Determination of long-lived fission products and actinides in Savannah River Site HLW sludge and glass for waste acceptance

Savannah River Site (SRS) is immobilizing the radioactive, high-level waste sludge in Tank 51 into a borosilicate glass for disposal in a geologic repository. A requirement for repository aceeptance is that SRS report the concentrations of certain fission product and actinide radionuclides in the glass. This paper presents measurements of many of these concentrations in both Tank 51 sludge and the final glass. The radionuclides were measured by inductively coupled plasma mass spectrometry and α, β, and γ counting methods. Examples of the radionuclides are⁹⁰Sr,¹³⁷Cs,²³⁸U and,²³⁹Pu. Concentrations in the glass are 3.1 times lower due to dilution of the sludge with a nonradio-active glass forming frit in the vitrification process. Results also indicated that in both the sludge and glass the relative concentrations of the long lived fission products insoluble in caustic are in proportion to their yields from the fission of²³⁵U waste in the SRS reactors. This allowed the calculation of a fission yield scaling factor. This factor in addition to the sludge dilution factor can be used to estimate concentrations of waste acceptance radionuclides that cannot be measured in the glass. Examples of these radionuclides are⁷⁹Se,⁹³Zr, and¹⁰⁷Pd.     

Analysis of cesium extracting solvent using GCMS and HPLC

A high-level waste (HLW) remediation process scheduled to begin in 2007 at the Savannah River Site is the Modular Caustic Side Solvent Extraction (CSSX) Unit (MCU). The MCU will use a hydrocarbon solvent (diluent) containing a cesium extractant, a calix[4]arene compound, to extract radioactive cesium from caustic HLW. The resulting decontaminated HLW waste or raffinate will be processed into grout at the Saltstone Production Facility (SPF). The cesium containing CSSX stream will undergo washing with dilute nitric acid followed by stripping of the cesium nitrate into a very dilute nitric acid or the strip effluent stream and the CSSX solvent will be recycled. The Defense Waste Processing Facility (DWPF) will receive the strip effluent stream and immobilize the cesium into borosilicate glass. Excess CSSX solvent carryover from the MCU creates a potential flammability problem during DWPF processing. Bench-scale DWPF process testing was performed with simulated waste to determine the fate of the CSSX solvent components. A simple high performance liquid chromatography (HPLC) method was developed to identify the modifier (which is used to increase Cs extraction and extractant solubility) and extractant within the DWPF process. The diluent and triocytlamine (which is used to suppress impurity effect and ion-pair disassociation) were determined using gas chromatography mass spectroscopy (GCMS). To close the organic balance, two types of sample preparation methods were needed. One involved extracting aqueous samples with methylene chloride or hexane, and the second was capturing the off gas of the DWPF process using carbon tubes and rinsing the tubes with carbon disulfide for analysis. This paper addresses the development of the analytical methods and the bench-scale simulated waste study results.     

New concepts for radiometric measurements of environmental samples

The Radiation Detection and Nuclear Sciences Group at Pacific Northwest National Laboratory has a long history in conducting measurements of radioisotopes for various applications. This experience includes ultra-low background measurements, arrays of germanium detectors, automated sampling and measurement systems and coincidence measurement systems. A recent lab-supported effort has been studying how these capabilities, both in terms of hardware and experience, can be leveraged to enable environmental sampling measurements. One area of interest is the release of fission products and actinides into the environment from a reactor incident. While the initial survey of this area is still under way, one isotope of interest that surfaced early in the study is ²³⁸Pu. Existing techniques to assay this isotope suffer from measurement challenges. In alpha counting, there can be significant interference with ²⁴¹Am, while in mass spectrometry, there can be interference with ²³⁸U. The authors are developing the concept for a detector that through coincidence counting techniques can distinguish ²³⁸Pu and ²⁴¹Am. In addition, we will design the system to conduct radiometric measurements of other plutonium isotopes to enable a direct comparison of those isotopes. We will present our concept of the detector system for ²³⁸Pu, as well as discuss other radiometric measurements of fission products and actinides with which we intend to advance the state of the art for environmental measurements.     

Organic Analyses of Highly Radioactive Solutions Requiring Pretreatment by 137Cs Removal

The beta-emitting radionuclide ¹³⁷Cs is precipitated from the Savannah River Site (SRS) high-level waste by adding sodium tetraphenylborate (TPB). The concentrated and washed precipitate slurry containing CsTPB is transferred to Defense Waste Processing Facility (DWPF) Salt Processing Cell and hydrolyzed to yield an aqueous product (PHA) free of benzene. The PHA is highly radioactive (1E+11 dpm) and contains some water-soluble organic compounds that need to be analyzed for process control and process history. High performance liquid chromatography (HPLC) methods were developed to analyze these compounds with instruments contained in unshielded fume hoods. Removing ¹³⁷Cs from PHA in a shielded cell prior to HPLC analyses is essential to minimize personnel radiation exposure. In this study ammonium molybdophosphate (Bio-Rad AMP-1) was used for removing ¹³⁷Cs in PHA (pH 3.8). With a two-step application of AMP slurry, a decontamination factor of 1E+4 was achieved for Cs removal. Two separate HPLC methods were used to analyze four polar organic compounds. The recovery of all the organic compounds were above 85%.     

