Long-term Safety Assessment Research Articles

Research on Geo-information Data Model for Preselected Areas of Geological Disposal of High-level Radioactive Waste

The geological disposal of high-level radioactive waste (hereinafter referred to "geological disposal") is a long-term, complex, and systematic scientific project, whose data and information resources in the research and development ((hereinafter referred to ”R&D”) process provide the significant support for R&D of geological disposal system, and lay a foundation for the long-term stability and safety assessment of repository site. However, the data related to the research and engineering in the sitting of the geological disposal repositories is more complicated (including multi-source, multi-dimension and changeable), the requirements for the data accuracy and comprehensive application has become much higher than before, which lead to the fact that the data model design of geo-information database for the disposal repository are facing more serious challenges.In the essay, data resources of the pre-selected areas of the repository has been comprehensive controlled and systematic analyzed. According to deeply understanding of the application requirements, the research work has made a solution for the key technical problems including reasonable classification system of multi-source data entity, complex logic relations and effective physical storage structures. The new solution has broken through data classification and conventional spatial data the organization model applied in the traditional industry, realized the data organization and integration with the unit of data entities and spatial relationship, which were independent, holonomic and with application significant features in HLW geological disposal. The reasonable, feasible and flexible data conceptual models, logical models and physical models have been established so as to ensure the effective integration and facilitate application development of multi-source data in pre-selected areas for geological disposal.

Long-term diffusion of U(VI) in bentonite: Dependence on density

As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3mm, 1.5mm, and 1mm into the clay plug at ρ=1.3, 1.6, and 1.9g/cm3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). The results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.

Corrosion of non-irradiated UAlx–Al fuel in the presence of clay pore solution: a quantitative XRD secondary phase analysis applying the DDM method

Abstract Corrosion experiments with non-irradiated metallic UAlx–Al research reactor fuel elements were carried out in autoclaves to identify and quantify the corrosion products. Such compounds, considering the long-term safety assessment of final repositories, can interact with the released inventory and this constitutes a sink for radionuclide migration in formation waters. Therefore, the metallic fuel sample was subjected to clay pore solution to investigate its process of disintegration by analyzing the resulting products and the remnants, i.e. the secondary phases. Due to the fast corrosion rate a full sample disintegration was observed within the experimental period of 1 year at 90°C. The obtained solids were subdivided into different grain size fractions and prepared for analysis. The elemental analysis of the suspension showed that, uranium and aluminum are concentrated in the solids, whereas iron was mainly dissolved. Non-ambient X-ray diffraction (XRD) combined with the derivative difference minimization (DDM) method was applied for the qualitative and quantitative phase analysis (QPA) of the secondary phases. Gypsum and hemihydrate (bassanite), residues of non-corroded nuclear fuel, hematite, and goethite were identified. The quantitative phase analysis showed that goethite is the major crystalline phase. The amorphous content exceeded 80 wt% and hosted the uranium. All other compounds were present to a minor content. The obtained results by XRD were well supported by complementary scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis.

Adsorption of actinides within speleothems

AbstractStalagmites and stalactites, as observed within natural caves, may develop inside geological repositories during constructional and post-operational periods. It is therefore important to understand actinide sorption within such materials. Towards this, experimental studies were carried out with233U,238Np (VI),238Np (IV),239Pu and241Am radiotracers using natural speleothem samples collected from the Dharamjali cave of the Kumaon Lesser Himalayas, India. Petrological/mineralogical studies showed that natural speleothems have three general domains: (1) columnar calcite; (2) microcrystalline calcite; and (3) botryoidal aragonite – each with ferruginous materials. Results showed that all domains of speleothems can take up >99% actinides, irrespective of valence state and pH (1–6 range) of the solution. However, distribution coefficients were found to be at a maximum in aragonite for most of the actinides. Such data are very important for long-term performance and safety assessments of the deep geological repositories planned for the disposal of high-level nuclear wastes.

Development of methodology of probabilistic safety assessment for radioactive waste disposal in consideration of epistemic uncertainty and aleatory uncertainty

ABSTRACTProbabilistic safety assessment has not been performed for radioactive waste disposal owing to the difficulty of dealing with the probability distributions of the parameters included in the long-term safety assessment of radioactive waste disposal. In this study, we develop a methodology of probabilistic safety assessment in consideration of both epistemic uncertainty and aleatory uncertainty, in which the probability density function (PDF) and cumulative distribution function (CDF) of the maximum annual dose can be calculated. We also propose an approach to demonstrating dose assessment results in compliance with the stepwise target annual doses of likely and less-likely scenarios according to the occurrence probability of the scenario without classifying the probabilities of parameters involved prior to the safety assessment. For the likely scenario, we can employ the larger of the modal value of the PDF and the 50th percentile of the CDF to meet the target annual dose (10 µSv y-1). For the less-likely scenario, we can adopt the 95th percentile of the CDF as the assessment result for comparison with the target annual dose (300 µSv y-1).

