To estimate the cesium sorption by the bentonite and to obtain the isotherms, some batch-adsorption experiments are being carried out, being the Kd (retardation coefficient) calculated from these isotherms. One-dimensional flow cell was constructed to measure the bentonite permeability regarding to a cesium solution, which results will be used to evaluate the diffusion coefficient – D. It will be used the PHREEQC software to model the transport of the cesium radionuclide through this bentonite with the Kd and D data. The modelling of radionuclide transport in the Brazilian materials will contribute to evaluate the efficiency of multi-barriers system of the national repository, because it is one of its safety criteria.

The apparent diffusion coefficients of strontium in compacted bentonites were investigated at various concentrations of NaHCO3. Purified sodium bentonite Kunipia-F® was compacted with a jig into cylindrical pellets 10 mm in diameter and 10 mm high with dry densities of 1.0 to 1.6 Mg/m3. Each bentonite pellet was inserted into an acrylic resin column and saturated with carbonated water containing 0.1 to 1.0 M NaHCO3 for more than 1 month. The face of the bentonite specimen was spiked with 5 μL of 1.0 M SrCl2 tracer solution. After a few weeks, the strontium diffusion profiles were measured by inductively coupled plasma-mass spectrometry. The apparent diffusion coefficients of strontium decreased slightly with increasing dry density. NaHCO3 concentrations of 0.5 M decreased the apparent diffusion coefficients of strontium by half at a dry density of 1.0 Mg/m3 and quarter at 1.6 Mg/m3. At a higher NaHCO3 concentration of 1.0 M, no strontium diffusion profile was observed, whereas white precipitate was observed on the face of the bentonite specimen where it was spiked with strontium. This white precipitate could be strontianite, which is strontium carbonate. Diffusion experiments using cesium were carried out for comparison, and the presence of carbonate had no effect on the apparent diffusion coefficient.

The accident at the Fukushima Dai-ichi Nuclear Power Plant occurred following the Great East Japan Earthquake on March 11, 2011, and led to the release of volatile radionuclides, which were deposited on the environment in the Fukushima prefecture and the neighbouring areas. After the short-lived I-131, radiocaesium such as Cs-134 and Cs-137 have controlled radiation dose rate. The authors derived the apparent diffusion coefficients (Da) of some radionuclides such as Cs-134 and Cs-137 based on time variation of the depth distributions of respective radionuclides in soil obtained in field investigations in earlier studies. Almost all Da-values were of order 10-14 (m2·s−1) and well consistent with distribution coefficients (Kd) obtained from batch experiments. Whilst, field investigations for the relaxation mass depths of Cs-137 in soil by a scraper plate method were conducted at totally 85 locations over a period of nearly 6 years from December 2011 in the Fukushima prefecture and the neighbouring prefectures, and time variation of the effective relaxation mass depths was recently reported. Consequently, the effective relaxation mass depths of Cs-137 showed a tendency to linearly increase with increasing time. This indicates that radiocaesium gradually moves to the deeper part of soil with time. In this study, Da based on Fick’s diffusion equation was derived based on time variation of the effective relaxation mass depths of Cs-137 in soil. In order to calculate the Da based on Fick’s law, correlation between relaxation depth and square root of elapsed time was derived from the correlation between effective relaxation mass depth and elapsed time (where, relaxation depth is defined as the depth of 1/e of radionuclide concentration at the ground surface and can calculate by relaxation mass depth/soil density). The calculated Da of Cs-137 was of order 10-12 (m2·s−1) , which was about 2 orders of magnitude higher than Da-values that the authors previously reported as described above. Considering that almost all relaxation depths of Cs-137 were shallow within 2cm in depth from the ground surface and near the surface layer of soil is unsaturated, it is considered that Da estimated in this analysis includes the effect of dispersion by advection (by flow in the vertical direction of rainwater).

Pure and Nb-doped zirconium germanate materials of composition K2-xZr1-xNbxGe3O9.H2O where x = 0, 0.1, 0.2 and 0.25 with the structure of the mineral umbite have been successfully synthesised. The parent material displays negligible ion exchange of K+ for Cs+ but the doped materials shows much improved exchange. Synchrotron X-ray diffraction shows substantial peak splitting which varies with increasing niobium content. Preliminary Rietveld refinements suggest a two phase model with a caesium and potassium rich doped umbite phase.

