cobalt concentration, and presence of other ions like sodium on cobalt removal was studied. The sorption process followed pseudo-second-order kinetics with necessary time of around 23–25 h to reach equilibrium and the cobalt uptake was quantitatively evaluated using the Freundlich model. The results indicated that the mechanism of cobalt removal by HAP was mainly due to chemisorption on a heterogeneous surface. In the presence of sodium, the sorption of cobalt on HAP was not affected. The sorption of cobalt on HAP was pH independent in the range from 4 to 8, because of its buffering properties. The adsorption of cobalt on HAP was fast and the percentage of cobalt sorption was >97 % during the first 30–40 min of the contact time.     

Quantitative calculations on the reoxidation behavior of oxide reduction system for pyroprocessing

This paper discusses the development of a separation method for isolation of ¹⁷¹Tm from a half-gram irradiated erbium target in support of stockpile stewardship and astrophysics research. The developed procedure is based on cation exchange separation using alpha-hydroxyisobutyric acid (α-HIBA) as chelating agent. It is able to achieve either a decontamination factor of 1.4(4) × 10⁵ with 68.9(3) % recovery or 95.4(3) % recovery with a decontamination factor of 5.82(7) × 10³ for a mock 500-mg target containing 17.9 mg thulium in a single pass-through at room temperature.     

Removal of Radionuclides from Fukushima Daiichi Waste Effluents

This paper describes the processes used at the Fukushima Daiichi plant, Japan, to purify the waste effluents generated in the cooling of damaged reactors. These include primary cesium removal with the Kurion zeolite system and the SARRY system utilizing silicotitanate to remove radiocesium from water recirculated to reactors for cooling. Another process is the ALPS system to purify the retentates of the reverse osmosis plant to further purify the water from radionuclides after primary cesium separation. In ALPS, a major role is played by the transition metal hexacyanoferrate product CsTreat and sodium titanate SrTreat in the removal of radiocesium and radiostrontium, respectively. The performance of these four exchangers (zeolite, silicotitanate, hexacyanoferrate, and sodium titanate) is critically analyzed with respect to processing capacities and the decontamination factors obtained in the processes. Furthermore, general information on preparation, structure and ion exchange of these ion-exchanger categories is given with additional information on their use in nuclear waste effluent treatment processes. Finally, the importance of selectivity and associated factors are discussed.     

Decontamination of spent ion-exchange resins contaminated with cesium radionuclides

Possible causes of the occurrence of radioactive contamination irremovable by acid–base regeneration of ion-exchange resins used in treatment of process media and liquid radioactive waste have been studied. It has been found that most of the irremovable cesium radionuclides are bound to inorganic deposits on the surface and in the bulk of ion-exchange resin granules. The nature of inorganic inclusions has been investigated on real and model spent ion-exchange resins (SIER). A method has been proposed for decontaminating SIER using resorcinol–formaldehyde resins selective to cesium radionuclides. Such an approach has been shown to be promising for deep decontamination of SIER.     

Sorption of radionuclides on natural materials

Information about the sorption of radionuclides on natural materials used for cementation of liquid radioactive wastes (RAW) is important for predictions of migration rates of radionuclides in the products of fixation. Cementation process for conditioning liquid RAW uses, besides cement, materials which improve quality of products. In Czechoslovakia technology among these materials are clinoptilolite tuffit, mordenite tuff, tobermorite and fly ash. Liquid RAW issued from nuclear power plants contains the principal radionuclides⁶⁰Co,¹³⁴Cs and¹³⁷Cs, therefore, a sorption study of these radionuclides was carried out. pH of liquid RAW was 12.5–13.7 and salt content ca. 200 g·dm^–3. Results of sorption are given by distribution coefficients. The best results for cesium in those pH region and salt content had mordenite tuff D_Cs=100 dm³·kg^–1 and the worst results had fly ash D_Cs=4.1 dm³·kg^–1. The best results for cobalt in those solutions had tobermorite D_Co=38 dm³·kg^–1 and the worst results had fly ash D_Co=6.9 dm³·kg^–1.     

Natural radioactivity level and radiological hazard assessment of commonly used building material in Xining,China

Natural radioactivity of the commonly used building materials in Xining of China was measured using gamma-ray spectrometer system comprising a NaI(Tl) detector. Radioactivity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the studied samples range from 11.6 to 120.6, 10.2 to 107.1 and 228.0 to 1,036.2 Bq kg^?1, respectively. The concentrations for these natural radionuclides were compared with the reported data of other countries and the mean value for soil. Radium equivalent activity, indoor air absorbed dose rate, annual effective dose rate as well as external and internal hazard indices were calculated to assess radiological hazards for people living in dwelling made of the building materials. The radiological hazard assessment results show that the studied building materials, except for some aerated concrete block samples, are safe for use in construction of dwellings in the study area and do not pose any significant source of radiation hazard.