High-level Radioactive Waste In China Research Articles

Using multiple isotopes to determine groundwater source, age, and renewal rate in the Beishan preselected area for geological disposal of high-level radioactive waste in China

Understanding hydrogeological conditions is crucial for selecting and assessing the long-term safety performance of a high-level radioactive waste (HLW) disposal repository. Utilizing environmental isotopes as effective markers for analysing groundwater movement, this study investigates groundwater recharge sources, age, and renewal rates using multiple isotopes in China's potential HLW repository site, the Beishan area. The results indicated deep bedrock groundwater primarily derives from ancient precipitation infiltration under cold climatic conditions. A noteworthy distinction is that loose sedimentary groundwater exhibits higher tritium content (>10 TU) compared to bedrock groundwater (<3.2 TU). Groundwater within the recharge area, especially within gullies and piedmont slope deposits, is relatively youthful, with an age of less than 30 years and an annual renewal rate exceeding 5 %. In contrast, the shallow groundwater age in the intermountain basins and depressions of the discharge area generally exceeds 50 years, with an annual renewal rate often falling below 0.5 %. At the Beishan underground research laboratory site, deep groundwater at the disposal repository depth displays a corrected 14C age exceeding 8,000 years, indicating an extremely slow movement and alteration rate. As a result, the hydrogeological conditions in the Beishan area are expected to be relatively beneficial for ensuring the safety of HLW repository.

Numerical modeling of site-scale groundwater flow with stochastic parameterized hydraulic conductivity fields for geological disposal of high-level radioactive waste in China

Deep geological disposal is internationally accepted as a feasible and safe approach for high-level radioactive waste (HLW) disposal. To evaluate hydrogeological conditions in support of safety assessments for HLW disposal at the Xinchang preselected site in China, stochastic inverse models of site-scale groundwater flow were developed in this study to generate highly parameterized hydraulic conductivity fields for the fractured medium by adopting pilot point and null-space Monte Carlo methods. The hydraulic influence zones of the faults were carefully considered to have homogenous parameter values across the zones. A total of 120 multiple random realizations were generated to characterize the 3D spatial variations in hydraulic conductivity by conditioning to 1218 fixed pilot points. The simulated hydraulic heads of the realizations were in good agreement with observational data. The hydraulic conductivity fields close to the boreholes could be characterized in detail and had relatively low uncertainties. Furthermore, the hydraulic conductivity (K) values around underground research laboratory (URL) at the HLW disposal zone depth were less than 10−9 m/s. The K values obtained for most of the influence zones of these faults at this depth were consistent with hydraulic test data and ranged from 10−10 to 10−9 m/s, thereby indicating that the surrounding rock has low permeability and is suitable for HLW disposal. These findings offer new insights into hydrogeological conditions by providing key information on the permeability characteristics that need further focus on HLW disposal.

The sensitivity of mechanical properties and pore structures of Beishan granite to large variation of temperature in nuclear waste storage sites.

Granite is the host rock of the Beishan Underground Research Laboratory (URL) for geological disposal of high-level radioactive waste in China. The mechanical behavior of Beishan granite is the key in determining whether the repository can serve safely for a long time. The surrounding rock of the repository will be exposed to thermal environment induced by radionuclide decay, resulting in significant changes in the physical and mechanical properties of the Beishan granite. This study investigated the pore structure and mechanical properties of Beishan granite after thermal treatment. The T2 spectrum distribution, pore size distribution, porosity, and magnetic resonance imaging (MRI) were obtained through nuclear magnetic resonance (NMR); uniaxial compressive strength (UCS) and acoustic emission (AE) signal characteristic of granite were investigated through uniaxial compression tests. The results showed that high temperature significantly affected the T2 spectrum distribution, pore size distribution, porosity, compressive strength, and elastic modulus of granite, and porosity gradually increases, whereas the strength and elastic modulus gradually decline with increasing temperature. The porosity of granite has a linear relationship with UCS and elastic modulus, indicating that the essential mechanism for the deterioration of macroscopic mechanical properties lies in changes of microstructure. In addition, the thermal damage mechanism of granite was revealed, and a damage variable was defined based on porosity and uniaxial compressive strength.