Sorption of trivalent lanthanides and actinides onto montmorillonite: Macroscopic, thermodynamic and structural evidence for ternary hydroxo and carbonato surface complexes on multiple sorption sites

The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-fields. In this study we couple macroscopic sorption experiments to surface complexation modelling and spectroscopic investigations, including extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS), to elucidate the uptake mechanism of trivalent lanthanides and actinides (Ln/AnIII) by montmorillonite in the absence and presence of dissolved carbonate. Based on the experimental sorption isotherms for the carbonate-free system, the previously developed 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) model needed to be complemented with an additional surface complexation reaction onto weak sites. The fitting of sorption isotherms in the presence of carbonate required refinement of the previously published model by reducing the strong site capacity and by adding the formation of Ln/AnIII-carbonato complexes both on strong and weak sites. EXAFS spectra of selected Am samples and TRLFS spectra of selected Cm samples corroborate the model assumptions by showing the existence of different surface complexation sites and evidencing the formation of Ln/AnIII carbonate surface complexes. In the absence of carbonate and at low loadings, Ln/AnIII form strong inner-sphere complexes through binding to three Al(O,OH)6 octahedra, most likely by occupying vacant sites in the octahedral layers of montmorillonite, which are exposed on {010} and {110} edge faces. At higher loadings, Ln/AnIII binds to only one Al octahedron, forming a weaker, edge-sharing surface complex. In the presence of carbonate, we identified a ternary mono- or dicarbonato Ln/AnIII complex binding directly to one Al(O,OH)6 octahedron, revealing that type-A ternary complexes form with the one or two carbonate groups pointing away from the surface into the solution phase. Within the spectroscopically observable concentration range these complexes could only be identified on the weak sites, in line with the small strong site capacity suggested by the refined sorption model. When the solubility of carbonates was exceeded, formation of an Am carbonate hydroxide could be identified. The excellent agreement between the thermodynamic model parameters obtained by fitting the macroscopic data, and the spectroscopically identified mechanisms, demonstrates the mature state of the 2SPNE SC/CE model for predicting and quantifying the retention of Ln/AnIII elements by montmorillonite-rich clay rocks.

Prediction of Radionuclide Inventory for the Low- and Intermediate-Level Radioactive Waste Disposal Facility by the Radioactive Waste Classification

To meet nuclear regulatory requirements, more than 95% individual radionuclides in the low- and intermediate-level radioactive waste inventory have to be identified. In this study, the radionuclide inventory has been estimated by taking the long-term radioactive waste generation, the development plan of disposal facility, and the new radioactive waste classification into account. The state of radioactive waste cumulated from 2014 was analyzed for various radioactive sources and future prospects for predicting the long-term radioactive waste generation. The predicted radionuclide inventory results are expected to contribute to secure the development of waste disposal facility and to deploy the safety case for its long-term safety assessment.

Progress of the long-term safety assessment of a reference disposal system for high level wastes in Korea

KAERI developed a reference repository system for the disposal of radioactive wastes resulting from the pyroprocessing of PWR spent nuclear fuels (A-KRS; Advanced Korean Reference Disposal System). To check the design feasibility of this system, we developed a total system performance assessment (TSPA) tool using Goldsim program (GoldSim, 2006) and assessed the exposure dose rates for the reference scenario and three alternative scenarios such as earthquake, well intrusion, and initial defect of waste packages by using this tool. And then, we compared the exposure dose rates for each scenario with a draft supplementary safety goal, 10 mSv/yr, which was suggested by the regulatory body in Korea. In the original TSPA tool, we use a single source term model by assigning the same reference radionuclide inventory data for each waste package and the same shortest distance from the waste package to the MWCF (Major Waster Conducting Features) for conservatism. We developed a multi-lattice source term model by assigning various radionuclide inventory data and various distance from the waste package to the MWCF for more realistic safety assessment. Then, we found that the exposure dose rates for the case of multi-lattice source term model was one order of magnitude lower than those for the case of single source term model. According to the draft safety guideline, the primary safety goal is expressed in risk, that is, the total annual risk for the representative person resulting from the radiation exposure should not exceed 1.0 × 10−6/yr. Therefore, we developed a methodology for complex scenarios to perform the risk-based safety assessment of a HLW repository, and applied it to a reference repository system. And we found that the suggested methodology can be used to perform the risk-based long-term safety assessment of a radioactive waste repository. We can make various risk profiles by making various kinds of complex scenarios with this methodology, and they can be used to support the development of safety cases for acquiring public acceptance.

