Search Results

You are looking at 1 - 10 of 114 items for :

  • Chemistry and Chemical Engineering x
  • All content x
Clear All

inhibitor in diminishing self-heating phenomena of Indian coal . J Mines Metals Fuels 50 : 356 – 359 . 5. Taraba , B , Peter , R , Slovák , V 2011 Calorimetric investigation of chemical

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Vladár, D. Nikodemová, I. Gomola, M. Vičanová, and M. Fojtík

Abstract  

Conclusions from monitoring of two main natural sources of human exposure in Slovak Republic are presented: the outdoor photon dose equivalent rateH x and indoor radon volume activity. Dose equivalent rates were determinated by on-line monitoring network IRIS, and off-line territorial TLD network as well. Radon volume activity was determinated by solid state track detectors CR-39. The annual effective dose from external exposure, determinated by IRIS network, is equal to 816 mSv · y–1. Lower value, 618 mSv · y–1 had been found from TLD network data. The effective dose caused by inhalation of radon and its progeny lays within the range 1.7 to 5.0 mSv · y–1. Such broad range is caused mainly by uncertainties in calculation procedures of radon effective doses.

Restricted access

Abstract  

Sorption of Sr on five Slovak bentonites of deposits has been studied with the use of batch technique. In the experiments there have been used natural, chemically modified and irradiated samples, in three different kinds of grain size. The pH influence on sorption of strontium on bentonites, pH change after sorption and influence of competitive ions have been studied. Distribution ratios have been determined for bentonite–strontium solution system as a function of contact time, pH and sorbate concentration. The data have been interpreted in term of Langmuir isotherm. The uptake of Sr has been rapid and the sorption of strontium has increased by increasing pH. The percentage sorption has decreased with increasing metal concentrations. The pH value after sorption for the natrificated forms of bentonite starts already in the alkaline area and moves to the higher values. For the natural bentonites the values occur in the neutral or in the acidic area. Sorption of Sr has been suppressed by presence of competitive cations as follows: Ba2+ > Ca2+ > Mg2+ > NH4 + > K> Na+. By sorption on natrificated samples colloidal particles and pH value increase have been formed. The bentonite exposure as a result of interaction of γ-rays has led to expansion of the specific surface, increasing of the sorption capacity and to the change in the solubility of the clay materials.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Galamboš, M. Daňo, O. Rosskopfová, F. Šeršeň, J. Kufčáková, R. Adamcová, and P. Rajec

Abstract  

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (137Cs and 90Sr), prior to and after irradiation of bentonites with a 60Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelšový potok, Kopernica, Lastovce, Lieskovec and Dolná Ves. The EPR spectra of bentonites from deposits Jelšový potok and Lieskovec with absorbed doses of 104 and 105 Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe–bentonite from deposit Lieskovec and Ca–Mg–bentonite from deposit Jelšový potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.

Restricted access

Abstract  

Ion exchange isotherms have been measured and plotted for the uptake of cesium, barium, cobalt, zinc, silver and amonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian origin selectively for both the natural and near homoionic Na form as well, using the radioanalytical determination. The higher quality clinoptilolite-rich tuff has been proven to be effective for a potential radionucleides removal in native form according to the following selectivity sequence: Ag+,Ba2,Cs+>NH4 +>Co2+, while parent tuff in Na exchanged variety exhibited a little different sequence according to: Ag+ > NH4 + > Ba2+ > Cs+. The raw and Na exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity : Ag+ > Zn2+ > Cs+, Ba2+ > Co2+ and Ag+ > Zn2+.

Restricted access

Abstract  

The basic strategic aims in the field of managing high-level radioactive waste and liquidation of nuclear power plants are all contained in the Energy policy of the Slovak Republic. Its aim is to resolve the concept of the backside of the nuclear energetics fuel cycle—long-term deposition of high-level radioactive waste and spent nuclear fuel (SNF). The most important form of high-level radioactive waste and SNF long-term deposition is their deposition in deep geological formations created by natural as well as engineering barriers used to isolate the long-lived radionuclides from the biosphere. The basic components of these barriers are clays, of which bentonite is generally referred to as the most suitable clay material. There are a few significant bentonite deposits in the Slovak Republic: Jelšový potok, Kopernica, Lastovce, Lieskovec, Dolná Ves. The review article summarizes the information on geotechnical properties of Slovak bentonites published up-to-date, which is inevitable to know for the intention of their use. It highlights the advantages and shows drawbacks of five Slovak deposits. It suggests further research direction, to draw a thorough hydraulical, microbial and radiation profile of Slovak bentonites.

Restricted access

Abstract  

The total -radioactivity of dry, wet and cumulative fallout and the radioactivity of cow milk was measured in Bratislava in the first month after the Chernobyl accident. The obtained results are in good agreement with the results of the monitoring net in Slovakia.

Restricted access

Abstract  

The building materials and products whose content of natural radionuclides are contributors to the radiation exposure of the population. In this study several types of building materials used for construction of living buildings in Slovakia were examined. The concentrations of natural radionuclides (226Ra,232Th and40K) were determined by -ray spectrometry with an HPGe detector. In the second part of the work, sixty samples of building products (panel), used for dwelling construction in several towns in Slovakia, were analysed. The concentration of natural radionuclides and the radium equivalent activity content in the inner-and outerside of the wall were estimated. The results were used for the calculation of the annual mean effective photon dose rates, by the model and calculation procedure of KRISIUK and KARPOV.

Restricted access

Abstract  

The results of radiocesium activity of some foodstuffs imported to the Slovak Republic in the period from January 1988 to July 1995 are presented. The analysed samples were homogenized, packed into 0.451 Marinelli beakers and then measured by direct semiconductor, -spectrometry for 10 000–50 000 seconds. The levels of137Cs in various foodstuffs varied quite widely from Minimum Detectable Activity (MDA)=0.4 to 80.2 Bq/kg. Concentrations of137Cs in fish and fish products were in general higher than those in beef and pork.

Restricted access

Abstract  

Radioecologically the most important radionuclide generated by the Chernobyl accident is137Cs at present. The actual geographic distribution of the137Cs concentrations in the soil in Central Slovakia for 1995 is presented. On the basis of measured data the relationships between137Cs concentration in soil profiles and some local parameters (average precipitation, specific activity of40K, soil types) was studie. Some problems in the modelling and prediction of137Cs migration in soils are discussed too. The activity of137Cs was measured at 45 sites. Approximately 66% of total deposition of137Cs in the upper 10 cm of soil.

Restricted access