Pure and Nb-doped zirconium germanate materials of composition K2-xZr1-xNbxGe3O9.H2O where x = 0, 0.1, 0.2 and 0.3 with the structure of the natural mineral umbite have been prepared in high yield using hydrothermal synthesis methods. The parent material displays virtually no ion exchange of the K+ for Cs+ but the doped materials show rapidly enhanced exchange with replacement of ca. 70% of the K+ by Cs+ for the 30% doped material. Rietveld analysis of the powder X-ray diffraction data is consistent with no change in the unit cell parameters or K+ bonding prior to the exchange, hence we propose the improved property is due to the creation of cation defect sites within the pores of the material that facilities greater cation mobility and leads to exchange.

In this work, a planar heterojunction superstrate n-i-p device based on Zn(O,S) electron transport layer and CsPbI2Br absorber material at 1.93 eV bandgap is presented. The CsPbI2Br films are deposited using a 2-step atmospheric solution deposition process and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL). Best device with an efficiency of 12.34 % and 11.94% in reverse and forward scans respectively and stabilized power output of 12.14 mW/cm2 has been demonstrated via atmospheric solution processing with minimal hysteresis between forward and reverse scans. The devices show voltage dependent current collection as well as light-dark crossover in forward bias. Light soaking tests at 65 °C and 1-sun at Voc, resulted in open-circuit voltage and fill-factor degradation. Electroluminescence (EL) after 100 hours of light soaking shows a reduction in overall EL intensity as well a shift in emission to lower wavelength. The devices exhibit a positive temperature coefficient of about 0.14 %/°C. It is found that Zn(O,S) is a viable alternative electron transport layer to replace TiO2. By replacing methylammonium cation with cesium and addition of Br has improved the stability of the perovskite phase.

We report experimental and computational studies of Ba doping for Cs in Cs2TiNb6O18, a material with potential to be an exceptional ceramic waste form for Cs sequestration. Three co-doping (simultaneous metal reduction for charge balance of Ba2+ for Cs+) schemes have been experimentally tested: Ti4+ for Nb5+, Ti3+ for Ti4+ and Nb4+ for Nb5+. Unfortunately, none showed conclusively that the co-substitution was successful. Atomistic modelling was then performed on all three schemes using novel potentials to assess the energetic feasibility, from these the most favourable scenario is reduction of Nb5+ to Nb4+.

For safety assessment analyses of the disposal of spent nuclear fuel (SNF) in deep geological repositories it is indispensable to evaluate the contribution of fission products to the instant release fraction (IRF). During the last three years the EURATOM FP7 Collaborative Project, “Fast / Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (CP FIRST-Nuclides)” was carried out to get a better understanding of the IRF.

Within CP FIRST-Nuclides, a leaching experiment with a cladded SNF pellet was performed in bicarbonate water (19 mM NaCl + 1 mM NaHCO3) under Ar /H2 atmosphere over 333 days. The cladded SNF pellet was obtained from a fuel rod segment which was irradiated in the Gösgen pressurized water reactor; the average burn-up of the segment was 50.4 MWd/kgUO2. In the multi-sampling experiment, gaseous and liquid samples were taken periodically. The moles of the fission gases Kr and Xe released in the gas phase and those of 129I and 137Cs released in solution were measured. Cumulative release fractions of (1.6 ± 0.2)·10-1 fission gases, (1.6 ± 0.1)·10-1129I and (3.9 ± 0.2)·10-2 137Cs, respectively, were achieved after 333 days of leaching. Accordingly the release ratio of fission gases to 129I was 1:1 and the release ratio of fission gases to 137Cs was 4:1, respectively.

The Knudsen Effusion Mass Spectrometer (KEMS) and the mechanistic MFPR (Module for Fission Product Release) code are tools which seem particularly interesting to support studies of the Instant Release Fraction (IRF) of Cs from spent nuclear fuel in a final repository. With KEMS, the thermal release of 137Cs and 136Xe were analysed by annealing up to total vaporization (2500K) of high burn-up (60 GWd/tU) Spent Nuclear Fuel (SNF) samples. Powder samples from the centre of the fuel, without high burn-up structure, were used. To determine the IRF, samples were analysed before and after being submitted to corrosion experiments in bicarbonated aqueous media.

