Iodine-129 (129I) is an important radionuclide in the context of nuclear waste disposal owing to its long half-life and potentially high mobility in the environment. The uptake of iodide and iodate by cement hydration phases, including calcium silicate hydrates (CSH), AFm and ettringite, as well as hardened cement paste made from Ordinary Portland cement, has been studied in batch-type sorption experiments to enhance understanding of iodine retention mechanisms in engineered repositories. Uptake kinetics were generally fast, leading to steady state within 30 days. Strong uptake of iodine by AFm and ettringite was observed, the mechanism dependent on the iodine speciation. Iodide is retained in both AFm and ettringite by exchange for sulphate, whereas with iodate, iodate-substituted ettringite is formed by phase transformation or ion exchange in the case of AFm and ettringite, respectively. The contribution of CSH phases to iodine retention in cementitious systems depends on the Ca/Si-ratio of the CSH and the alkalinity of the solution, with stronger retention in young hyperalkaline cementitious materials. These findings have implications when selecting grouts for the immobilisation of radioactive waste streams containing 129I or for choosing cementitious grouts and/or backfill materials in nuclear waste repositories.

The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes.

This report is one of a series produced by the IAEA to assist member states in assessing the likely consequences of mining, refining and disposing of residues containing natural uranium and thorium series radionuclides. It follows similar reports on the environmental behaviour of radium (2014) and polonium (2017). Many countries around the world are affected by the legacies of uranium mining, particularly from exploitation of ores during the early years of nuclear power production when environmental protection was less of a priority than it is today. In keeping with the environmental focus, emphasis is placed on exposures to members of the public via the ingestion route rather than occupational exposures where inhalation tends to be the main concern. Following a

The use of copper canisters in the Swedish KBS-3 concept for spent nuclear fuel disposal could result in the formation of copper-bearing uranyl phases should a canister suffer from defects or if the containment were to fail before reducing conditions are established in the repository. Most uranyl species would be expected to display higher solubility than the original uranium(IV) dioxide fuel, leading to enhanced release, though this would depend on the phase and prevailing groundwater conditions. Secondary alteration products may also be poorly crystalline or even amorphous, making characterization difficult during the pre-closure period owing to the high radiation field close to the canister. Vandenbrandeite, [CuUO2(OH)(4)], is a rare mineral in nature but known to form by alteration of primary uraninite through interaction with oxidizing groundwater containing dissolved copper. Consequently, an attempt has been made to characterize two vandenbrandeite specimens of varying crystallinity by luminescence and multiple-laser Raman spectroscopy; techniques amenable to remote, robotic deployment and which have proved useful in discriminating other uranyl oxy-hydroxides, silicates, and phosphates. The first reported luminescence emission and excitation spectra for vandenbrandeite revealed near-negligible luminescence, with a slightly enhanced signal for the specimen displaying poorer crystallinity. This observation agrees well with density functional theory calculations. The simulated projected density of state and band structure show an unlikely transition from the U f-orbitals to Cu d-orbitals, or O states, would be required for luminescence to be detectable; this probably improves for poorly crystalline specimens as the spatial overlap between the orbitals increases. Furthermore, negligible differences in the number of peaks and peak positions were detected in the laser wavelength-dependent Raman spectra although again, variation in background noise and peak shape was observed based on the degree of crystallinity. Good agreement was obtained between experimental and simulated Raman spectra, particularly with the environmentally sensitive axial uranyl stretching modes, validating the crystal system derived in this study. The findings of this study suggest luminescence spectroscopy, when combined with Raman spectroscopy, may be able to both identify vandenbrandeite and distinguish between crystalline and amorphous forms based on their relative luminescence intensity.