Determination of uranium isotopes in environmental samples

The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) in environmental samples and provides the most accurate determination of isotopic activity ratios between ²³⁴U and ²³⁸U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values ²³⁴U/²³⁸U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).     

Monitoring of <Superscript>137</Superscript>Cs in electric arc furnace steel making process

This article presents the results of ¹³⁷Cs and other radionuclide monitoring in EAF steel-making process in the Croatian CMC Sisak Steel Mill. The presence of ¹³⁷Cs and natural isotopes ⁴⁰K, ²³²Th, ²²⁶Ra and ²³⁸U was established. Investigations on the occurrence of the isotope cesium, as well as natural isotopes and their distribution in waste from the process of carbon steel production by EAF have been conducted. Detection of artificial isotope cesium in EAF dust indicates that it might originate from steel scrap or from the residue of the material that was used in the technological process, thus deserving special attention.     

Activity disequilibrium between 234U and 238U isotopes in natural environment

The aim of this work was to calculate the values of the ²³⁴U/²³⁸U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wi?linka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the ²³⁴U/²³⁸U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the ²³⁴U/²³⁸U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the ²³⁴U/²³⁸U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wi?linka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes ²³⁴U and ²³⁸U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the ²³⁴U/²³⁸U activity ratio really oscillates around unity.     

A device for uranium series leaching from glass fiber in HEPA filter

For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0?M HNO₃?C0.1?M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution, chemical consecutive chemical leaching by a 4.0?M HNO₃ solution, and repeated chemical leaching by a 4.0?M HNO₃ solution were used to remove the uranium series. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 5?h by the 4.0?M HNO₃?C0.1?M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 36?h by 4.0?M HNO₃?C0.1?M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 8?h by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution were 8.9, 0.0, 1.91, and 6.4?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after consecutive leaching for 8?h by the 4.0?M HNO₃ solution were 2.08, 0.12, 1.55, and 2.0?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after three repetitions of leaching for 3?h by the 4.0?M HNO₃ solution were 0.02, 0.02, 0.29, and 0.26?Bq/g. Meanwhile, the removal efficiencies of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th from the waste solution after its precipitation?Cfiltration treatment with NaOH and alum for reuse of the 4.0?M HNO₃ waste solution were 100, 100, 93.3, and 100%.     

Ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) and radiometric techniques for the determination of actinides in aqueous leachate solutions from uranium oxide

The choice of the analytical method for the determination of actinide isotopes in leachate solutions has to be made considering several parameters: detection limit for each isotope, sample preparation procedure in terms of duration and complexity, counting time and interferences. A leachate solution obtained by keeping a pellet of UO₂ doped with ²³⁸Pu in contact with distilled water was investigated for the content of U and Pu isotopes by radiometric methods (α-, γ-spectrometry and liquid scintillation counting). The results of the radiometric methods were compared with those obtained from the analysis performed by inductively coupled plasma mass spectrometry on-line to a system for chromatographic separation (IC-ICP-MS). The comparison confirmed that IC-ICP-MS is a powerful method for the detection of long-lived radionuclides. The radiometric methods have a detection limit two orders of magnitude lower than IC-ICP-MS in the case of short-lived radioisotopes mostly due to the low background in the detector. On the other hand, the sample preparation and the analysis duration are more time-consuming compared to IC-ICP-MS; moreover, not all isotopes can be determined by using only one radiometric technique.     

Radioecology around a closed uranium mine

The uranium mine and mill at ?irovski vrh, Slovenia, operated from 1982 to 1990. After processing, the uranium mill tailings were deposited onto the Bor?t waste pile lying close to the mine. Radioecological studies focused on assessing the mobility and bioavailability of deposited radionuclides were initiated some five years ago. The mobility of ²³⁸U, ²³⁴U, ²³⁰Th and ²²⁶Ra in soil was studied by applying sequential extraction protocols. The highest activity concentrations were found at the bottom of the waste pile. Uranium isotopes were the most mobile, followed by ²²⁶Ra whose mobility appeared to be suppressed by high sulphate concentrations and ²³⁰Th. The wetland plants grown in soils contaminated with seepage waters from the tailings contained higher levels of ²³⁸U, ²²⁶Ra and ²³⁰Th compared to plants from a control site. The activity concentration of ²²⁶Ra was the highest in all studied plant species. The radiological risk to wildlife around the mine area as assessed by the ERICA Tool was negligible. Activity concentrations in bovine milk from the area of ?irovski vrh were comparable to the reference location, except for uranium where the content was higher. The combined annual effective dose for adults consuming milk from the ?irovski vrh area is 13.0 ± 1.7 μSv a^?1.     

