Madlena Tsvetkova | Bulgarian Academy of Sciences (original) (raw)

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Papers by Madlena Tsvetkova

Списание на Българското геологическо дружество, Nov 30, 2023

Previous analyses of the Sumer Formation sediments have been limited to samples up to 400 m deep ... more Previous analyses of the Sumer Formation sediments have been limited to samples up to 400 m deep near the village of Varbitsa. This study extends the investigation, exploring the mineral composition and carbonate content of the sediments near the village of Sumer. Samples were collected from two outcrops at the Montana-Vratsa Road junction (C-1) and the Shugavitsa river basin (C-2). Both outcrops revealed a quartz and calcite content of approximately 75-80%, with a significant variance in calcite levels: 11.4% at C-1 and 31.3% at C-2. Illite (4.5%) and kaolinite (2%), these clay minerals essential for the marls' sorption properties, were only detected in C-1 samples. The C-2 outcrop exhibits a higher carbonate content (17.65%) compared to C-1 (10.85%). These findings mirror the mineral composition trends observed near Varbitsa, where the content of illite and kaolinite increases with depth. The results provide valuable data for future geochemical and geotechnical evaluations pertinent to the development of geological repositories.

Review of the Bulgarian Geological Society, 2023

When selecting a site for the construction of a repository for high-level radioactive waste (HLW)... more When selecting a site for the construction of a repository for high-level radioactive waste (HLW), the mineral composition of the geological environment is of primary importance. The content and type of the clay component and its structure have important implications for the insulating and sorption properties of the host rock and migration of radionuclides. In such previous studies in Bulgaria for site selection of the geological disposal of HLW the Lower Cretaceous marls (argillites) of the Sumer Formation (Western Pre-Balkans) were considered as ones of the prospective formations. This paper presents data about grain size distribution and mineral composition of the marls (argillites) at depths of 50 m and 400 m. A study was conducted on the structure of samples taken at a depth of 800 m from the Golyamo Pestene borehole. The obtained results are compared in order to clarify the homogeneity of the formation in depth. An increase in the clay fraction and the illite contained in it a...

Review of the Bulgarian Geological Society, 2022

The construction of an underground research laboratory (URL) precedes the construction of a repos... more The construction of an underground research laboratory (URL) precedes the construction of a repository for geological disposal of а radioactive waste. The article considers the types of laboratories, their main objectives and tasks. Based on a comparative analysis between the sites selected as prospective for geological disposal in Bulgaria, the Sumer site in the Sumer Formation is proposed for further investigation as an alternative for URL construction.

Geologica Balcanica, 2022

Geological settings are of major importance in selecting appropriate environment for disposal of ... more Geological settings are of major importance in selecting appropriate environment for disposal of high-level radioactive waste from nuclear power plants. Clay rocks are preferred in a number of countries as a suitable host rocks due to their insulating properties and ability to self- seal cracks and other disturbances. In Bulgaria, on the basis of multi-criterion comparative analysis, several prospective sites have been selected for further consideration. One of them is the Varbitsa site located in the Fore-Balkan Unit. The marls of the Sumer Formation are the host rock. Similar clay host rocks for high-level radioactive waste disposal have been extensively studied in France, Switzerland and Belgium. In this context, the experience gained in these countries is particularly valuable for the further development of the geological disposal in Bulgaria. The current paper presents a comparison between the geological settings of the Varbitsa site (NW Bulgaria) and the Bure site (SE France),...

Geologica Balcanica, 2020

In Bulgaria, from the preliminary analyses performed for site selection of deep geological dispos... more In Bulgaria, from the preliminary analyses performed for site selection of deep geological disposal of high-level waste (HLW) and spent fuel (SF), it was concluded that the most promising host rocks are the argillaceous sediments of the Sumer Formation (Lower Cretaceous), situated in the Western Fore-Balkan Mts. The present paper aims to compare the transport of three major radionuclides from a hypothetical radioactive waste disposal facility, which incorporates an engineering barrier of bentonite into the argillaceous (marl) medium. The simulations were performed by using HYDRUS-1D computer programme. The results are used for a preliminary estimation of argillaceous sediments as a host rock for geological disposal of HLW.

BULGARIAN GEOLOGICAL SOCIETY, National Conference with international participation “GEOSCIENCES 2016”, 2016

Previous studies on the problem of geological disposal of high level radioactive waste (HLW) in ... more Previous studies on the problem of geological disposal
of high level radioactive waste (HLW) in the country,
carried out mostly by Geological Institute, BAS
(Kozhukharov et al., 2000f1; Evstatiev, Kozhukharov,
2001; Karastanev et al., 2010f 2), selected marls from
the Sumer Formation as one of the most suitable host
rocks for the purpose of constructing a deep geological
repository.
In this study the mineral composition and effective
porosity of marl from the Sumer Formation have been
investigated as the determining characteristics for retardation
capacity of the host environment against the
radionuclide migration.

REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, 2019

The study deals with unsaturated hydraulic model of the marls from Sumer Formation in connection ... more The study deals with unsaturated hydraulic model of the marls from Sumer Formation in connection with geological disposal of radioactive waste. The model profile of 400 m in depth from the surface was implemented in HYDRUS-1D code. Two simulation periods were chosen – 1 000 and 10 000 years. In both simulations, the results showed that after 940 years of modeling the bottom flux tends to stabilization regime when 10% of the rainfalls were used as an infiltration rate.

