HITEC – Small and mid-scale laboratory experiments

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68407700%3A21110%2F24%3A00382960" target="_blank" >RIV/68407700:21110/24:00382960 - isvavai.cz</a>

Výsledek na webu

<a href="https://www.ejp-eurad.eu/publications/d79-experimental-works-small-and-mid-scale-laboratory-experiments-final-report-results" target="_blank" >https://www.ejp-eurad.eu/publications/d79-experimental-works-small-and-mid-scale-laboratory-experiments-final-report-results</a>

DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

HITEC – Small and mid-scale laboratory experiments

Popis výsledku v původním jazyce

CIEMAT and SÚRAO [CTU] performed thermo-hydraulic tests intended to simulate the conditions of the bentonite buffer in the repository. Namely two kinds of tests were performed: 1. hydration tests under thermo-hydraulic gradient (TH tests), and 2. hydration tests under high isothermal temperature. The first group of tests, in which the buffer material is simultaneously submitted to thermal and hydraulic gradients in opposite directions, aimed to simulate the conditions of the whole barrier during operation, where the temperatures may be significantly different from those areas closest to the canister to those at the host rock contact. These tests were performed using different bentonites (MX-80, Bara-Kade, FEBEX, BCV), cell dimensions (height from 10 to 50 cm, diameter from 7 to 30 cm), initial buffer conditions (powder, pellets, water contents from 6 to 17%, dry density from 0.9 to 1.6 g/cm3 ) and testing protocols (heating followed by hydration, hydration followed by heating, simultaneous heating and hydration). The tests can be considered medium-scale ones, since their dimensions are relevant for the usual barrier thickness envisaged by most repository concepts. In all of them the heater plate simulating the canister surface was placed at the bottom (at temperatures 140-150°C) and the temperature on top was regulated either at 20°C or at room temperature. Hydration water (deioinised, glacial or saline) was supplied through the top at a low injection pressure. Out of the TH tests included in this Subtask, test HEE-B reproduced the conditions of a large-scale in situ experiment (HE-E at Mont Terri), whereas the others were not representative of any particular disposal concept. The second group of tests aimed at assessing how the high temperatures close to the heater could affect the hydration rate and swelling development. Thus, they were carried out under isothermal high temperatures (120, 140°C) with FEBEX bentonite compacted at dry density 1.6 g/cm3 with its hygroscopic water content. The tests are described in detail in this report (or in cited published literature) and the results concerning online measurements during operation (temperature, relative humidity, pore pressure, axial and radial mechanical pressures, water intake) and postmortem physical state of the bentonite (water content, dry density) are presented herein. The following conclusions could be reached: - The testing sequence (heating before or after hydration) impacts the thermo-hydro-mechanical evolution of the system. - Hydration under thermal gradient can progress even if the water injection pressure is very low, but full saturation may take much longer than under lower isothermal conditions. However, the tests reported did not allow to check if full saturation of the areas closest to the heater is possible, either because the tests were too short or because of experimental artefacts, namely evaporation through the cell sensors’ inlets. - Relevant radial swelling stresses –associated to the increase in water content– were recorded during hydration under high temperature, higher when diluted water was used instead of saline one. - The postmortem state was linked to the testing protocol: - In those tests in which no full saturation was reached (because there was not an initial saturation phase), significant gradients in the water content and dry density distributions developed in the bentonite, with higher water contents close to the hydration surface, where the dry density was lower. - Only in the test in which bentonite –with a very low dry density– was first saturated and then heated, the final dry density and water content were homogeneous in most of the bentonite column. - In the isothermal tests, where hydration took place through the bottom of the samples, the dry density was lower on the bentonite block side opposite to the hydration surface, where also the highest water contents were measured. This distribution likely results from the upwards vapour movement, which concentrated on top of the cell and would also trigger bentonite swelling and increase in porosity.

Název v anglickém jazyce

HITEC – Small and mid-scale laboratory experiments

Popis výsledku anglicky

CIEMAT and SÚRAO [CTU] performed thermo-hydraulic tests intended to simulate the conditions of the bentonite buffer in the repository. Namely two kinds of tests were performed: 1. hydration tests under thermo-hydraulic gradient (TH tests), and 2. hydration tests under high isothermal temperature. The first group of tests, in which the buffer material is simultaneously submitted to thermal and hydraulic gradients in opposite directions, aimed to simulate the conditions of the whole barrier during operation, where the temperatures may be significantly different from those areas closest to the canister to those at the host rock contact. These tests were performed using different bentonites (MX-80, Bara-Kade, FEBEX, BCV), cell dimensions (height from 10 to 50 cm, diameter from 7 to 30 cm), initial buffer conditions (powder, pellets, water contents from 6 to 17%, dry density from 0.9 to 1.6 g/cm3 ) and testing protocols (heating followed by hydration, hydration followed by heating, simultaneous heating and hydration). The tests can be considered medium-scale ones, since their dimensions are relevant for the usual barrier thickness envisaged by most repository concepts. In all of them the heater plate simulating the canister surface was placed at the bottom (at temperatures 140-150°C) and the temperature on top was regulated either at 20°C or at room temperature. Hydration water (deioinised, glacial or saline) was supplied through the top at a low injection pressure. Out of the TH tests included in this Subtask, test HEE-B reproduced the conditions of a large-scale in situ experiment (HE-E at Mont Terri), whereas the others were not representative of any particular disposal concept. The second group of tests aimed at assessing how the high temperatures close to the heater could affect the hydration rate and swelling development. Thus, they were carried out under isothermal high temperatures (120, 140°C) with FEBEX bentonite compacted at dry density 1.6 g/cm3 with its hygroscopic water content. The tests are described in detail in this report (or in cited published literature) and the results concerning online measurements during operation (temperature, relative humidity, pore pressure, axial and radial mechanical pressures, water intake) and postmortem physical state of the bentonite (water content, dry density) are presented herein. The following conclusions could be reached: - The testing sequence (heating before or after hydration) impacts the thermo-hydro-mechanical evolution of the system. - Hydration under thermal gradient can progress even if the water injection pressure is very low, but full saturation may take much longer than under lower isothermal conditions. However, the tests reported did not allow to check if full saturation of the areas closest to the heater is possible, either because the tests were too short or because of experimental artefacts, namely evaporation through the cell sensors’ inlets. - Relevant radial swelling stresses –associated to the increase in water content– were recorded during hydration under high temperature, higher when diluted water was used instead of saline one. - The postmortem state was linked to the testing protocol: - In those tests in which no full saturation was reached (because there was not an initial saturation phase), significant gradients in the water content and dry density distributions developed in the bentonite, with higher water contents close to the hydration surface, where the dry density was lower. - Only in the test in which bentonite –with a very low dry density– was first saturated and then heated, the final dry density and water content were homogeneous in most of the bentonite column. - In the isothermal tests, where hydration took place through the bottom of the samples, the dry density was lower on the bentonite block side opposite to the hydration surface, where also the highest water contents were measured. This distribution likely results from the upwards vapour movement, which concentrated on top of the cell and would also trigger bentonite swelling and increase in porosity.

Druh

O - Ostatní výsledky

CEP obor

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OECD FORD obor

20101 - Civil engineering

Projekt

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Návaznosti

R - Projekt Ramcoveho programu EK

Rok uplatnění

2024

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů