Physical evolution of a bentonite buffer during 18 years of heating and hydration

AbstractNuclear waste disposal in geological formations relies on a multi-barrier concept that includes engineered components – which, in many cases, include a bentonite buffer surrounding waste packages – and the host rock. Contrasts in materials, together with gradients across the interface between the engineered and natural barriers, lead to complex interactions between these two subsystems. Numerical modelling, combined with monitoring and testing data, can be used to improve our overall understanding of rock–bentonite interactions and to predict the performance of this coupled system. Although established methods exist to examine the prediction uncertainties due to uncertainties in the input parameters, the impact of conceptual model decisions on the quantitative and qualitative modelling results is more difficult to assess. A Swedish Nuclear Fuel and Waste Management Company Task Force project facilitated such an assessment. In this project, 11 teams used different conceptualizations and modelling tools to analyse the Bentonite Rock Interaction Experiment (BRIE) conducted at the Äspö Hard Rock Laboratory in Sweden. The exercise showed that prior system understanding along with the features implemented in the available simulators affect the processes included in the conceptual model. For some of these features, sufficient characterization data are available to obtain defensible results and interpretations, whereas others are less supported. The exercise also helped to identify the conceptual uncertainties that led to different assessments of the relative importance of the engineered and natural barrier subsystems. The range of predicted bentonite wetting times encompassed by the ensemble results were considerably larger than the ranges derived from individual models. This is a consequence of conceptual uncertainties, demonstrating the relevance of using a multi-model approach involving alternative conceptualizations.

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Bentonite Interaction with Saline High-pH Solutions

MRS Proceedings ◽

10.1557/opl.2012.594 ◽

2012 ◽

Vol 1475 ◽

Author(s):

Heikola Tiina ◽

Vuorinen Ulla

Keyword(s):

Cementitious Materials ◽

Buffering Capacity ◽

Ongoing Research ◽

High Ph ◽

Ph Values ◽

Safety Function ◽

Bentonite Buffer ◽

Different Temperatures ◽

Leaching Solution ◽

In The Beginning

ABSTRACTDegradation of cementitious materials produces leachates of high pH. Such an alkaline plume, if reaching the bentonite buffer, is likely to induce mineralogical and chemical changes in bentonite over long times and may jeopardise the set safety function of the buffer.The objective of this ongoing research is to study the possible alterations of two bentonites, MX-80 and Deponit CA-N, in alkaline leachates at two different temperatures. Also the buffering capacity of the bentonites against high pH will be evaluated.The ongoing batch experiments are carried out in an anaerobic glove-box (Ar atmosphere, low CO2) at two temperatures (25/60 °C) with three types of simulated cement waters (pH 9.7/9,3, 11.3/10.2 and 12.0/10.9) at 25/0 °C) and one saline groundwater simulate (pH 8.3/7.9) as reference. The solid to liquid ratio used is 1/10. For each set of experiments there are three parallels so that bentonite alteration can be analysed after three different time periods. In the experiment each bentonite sample is leached with several batches of leaching solution. For each renewal of the leaching solution the phases are separated by centrifugation, the reacted solution withdrawn and the chemical composition analysed.The high-pH experiments (11.3 and 12.0, at 25°C) have continuously shown an initial decrease in the pH-values after each leachate renewal, albeit less dramatic than in the beginning, indicating remaining buffering capacity of the bentonites. The other two experiments (pH 8.3 and 9.7 at 25°C) have shown rather unaltered pH-values. In general, slightly lower pH-values were observed in the Deponit CA-N samples than in those of MX-80. The main cations (Na and Ca) analysed in the leachates have shown a rather expected trends as a result of ion-exchange occurring in the bentonites. The analysed Si concentrations indicate possible dissolution of smectite. More conclusions are possible after the bentonites have been characterized. One experimental set of the 25 °C experiments has been finished and the bentonite phases are being characterized. Other experiment sets are still continued.

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On the long term estimation of hydrogen embrittlement risks of titanium for the fabrication of nuclear waste container in bentonite buffer of nuclear waste repository

Journal of Nuclear Materials ◽

10.1016/j.jnucmat.2020.152092 ◽

2020 ◽

Vol 533 ◽

pp. 152092 ◽

Cited By ~ 1

Author(s):

Qichao Zhang ◽

Yanliang Huang ◽

Daniel John Blackwood ◽

Binbin Zhang ◽

Dongzhu Lu ◽

...

