scholarly journals Effects of OH− activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 267-278 ◽  
Author(s):  
Takuma Sawaguchi ◽  
Manabu Tsukada ◽  
Tetsuji Yamaguchi ◽  
Masayuki Mukai

AbstractThe highly alkaline environment induced by cementitious materials in a deep geological disposal system of high-level radioactive waste is likely to alter montmorillonite, the main constituent of bentonite buffer materials. Over long time periods, the alteration may cause the physical and/or chemical barrier functions of the buffer materials to deteriorate. In order to evaluate the long-term alteration behaviour, the dissolution rate, RA (kgm−3 s−1), of compacted pure montmorillonite (Kunipia-F) was investigated experimentally under conditions of hydroxide ion concentration of 0.10—1.0 mol dm−3 at temperatures of 50—90°C. The dissolution rate data, including those from a previous study at 130°C, were formulated as a function of the activity of hydroxide ions, aOH− (mol dm−3), and temperature, T (K), and expressed as RA = 104.5·(aOH−)1.3·e−55000/RT by multiple regression analysis, where R is the gas constant. The dissolution rate of montmorillonite was greater in the compacted montmorillonite than in the compacted sand-bentonite mixtures. The difference can be explained by considering the decrease in aOH− in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in aOH− is achieved somehow.

2020 ◽  
Vol 205 ◽  
pp. 10004
Author(s):  
Daichi Ito ◽  
Hideo Komine ◽  
Hailong Wang

In Japanese project for disposal of high-level radioactive waste, the self-sealing capability of bentonite buffer material, which results from the swelling deformation to fill the gaps between waste container and wall of disposal pit, must be retained thousands of years. However, because of the effect of high pressures, occurrence of cementation and property changes of the buffer material are a concern. Few studies had examined cementation effects because of the difficulties for simulating long-term alteration process experimentally. In this paper, swelling properties of consolidated buffer are regarded as similar as those of naturally consolidated bentonite ore. Therefore, three kinds of bentonite ores were used for experiments to elucidate influences of cementation on self-sealing capabilities. Undisturbed and reconstituted specimens were prepared to assess their swelling pressures after filling a preset gap in a swelling pressure apparatus. Results show that for Japanese ores, the swelling pressure of undisturbed specimens is about half that of reconstituted specimens. For American and Chinese ores, the difference of swelling pressure is greater when the preset gap is smaller. Results imply that effects of cementation on self-sealing capability are smaller when swelling deformation is allowed.


Author(s):  
Masashi Nakayama ◽  
Haruo Sato ◽  
Yutaka Sugita ◽  
Seiji Ito ◽  
Masashi Minamide ◽  
...  

In Japan, any high level radioactive waste (HLW) repository is to be constructed at over 300 m depth below surface. Tunnel support is used for safety during the construction and operation, and shotcrete and concrete lining are used as the tunnel support. Concrete is a composite material comprised of aggregate, cement and various admixtures. Low alkaline cement has been developed for the long term stability of the barrier systems whose performance could be negatively affected by highly alkaline conditions arising due to cement used in a repository. Japan Atomic Energy Agency (JAEA) has developed a low alkaline cement, named as HFSC (Highly Fly-ash Contained Silicafume Cement), containing over 60 wt% of silica-fume (SF) and fly-ash (FA). HFSC was used experimentally as the shotcrete material in construction of part of the 140m deep gallery in the Horonobe Underground Research Laboratory (URL). The objective of this experiment was to assess the performance of HFSC shotcrete in terms of mechanics, workability, durability, and so on. HFSC used in this experiment is composed of 40 wt% OPC (Ordinary Portland Cement), 20 wt% SF, and 40 wt% FA. This composition was determined based on mechanical testing of various mixes of the above components. Because of the low OPC content, the strength of HFSC tends to be lower than that of OPC. The total length of tunnel using HFSC shotcrete is about 73 m and about 500 m3 of HFSC was used. The workability of HFSC shotcrete was confirmed in this experimental construction.


Doklady BGUIR ◽  
2021 ◽  
Vol 19 (5) ◽  
pp. 35-44
Author(s):  
S. V. Kozlov ◽  
Van Cuong Le

The purpose of the article is to present computationally economical algorithms for long-term coherent accumulation of signals reflected from a point target with compensation for range and frequency migration and accumulation of signals in the spectral region. The algorithms include intra-period processing with simultaneous correction of range and frequency migration and inter-period processing with coherent accumulation of signals at the output of intra-period processing. In the first variant of the algorithm, intra-period processing is implemented by calculating the spectra of the received signals in each repetition period, multiplying the samples of the spectra by the samples of the amplitude-phase-frequency characteristic of the matched filter of a single signal and correcting phase coefficients determined by the number of the repetition period and the values of the range derivatives, and the inverse Fourier transform of the transformed spectra. The difference between the second version of the algorithm at the stage of intraperiod processing is the correction of only the quadratic and subsequent components of the range and frequency migration and the use of the keystone transformation, which eliminates the linear range migration. Coherent accumulation for both variants is realized due to the fast Fourier transform of the signal samples over the repetition periods for all samples over the range. The concept of “rough speed resolutionˮ is introduced, which determines the arrangement of channels when compensating for range migration. The uncertainty function in the coordinates “velocity–acceleration” is obtained. The equivalence of the two variants of the algorithm is shown and estimates for the required number of receiver channels are given. The simulation results confirming the operability of the proposed algorithms are presented.