Progress on rock mechanics research of Beishan granite for geological disposal of high-level radioactive waste in China

The mechanical behavior of host rock for a deep geological repository of high-level radioactive waste plays a key role in ensuring the isolation function of host rock as a natural barrier under the multi-field coupling environment. For a better understanding of granite in China's Beishan pre-selected area for geological disposal of high-level radioactive waste, a series of investigations were carried out on in-situ stress field of rock mass at depth, strength and deformation characteristics of rocks under different stress and temperature conditions, and rock boreability and adaptability to Tunnel Boring Machine (TBM) technology. The results indicate that Beishan granite shows typical characteristics as a hard and brittle rock with a quite low permeability, and it is favorable to geological disposal. Meanwhile, a new rock mass suitability evaluation system was proposed, and the rock mass mainly composed of Beishan granite was proven to be suitable for geological disposal. Besides, the constructability of Beishan granite at engineering scale was tested and verified through field tests in the Beishan Exploration Tunnel (BET). Here, we summarize the main outcomes of rock mechanics research on Beishan granite in the past years and introduced the current progress of Beishan underground research laboratory (URL) for geological disposal.

Americium solubility and solubility limiting solid phase (SLSP) analysis in groundwater of Beishan, a proposed site for the disposal of high-level radioactive waste in China

The disposal of high-level radioactive waste (HLW) in deep geological repository requires reliable data including the solubility and speciation of americium and other actinides in safety assessment. In this work, a generic thermodynamic equilibrium model using the geochemical codes PHREEQC-3 and PhreePlot was used to investigate the solubility of americium in the groundwaters of Beishan in the possible ranges of pH (6–11) and PCO2 (10−5.5 - 10−2.5 bar). The pH-logPCO2 diagram of solid phases and aqueous species of Am was computed and plotted with Am solubility contour lines. The results indicate that the solubility of Am under the repository far-field conditions is dependent on pH and under the near-field conditions on pH and PCO2. Based on our calculations, we have determined that AmCO3OH·0.5H2O(cr) is thermodynamically stable in both the near- and far-field conditions, leading to an Am solubility of 4.0 × 10−9 mol/kg and 1.5 × 10−8 mol/kg under, respectively, the near- and far-field conditions of the proposed Beishan repository. However, the amorphous AmCO3OH(am, hyd) phase, while thermodynamically metastable, is expected to persist for an extended period of time, possibly hundreds of years or more after the closure of a repository. As such, it is assumed to be the solid phase that limits the solubility of americium, leading to much enhanced Am solubilities of 6.3 × 10−7 and 2.4 × 10−6 mol/kg for the Beishan near- and far-field conditions, respectively. Therefore, solely based on the solubility data, Am could be more toxic than the natural uranium in the Beishan granitic groundwater within ∼5000 years after the proposed repository's closure. It is thus important to ensure that Am is well contained by the engineered barriers within this timeframe. Since Am solubilities in Beishan groundwater are rather low, the effect of sorption and colloidal formation could be potentially more important for Am migration in groundwaters, however further studies are required before these processes can be properly evaluated.

Retracted: Classification Method of Rock Structure and Rock Mass Quality of Surface Granite: Geological Disposal of High-Level Radioactive Waste in China

Retracted: Classification Method of Rock Structure and Rock Mass Quality of Surface Granite: Geological Disposal of High-Level Radioactive Waste in China

Groundwater circulation patterns in bedrock aquifers from a pre-selected area of high-level radioactive waste repository based on two-dimensional numerical simulation

Deep geological disposal is internationally accepted as a feasible and safe way to dispose the high-level radioactive waste (HLW) in low permeability fractured bedrocks. It is essential to understand the regimes of groundwater flow, circulation, and predict the characteristics of long-term flow systems for site selection and safety assessment of deep geological HLW disposal by using numerical simulation technology. In this study, TOUGH3/EOS9 software with an improved evaporation module is used to develop a two-dimensional variably saturated numerical model of a typical profile at Xinchang site, which is considered as a potential deep geological repository for spent HLW in China. Results reveal that almost 99% of the precipitation is discharged through evaporation, and less than 1% infiltrates into shallow groundwater. The groundwater flow pattern is closely related to topography and lithological distribution, and the groundwater flow in Xinchang rock mass cannot discharge to the south Hexi Corridor. Groundwater in the typical profile is divided into three types of groundwater flow system, namely local, intermediate and regional flow system, and each has its own characteristics based on aspects of flow path, cycle amount, cycle path, residence time and discharge position. The circulation flux of these three systems accounts for 79.25%, 13.24% and 7.51% of the total groundwater quantity of Xinchang site, respectively. Meanwhile, different-depth models were constructed to validate the influence of bottom boundary depths on groundwater characteristics. Increasing the bottom boundary depth has limited influence on the maximum circulation depth of regional flow system, but negligible impact on circulation flux. This study can enhance the understanding of groundwater circulation and evolution in fractured bedrock aquifers with low permeability, and provide the feasibility of geological repository for spent HLW for the view point of groundwater flow.

