Lyuben Dobrev - Academia.edu (original) (raw)
Papers by Lyuben Dobrev
Dokladi na Bʺlgarskata akademiâ na naukite, Dec 20, 2023
In reactor dosimetry it is well known that the empirical determination of the neutron flux is per... more In reactor dosimetry it is well known that the empirical determination of the neutron flux is performed by determining the isotope 54 Mn generated in a (n,γ) nuclear reaction. This study presents a procedure for the simultaneous determination of the radioisotopes 54 Mn and 59 Fe, developed to obtain more complete information about the process. The basis of the method is the irradiation of iron-plate detectors with a neutron flux generated in a VVER-type nuclear reactor and subsequent gamma spectrometric analysis of the samples to determine the two radionuclides obtained in two simultaneous (n,x) and (n,γ) nuclear reactions. A very important stage of the assay is the preliminary radiochemical treatment of the samples involving the removal of oxides and corrosion products and the dissolution of the plates in strong mineral acids. The results show that our approach of simultaneous determination of 54 Mn and 59 Fe significantly improves the time of analyses, reduces the radiation dose, and increases the accuracy and efficiency of neutron fluence determination. The procedures are relatively easy to perform and are suitable for application in routine studies.
Journal of Radioanalytical and Nuclear Chemistry
Journal of Radioanalytical and Nuclear Chemistry
Proceedings of the Bulgarian Academy of Sciences
This paper presents data on the content of toxic elements (Mn, Ni, Zn, Cu, Pb, As, Cr, Cd and Co)... more This paper presents data on the content of toxic elements (Mn, Ni, Zn, Cu, Pb, As, Cr, Cd and Co), technogenic (137Cs, 134Cs) and natural radionuclides of the 238U and 232Th series (234Th, 226Ra, 210Pb, 232Th) and 40K in sediments collected from ten sampling stations along the northern Bulgarian Black Sea coast for a period of more than twenty years. Measurements were made by Gamma Spectrometry and Inductively Coupled Plasma Mass Spectrometry. The results show that the nuclides and toxic elements concentration in sediments strongly depend on the sediments nature. The obtained data create a database on the concentrations of radionuclides and toxic elements in sediments from the Northern Bulgarian Black Sea coast and can be used for assessment of the ecological status of the marine environment along the whole northern coastal zone.
Journal of Soils and Sediments
Journal of Hazardous Materials, 2021
Not only does pyrolysis recover energy and value-added by-products but also reduces waste stream ... more Not only does pyrolysis recover energy and value-added by-products but also reduces waste stream volume. The low volatiles and high ash contents of textile dyeing sludge (TDS) limit its mono-pyrolysis performance. This study aimed to conduct an in-depth analysis of its co-pyrolytic performance with cattle manure (CM). The co-pyrolysis enhanced the volatiles emission from the early devolatilization stage whose reaction mechanism shifted from a diffusion model to a reaction-order model. The further cracking of macromolecular materials was mainly elucidated by the reaction-order model. The temperature dependency of the co-pyrolytic gases was of the following order: aliphatic hydrocarbons > CO2 > alcohols, phenols, ethers, aldehydes, ketones, and carboxylic acids. The main co-pyrolytic volatile products were coumaran and 4-vinylguaiacol. The relative content of guaiacol-type components could be enhanced by co-pyrolysis and lowering the operational temperature to 450 °C. The interaction of co-pyrolysis enriched the char aromaticity. Our findings provide practical insights into the control and application opportunities and limitations on the high value-added energy and products from the co-pyrolysis of TDS and CM.
Radiation Protection Dosimetry
The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have be... more The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have been determined for the first time in drinking water from certain sources in Southern Bulgaria using nuclear and radiochemical methods. The results obtained for the water samples vary in the intervals 0.6–678 mBq l−1 for 238U, 1.4–1484 mBq l−1 for 234U, <0.3–13.6 mBq l−1 for 210Po and 1.04–10.6 for the 234U/238U ratio. The annual effective dose from 238U, 234U and 210Po ranges from 1.09 to 44.1 μSv y−1, 0.78 to 46.8 μSv y−1 and 0.77 to 62.8 μSv y−1 for infants, children and adults, respectively. The annual effective dose due to consumption of drinking water is below the individual dose criterion of 100 μSv y−1 recommended by the World Health Organization. The natural radioactivity of the water sources investigated is below the national and international limits.