A systematic review of the safety of incretin-based therapies in type 2 diabetes

ABSTRACTIntroduction: Large randomized clinical trials have demonstrated that incretin-based therapies provide effective glycemic control in type 2 diabetes. Long-term safety assessments are ongoing.Methods: This systematic review of incretin-based therapy safety is based on 112 randomized clinical trials of duration ≥26 weeks published between January 2000 and February 2015 in patients with type 2 diabetes.Results: As expected, hypoglycemia rates were lower with dipeptidyl peptidase-4 inhibitors (DPP-4is) and glucagon-like peptide-1 receptor agonists (GLP-1 RAs) versus other oral antidiabetic drugs and insulin. The most common adverse events were infection and infestation (DPP-4is) and gastrointestinal (GLP-1 RAs). Pancreatitis cases were rare across all studies and, in the SAVOR-TIMI and EXAMINE trials, pancreatitis rates were similar in DPP-4i- and placebo-treated patients. No thyroid tumors were reported, and increased risk of cardiovascular events was not associated with DPP-4is in SAVOR-TIMI and EXAMINE, albeit over a short follow-up period.Conclusions: Overall, incretin-based therapies were well tolerated; however, their long-term safety profile should continue to be periodically assessed.

Hydrolysis of trivalent plutonium and solubility of Pu(OH)3 (am) under electrolytic reducing conditions.

The aim of this work is to determine the solubility product of plutonium hydroxide under reducing conditions and to ascertain the stability of Pu(OH)3 (am) in water. Hydrolysis of Pu(iii) and solubility of Pu(OH)3 (am) were investigated at a constant ionic strength of 0.1 M NaClO4. Coulometric titration was adopted to adjust the pH of plutonium solutions, during which the electrolytic reducing conditions maintained the oxidation state of Pu(iii). Chemical speciation for dissolved plutonium was investigated using sensitive spectrophotometry coupled with a liquid waveguide capillary cell. The spectroscopic investigations indicated that dissolved Pu(iv), Pu(v), and Pu(vi) species were ignorable under these experimental conditions. The absorbance of Pu3+ ions decreased due to hydrolysis of Pu(iii) but the absorbance of Pu(iii) hydrolysis species was not distinguishable. The formation constant for the first hydrolysis species (log *β'1) determined in the present study is -6.62 ± 0.25. The non-crystalline structure of the plutonium precipitate was observed through X-ray diffraction. The solubility product of Pu(OH)3 (am), log *K's,0 is determined to be 15.23 ± 0.50. These results indicate a stronger tendency for the hydrolysis of Pu(iii) and higher stability (lower solubility) of Pu(OH)3 (am) compared to Am(iii).

Estimation and comparison of the radionuclide inventories in vitrified high-level wastes from reprocessing plant

An accurate estimation of the radionuclide inventory of vitrified high-level waste is a prerequisite to assessing the radiological consequences of its geological disposal. The inventories of 34 radionuclides in this waste are provided by the waste producer for individual canisters at the time of loading/delivery. Of these, the inventories of 25 nuclides are measured directly during vitrification and the others are determined by calculation and/or correlation to measured contents. One purpose of the present work was to cross-check between the average and maximum radionuclide inventories of vitrified waste produced at the same facility in La Hague for Switzerland and Germany as of the data sets reported by the producer for 364 and 3017 canisters, respectively. Long-term safety assessments of geological repositories require the average and maximum inventories of a further 23 nuclides in addition to the 34 reported ones, which should be estimated by calculation or some correlation based on the technical specifications of the waste and of the reprocessing and vitrification processes. Another purpose of this work was therefore to cross-check these inventories and methods for their estimation as used by NAGRA and GRS. The results of this comparison show a good agreement for nuclides provided by the waste producer. The long-term safety relevant fission products show an agreement within 8%. The actinides have been found to show an agreement within 19%. The comparison between nuclides estimated on the basis of technical specifications shows higher deviations. The reasons for these discrepancies are addressed here.