Safety assessment of Beishan pre-selection area for geological disposal of high-level radioactive waste in China

Safety assessment of Beishan pre-selection area for geological disposal of high-level radioactive waste in China

Classification Method of Rock Structure and Rock Mass Quality of Surface Granite: Geological Disposal of High-Level Radioactive Waste in China

The engineering quality of rock mass is a key factor to evaluate the long-term stability and safety of high-level radioactive waste (HLW) geological disposal engineering and is also the important basis for disposal site selection. Traditional rock mass quality classification methods, such as RMR and [Formula: see text], can meet underground engineering but still should be studied further for the site evaluation in the HLW disposal engineering. In this study, rock mass structure rating (RMSG) was proposed based on the quantitative control index of rock mass structure which was from the rock mass quality classification methods. Based on the statistical results of rock mass structure, the relationship between the number of RMSG and the modified RMR ([Formula: see text]) and [Formula: see text] ([Formula: see text]) was established, China, as a case study. Results from this study show that RMSG is linearly related to [Formula: see text] and negatively exponential to [Formula: see text]. The research results can solve the evaluation of rock mass quality for HLW geological disposal engineering, and the addition of more engineering examples over time will enable further verification.

A New Method for Estimating Elastic Parameters of Clay Rock Host Rock in Geological Disposal of High-Level Radioactive Waste in China

Taking the clay rock from the Tamusu pre-selected area of China’s high-level radioactive waste geological repository as the research background. Using the methods of triaxial compression testing, X-ray diffraction and microscopic analysis, the main mineral composition, structure and mechanical properties of clay rock under different confining pressures were systematically obtained. Combined with the classical elastic parameter estimation methods at home and abroad, the elastic modulus of the clay rock in the Tamusu pre-selected area is estimated. It finds that the classical elastic parameter estimation method has a large error with the actual test value when calculating the elastic modulus of Tamusu clay rock. The maximum error can reach 788%, and the error decreases with the increase of confining pressure, however, the minimum error is still also 46%. In order to establish the deformation evaluation index suitable for the clay rock in the Tamusu pre-selected area of high-level radioactive waste, considering the influence of the mineral properties and structure of the clay rock on the macro-mechanics properties, a new method for estimating the elastic parameters of the clay rock was established. Compared with the classic elastic parameter estimation method, the maximum error is reduced to 33% and the minimum error is only 2%. Therefore, we suggest that the new elastic parameter estimation method proposed here may be used to evaluate and predict the elastic modulus parameters of the clay rock in the Tamusu pre-selected area for geological disposal of high-level radioactive waste in China.

Exploring sorption behaviors of Se(IV) and Se(VI) on Beishan granite: Batch, ATR-FTIR, and XPS investigations