Man-made transuranic elements have been released into the environment since the use of nuclear we... more Man-made transuranic elements have been released into the environment since the use of nuclear weapons and nuclear tests. Other releases into the environment have been associated with nuclear fuel cycles and some accidents but also through the active dumping of wastes into oceans. Most of the isotopesof these elements are alpha-active with long physical and biological half-lives, which make them highly radiotoxic. Brief description and classification of the Radioactive Waste produced in the nuclear electricity generation chain is given. A procedure for determination of Plutonium, Americium and Curium isotopes in Low Level Radioactive Waste (LL LRAW) was developed and applied on alkaline waste from Nuclear Power Plant (NPP) Kozloduy in Bulgaria. This waste has been collected during more than thirty years of operation of NPP Kozloduy. The proposed procedure was a part of inventory waste characterization of 15 storage tanks that involved determination of eighteen isotopes. The modifica...
2021 6th International Symposium on Environment-Friendly Energies and Applications (EFEA)
Natural Science and Advanced Technology Education
The radioactivity of selected sources of drinking water in Southern Bulgaria was investigated usi... more The radioactivity of selected sources of drinking water in Southern Bulgaria was investigated using 238U, 234U and 210Po activity measurements and dose calculation, respectively. The activities of 238U, 234U and 210Po varied from 226 to 826 mBq/L, 274 to 1623 mBq/L and < 0.6 to 25.5 mBq/L, respectively, being lower then derived concentrations for radioactivity in water intended for human consumption of the considered radionuclides, given in EC Directive 2013/51/EURATOM. In some drinking waters the mass concentration of natural uranium exceeded the set maximum chemical concentration level of 0.030 mg/L. A radioactive disequilibrium between 234U and 238U in water was detected. Based on the radionuclide activity concentrations total annual effective ingestion doses for adults, as well as contribution of each particular radionuclide to the total doses, were assessed and discussed. Тhe lowest contribution to the annual effective doses was found for 210Po and the highest for 234U. The ...
Journal of Radioanalytical and Nuclear Chemistry
По-ниското произведение на разтворимост на AgI прави възможно очистване на утайката от AgI чрез п... more По-ниското произведение на разтворимост на AgI прави възможно очистване на утайката от AgI чрез последователно и неколкократно третиране с амоняк, вода и етилов алкохол.
Dokladi na Bʺlgarskata akademiâ na naukite, Dec 20, 2023
In reactor dosimetry it is well known that the empirical determination of the neutron flux is per... more In reactor dosimetry it is well known that the empirical determination of the neutron flux is performed by determining the isotope 54 Mn generated in a (n,γ) nuclear reaction. This study presents a procedure for the simultaneous determination of the radioisotopes 54 Mn and 59 Fe, developed to obtain more complete information about the process. The basis of the method is the irradiation of iron-plate detectors with a neutron flux generated in a VVER-type nuclear reactor and subsequent gamma spectrometric analysis of the samples to determine the two radionuclides obtained in two simultaneous (n,x) and (n,γ) nuclear reactions. A very important stage of the assay is the preliminary radiochemical treatment of the samples involving the removal of oxides and corrosion products and the dissolution of the plates in strong mineral acids. The results show that our approach of simultaneous determination of 54 Mn and 59 Fe significantly improves the time of analyses, reduces the radiation dose, and increases the accuracy and efficiency of neutron fluence determination. The procedures are relatively easy to perform and are suitable for application in routine studies.
Journal of Radioanalytical and Nuclear Chemistry
Journal of Radioanalytical and Nuclear Chemistry
Proceedings of the Bulgarian Academy of Sciences
This paper presents data on the content of toxic elements (Mn, Ni, Zn, Cu, Pb, As, Cr, Cd and Co)... more This paper presents data on the content of toxic elements (Mn, Ni, Zn, Cu, Pb, As, Cr, Cd and Co), technogenic (137Cs, 134Cs) and natural radionuclides of the 238U and 232Th series (234Th, 226Ra, 210Pb, 232Th) and 40K in sediments collected from ten sampling stations along the northern Bulgarian Black Sea coast for a period of more than twenty years. Measurements were made by Gamma Spectrometry and Inductively Coupled Plasma Mass Spectrometry. The results show that the nuclides and toxic elements concentration in sediments strongly depend on the sediments nature. The obtained data create a database on the concentrations of radionuclides and toxic elements in sediments from the Northern Bulgarian Black Sea coast and can be used for assessment of the ecological status of the marine environment along the whole northern coastal zone.