A micro-scale inspired chemo-mechanical model of bonded geomaterials

Chemical processes influence the mechanical properties of geomaterials, resulting in either strengthening or weakening effects, the latter being particularly critical for long-term safety assessment in civil and energy engineering. Coupling of chemical and mechanical processes in cemented soils and rocks is investigated starting form a micro-structural chemo-mechanical model. The model consists of an assembly of grains and bonds undergoing dissolution or precipitation of mineral mass, affecting geometrical characteristics of the assembly. The principal such characteristics are the evolution of specific surface area and of bond cross-sectional area at the micro-scale, and of porosity at the macro-scale, which become key variables linking the micro-scale and macro-scale mechanisms. This framework has the advantage of avoiding unphysical situations, such as the occurrence of mineral precipitation with no pore space available or the occurrence of dissolution with no cementing material left. The evolution of important micromechanical quantities, such as the number of active bonds and their cross section is tracked. At the macro-scale, a reactive chemo-plasticity model is combined with a model for bonded geomaterials. The resulting micro- to macro-scale transition, schematically applicable to both materials with reactive grains and bonds and materials with only reacting bonds, is validated against the available experimental evidence, concerning calcarenite with both reactive bonds and grains made of the same mineral. The model is thus shown to provide a flexible framework for a consistent interpretation of experimental loading paths, and can be readily extended to more complex circumstances.

Long-Term Safety of Adalimumab in Clinical Trials in Adult Patients With Crohnʼs Disease or Ulcerative Colitis

Introduction: Adalimumab (ADA) is a fully human anti-tumor necrosis factor (TNF) monoclonal antibody used for the treatment of moderate to severe Crohn's disease (CD) and ulcerative colitis (UC) in patients who have inadequately responded to conventional therapies. Safety from ongoing ADA trials continues to be collected, allowing assessment of long-term safety as the number of patients and the amount of exposure to ADA increase. The aim is to provide an update on the long-term safety profile of ADA in CD and UC patients. Methods: Safety data were evaluated for adult patients with CD or UC treated with ADA in randomized, placebo-controlled, phase 3 and 3b trials as well as their open-label extension studies. Treatmentemergent adverse events (AEs) were coded using the Medical Dictionary for Regulatory Activities, version 17.1(2014), and collected from the first dose to up to 70 days after the last dose or through the cutoff date of 31 Dec 2014. AE rates were assessed as events (E) per 100 patient-years (PYs) of exposure to ADA. Results: As of 31 Dec 2014, the ADA clinical safety database contained data for 3689 CD patients and 1789 UC patients, representing 4178.7 and 3371.9 PYs of ADA exposure, respectively. Overall, AE, SAE, and malignancy rates per PYs exposure were similar between the prior and the most recent data cutoffs for each disease state (Table). The type of infections in the Opportunistic infections (excluding TB) category changed in 2014 resulting in an apparent decreased rate (Table). Conclusion: ADA continues to be well tolerated in patients with moderately to severely active CD and UC. No new safety signals were identified with prolonged ADA use in these patient groups.Table 1: Safety Profile of Adalimumab in Adult CD and UC Patients

Sensitive redox speciation of iron, neptunium, and plutonium by capillary electrophoresis hyphenated to inductively coupled plasma sector field mass spectrometry.

The long-term safety assessment for nuclear waste repositories requires a detailed understanding of actinide (geo)chemistry. Advanced analytical tools are required to gain insight into actinide speciation in a given system. The geochemical conditions in the vicinity of a nuclear repository control the redox state of radionuclides, which in turn has a strong impact on their mobility. Besides the long-lived radionuclides plutonium (Pu) and neptunium (Np), which are key elements in high level nuclear waste, iron (Fe) represents a main component in natural systems controlling redox-related geochemical processes. Measuring the oxidation state distribution for redox sensitive radionuclides and other metal ions is challenging at trace concentrations below the detection limit of most available spectroscopic methods (≥10(-6) M). Consequently, ultrasensitive new analytical techniques are required. Capillary electrophoresis (CE) is a suitable separation method for metal cations. CE hyphenated to inductively coupled plasma sector field mass spectrometry (CE-ICP-SF-MS) was used to measure the redox speciation of Pu (III, IV, V, VI), Np (IV, V, VI), and Fe (II, III) at concentrations lower than 10(-7) M. CE coupling and separation parameters such as sample gas pressure, make up flow rate, capillary position, auxiliary gas flow, as well as the electrolyte system were optimized to obtain the maximum sensitivity. We obtain detection limits of 10(-12) M for Np and Pu. The various oxidation state species of Pu and Np in different samples were separated by application of an acetate-based electrolyte system. The separation of Fe (II) and Fe (III) was investigated using different organic complexing ligands, EDTA, and o-phenanthroline. For the Fe redox system, a limit of detection of 10(-8) M was calculated. By applying this analytical system to sorption studies, we were able to underline previously published results for the sorption behavior of Np in highly diluted concentrations, and we monitored the time-dependent reduction of Pu(VI) by Fe(II). This study clearly shows that CE-ICP-SF-MS is a suitable separation method for the redox states of Pu, Np, and Fe.