Keyword(s):

Hydrogen Embrittlement ◽

Nuclear Waste ◽

Nuclear Waste Repository ◽

Bentonite Buffer ◽

Waste Container ◽

Waste Repository

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Hydraulic Properties of Bentonite Buffer and Backfill Materials and Simplified Evaluation.

Doboku Gakkai Ronbunshu ◽

10.2208/jscej.2002.708_133 ◽

2002 ◽

pp. 133-144 ◽

Cited By ~ 2

Author(s):

Hideo KOMINE ◽

Nobuhide OGATA

Keyword(s):

Hydraulic Properties ◽

Bentonite Buffer ◽

Backfill Materials

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Evaluation of Long-term behavior of bentonite buffer based on Molecular Dynamics and Homogenization Analysis

The Proceedings of the National Symposium on Power and Energy Systems ◽

10.1299/jsmepes.2004.9.477 ◽

2004 ◽

Vol 2004.9 (0) ◽

pp. 477-480

Author(s):

Kenichi NAKAOKA ◽

Hideki KAWAMURA ◽

Yasuaki ICHIKAWA ◽

Katsuuki KAWAMURA ◽

Noriyuki SAITO

Keyword(s):

Molecular Dynamics ◽

Bentonite Buffer ◽

Long Term Behavior

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CO2 effect on the pH of compacted bentonite buffer on the laboratory scale

Clay Minerals ◽

10.1180/claymin.2013.048.2.09 ◽

2013 ◽

Vol 48 (2) ◽

pp. 277-284 ◽

Cited By ~ 1

Author(s):

A. Itäla ◽

J. Järvinen ◽

A. Muurinen

Keyword(s):

Partial Pressure ◽

Spent Nuclear Fuel ◽

Buffering Capacity ◽

Test Cases ◽

Experimental Setup ◽

Atmospheric Conditions ◽

Compacted Bentonite ◽

Bentonite Buffer ◽

Insight Into

AbstractDisposal of Finnish spent nuclear fuel is planned to be based on the KBS-3 repository concept. The role of the bentonite buffer in this concept is essential, and thus the behaviour of the bentonite has to be known. The experiments in this paper concentrated on providing information about the effects of carbon dioxide CO2(g) partial pressure on compacted sodium bentonite, giving an insight into the buffering capacity. The experimental setup consisted of a hermetic box which had a CO2-adjusted atmosphere, and the bentonite was in contact with this atmosphere through water reservoirs. The results indicated that it is possible to measure online the changing pH in the porewater inside compacted bentonite using IrOx electrodes. It was found that the pH fell if the CO2 partial pressure increased above atmospheric conditions. The experimental results indicated a greater fall in pH than in our model in the test cases where CO2 was present. The pH in the experiment with 0 PCO2 remained nearly constant throughout the 5 month period. On the other hand, the pH dropped to near 6 with 0.3 PCO2 and to 5.5 with 1 PCO2.

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Na/Ca selectivity coefficients of montmorillonite in perchlorate solution at different temperatures

MRS Proceedings ◽

10.1557/opl.2012.596 ◽

2012 ◽

Vol 1475 ◽

Author(s):

Aku Itälä ◽

Arto Muurinen

Keyword(s):

Cation Exchange ◽

Spent Nuclear Fuel ◽

Spent Fuel ◽

Selectivity Coefficients ◽

Crystalline Bedrock ◽

Bentonite Buffer ◽

Different Temperatures ◽

C 50 ◽

Exchange Selectivity

ABSTRACTThe Finnish spent nuclear fuel disposal is based on the Swedish KBS-3 concept in crystalline bedrock. The concept aims at long-term isolation and containment of spent fuel in copper canisters surrounded by bentonite buffer which mostly consists of montmorillonite. For the long-term modelling of the chemical processes in the buffer, the cation-exchange selectivity coefficients have to be known at different temperatures. In this work, the cation-exchange selectivity coefficients and cation-exchange isotherms were determined in batch experiments for montmorillonite at three different temperatures (25 °C, 50 °C and 75 °C). Five different ratios of NaClO4/Ca(ClO4)2 were used in the experimental solutions. After equilibration the solution and montmorillonite were separated and the solution analysed to get the desired exchange parameters. The experiments were modelled with a computational model capable of taking into account the physicochemical processes that take place in the experiment.

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