The present concept for the disposal of some low- and all intermediate-level radioactive waste in the United Kingdom involves grouting with cement in steel drums and placement in a geological facility. The vaults would then be backfilled with low strength, high porosity cement-based materials designed to promote a pervasive, alkaline environment in which many of the radioactive species present are sparingly soluble. This work investigates the interaction of strontium with such a backfill under both diffusive and advective conditions given the potential significance of the fission product 90 Sr. An important characteristic of the United Kingdom waste inventory is the abundance of organic compounds, including cellulosic materials; consequently, the experiments were repeated with products of alkaline cellulose degradation. Additional experiments were performed at high ionic strength simulating anticipated changes in the salinity of the groundwater. The effective diffusivity (D e ) of strontium in the absence of the organic compounds ranged between 5.5 × 10 −11 and 8.5 × 10 −11 m 2 s −1 , with a distribution coefficient (R d ) of between 2.8 × 10 −3 and 3.1 × 10 −3 m 3 kg −1 . The presence of organic compounds and/or an increase of ionic strength enhanced the retardation of strontium. The results indicate that the retention of strontium by hydrated cement paste occurs via a reversible ion exchange mechanism rather than mineralisation and is promoted by decalcification of the calcium silicate hydrate phases.

Among the wide range of natural uranium minerals, uranyl vanadates have attracted particular attention due to the economic viability of co-producing uranium and vanadium for industrial applications The typically remote locations of the ore deposits favour in situ analytical techniques offering rapid, minimally destructive characterisation wherever possible. This study reports on the use of luminescence, Raman and laser-induced breakdown spectroscopy to characterise the two most commonly found uranyl vanadates in nature, carnotite (K2(UO2)2V2O8·3H2O) and tyuyamunite (Ca(UO2)2V2O8·5–8H2O); the first attempt to use all three laser-based techniques in tandem for these phases. Significant differences in the luminescence emission signal intensity along with a noticeable shift in the resolved emission peak positions enable carnotite and tyuyamunite to be readily distinguished. Extraction of the band spacing from luminescence emission spectra provides confirmation of the position of the equivalent Raman uranyl symmetric stretch, ν1(UO2)2+, vibration for each mineral. Raman itself, was unable to differentiate carnotite and tyuyamunite owing to the weak signals obtained; however, the degree of splitting in the vanadate symmetric stretch, ν1(VO3)3-, feature and, to a lesser extent, the position of the ν1(UO2)2+ peak might be used to distinguish between tyuyamunite and metatyuyamunite, although further studies are required for confirmation. Compositional LIBS analysis was successful in identifying minor quartz, gypsum, Mg- and Fe-bearing inclusions, subsequently confirmed by optical and scanning electron microscopy. The findings indicate that multiple laser-based techniques offer the potential for real-time characterisation of uranyl vanadate phases where intrusive sampling, transportation and ‘off-site’ laboratory analysis is impracticable.

Among the wide range of spent nuclear fuel alteration products, uranophane-type uranyl silicates have attracted particular attention due to their ability to incorporate additional ions into their crystal structures, including other radionuclides. Two such mineral phases, uranophane (s.s.) (Ca(UO2)2(SiO3OH)2·5(H2O)) and boltwoodite ((K,Na)(UO2)(SiO3OH)·1.5H2O), have been characterised by Raman, luminescence and laser-induced breakdown spectroscopy. Well-defined Raman features were observed in each case with the two minerals being differentiated by detection of the ν3(SiO4)2- and δ(SiOH) modes for uranophane but not boltwoodite. Some distinction between uranophane-α and -β was observed by Raman, but the phase sensitivity was more apparent in the luminescence emission peak positions. The luminescence signal emitted for boltwoodite was much weaker than with uranophane, suggesting that the associated K+ and Na+ cations in the former are more efficient at chemical quenching than Ca2+. This study also reports the first luminescence excitation data for uranophane and boltwoodite.