Списание на Българското геологическо дружество, Nov 30, 2023

Previous analyses of the Sumer Formation sediments have been limited to samples up to 400 m deep ... more Previous analyses of the Sumer Formation sediments have been limited to samples up to 400 m deep near the village of Varbitsa. This study extends the investigation, exploring the mineral composition and carbonate content of the sediments near the village of Sumer. Samples were collected from two outcrops at the Montana-Vratsa Road junction (C-1) and the Shugavitsa river basin (C-2). Both outcrops revealed a quartz and calcite content of approximately 75-80%, with a significant variance in calcite levels: 11.4% at C-1 and 31.3% at C-2. Illite (4.5%) and kaolinite (2%), these clay minerals essential for the marls' sorption properties, were only detected in C-1 samples. The C-2 outcrop exhibits a higher carbonate content (17.65%) compared to C-1 (10.85%). These findings mirror the mineral composition trends observed near Varbitsa, where the content of illite and kaolinite increases with depth. The results provide valuable data for future geochemical and geotechnical evaluations pertinent to the development of geological repositories.

Review of the Bulgarian Geological Society, 2023

When selecting a site for the construction of a repository for high-level radioactive waste (HLW)... more When selecting a site for the construction of a repository for high-level radioactive waste (HLW), the mineral composition of the geological environment is of primary importance. The content and type of the clay component and its structure have important implications for the insulating and sorption properties of the host rock and migration of radionuclides. In such previous studies in Bulgaria for site selection of the geological disposal of HLW the Lower Cretaceous marls (argillites) of the Sumer Formation (Western Pre-Balkans) were considered as ones of the prospective formations. This paper presents data about grain size distribution and mineral composition of the marls (argillites) at depths of 50 m and 400 m. A study was conducted on the structure of samples taken at a depth of 800 m from the Golyamo Pestene borehole. The obtained results are compared in order to clarify the homogeneity of the formation in depth. An increase in the clay fraction and the illite contained in it a...

Review of the Bulgarian Geological Society, 2022

The construction of an underground research laboratory (URL) precedes the construction of a repos... more The construction of an underground research laboratory (URL) precedes the construction of a repository for geological disposal of а radioactive waste. The article considers the types of laboratories, their main objectives and tasks. Based on a comparative analysis between the sites selected as prospective for geological disposal in Bulgaria, the Sumer site in the Sumer Formation is proposed for further investigation as an alternative for URL construction.

Geologica Balcanica, 2022

Geological settings are of major importance in selecting appropriate environment for disposal of ... more Geological settings are of major importance in selecting appropriate environment for disposal of high-level radioactive waste from nuclear power plants. Clay rocks are preferred in a number of countries as a suitable host rocks due to their insulating properties and ability to self- seal cracks and other disturbances. In Bulgaria, on the basis of multi-criterion comparative analysis, several prospective sites have been selected for further consideration. One of them is the Varbitsa site located in the Fore-Balkan Unit. The marls of the Sumer Formation are the host rock. Similar clay host rocks for high-level radioactive waste disposal have been extensively studied in France, Switzerland and Belgium. In this context, the experience gained in these countries is particularly valuable for the further development of the geological disposal in Bulgaria. The current paper presents a comparison between the geological settings of the Varbitsa site (NW Bulgaria) and the Bure site (SE France),...

Geologica Balcanica, 2020

In Bulgaria, from the preliminary analyses performed for site selection of deep geological dispos... more In Bulgaria, from the preliminary analyses performed for site selection of deep geological disposal of high-level waste (HLW) and spent fuel (SF), it was concluded that the most promising host rocks are the argillaceous sediments of the Sumer Formation (Lower Cretaceous), situated in the Western Fore-Balkan Mts. The present paper aims to compare the transport of three major radionuclides from a hypothetical radioactive waste disposal facility, which incorporates an engineering barrier of bentonite into the argillaceous (marl) medium. The simulations were performed by using HYDRUS-1D computer programme. The results are used for a preliminary estimation of argillaceous sediments as a host rock for geological disposal of HLW.

BULGARIAN GEOLOGICAL SOCIETY, National Conference with international participation “GEOSCIENCES 2016”, 2016

Previous studies on the problem of geological disposal of high level radioactive waste (HLW) in ... more Previous studies on the problem of geological disposal
of high level radioactive waste (HLW) in the country,
carried out mostly by Geological Institute, BAS
(Kozhukharov et al., 2000f1; Evstatiev, Kozhukharov,
2001; Karastanev et al., 2010f 2), selected marls from
the Sumer Formation as one of the most suitable host
rocks for the purpose of constructing a deep geological
repository.
In this study the mineral composition and effective
porosity of marl from the Sumer Formation have been
investigated as the determining characteristics for retardation
capacity of the host environment against the
radionuclide migration.

REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, 2019

The study deals with unsaturated hydraulic model of the marls from Sumer Formation in connection ... more The study deals with unsaturated hydraulic model of the marls from Sumer Formation in connection with geological disposal of radioactive waste. The model profile of 400 m in depth from the surface was implemented in HYDRUS-1D code. Two simulation periods were chosen – 1 000 and 10 000 years. In both simulations, the results showed that after 940 years of modeling the bottom flux tends to stabilization regime when 10% of the rainfalls were used as an infiltration rate.