As the important anions in the high-level radioactive waste (HLRW), and the sorption behaviors of Se(VI) and Se(IV) on Beishan granite are important to the safe evaluation and performance assessment of the deep geological repository for HLRW in China. In this study, the sorption behaviors of Se(IV) and Se(VI) on Beishan granite were investigated under different environmental factors combining batch and spectroscopic approaches, such as X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transformed infrared (ATR-FTIR). The results showed that Se(IV) sorption on Beishan granite was much higher than that of Se(VI) mainly due to their molecule charge densities and speciation in solution. The sorption of Se(IV) was independent of ionic strength, suggesting that the inner-sphere complexes (ISCs) was dominant for Se(IV) sorption on granite. However, Se(VI) sorption on Beishan granite was strongly dependent on ionic strength, which indicated that ion exchange and outer-sphere complexes (OSCs) dominated Se(VI) sorption. ATR-FTIR confirmed that Se(IV) and humic acid (HA) could form a soluble complex of HA-Se(IV) in solution. Therefore, under low pH and HA concentration conditions, the presence of HA could enhance Se(IV) sorption; while inhibited Se(IV) sorption on granite to some extent under high pH and HA concentration conditions. In case of Se(VI), the presence of HA greatly reduced the surface charge density of the Beishan granite, which in turn enhanced the electrostatic repulsion of Se(VI) and granite surfaces, thereby inhibiting Se(VI) sorption on granite surface. When Se(IV) coexisted with Eu (III), the sorption of Se(IV) on granite could be enhanced to a large extent, which might be due to the formation of Eu2(SeO3)3 complex with Se(IV) under alkaline condition (consistent with ATR-FTIR), or surface charge modifications of Beishan granite caused by Eu(III) sorption. Owing to the ISCs of Se(IV) on granite, the presence of anions almost no obvious effect on Se(IV) sorption except for SO32− and HPO42− in terms of the competitive sorption, which inhibited Se(IV) sorption to some extent. It was interesting that CO32− could enhance Se(IV) sorption to a large extent, however the mechanism was still not clear. Furthermore, XPS further confirmed that Se(IV) sorption on granite was dominated by Fe(II) and Fe(III), and the host mineral was biotite.

Study on Structural Plane of Deep Rock Mass in Xinchang Preferred Site for Underground Research Laboratory on Geological Disposal of High-Level Radioactive Waste in China

Structural plane is an important influence factor for the rock mass quality, 3D modelling, borehole hydraulic test and engineering design of underground research laboratory. Xinchang rock mass in Beishan area of Gansu province has been confirmed the preferred site for URL on geological disposal of high-level radioactive waste in China. The characteristics of structural plane in Xinchang rock mass are obtained based on acoustic borehole televiewer and other geological information. The results indicate that the granite rock mass with a high integrity is beneficial for construction of URL. The width of faults around preferred site and incidence in horizontal and vertical decrease as the depth increases. Characteristics of dip and strike of structural plane is the same as other structure in this area. All research results provide meaning information for design of URL and further geological research.

The Beishan underground research laboratory for geological disposal of high-level radioactive waste in China: Planning, site selection, site characterization and in situ tests

With the rapid development of nuclear power in China, the disposal of high-level radioactive waste (HLW) has become an important issue for nuclear safety and environmental protection. Deep geological disposal is internationally accepted as a feasible and safe way to dispose of HLW, and underground research laboratories (URLs) play an important and multi-faceted role in the development of HLW repositories. This paper introduces the overall planning and the latest progress for China's URL. On the basis of the proposed strategy to build an area-specific URL in combination with a comprehensive evaluation of the site selection results obtained during the last 33 years, the Xinchang site in the Beishan area, located in Gansu Province of northwestern China, has been selected as the final site for China's first URL built in granite. In the process of characterizing the Xinchang URL site, a series of investigations, including borehole drilling, geological mapping, geophysical surveying, hydraulic testing and in situ stress measurements, has been conducted. The investigation results indicate that the geological, hydrogeological, engineering geological and geochemical conditions of the Xinchang site are very suitable for URL construction. Meanwhile, to validate and develop construction technologies for the Beishan URL, the Beishan exploration tunnel (BET), which is a 50-m-deep facility in the Jiujing sub-area, has been constructed and several in situ tests, such as drill-and-blast tests, characterization of the excavation damaged zone (EDZ), and long-term deformation monitoring of surrounding rocks, have been performed in the BET. The methodologies and technologies established in the BET will serve for URL construction. According to the achievements of the characterization of the URL site, a preliminary design of the URL with a maximum depth of 560 m is proposed and necessary in situ tests in the URL are planned.