Andersonite (Na2Ca[UO2(CO3)(3)].(5+x)(H2O) where x <= 1) has been reported from oxidised, hydrothermal uranium ores, typically as efflorescent coatings on the underground walls of mine workings. It may also occur in underground repositories for spent nuclear fuels owing to the preponderance of cementitious materials used as grouts, backfill and for structural stability. Should this be the case, its high solubility would be expected to lead to enhanced uranium mobility. This study reports on the use of Raman, time-resolved luminescence and laser induced breakdown spectroscopy to characterise andersonite; the first attempt to use all three laser-based techniques in tandem for this mineral. Well defined Raman features were observed with the resolved peaks corresponding well with previous studies, although differences were found in the number of resolvable peaks due to the low Raman signal emitted in some of the wavenumber regions selected. Seven emission and eight excitation luminescence peaks were resolved for the phase and a lifetime value of 96.8 +/- 6.7 mu s was extracted from luminescence decay measurements. Compositional LIBS analysis was successful in identifying minor K-bearing inclusions in the specimen, confirmed by optical and scanning electron microscopy, that were not detectable by the other methods employed. The findings indicate that multiple laser-based techniques offer the potential for real-time characterisation of uranyl phases formed in environments where intrusive sampling and 'off-site' laboratory analysis is impracticable.

Uranyl sulphate minerals are common alteration phases in uranium mines and uraniferous waste deposits where they occur in conjunction with other products of acidic drainage such as jarosite. Although not persistent in nature due to their high solubility, they may play an important role in governing uranium mobility during the operational and immediate post-closure environment of an engineered radioactive waste repository where oxidising conditions prevail. One such mineral, johannite (Cu(UO2)2(SO4)2(OH)2·8H2O), is of particular interest given the stated intention of several countries to use copper canisters in the disposal of spent nuclear fuel. A museum reference sample of johannite has been characterised by luminescence and multiple-laser Raman spectroscopy, resulting in the first reported luminescence excitation and emission spectra for this mineral. Well-defined Raman features were observed using 785, 633, and 532 nm lasers with the resolved peaks corresponding well to the published spectra. The Raman spectrum measured with the 457 nm laser was mostly masked by a series of repeating doublets attributed to the luminescence emission features, from which band spacing values of 831 and 823 cm−1 were extracted; the former corresponded to both the resolved 785 nm ν1(UO2)2+ peak position and the band spacing value obtained from the first reported luminescence emission spectrum for johannite. Four emission and nine excitation peaks were resolved from the luminescence spectra. The findings indicate that a suite of complementary laser-based techniques offer the potential for real-time characterisation of johannite formed in environments where intrusive sampling, transportation, and ‘off-site’ laboratory analysis are not feasible.

The coronavirus pandemic has highlighted the global nature of threats to our health and economic well-being, emphasising the need for international cooperation and the importance of timely disclosure. As arguments rage over the ultimate source of the virus and who knew what and when, parallels with past radiological incidents are readily apparent. Although hugely overshadowed by the current crisis, the release and atmospheric dispersion of ruthenium-106 (106Ru) across Europe in September 2017 [1] was nevertheless, a serious event. To date, no one has accepted responsibility for the contamination, leaving the scientific community to explore a range of hypotheses. These include, re-entry and combustion of a military surveillance satellite containing a ruthenium isotope battery [2]; an accident at the Mayak Production Association, Russia, during production of a high activity 144Ce source for the European sterile neutrino project [3]; accidental release from a reactor and incineration of a radiotherapy device [1]. An official statement from Rosatom, the Russian Atomic Energy Corporation, in November 2017 raised the possibility of a source in Romania, noting that 106Ru levels detected in that country (176 ± 18 mBq m−3) were higher than those reported in the Russian Federation [4]. This appears at odds with the results of meteorological modelling, including studies by Russian scientists, which suggest an origin in the southern Urals e.g. [5, 6]. The various hypotheses have been assessed by Masson et al [1] who conclude that the most plausible, by far, is an accident at Mayak during reprocessing of relatively ‘fresh’ (~2 y post-irradiation) spent nuclear fuel to recover PBq quantities of 144Ce, causing a release of ~250 TBq 106Ru. However, the Russian authorities have categorically denied that any incidents occurred at their nuclear power plants or fuel reprocessing sites during the period September–October 2017 [4]. Consequently, and despite strong circumstantial evidence, the case was considered unproven when Richard Wakeford provided an update in the March 2020 issue of this journal [7]. The situation may be about to change following the publication of two recent papers dealing with, respectively, the chemical speciation of deposited 106Ru [8] and isotopic fingerprinting involving stable ruthenium isotopes [9]. These high sensitivity analyses of filter papers from air sampling stations in Austria, Germany and Sweden confirm the unusual radioactive inventory, which contains only the beta-emitting fission product 106Ru together with ultra-trace quantities of 103Ru [8, 9]. Neither of these isotopes occurs naturally and their short half-lives (373.6 and 39.3 d, respectively) have allowed the date of release to be narrowed to a small window on 25–26 September 2017.

Non-invasive techniques capable of distinguishing the alteration products of spent nuclear fuel during prolonged storage would be of great benefit when assessing the potential mobility of uranium from the fuel matrix. Two potential alteration products, becquerelite (Ca(UO2)6O4(OH)6.8(H2O)) and vandendriesscheite (Pb1.5(UO2)10O6(OH)11.11(H2O)), were characterised by multiple laser-wavelength Raman and time-resolved laser fluorescence spectroscopy (TRLFS). Chemical composition was confirmed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Well-defined Raman features were obtained, particularly with a 785 nm laser, allowing subtle differences between the two minerals to be observed. Differences were also found in the Raman spectra using lasers at 457, 532 and 633 nm, with the degree of luminescence depending on the metal cation present. Chemical quenching of luminescence in Raman data correlated with luminescence excitation and emission spectra results. Five and seven luminescence emission peaks were resolved for becquerelite and vandendriesscheite, respectively. The first reported luminescence excitation spectra were collected for each mineral but not all of the spectral ranges could be resolved into individual peaks. A luminescence decay lifetime of 5.5 +/- 0.9 mu s was obtained for vandendriesscheite. This study demonstrates that Raman spectroscopy and TRLFS are potentially valuable techniques for characterising uranyl oxy-hydroxides and could be used in conjunction with other methods, such as laser induced breakdown spectroscopy (LIBS), as part of a remote analysis package in nuclear waste management.

Accurate measurement of naturally occurring radionuclides in blast furnace slag, a by-product of the steel industry, is required for compliance with building regulations where it is often used as an ingredient in cement. A matrix reference blast furnace slag material has been developed to support traceability in these measurements. Raw material provided by a commercial producer underwent stability and homogeneity testing, as well as characterisation of matrix constituents, to provide a final candidate reference material. The radionuclide content was then determined during a comparison exercise that included 23 laboratories from 14 countries. Participants determined the activity per unit mass for Ra-226, Th-232 and K-40 using a range of techniques. The consensus values obtained from the power-moderated mean of the reported participant results were used as indicative activity per unit mass values for the three radionuclides: A(0)(Ra-226) = 106.3 (34) Bq.kg(-1), A(0)(Th-232) = 130.0 (48) Bq.kg(-1) and A(0)(K-40) = 161 (11) Bq.kg(-1) (where the number in parentheses is the numerical value of the combined standard uncertainty referred to the corresponding last digits of the quoted result). This exercise helps to address the current shortage of NORM industry reference materials, putting in place infrastructure for production of further reference materials. (C) 2020 Elsevier B.V. All rights reserved.