Journal of Soils and Sediments
Journal of Hazardous Materials, 2021
Not only does pyrolysis recover energy and value-added by-products but also reduces waste stream ... more Not only does pyrolysis recover energy and value-added by-products but also reduces waste stream volume. The low volatiles and high ash contents of textile dyeing sludge (TDS) limit its mono-pyrolysis performance. This study aimed to conduct an in-depth analysis of its co-pyrolytic performance with cattle manure (CM). The co-pyrolysis enhanced the volatiles emission from the early devolatilization stage whose reaction mechanism shifted from a diffusion model to a reaction-order model. The further cracking of macromolecular materials was mainly elucidated by the reaction-order model. The temperature dependency of the co-pyrolytic gases was of the following order: aliphatic hydrocarbons > CO2 > alcohols, phenols, ethers, aldehydes, ketones, and carboxylic acids. The main co-pyrolytic volatile products were coumaran and 4-vinylguaiacol. The relative content of guaiacol-type components could be enhanced by co-pyrolysis and lowering the operational temperature to 450 °C. The interaction of co-pyrolysis enriched the char aromaticity. Our findings provide practical insights into the control and application opportunities and limitations on the high value-added energy and products from the co-pyrolysis of TDS and CM.
Radiation Protection Dosimetry
The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have be... more The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have been determined for the first time in drinking water from certain sources in Southern Bulgaria using nuclear and radiochemical methods. The results obtained for the water samples vary in the intervals 0.6–678 mBq l−1 for 238U, 1.4–1484 mBq l−1 for 234U, <0.3–13.6 mBq l−1 for 210Po and 1.04–10.6 for the 234U/238U ratio. The annual effective dose from 238U, 234U and 210Po ranges from 1.09 to 44.1 μSv y−1, 0.78 to 46.8 μSv y−1 and 0.77 to 62.8 μSv y−1 for infants, children and adults, respectively. The annual effective dose due to consumption of drinking water is below the individual dose criterion of 100 μSv y−1 recommended by the World Health Organization. The natural radioactivity of the water sources investigated is below the national and international limits.
Man-made transuranic elements have been released into the environment since the use of nuclear we... more Man-made transuranic elements have been released into the environment since the use of nuclear weapons and nuclear tests. Other releases into the environment have been associated with nuclear fuel cycles and some accidents but also through the active dumping of wastes into oceans. Most of the isotopesof these elements are alpha-active with long physical and biological half-lives, which make them highly radiotoxic. Brief description and classification of the Radioactive Waste produced in the nuclear electricity generation chain is given. A procedure for determination of Plutonium, Americium and Curium isotopes in Low Level Radioactive Waste (LL LRAW) was developed and applied on alkaline waste from Nuclear Power Plant (NPP) Kozloduy in Bulgaria. This waste has been collected during more than thirty years of operation of NPP Kozloduy. The proposed procedure was a part of inventory waste characterization of 15 storage tanks that involved determination of eighteen isotopes. The modifica...
2021 6th International Symposium on Environment-Friendly Energies and Applications (EFEA)
Natural Science and Advanced Technology Education
The radioactivity of selected sources of drinking water in Southern Bulgaria was investigated usi... more The radioactivity of selected sources of drinking water in Southern Bulgaria was investigated using 238U, 234U and 210Po activity measurements and dose calculation, respectively. The activities of 238U, 234U and 210Po varied from 226 to 826 mBq/L, 274 to 1623 mBq/L and < 0.6 to 25.5 mBq/L, respectively, being lower then derived concentrations for radioactivity in water intended for human consumption of the considered radionuclides, given in EC Directive 2013/51/EURATOM. In some drinking waters the mass concentration of natural uranium exceeded the set maximum chemical concentration level of 0.030 mg/L. A radioactive disequilibrium between 234U and 238U in water was detected. Based on the radionuclide activity concentrations total annual effective ingestion doses for adults, as well as contribution of each particular radionuclide to the total doses, were assessed and discussed. Тhe lowest contribution to the annual effective doses was found for 210Po and the highest for 234U. The ...
Journal of Radioanalytical and Nuclear Chemistry
По-ниското произведение на разтворимост на AgI прави възможно очистване на утайката от AgI чрез п... more По-ниското произведение на разтворимост на AgI прави възможно очистване на утайката от AgI чрез последователно и неколкократно третиране с амоняк, вода и етилов алкохол.