Regional Groundwater Flow Assessment in a Prospective High-Level Radioactive Waste Repository of China

The production of nuclear energy will result in high-level radioactive waste (HLRW), which brings potential environmental dangers. Selecting a proper disposal repository is a crucial step in the development of nuclear energy. This paper introduces firstly the hydrogeological conditions of the Beishan area in China. Next, a regional groundwater model is constructed using a multiphase flow simulator to analyze the groundwater flow pattern in the Beishan area. Model calibration shows that the simulated and observed hydraulic heads match well, and the simulated regional groundwater flow pattern is similar to the surface flow pattern from the channel network, indicating that the groundwater flow is mainly dependent on the topography. In addition, the simulated groundwater storage over the period from 2003 to 2014 is similar to the trend derived from the Gravity Recovery and Climate Experiment satellite-derived results. Last, the established model is used to evaluate the influences of the extreme climate and regional faults on the groundwater flow pattern. It shows that they do not have a significant influence on the regional groundwater flow patterns. This study will provide a preliminary reference for the regional groundwater flow assessment in the site of the HLRW in China.

Development of geo-information data management system and application to geological disposal of high-level radioactive waste in China

In this paper, based on information technology, a geo-information database was established and a geo-information data management system (named as HLW-GIS) was developed to facilitate data management work of the multi-source and multidisciplinary data been which are generated during site selection process of geological repository in China. Many important functions, such as basic create, retrieve, update, and delete operations, full text search and download functions, can be achieved through this management system. Even the function of statistics and analysis for certain professional data can be provided. Finally, a few hundred gigabytes of data from numerous different disciplines were integrated, stored, and managed successfully. Meanwhile, the management system can also provide a significant reference for data management work of related research fields, such as decommissioning and management of nuclear facilities, resource prospection and environmental protection.

Alteration of compacted GMZ bentonite by infiltration of alkaline solution

AbstractConcepts for geological disposal of high-level radioactive waste usually include bentonite buffer materials. Numerous studies have been performed with most usingWyoming bentonite. Gaomiaozi (GMZ) bentonite has been selected as a potential buffer/backfill material for the deep geological repository of high-level radioactive waste in China. In this context, the highly alkaline environment induced by cementitious materials in the repository is likely to alter montmorillonite, the main clay mineral in GMZ bentonite. This alteration may result in deterioration of the physical and/or chemical properties of the buffer material. To acquire quantitative data which would allow us to assess the dissolution of montmorillonite and changes in the diffusivity of hydroxide ions as well as their effects on the swelling pressure and permeability of the compacted GMZ bentonite, an experimental study was conducted under highly alkaline (NaOH solutions with various pH values were used), simulated groundwater conditions. The GMZ bentonite also contains cristobalite which may also have been dissolved. The microstructure of the compacted bentonite samples after the experiments was determined by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDX) was carried out to identify mineralogical changes. At pH &gt;13, the permeability of specimens increased significantly; the swelling potential decreased with increasing pH. Furthermore, the pore volume and pore size of GMZ bentonite changed when exposed to alkaline solution, resulting in an increase in porosity and permeability. The main alteration mechanisms of compacted GMZ bentonite undergoing infiltration by highly alkaline solution are likely to be dissolution and modifications in terms of the microstructure and mineralogy.

Swelling pressure characteristics of compacted Chinese Gaomiaozi bentonite GMZ01

Gaomiaozi bentonite (GMZ01) has been decided upon as the first option for use as buffer/backfill materials in the deep disposal of high-level radioactive waste in China. The basic functions of the materials used in the waste repositories request among others a sufficient swelling pressure and low hydraulic conductivity in order to provide long-term stability to the barrier system under environmental pressure and behavior of the waste loads. As such, it is necessary to investigate the influence of initial dry density on the swelling properties of Gaomiaozi bentonite (GMZ01) in order to achieve better design of buffer/backfill materials. In this study the swelling pressure of GMZ01 has been studied and analyzed by multi and one-step wetting constant volume tests with five different dry densities (1.15, 1.35, 1.50, 1.60 and 1.75mg/m3). Results show that swelling pressure changes with time nonlinearly, while there is a linear relationship between time/swelling pressure and time. Curves of swelling pressure and the amount of absorbed water varying with time can be classified into typical phases. For the GMZ01 tested here, the initial dry density is an important factor influencing the swelling pressure. The results show that there is an exponential relationship between swelling pressure and dry density. Moreover, comparison was done between the experimental swelling pressure results of used GMZ bentonite in this study and other bentonites cited in literature: (i) other GMZ׳s and (ii) different types of bentonites proposed as buffer/backfill materials (i.e., MX80, Kunigel, Montigel, and Calcigel). The effect on the microstructure of the density and the wetting under the constant volume condition (after the swelling pressure test) has been investigated by studying the results of pore size distribution for GMZ01 by using the mercury intrusion porosimetry (MIP) test and the environmental scanning electron microscope (ESEM) photos. Finally, two different theoretical concepts were used to estimate the swelling pressure (the modified DDL and thermodynamics approaches). The results of the two methods show that the swelling pressure results compare relatively well with the experimental data for the GMZ bentonite.