It has been known since the 1990s that two natural radioisotopes from the uranium-238 (238U) decay series, polonium-210 (210Po) and lead-210 (210Pb), originally present in trace amounts in raw materials, are volatilised and concentrate in the form of dusts during iron ore sintering. In the UK, most of the dust generated during this process is collected by means of electrostatic precipitators and recycled back into the production system using conveyor belts. Nevertheless, a small proportion passes into the atmosphere via stack emissions and some fugitive dusts can also escape into the workplace during maintenance operations. Tata Steel UK Ltd, a major European steel making company, has developed and validated in-house radioanalytical methods for the measurement of 210Po and 210Pb in a wide range of iron-making materials including raw feedstock, waste dusts, occupational and emission filter samples. The data gathered have enabled a better understanding of the fate of 210Po and 210Pb throughout the integrated steel making route, providing essential information to support environmental permits for discharges to the atmosphere and for confirming that chronic exposure to these two natural radioisotopes does not lead to significant radiological doses to the workforce. Additionally, since the implementation of the BSS Directive 2013/59 Euratom and the Construction Products Regulation (CPR), there is a need for the European steel industry to characterise the levels of radium-226 (226Ra), thorium-232 (232Th) and potassium-40 (40K) in slag materials and confirm that those materials do not pose a significant risk of internal and external exposure to radiation when reused or recycled in building materials. This paper highlights the technical challenges encountered when measuring those natural radioisotopes in various iron-making materials, including the difficulty of validating radioanalytical methods in the absence of suitable certified reference materials.

Technetium-99 (99Tc) is an important radionuclide when considering the disposal of nuclear wastes owing to its long half-life and environmental mobility in the pertechnetate (Tc(VII)) redox state. Its behaviour in a range of potential cement encapsulants and backfill materials has been studied by analysing uptake onto pure cement phases and hardened cement pastes. Preferential, but limited, uptake of pertechnetate was observed on iron-free, calcium silicate hydrates (C–S–H) and aluminate ferrite monosulphate (AFm) phases with no significant adsorption onto ettringite or calcium aluminates. Diffusion of 99Tc through cured monolithic samples, representative of cements being considered for use in geological disposal facilities across Europe, revealed markedly diverse migration behaviour, primarily due to chemical interactions with the cement matrix rather than differential permeability or other physical factors. A backfill cement, developed specifically for the purpose of radionuclide retention, gave the poorest performance of all formulations studied in terms of both transport rates and overall technetium retention. Two of the matrices, pulverised fuel ash: ordinary Portland cement (PFA:OPC) and a low-pH blend incorporating fly ash, effectively retarded 99Tc migration via precipitation in narrow, reactive zones. These findings have important implications when choosing cementitious grouts and/or backfill for Tc-containing radioactive wastes.

Concretes, mortars and grouts are used for structural and isolation purposes in radioactive and nuclear waste repositories. For example, concrete is used for deposition tunnel end plugs, engineered barriers, mortars for rock bolting and injection grouts for fissure sealing. Despite of the materials anticipated functionality, it is extremely important to understand the long-term material behaviour in repository environments. A reference concrete and mortar for the Cebama project based on a cement, silica and blast furnace slag ternary blend were designed and characterized in different laboratories with multiple experimental methods (XRD, XAS at the Fe and Cl K-edges, SEM-EDX, Si-29 and Al-27 MAS-NMR, TG-DSC, MIP and Kerosene porosimetry) and techniques (punch strength tests). The reference concrete enabled comparison of results from different institutes and experimental techniques, unifying the individual results to more comprehensive body. The Cebama reference concrete and mortar were designed to have high durability and compatible formulation with respect to an engineered barrier system in clay or crystalline host-rocks, having pore solution pH significantly lower than traditional concretes. This work presents main results regarding their characterization and alteration in contact with representative waters present in radioactive waste repositories. Pore solution pH of the matured reference concrete was 11.4-11.6. The main hydrated phases were C-S-H and CASH gels with a Ca:Si ratio between 0.5 and 0.7 and an Al:Si ratio of 0.05. Minor phases were ettringite and hydrotalcite. Iron(III) could be in the C-S-H phases and no Cl-bearing solid phases were identified. Connected porosity and pore size distribution was characterized by MIP observing that, as expected, the size of the pores in the hydrated cement phases varies from the micro-to the nanoscale. Connected porosity of both materials were low. Compressive strength of the concrete was 115 MPa, corresponding to traditional high-performance concrete. Degradation of these materials in contact with different waters mainly produce their decalcification and enrichment in Mg for waters containing high amount of this element, like the clay waters.

Naturally occurring radioactive material is a problematic by-product of a range of industries and needs to be handled, stored, processed and disposed of in a safe and economic manner. Accurate characterisation of such material should be underpinned by measurement of certified reference materials in order to validate the methods employed and ensure quality control. This work highlights the current shortage of suitable reference materials and the approach being followed to address this issue, initially for the steel and oil and gas industries.

When combined with established primary counting techniques, atom counting using inductively coupled plasma mass spectrometry (ICP-MS) can be a powerful metrological tool for providing updated, precise half-life values for medium and long-lived radionuclides, giving end-users increased confidence in measurement for a range of nuclear applications. ICP-MS is increasingly being used for this application, and this study outlines the methods for atom counting using the latest generation tandem ICP-MS/MS. The aim is to provide a consistent methodology that is currently lacking, and attention is paid to the importance of interference removal and minimising uncertainties, with preliminary results given for uranium isotopes.

Laser-based spectroscopic techniques offer potential for characterising the alteration products of spent nuclear fuel in settings where the use of more traditional analytical methods is impracticable. Among these alteration products, uranyl phosphate phases have long attracted interest owing to their potential to form passivating surfaces on primary uranium phases inhibiting further uranium dissolution. Two strontium-rich meta-autunite ((Ca,Sr)(UO2)(2)(PO4)(2)center dot 2-8(H2O)) samples from the Mount Spokane uranium deposit, Washington, USA were characterised by multiple laser wavelength Raman and time-resolved laser fluorescence spectroscopy. Well-defined Raman features were obtained, particularly at a laser wavelength of 785 nm, but partially hydrated meta-autunite phases could not be differentiated by Raman alone. However, subtle differences in three key modes were observed between meta-autunite and published data for fully hydrated autunite specimens enabling these minerals to be distinguished. Seven luminescence emission and several excitation features were resolved for the two samples, with the latter being the first reported excitation data for meta-autunite. The luminescence decay lifetime was found to be significantly longer than previously reported and sensitive to the meta-autunite dehydration phase.

A sample of meta-autunite (Ca(UO2)2(PO4)2·6-8(H2O)) from a national reference collection was characterised by Raman spectroscopy as a representation of a potential spent nuclear fuel corrosion product. Raman spectra were collected at 457, 532, 633 and 785 nm; all exhibited some fluorescence effects, though to a lesser extent at 785 nm. The phosphate (v2(PO4)3−, v3(PO4)3−, v4(PO4)3−) and uranyl (v1(UO2)2+ and v2(UO2)2+) features could be unambiguously assigned in the resolved 785 nm spectrum. The position of the v3(UO2)2+ mode was predicted but not observed. The uranyl bond lengths and force constants were determined from the v1(UO2)2+ dominant and shoulder peak, as 1.78±0.01 and 1.79±0.01 Å and 5.69±0.08 and 5.29±0.08 millidynes Å−1, respectively.

Unconventional shale gas exploitation presents complex problems in terms of radioactive waste disposal. Large volumes of saline produced water resulting from hydraulic fracturing are typically enriched in radium isotopes, up to several hundred Bq/dm(3), orders of magnitude above national discharge limits. There is a need, therefore, to decontaminate the fluid prior to discharge, preferably by creating a less problematic radium-containing, solid waste form. Barite (barium sulphate) co-precipitation is a cost-effective method for achieving these objectives, provided the process can be controlled. In this work, radium recovery of 90% has been achieved for simulant produced waters containing 100 Bq/dm(3), using a single, optimised co-precipitation step. However, salinity has a significant effect on the efficiency of the process; higher salinity solutions requiring substantially more reagent to achieve the same recovery. If >90% radium removal is sought, multiple co-precipitation steps provide a much faster alternative than post-precipitation recrystallization of the barite solid phase, albeit at higher cost. The resulting solid waste has a relatively high specific radium activity but a much smaller volume, which presents a less intractable disposal problem for site operators than large volumes of radium-contaminated fluid.