MFPR was applied to determine the localization of Cs and fission gases in the SNF at the end of irradiation; the results are compared and supported by dedicated thermodynamics calculations performed for equilibrium conditions at various temperatures and fuel oxygen potentials by the non-ideal thermodynamic MEPHISTA (Multiphase Equilibria in Fuels via Standard Thermodynamic Analysis) database. A possible mechanism for Cs release during thermal annealing is proposed, taking into account inter-granular release and Cs oxide vaporization, atomic diffusion, ternary oxide phase formation and bubble release.

Differences in KEMS release profiles before and after submitting the samples to aqueous corrosion are attributed to the IRF and to changes in the vaporisation mechanism because of differences in the oxygen potential (pO2). The IRF of Cs estimated from the KEMS spectra, consisting on the part located at the grain boundaries and in inter-granular bubbles, is not significantly different from that corresponding to the experimental results found using classical static leaching experiments.

New experimental campaigns are being designed to confirm our interpretation proposed after this first run.

Cs-137 was accidentally spilled in an industrial waste repository located in a salt marsh in southern Spain, and a permeable reactive barrier was proposed to retain it. Cs adsorption properties of different natural clayey materials were analyzed. The salt marsh waters show high salinity and high chemical variability, therefore Cs adsorption was also analyzed in the presence of competitive ions, especially K+ and NH4+.

Cs adsorption was non-linear in all the analyzed materials, indicating more than one adsorption sites with different selectivity. It was shown that in mixed clay systems with illite, montmorillonite and kaolinite, the presence of illite favors Cs retention at low and medium Cs loadings and montmorillonite at high Cs loadings. In the presence of illite and montmorillonite, kaolinite plays almost no role in Cs retention. The presence of K+ and NH4+ significantly hinders cesium adsorption.

Some kinds of material in the environment due to the accident at the Fukushima Nuclear Power Plant have been contaminated by radioactive cesium (134Cs and 137Cs), which are represented by dehydrated sludge, surface soil and disaster wastes generated by the Great East Japan Earthquake. Treatment (transportation, temporary storage and incineration) and disposal of the contaminated materials should be carried out while ensuring the safety of radiation for the workers and the public. In this study, in order to provide the technical information for making the criteria, the dose estimation for scenarios on the treatment and disposal is conducted, based on the method used for driving the clearance levels in Japan. Minimum radioactive cesium concentration in contaminated material, that is, limiting activity concentration which is practicable for ordinary treatment and/or disposal, is calculated from the dose results, corresponding to the effective dose criteria indicated by the Nuclear Safety Commission of Japan. From the calculation result, it is suggested that it is necessary to forbid reusing the disposal site as construction, resident and agriculture in which the calculated doses for the public are higher than those in the other exposure pathways. Limiting concentration of radioactive cesium (134Cs and 137Cs) is derived to be 8,900Bq/kg for the external exposure pathway in landfill work under the condition of limited reuse of the site. In the case of the concentration below 8,900Bq/kg, the calculated dose of the resident due to direct and sky-shine radiation scattered in the air and ground from the interim storage place is less than 1mSv/y, irrespective of the distance from the storage place.

The potential effect of high pH plume caused by cementitious materials must be evaluated in the performance assessment for HLW geological disposal. Alkaline plume would lead to change sorption properties of host rock by primary mineral dissolution, secondary mineral precipitation and sequential change of pore water chemistry. In this study, the effect of alkaline alteration on sorption of Cs, Ni and Th was investigated using rock samples from the Horonobe Underground Research Laboratory. Crushed rock samples were reacted in high pH alkaline solution at 90 °C for 45 days, 95 days and 1,383 days, respectively. As a result of sample analysis, it was supposed that zeolitic mineral was precipitated as secondary mineral. The cation exchange capacity slightly increased in comparison with the unaltered sample. Distribution coefficients (Kd) of Cs, Ni and Th on unaltered and altered rock sample were measured by batch sorption experiment in synthetic groundwater. Kd of Cs increased with the alteration period. These results show that secondary minerals contribute to the increase in Cs sorption. By contrast, Kd of Ni and Th decreased with the alteration period. This change might be caused by dissolution of clay minerals and amorphous silicates controlling Ni and Th sorption by surface complexation. These results imply that effects of alkaline alteration on Kd of rocks depend on the dissolution/precipitation of minerals, their surface properties and sorption mechanisms.