On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China

Underground research laboratories (URLs), including “generic URLs” and “site-specific URLs”, are underground facilities in which characterisation, testing, technology development, and/or demonstration activities are carried out in support of the development of geological repositories for high-level radioactive waste (HLW) disposal. In addition to the generic URL and site-specific URL, a concept of “area-specific URL”, or the third type of URL, is proposed in this paper. It is referred to as the facility that is built at a site within an area that is considered as a potential area for HLW repository or built at a place near the future repository site, and may be regarded as a precursor to the development of a repository at the site. It acts as a “generic URL”, but also acts as a “site-specific URL” to some extent. Considering the current situation in China, the most suitable option is to build an “area-specific URL” in Beishan area, the first priority region for China's high-level waste repository. With this strategy, the goal to build China's URL by 2020 may be achieved, but the time left is limited.

Outline of Research on Interactions between Microorganisms and Geological Disposal of High-Level Radioactive Waste

At present, in the geological disposal domain of high-level radioactive waste, little is known about microorganisms in deep underground geological environment in our country. This paper introduces some interactions between microbiological and geological disposal of high-level radioactive waste. There is a huge biosphere in the deep underground, mainly held by extremophiles. Microorganisms can influence the waste geological disposal environment in two aspects. On the one hand, the storehouse security will be confronted with serious problems of microorganisms because of their material corrosion capability. The main species of corrosion microorganisms include sulfate reducing bacteria, sulfur-oxidizing bacteria, saprophytic bacteria, iron bacteria and fungi. About research development on interactions between microbiological and geological disposal of high-level radioactive waste in China and abroad, foreign countries started early. Specialized research field has been formed and many achievements has been made by a series of research in Sweden, US, France, Canada, and so on. But relevant study is very few in our country. Therefore, there are special necessity and urgency to carry out this research.

RESEARCH ON PITTING CORROSION BEHAVIOR OF COPPER IN THE SOLUTION WITH HCO 3 - AND Cl -

The strategy for disposal of high-level radioactive waste in china is to enclose the spent nuclear fuel in sealed metal canisters which are embedded in bentonite clay hundreds meters down in the bed-rock.The choice of container material depends largely on the redox conditions and the aqueous environment of the repository.One of the choices for the fabrication of waste canisters is copper,because it is thermodynamically stable under the saline,anoxic conditions over the large majority of the container lifetime.However,in the early aerobic phase of the geological disposal the corrosion of copper could take place,and the corrosion behavior of copper would be influenced by the complex chemical conditions of groundwater markedly.Pitting corrosion of copper often takes place in power plants or air-conditioning condensate water.The corrosion environment usually contains HCO_3~-, SO_4~(2-)and Cl~-.In the early stage of geological disposal,if the aerobic water with HCO_3~-,SO_4~(2-)and Cl~- immersion repository,the pitting corrosion of copper may occur.Some researchers believed that SO_4~(2-)and Cl~- would promote the occurrence of pitting corrosion of copper,and HCO_3~- will lead to surface passivation and inhibit pitting.It is considered that in the solution with HCO_3~- and SO_4~(2-), HCO_3~- could firstly promote and then inhibit pitting.However,there is no systematic work about pitting in the solution with HCO_3~- and Cl~-.In this work,the cycle polarization behavior and surface morphology of pitting on copper has been investigated in HCO_3~- and Cl~- mixed solution,respectively by electrochemical cyclic polarization test and SEM.The results showed that the circular polarization curves of copper could be divided into four types.The pitting on the surface of copper occurs only in the environment with both Cl~- and HCO_3~-.In the area of active dissolve pitting,the pitting susceptibility increased with the increase of concentration of Cl~-,while it increased then decreased with the increase of the concentration of HCO_3~-.In the area of passive film rupture pitting area,pitting susceptibility increased with the increase of concentration of Cl~- and with the decrease of the concentration of HCO_3~-.