2020 ◽  
Author(s):  
Juzhi Hou

<p><strong><span>Knowledge of the alpine glacier mass fluctuations is a fundamental prerequisite for understanding glacier dynamics, projecting future glacier change, and assessing the availability of freshwater resources. The glaciers on the Tibetan Plateau (TP) are sources of water for most of the major Asian rivers and their fate remains unclear due to accurate estimates of glacier mass fluctuations are lacking over long time scales. Here, we used d</span><sup><span>18</span></sup><span>O record at a proglacial open lake as proxy to estimate the Holocene glacier mass fluctuations in the Western Kunlun Mountain (WKM) quantitatively and continuously. Relative to past decades, maximum WKM glacier mass loss (-28.62±25.76 Gt) occurred at 9.5-8.5 ka BP, and maximum glacier mass gain (24.53±25.02 Gt) occurred at 1.3~0.5 ka BP, the difference in WKM glacier mass between the two periods account for ~20% of the total glaciers. Long-term changes in glacier mass suggests the TP glaciers likely face severe threats at the current rates of global warming. </span></strong></p>


1987 ◽  
Vol 112 ◽  
Author(s):  
Kenneth W. Stephens

AbstractFor a number of years, nuclear regulators have grappled with difficult questions such as: “How safe is safe enough?” Such issues take on new dimensions in the long time-frame of high-level waste disposal.Many of the challenges facing regulators involve assessment of long-term materials performance. Because real-time experiments cannot be conducted, it is necessary to rely extensively on modeling. This raises issues regarding the extent to which long-term extrapolations of short-term data are justified, the question of how closely models must represent reality to be trusted, and practical matters such as methods for validating unique computer codes.Issues such as these illustrate how regulators must make decisions in a climate of uncertainty. Methods used by non-technical disciplines to make decisions under uncertainty have been examined and offer solutions for regulators and licensees alike.


2020 ◽  
Vol 4 (1) ◽  
pp. 049-054
Author(s):  
Plopa Mieczysław

The issues investigated in the current study pertain to selected psychological aspects of human functioning in long-term stress conditions. Results of the analyses performed in this study have submitted evidence to confirm the hypothesis in which it is stated that staying on the sea for a long time is a difficult situation which contributes - to a greater or smaller extent - to starting the stress process in sailors. The role of interpersonal competencies that has been found most distinct; high level of this variable contributed to reducing both anxiety and the feeling of loneliness. It has been evidenced in the research that the skill of good functioning in varied social groups, which results from high level of development of several traits including: openness, spontaneity, responsibility, and sensitivity, becomes particularly important in long-term difficult situations in which there is little possibility of eliminating the real menace. Another conclusion to be inferred from the research is the one confirming the theoretical suggestion in which the importance of ‘ego strength’ in modifying the course of stress process is emphasised. This personality dimension has turned out to constitute the factor capable of protecting an individual against increase in both anxiety states and the feeling of loneliness during sea isolation. Another issue considered in the current study pertains to defining the role of ‘family variable’ in mediating the course of stress process under conditions of long-term task isolation. The analyses have confirmed the hypothesis in which it was assumed that sailors functioning in family systems characterised by high level of integration and quality, experience lower emotional costs during a voyage. Generally, it may be claimed that - according to the research results of the study - ‘family variables’ may constitute a significant predictor of both the ‘quality’ of a man’s functioning and personal costs he experiences in long-term stress conditions.


2018 ◽  
Vol 11 (2) ◽  
Author(s):  
Véronique Drai-Zerbib ◽  
Thierry Baccino

The study investigated the cross-modal integration hypothesis for expert musicians using eye tracking. Twenty randomized excerpts of classical music were presented in two modes (auditory and visual), at the same time (simultaneously) or successively (sequentially). Musicians (N = 53, 26 experts and 27 non-experts) were asked to detect a note modified between the auditory and visual versions, either in the same major/minor key or violating the key. Experts carried out the task faster and with greater accuracy than non-experts. Sequential presentation was more difficult than simultaneous (longer fixations and higher error rates) and the modified notes were more easily detected when violating the key (fewer errors), but with longer fixations (speed/accuracy trade-off strategy). Experts detected the modified note faster, especially in the simultaneous condition in which cross-modal integration may be applied. These results support the hypothesis that the main difference between experts and non-experts derives from the difference in knowledge structures in memory built over time with practice. They also suggest that these high-level knowledge structures in memory contain harmony and tonal rules, arguing in favour of cross-modal integration capacities for experts, which are related to and can be explained by the long-term working memory (LTWM) model of expert memory (e.g. Drai-Zerbib & Baccino, 2014; Ericsson & Kintsch, 1995).


