Development and application of smectitic buffer and backfill materials in geological repository systems

2011 ◽  
pp. 323-352
Author(s):  
R. PUSCH
Keyword(s):  
Geological Repository ◽  
Backfill Materials

Temperature Criterion Related to Clay Based Backfill Materials in the Framework of a Geological Repository of Heat Producing Radioactive Waste (HLW)

2001 ◽  
Author(s):  
Johan Bel ◽  
Fréderic Bernier
Keyword(s):  
Radioactive Waste ◽  
Host Rock ◽  
Temperature Increase ◽  
Maximum Temperature ◽  
High Level Waste ◽  
Geological Repository ◽  
Temperature Criterion ◽  
Backfill Materials ◽  
Lower Temperature ◽  
New Criterion

Abstract The objective of this paper is to define a criterion for the maximum temperature allowed within clay based backfill materials, used as engineered barriers, in the framework of a geological repository of heat emitting radioactive waste. This criterion applies to all candidate geological formations in Belgium (non-indurated clay). According to the current Belgian reference repository for vitrified High Level Waste (HLW), waste packages will be disposed in deep geological clay formations after a cooling period of about 50 years in surface storage facilities. The heat release of this waste has a important impact on the design of the different components of the disposal system. The temperature increase and the possible effects of this increase will have to be considered on different locations (e.g. disposal galleries, backfill, lining, host rock, aquifer, and biosphere). In this paper, we will focus mainly on the temperature increase in the backfill material of the galleries. In the past the temperature in the host rock (Boom Clay) was limited to 100°C. Consequently, higher temperatures (above 100°C) were allowed in the components between the waste and the host rock. During the preparation of the in situ demonstration project PRACLAY, a new more stringent criterion for the limitation of the temperature in the backfill has been proposed, namely the limitation of the temperature in the backfill to 100°C. The different scientific and technical reasons for the use of this lower temperature design criterion are described in this paper. Phenomena like steam generation, mineral transformations and thermally induced, coupled effects can be reduced or avoided at lower temperatures. Another important advantage is the reduction of the corrosion rate of metal components (e.g. overpack). Finally, problems of a more technical nature (difficulty of characterization of materials, uncertainty in modeling and problems with instrumentations) can also be avoided by the use of this new criterion. Thermal calculations point out that this new criterion can be met by respecting a cooling time, for the present repository design of vitrified HLW, of 60 years instead of 50 years. We can conclude that the application of this lower temperature criterion provides better predictability of coupled effects and increases the performance, lifetime and robustness of the different barriers of the repository and of the disposal system as a whole.

scholarly journals The fate of Si and Fe while nuclear glass alters with steel and clay

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
C. Carriere ◽  
P. Dillmann ◽  
S. Gin ◽  
D. Neff ◽  
L. Gentaz ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Protective Layer ◽  
Glass Dissolution ◽  
A Value ◽  
Waste Forms ◽  
Controlling Mechanism ◽  
Geological Repository ◽  
The Mean ◽  
High Level ◽  
Initial Dissolution Rate

AbstractThe French concept developed to dispose high-level radioactive waste in geological repository relies on glassy waste forms, isolated from the claystone host rock by steel containers. Understanding interactions between glass and surrounding materials is key for assessing the performance of a such system. Here, isotopically tagged SON68 glass, steel and claystone were studied through an integrated mockup conducted at 50 °C for 2.5 years. Post-mortem analyses were performed from nanometric to millimetric scales using TEM, STXM, ToF-SIMS and SEM techniques. The glass alteration layer consisted of a crystallized Fe-rich smectite mineral, close to nontronite, supporting a dissolution/reprecipitation controlling mechanism for glass alteration. The mean glass dissolution rate ranged between 1.6 × 10−2 g m−2 d−1 to 3.0 × 10−2 g m−2 d−1, a value only 3–5 times lower than the initial dissolution rate. Thermodynamic calculations highlighted a competition between nontronite and protective gel, explaining why in the present conditions the formation of a protective layer is prevented.