In the autumn of 2012, the Japan Atomic Energy Agency (JAEA) launched a new research project named F-TRACE (Long-Term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima). The aims of this project are to develop a system for prediction of radiation exposure, taking into consideration the transport, deposition, and remobilization behavior of radiocaesium (RCs) from the highest contaminated mountain forests, down through the biosphere, before deposition in a number of different aquatic systems. Especially, it is important to understand balances of suspended and deposited particles and RCs inventory in inflow water, discharge water and bottom sediments of an upland reservoir. In this paper, we describe current research activities performed by JAEA at the Ogi Reservoir, Fukushima prefecture, Japan.

According to our analyses the specific sediment yield and the average rate of storage capacity loss at the Ogi Reservoir are 210 m3 km-2 year-1 and 0.15 % year-1, respectively. The vertical distribution of RCs exhibits clear peaks at several sites in the reservoir formed by deposition of eroded soil particles from the catchment that were contaminated by accident fallout. Above the depth of each of the RCs peaks, the distribution of RCs was found to be variable with depth, with concentrations ranging over five orders of magnitude for a single core. The peaks in the sedimentation profiles are probably formed from eroded soil particles entering the reservoir from the surrounding contaminated watershed (most probably during storm events). Results from grain size analyses suggest that contaminated fine sediment tends to be deposited thickly within deeper parts of the reservoir. In addition, above the depth of RCs peaks at these deeper sites, the concentration of RCs approximately increased or decreased as the proportion of fine sediments increased or decreased. However, some fine particles are possibly discharged downstream during operational releases from the dam.

Following the release of radionuclides into the environment as a result of the accident at Fukushima Daiichi nuclear power plant, Japan Atomic Energy Agency (JAEA) had to develop an immediate and effective method of reducing the dose rate received by students in school facilities. A demonstration of a reducing method was carried out by JAEA at a junior high school ground and kindergarten yard in the center of Fukushima-city. Dose rates of the released radionuclides are largely controlled by the ground level contamination and accumulation of mainly Cesium137 (Cs-137) and Cesium 134 (Cs-134) in populated areas. An effective means of reducing dose rate was to remove the surface soil and to bury it on-site under fresh uncontaminated soil or soil collected under deep depth at the site for shielding. The dose rate at1 m above ground level was reduced from 2.5 µSv/h to 0.15 µSv/h.

The accident of the TEPCO Fukushima Dai-ichi Nuclear Power Plant occurred by the 2011 off the Pacific coast of Tohoku Earthquake on 11 Mar. 2011. It is estimated that totally 1.2-1.5x1016 Bq for 137Cs and 1.5-1.6x1017 Bq for 131I were released until the beginning of Apr. and those radionuclides (RN) were deposited on soil surface and forest etc. widely around Fukushima Pref. This work was carried out as one of the investigations for making the distribution maps of radiation dose rate and soil contaminated by RNs which the MEXT promotes. The Geoslicer investigation on the depth distribution of RNs in soil was performed after 3 months from the accident. The investigation was conducted at 11 locations in Nihonmatsu City, Kawamata Town and Namie Town, and soil samples of depth 50 cm to 1 m were taken. Both of 134Cs and 137Cs were detected in all investigated locations, and 129mTe and 110mAg were detected only in locations where radiation dose rates are high. At many locations investigated, radiocaesium more than 99 % distributed within a depth of 10 cm in soil in the surface layer. On the other hand, RNs tended to distribute to deeper part in soil at locations that are supposed to have been used as farmland than in soil in the surface layer, and radiocaesium more than 99 % in soil at locations that are supposed to have been used as farmland also distributed within a depth of around 14 cm. The apparent diffusion coefficients (Da) of RNs derived from penetration profiles near the surface layer showed a tendency to be higher in soil at locations that are supposed to have been used as farmland (Da=0.1-1.5x10-10 m2/s) than in soil in the surface layer (Da=0.65-4.4x10-11 m2/s), and most Da-values were nearly 10-11 m2/s. The distribution coefficients (Kd) by a batch method were in the range of Kd=2,000-61,000 ml/g for Cs and Kd=0.5-140 ml/g for I. Although the Kd-values are different between cation (Cs+) and anion (I-), the Da-values (134Cs, 137Cs, 129mTe and 110mAg) were similar levels. This is considered to be due to that the Da-values were controlled by dispersion by flow of rain water.

After the Fukushima Dai-ichi nuclear accident, Japan Atomic Energy Agency (JAEA)was chosen by the Government to conduct decontamination pilotprojects at selected sitesin the contaminated area of Fukushima. Despite tight boundary conditions in terms of timescale and resources, the projectsprovide a good basis for developing recommendations on how to assure clean-up efficiency and worker safety and reduce time, cost, subsequent waste management and environmental impact. The results of the project can be summarised in terms of site characterisation and data interpretation, clean-up and waste minimisation and storage.

Influence of operation factors in diffusion test of compacted bentonite (such as agitation of test solution in the reservoir, feed rate of the test solution and mass transfer resistance in the filter) on the diffusion data was examined by reservoir depletion (RD) test method using Cs+. The influence of these factors on the diffusion data was also analyzed based on the mathematical sorption-diffusion model which considered the feed of test solution and mass transfer resistance in the filter as well. The reservoir depletion data showed some remarkable influences of these operational conditions, especially in the system with low ionic strength. Change in mass transfer resistance at filter-compacted bentonite due to the operational conditions was found to be potential factor which disturb the diffusion data. The influence was reduced in the system with high ionic strength of solution.

Low-cost, high-performance gamma-ray spectrometers are urgently needed for nonproliferation and homeland security applications. Available scintillation materials fall short of the requirements for energy resolution and sensitivity at room temperature. The emerging lanthanide halide based materials, while having the desired luminosity and proportionality, have proven difficult to produce in the large sizes and low cost required due to highly anisotropic properties caused by the non-cubic crystal structure. New cubic materials, such as the recently discovered elpasolite family (A2BLnX6; Ln-lanthanide and X-halogen), hold promise for scintillator materials due to their high light output, proportionality, and toughness. The isotropic nature of the cubic elpasolites leads to minimal thermomechanical stresses during single-crystal solidification, and eliminates the problematic light scattering at the grain boundaries. Therefore, it may be possible to produce these materials in large sizes as either single crystals or transparent ceramics with high production yield and reduced costs. In this study, we investigated the “cubic” elpasolite halide synthesis and studied the structural variations of four different compounds, including Cs2NaLaBr6, Cs2LiLaBr6, Cs2NaLaI6, and Cs2LiLaI6. Attempts to produce a large-area detector by a hot forging technique were explored.

Thermal conductivities of Cs-M-O (M = Mo or U) ternary compounds, observed in the pellet-cladding gap region and in the pellet periphery in irradiated oxide fuels with high oxygen potentials, were investigated. Bulk samples of Cs2MoO4 and Cs2UO4 were prepared by hot pressing or spark plasma sintering, and their thermal diffusivities were measured by the laser flash method from room temperature to 823 K for Cs2MoO4 and to 900 K for Cs2UO4. The thermal conductivities were evaluated from the thermal diffusivity and bulk density, and the specific heat capacity values available in the literature. The thermal conductivities of Cs2MoO4 and Cs2UO4 were quite low compared with UO2 (e.g. 0.5 Wm−1K−1 at 800 K for Cs2MoO4).

Once-through fuel cycles directly dispose of one primary waste form: spent nuclear fuel (SNF). In contrast, the reprocessed SNF yields multiple waste streams with different chemical, physical, and radionuclide characteristics. These different characteristics of each waste stream imply that there are potential cost and performance benefits to developing different disposal sites that best match the disposal requirements of each waste stream. Disposal sites as defined herein may be located in different geologies or in a single repository containing multiple sections, each with different design characteristics. The paper describes the results of a series of studies on disposal options for specific wastes and the potential for a waste management system that better couples various reprocessing plant wastes with disposal facilities.