Author(s):  
Mazlini Adnan Et.al

This study aimed to examine the level of students' conceptual knowledge on mathematics. In addition, the difference between conceptual knowledge based on gender and program was also studied. Measurement of knowledge is based on the Conceptual Knowledge Test (CKT). A total of 350 respondents were selected from five daily secondary schools in PetalingUtama, Selangor as a sample of the study. The data were analyzed using descriptive analysis to find out the level of variables measured. In order to identify the main effects and interactions between gender and program variables, inference analysis is a two-way ANOVA test performed for conceptual knowledge dimensions. The findings showed no interaction effects between gender for conceptual knowledge of mathematics (p <.05), but it showed a significant effect on the program (p> .05). In conclusion, mathematical knowledge is very important at the upper secondary level as a high level of mathematical thinking is required to ensure excellent in mathematical achievement.This is essentially as a long time learning system and methods as well as the imitation approach and dependent on the examinations orientation has long been a measure of student achievement. The implication of this study is that basic conceptual knowledge of students' mathematics needs to be enhanced to realize Malaysia's aspiration to be in the top third place in international assessments such as TIMSS and PISA.


1990 ◽  
Vol 212 ◽  
Author(s):  
M. Onofrei ◽  
M. N. Gray ◽  
D. Breton ◽  
G. Ballivy

ABSTRACTResearch on the longevity of cement-based grout materials for sealing a deep geological disposal vault is an important aspect of the Canadian and other nuclear waste management programs. These studies include assessments of the chemical durability of cement grouts, and the effects of leaching and phase transformation on the long-term hydraulic and diffusion characteristics of grouts.This paper presents the results of laboratory studies carried out to assess the effects of leaching of cement phases on the pore structure of hardened grouts. Measurements of mercury intrusion and scanning electron microscopy with energy dispersive x-ray analysis, have been used to investigate the changes in pore structure of both a reference grout (90% Type 50 cement, 10% silica fume, water-to-cementitious materials ratio between 0.4 and 0.7) and ALOFIX-MC (a fine cement product of Japan), as a function of leaching time.The work discussed here reveals that the porosity of hardened grout does change during leaching, but within limits that depend on grout composition and initial porosity. The results confirm that the materials have the potential to self-seal and maintain their performance for longer periods than those currently predicted by longevity models.Our studies of the porosity and permeability of grouts suggest that pore size distribution rather than total porosity is the more important parameter in determining longevity.


Author(s):  
Stan Gordelier ◽  
Pa´l Kova´cs

The world is facing energy difficulties for the future, in terms of security of supply and climate change issues. Nuclear power is virtually carbon free and it contributes to energy security, being a quasi-domestic source. Whilst it cannot provide a complete answer to these challenges, it is certainly capable of providing a significant component of the answer. However, nuclear power remains controversial. In order to gain public acceptance, it is widely recognised that a number of key issues need to be addressed, amongst which is resolution of the high-level radioactive waste (HLW) (including spent fuel) disposal issue. This is an important issue for all countries with an existing nuclear programme, whether or not it is intended that nuclear power should be phased out or expanded — the waste already exists and must be managed in any event. It is equally important for countries planning a new nuclear power programme where none has previously existed. Since nuclear power was first developed over fifty years ago, HLW arisings have been stored as an interim measure. It is widely believed by experts (though not by many opponents of the nuclear industry, nor by the public) that deep geological disposal, after a reasonable cooling time in interim storage, is technically feasible and constitutes a safe option [1] at an acceptable cost. The total volume of HLW from nuclear reactors is relatively small. A key issue, however, is the time-scale for developing such a final disposal solution. Considerations of security and inter-generational equity suggest that geological disposal should be implemented as soon as possible irrespective of whether or not new arisings are created. The question of managing HLW is not necessarily related to the issue of building new nuclear power stations. However, many opponents argue that there has been insufficient demonstration of the long-term safety of deep geological disposal. The same opponents also argue that there should be a moratorium on building new nuclear power plants (NPPs) until the issue of long-term management of HLW is resolved. These arguments have a powerful influence on public opinion towards both the construction of a waste repository and the building of new NPPs. The intent of this paper (developed from the current OECD NEA study on “Timing of High Level Waste Disposal”) is to identify and discuss some of the factors influencing the timing of the implementation of a HLW disposal strategy and to demonstrate to decision makers how these factors are affecting country strategies, based on current experience. Determining an optimum timescale of HLW disposal may be affected by a wide range of factors. The study examines how social acceptability, technical soundness, environmental responsibility and economic feasibility impact on the timing of HLW disposal and can be balanced in a national radioactive waste management strategy taking the social, political and economic environment into account. There is clear evidence that significant fractions of the public still have serious misconceptions with respect to the issues surrounding nuclear waste. The nuclear industry, together with governments in those countries who would like a component of nuclear power in their energy mix, has a responsibility for and a significant challenge in presenting its case to the public.


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