Determination of alpha-emitting isotopes in radioactive wastes

An analytical procedure was developed for the alpha-spectrometric determination of uranium (²³⁸U, ²³⁵U, ²³⁴U) and transuranium isotopes (^239+240Pu, ²⁴⁴Cm) in liquid radioactive wastes (sludges, evaporation residues) of low and medium activity from the VVER-440 reactor of the nuclear power plant in Paks, and in waste waters to be released into the environment. Radioactive sludge samples were separated to a liquid phase and a wet suspension (solid) phase by centrifuging, and the two phases were treated and analyzed separately, in different ways. A sample preparation procedure based on chemical separation was worked out for the isolation of the alpha-emitting components of radioactive evaporation residues which were saturated with boric acid. To the separate determination of the low activity alpha-emitting isotopes appearing in waste waters to be released into the environment, a microvawe concentration technique was applied. The accuracy of the results obtained using the above chemical separation and alpha-spectrometry was tested in the framework of the international U. S. DOE EML Quality Assessment Program.     

Concentrations and activity ratios of radionuclides around the nuclear facilities in Korea

The concentrations and activity ratios of the radionuclides aroundthe nuclear facilities located in Taejon were determined. The concentrationsand activity ratios of uranium isotopes in the downstream decreased with increasingdistances from the point of discharge and reached the reference value after4 km. The concentrations of uranium isotopes in the brook around LWR fuelfabrication facilities were lower than those in the downstream around HWRand LWR fuel fabrication facilities, while the activity ratios of ²³⁴U/²³⁸U in the brook were higher than those in the downstream.The concentrations of uranium isotopes in the ground water measured quarterlywere variable depending on the sampling time. The concentrations of the grossalpha of airborne particulates collected around the nuclear facilities werefound to be in the narrow range of 0.02 to 0.10 mBq/m³ with a meanvalue of 0.05 mBq/m 3 . Both the concentrations and activity ratios of ¹³⁷Cs, ^239,240Pu and ⁹⁰ Sr around the nuclearfacilities were not very different from the worldwide fallout. The concentrationsof uranium isotopes in the soil samples around the nuclear facilities werevery close to natural background levels.     

Recovery of hafnium radioisotopes from a proton irradiated tantalum target

The^178m2Hf nucleus, with its long half-life (31 y) and high-spin isomeric state (16⁺) is desired for new and exotic nuclear physics studies. The Los Alamos Radioisotope Program irradiated a kilogram of natural tantalum at the Los Alamos Meson Physics Facility in early 1981. After fifteen years of decay, this target was ideal for the recovery of^178m2Hf. There was more than a millicurie of^178m2Hf produced during this irradiation and there has been a sufficient period of time for most of the other hafnium radioisotopes to decayed away. Traditionally, separation techniques for recovering hafnium isotopes from tantalum targets employ solvent extractions with reagents that are considered hazardous. These techniques are no longer condoned because they generate a mixed-waste (radioactive and hazardous components) that can not be treated for disposal. In this paper we describe a new and unique procedure for the recovery of hafnium radioisotopes from a highly radioactive, proton irradiated, tantalum target using reagents that do not contribute a hazardous waste component.     

Radionuclides in biota collected near a dicalcium phosphate plant, southern Catalonia, Spain

Industrial waste containing radioactive U-decay series isotopes was released into the Ebro River, Spain, over a period of >20 years from a dicalcium phosphate (DCP) plant. This release raised activities of several natural radionuclides (e.g. ²³⁸U, ²³⁴U, ²³⁰Th, ²³²Th and ²²⁶Ra) in biota taken from the area near the DCP plant. Plants and animals selected for this study included the green algae (Cladophora glomerata), the blue mussel (Mytilus edulis), the zebra mussel (Dreissena polymorpha) and the scavenger catfish (Silurus glanis) because they are all common in the area. Multiple sampling points were chosen for this study: (1) a site in the Riba-Roja Reservoir, above the DCP plant’s area of influence, (2) four sites in the area surrounding the DCP plant, close to the town of Flix, and (3) a location in the Ebro Delta Estuary in Fangar Bay. Significant differences in the activities (in Bq kg^?1 of dry weight) for the radioisotopes included in this study among samples were attributed to sample location and the species evaluated. For instance, relatively high activities for uranium and radium were obtained in algae collected around the DCP plant, compared to results obtained for algae samples taken from the unimpacted Riba-Roja Reservoir. In contrast, for zebra mussels, enhanced activities were observed for all radionuclides and, in particular, for thorium and radium isotopes within the area of influence. Among catfish samples, activity values from different locations were not significantly different, though slightly higher activities were observed at the sampling point just downstream of the DCP factory.     