Diffusion of Radionuclides in Brine-Saturated Backfill Barrier Materials

1982 ◽  
Vol 15 ◽  
Author(s):  
E. J. Nowak
Keyword(s):  
Sodium Titanate ◽  
Distribution Coefficients ◽  
Barrier Materials ◽  
Compacted Bentonite ◽  
Metal Diffusion ◽  
Diffusion Cells ◽  
Linear Sorption ◽  
Backfill Materials ◽  
Cylindrical Diffusion ◽  
Apparent Distribution

ABSTRACTThe diffusion of cesium(I), strontium(II), pertechnetate and europium in brine-saturated backfill materials was measured. Plastic diffusion cells containing cylindrical diffusion columns were used for low density backfill materials. The diffusion of gamma-emitters was followed by a gamma scanning technique. Metal diffusion cells constructed entirely from Hastelloy C-276 were used for the diffusion of pertechnetate in highly compacted bentonite. Apparent distribution coefficients calculated from diffusion data are (a) 0.02 m3 /kg for cesium(I) in 40 wt.% mordenite and 60 wt.% bentonite; (b) 0.04 m3/kg for strontium(II) in 10 wt.% sodium titanate and 90 wt.% bentonite; (c) 0.5 m3/kg for pertechnetate in 70 wt.% charcoal and 30 wt.% bentonite; and (d) 3 m3/kg for europium in 100% bentonite. Backfill effectiveness estimates based on batch sorption measurements were supported by these results;however, the diffusion results for europium did not agree well with a model for diffusion retarded by linear sorption. First measurements of pertechnetate diffusion in highly compacted bentonite suggest that anion exclusion may play a role in reducing mass transport rates of anions in this material. Needs for diffusion measurements that take into account site-specific materials interactions are described.

Influences of subsurface geological structure neighboring geological repository on earthquake motion of the site

2009 ◽  
Vol 1193 ◽  
Author(s):  
Taishi Oouchi ◽  
Hiroyuki Tsuchi ◽  
Tetsuya Ota ◽  
Koji Hane ◽  
Toru Sasaki
Keyword(s):  
Ground Motion ◽  
Velocity Structure ◽  
Geological Structure ◽  
Earthquake Ground Motion ◽  
Seismic Motion ◽  
Earthquake Resistant Design ◽  
Geological Repository ◽  
Subsurface Layers ◽  
Deep Underground ◽  
Structural Boundary

AbstractAccording to recent seismic observation records, there are some cases where unexpectedly large seismic motion was observed deep underground and that was larger than at the surface. The factors influencing such phenomena are assumed to be deep geological structures with topographic irregularity, velocity structure and non-linearity of subsurface layers. These factors should be taken into account in the earthquake-resistant design of a geological repository. The influence of a deep underground geological structure with topographic irregularity on ground motion has been studied and it has been confirmed that such a structure have a significant impact on ground motion and the constructive interference of waves may result in strong earthquake ground motion in the vicinity of a structural boundary deep underground.

Experiments and Optimization of Mix Proportions for Cement Paste Backfill Materials with Extra-Fine Unclassified Tailings

2017 ◽  
Vol 744 ◽  
pp. 146-151
Author(s):  
Ming Qing Huang ◽  
Xiao Hui Liu ◽  
Hai Yong Cheng
Keyword(s):  
Cement Paste ◽  
Mass Concentration ◽  
Influential Factors ◽  
Range Analysis ◽  
Bleeding Rate ◽  
Orthogonal Experiments ◽  
Optimal Mix ◽  
Backfill Materials ◽  
Unclassified Tailings ◽  
Paste Backfill

To produce effective cement paste backfill materials at iron mines technologically and economically, orthogonal experiments of mix proportions with extra-fine unclassified tailings were carried out. The results of the range analysis showed that the sensitivity of influential factors to the slurry slump is sequentially mass concentration, tailing/rock ratio, and cement/(tailing+rock) ratio. The sensitivity to bleeding rate, concretion time and 28-day uniaxial compressive strength is sequentially mass concentration, cement/(tailing+rock) ratio and tailing/rock ratio. Relationships of paste properties and influential factors can be demonstrated with regression analysis. Additionally, the optimal mix proportion for cement paste backfill was obtained with 78% mass concentration, 7:3 tailing/rock ratio and 1:25 cement/(tailing+rock) ratio. The slump, bleeding rate, concretion time and R28 of the optimal mixture are 25.2 cm, 8.77%, 20.9 h and 1.29 MPa, respectively. The experimental results show a feasible way to produce the industry standard backfilling materials.

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