Physical and Mechanical Properties of Cementitious Specimens Exposed to an Electrochemically Derived Accelerated Leaching of Calcium

Simulating natural leaching process for cementitious materials is essential to perform long-term safety assessments of repositories for nuclear waste. However, the current test methods in literature are time consuming, limited to crushed material and often produce small size samples which are not suitable for further testing. This paper presents the results from the study of the physical (gas permeability as well as chloride diffusion coefficient) and mechanical properties (tensile and compressive strength and elastic modulus) of solid cementitious specimens which have been depleted in calcium by the use of a newly developed method for accelerated calcium leaching of solid specimens of flexible size. The results show that up to 4 times increase in capillary water absorption, 10 times higher gas permeability and at least 3 times higher chloride diffusion rate, is expected due to complete leaching of the Portlandite. This coincides with a 70 % decrease in mechanical strength and more than 40 % decrease in elastic modulus.

Assessment of long-term safety and efficacy of intranasal mesenchymal stem cell treatment for neonatal brain injury in the mouse.

Background:For clinical translation, we assessed whether intranasal mesenchymal stem cell (MSC) treatment after hypoxia–ischemia (HI) induces neoplasia in the brain or periphery at 14 mo. Furthermore, the long-term effects of MSCs on behavior and lesion size were determined.Method:HI was induced in 9-d-old mice. Pups received an intranasal administration of 0.5 × 106 MSCs or vehicle at 10 d post-HI. Full macroscopical and microscopical pathological analysis of 39 organs per mouse was performed. Sensorimotor behavior was assessed in the cylinder-rearing test at 10 d, 28 d, 6 mo, and 9 mo. Cognition was measured with the novel object recognition test at 3 and 14 mo post-HI. Lesion size was determined by analyzing mouse-anti-microtubule-associated protein 2 (MAP2) and mouse-anti-myelin basic protein (MBP) staining at 5 wk and 14 mo.Results:At 14 mo post-HI, we did not observe any neoplasia in the nasal turbinates, brain, or other organs of HI mice treated with MSCs. Furthermore, our results show that MSC-induced improvement of sensorimotor and cognitive function is long lasting. In contrast, HI-vehicle mice showed severe behavioral impairment. Recovery of MAP2- and MBP-positive area lasted up to 14 mo following MSC treatment.Conclusion:Our results provide strong evidence of the long-term safety and positive effects of MSC treatment following neonatal HI in mice.

Influence of strain-rate on hydromechanical behavior of highly compacted GMZ01 bentonite

During the long-term operation of a deep geological repository in crystalline rock, saturation of buffer/backfill materials will last for a long period of time. Investigation on time-dependent property of buffer/backfill materials is of great importance for long-term safety assessment of the repository. In this work, GMZ01 bentonite powder was statically compacted to specimens with a dry density of 1.70g/cm3 and suction-equilibrated to their target values. Then, a series of suction-controlled constant rate of strain (CRS) tests (including single-stage and step-wise CRS tests) were conducted for the investigation of the strain rate-dependent compression behavior of highly compacted GMZ01 bentonite. Comparisons were made between the results of the single-stage and step-wise CRS tests under given suctions for the verification of the applicability of the isotache concept on the compacted GMZ01 bentonite. Based on that, the step-wise CRS compression tests were performed and results were presented in terms of vertical stress–vertical strain curves. Based on the test results, the virgin compression index λ and the yield stress p0 were determined. Analysis indicates that λ decreases, while p0 increases with increasing suction. Furthermore, p0 increases with increasing CRS, which is consistent with previous researches on saturated soils. Finally, a logarithm function proposed between α(s) and suction s is verified and several relevant parameters are fitted, which represents the coupling of suction, time and stress of GMZ01 bentonite.

Application of time-temperature-stress superposition principle on the accelerated physical aging test of polycarbonate

The effect of physical aging on the polymer mechanical properties is very important for long-term safety assessment of engineering application. In this paper, the physical aging tests of polycarbonate (PC) were conducted systemically under different temperature and uniaxial tensile stress level. It was shown that both temperature and stress have obvious accelerated effect on the physical aging of PC. The higher the temperature and stress level are, the faster the aging process is. To predict the long-term behavior after physical aging using the short-term test results of PC, the elongation-at-break was chosen as the index of the severity of physical aging. An Arrhenius-type time–temperature–stress superposition principle (TTSSP) was proposed to evaluate long-term performance using short-term test data. Using the proposed method, time and cost can be dramatically reduced for the assessment of long-term physical aging performance of polymeric material. POLYM. ENG. SCI., 55:2215–2221, 2015. © 2015 Society of Plastics Engineers

Large scale in-situ experiments on sealing constructions in underground disposal facilities for radioactive wastes – Examples of recent BfS- and GRS-activities

This paper shows examples of in-situ constructions and laboratory tests that have been designed and implemented by BfS and GRS in order to demonstrate the technical feasibility of special constructions for the sealing of drifts and shafts in different salt formations.Since it is often not possible to directly verify the long-term functionality (for times scales envisaged in long-term safety assessments) of such constructions, an overall understanding of the main chemical and physical processes involved needs to be developed. Such an understanding is required in order to extrapolate the evolution of a sealing system with a sufficient degree of reliability. Laboratory tests and large-scale in-situ tests are necessary and integral parts of the procedures for enhancing the process understanding.Based on a safety case, BfS has developed a robust decommissioning concept for the closure of the low- and intermediate-level waste disposal facility Morsleben (ERAM) which also takes into account the retention of radionuclides by combined effects of different sealing components.GRS has contributed to this concept with laboratory tests and modelling of the long-term behaviour of the sealing material “salt concrete” foreseen for the sealing constructions in Morsleben. Salt concrete is based on the cement Portlandite i.e., on CaO. Furthermore GRS has also investigated the MgO based “sorel concrete” employed by BfS for the Asse project. The chemical corrosion path and the subsequent permeability changes for both concretes have been investigated with test procedures developed in the GRS laboratory. GRS has also developed a new Self-Sealing material “Selbst Verheilender Versatz – SVV” (SVV, German for Self Sealing Backfill) and tested in laboratory and in-situ experiments. With this material it is possible to achieve an instantaneous and long-lasting permeability reduction within the complex system consisting of the sealing construction and the Excavation Demaged Zone (EDZ) upon brine intrusion.The presentation demonstrates details of the concepts and highlights results from the BfS in-situ experiments in Morsleben and the preceding GRS laboratory and in-situ tests.

Factors affecting the sorption of cesium in a nutrient-poor boreal bog

135Cs is among the most important radionuclides in the long-term safety assessments of spent nuclear fuel, due to its long half-life of 2.3 My and large inventory in spent nuclear fuel. Batch sorption experiments were conducted to evaluate the sorption behavior of radiocesium (134Cs) in the surface moss, peat, gyttja, and clay layers of 7-m-deep profiles taken from a nutrient-poor boreal bog. The batch distribution coefficient (Kd) values of radiocesium increased as a function of sampling depth. The highest Kd values, with a geometric mean of 3200 L/kg dry weight (DW), were observed in the bottom clay layer and the lowest in the 0.5–1.0 m peat layer (50 L/kg DW). The maximum sorption in all studied layers was observed at a pH between 7 and 9.5. The in situ Kd values of 133Cs in surface Sphagnum moss, peat and gyttja samples were one order of magnitude higher than the Kd values obtained using the batch method. The highest in situ Kd values (9040 L/kg DW) were recorded for the surface moss layer. The sterilization of fresh surface moss, peat, gyttja and clay samples decreased the sorption of radiocesium by 38%, although the difference was not statistically significant. However, bacteria belonging to the genera Pseudomonas, Paenibacillus, Rhodococcus and Burkholderia isolated from the bog were found to remove radiocesium from the solution under laboratory conditions. The highest biosorption was observed for Paenibacillus sp. V0-1-LW and Pseudomonas sp. PS-0-L isolates. When isolated bacteria were added to sterilized bog samples, the removal of radiocesium from the solution increased by an average of 50% compared to the removal recorded for pure sterilized peat. Our results demonstrate that the sorption of radiocesium in the bog environment is dependent on pH and the type of the bog layer and that common environmental bacteria prevailing in the bog can remove cesium from the solution phase.