Radioanalytical investigations of uranium concentrations in natural spring, mineral, spa and drinking waters in Hungary

Within this work, the activity concentrations of uranium isotopes (²³⁴U, ²³⁵U, and ²³⁸U) were analyzed in some of the popular and regularly consumed Hungarian mineral-, spring-, therapeutic waters and tap waters. Samples were selected randomly and were taken from different regions of Hungary (Balaton Upland, Bükk Mountain, Somogy Hills, Mez?föld, and Lake Hévíz). Concentration (mBq L^?1) of ²³⁴U, ²³⁵U, and ²³⁸U in the waters varied from 1.1 to 685.2, from <0.3 to 7.9, and from 0.8 to 231.6 respectively. In general, the highest uranium concentrations were measured in spring waters, while the lowest were found in tap waters. In most cases radioactive disequilibrium was observed between uranium isotopes (²³⁴U and ²³⁸U). The activity ratio between ²³⁴U and ²³⁸U varies from 0.57 to 4.97. The calculated doses for the analyzed samples of spring water are in the range 0.07–32.39 μSv year^?1 with an average 4.32 μSv year^?1. This is well below the 100 μSv year^?1 reference level of the committed effective dose recommended by WHO and the EU Council. The other naturally occurring alpha emitting radionuclides (²²⁶Ra and ²¹⁰Po) will be analyzed later to complete the dose assessment. This study provides preliminary information for consumers and authorities about their internal radiological exposure risk due to annual intake of uranium isotopes via water consumption.     

Behavior of plutonium isotopes in the marine environment of Enewetak atoll

There continue to be reports in the literature that suggest a difference in the behavior of^239+240Pu and²³⁸Pu in some aquatic environments. Plutonium isotopes have been measured in marine samples collected over 3 decades from Enewetak atoll, one of the sites in the Marshall Islands used by the United States between 1946 and 1958 to test nuclear devices. The plutonium isotopes originated from a variety of complex sources and could possibly coexist in this environment as different physical-chemical species. However results indicate little difference in the mobility and biological availability of^239+240Pu and²³⁸Pu.     

Dosage du237Np en trances dans l'uranium et le plutonium

The²³⁷Np content of²³⁸Pu or²³⁹Pu samples were determined by the gammaspectrometry of²³⁸Np formed by thermal neutron activation. The measurements were carried out on irradiated²³⁸Pu samples directly, and after the chemical separation of²³⁹Pu samples. The²³⁷Np content of natural uranium was determined from the ratio of the alpha-activities of²³⁸Pu and²³⁹Pu isotopes formed from the decay of neptunium isotopes produced by the activation of²³⁷Np and²³⁸U isotopes, respectively.      

Activity concentration of226Ra and238U in various soils

The distribution of²²⁶Ra and²³⁸U in various soils has been studied. Supposing that radioactive equilibrium were in existence, the average activities of²²⁶Ra and²³⁸U would show a nearly 11 correlation. As weathering affects radioactive equilibrium in surface soil, radioactive equilibrium was not in existence. Therefore, four kinds of soil were selected from different weathering conditions, viz. river bed soil, paddy field soil, field soil and uncropped soil. The²²⁶Ra/²³⁸U ratio of various soils lies in the range of 1.63 to 2.41. The activity concentrations of²²⁶Ra were greater than²³⁸U in various soils. The ratio²²⁶Ra/²³⁸U can be shown to be a quantitative index of weathering. Phosphatic manure contains²³⁸U and its daughter isotopes in concentrations far exceeding the average abundance in the earth's crust. But the cultivated soils (paddy field soil, field soil) are not affected by fertilizers in Kamisaibara.     

Surface and depth fallout distribution of137Cs and90Sr in soils of Caceres (Spain). Dose commitments due to external irradiation

An analysis has been made of the surface distribution of¹³⁷Cs and⁹⁰Sr in soils of the province of Cáceres (Spain), of some 20.000 km² area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding¹³⁷Cs/⁹⁰Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.     

Ultratrace analysis and isotope ratio measurements of long-lived radioisotopes by resonance ionization mass spectrometry (RIMS)

Resonance Ionization Mass Spectrometry (RIMS) is a sensitive and selective method for ultratrace analysis of long-lived radioisotopes and isotope ratio measurements. It provides extremely high isobaric suppression and good overall efficiency. The experimental limits of detection are as low as 10⁶ atoms per sample and isotopic selectivities of 5×10¹² have been obtained. The widespread potential of RIMS, using different experimental arrangements, is demonstrated for the determination of the radiotoxic isotopes Pu-238 to Pu-244 and Sr-89/Sr-90 in various environmental samples as well as for Ca-41 in nuclear reactor components and biomedical samples.