A comparison of different detection techniques for 137Cs measurements of cattle in vivo.

Agricultural lands with farm animals (e.g. cattle) can be significantly affected by radioactive contamination following nuclear or radiation accidents. In order to optimise the techniques for measuring 137Cs in contaminated cattle, selected radiation detectors have been tested and calibrated using volumetric radiation sources. In addition, a mathematical phantom of a cow was created within Monte Carlo simulations. The main aim of the research was to propose a method for making rapid measurements of 137Cs in cattle in vivo/in situ and to select the most suitable measurement set-up. Measurements of contaminated cattle in vivo were carried out in Belarus with one selected detector, and were then compared with measurements of meat in a laboratory and with measurements of a control group of cows. The proposed measurement method was also tested on measurements of 137Cs in wild boars in Czechia with higher levels of the 137Cs activity.

Aggregated transfer factors of fresh Cs and Sr pollution to various vegetables from six common European soils - mesocosm experiment.

Aggregated transfer factors (Tag) were identified for three common vegetables grown in six common European soils freshly contaminated by 134Cs and 85Sr. The experiment was carried out as a mesocosm experiment in pots with an average soil weight of 15.8 kg per pot. The vegetables were grown one after the other during one vegetation season, in the order lettuce, onion, and radish (the order usually applied in private gardens and small farms). Despite the fact that lettuce was grown in the most contaminated soil, it had the lowest Tag (in m2/kg) of both radionuclides (3.6E-4 for Cs, 2.0E-2 for Sr), while onion had 6.4E-3 for Cs and 3.2E-2 for Sr and radish had 1.9E-3 for Cs and 8.1E-2 for Sr. Potassium supply did not show any statistically significant effect on Cs Tag; there was a significant impact of K on the decrease in Sr Tag. The experiments indicated that Tag is more affected by plant species than by soil type; therefore, selection of plants with a lower capacity to uptake radionuclides may be an important measure to reduce food contamination and thus minimize the committed effective dose.

Anaerobic digestion: A promising technology of utilizing radioactively contaminated plant biomass.

Anaerobic digestion (AD) is a widely used technology that allows for the reprocessing and reduction of waste biomass. A study was conducted to see if the AD technology might be used to process radioactively polluted agricultural biomass. For this purpose, laboratory tests were carried out with a 20-liter model biogas plant (BGP) with the radionuclide 134Cs and operational tests with the South Bohemian commercial biogas plant monitoring the radionuclide 137Cs. The activities of 134Cs in inputs, contaminated grass or maize silage and in emerging fractions were investigated in the model fermenter. The activity of 134Cs in the dry matter during the fermentation process increased by 46% on average, which corresponds to a reduction of dry matter by 43% due to the production of biogas. 137Cs activities were measured in commercial BGP maize, grass, and whole plant silage, wheat, digestate, biogas, and aerosol samples. The commercial BGP fermentation process was more efficient, with an 80% reduction in dry mass weight. Dry biomass (1.37 Bq/kg) had a 137Cs massic activity that was 4.4 times lower than the activity of dry digestate mass (6.01 Bq/kg). The activity of the 137Cs in biogas aerosol was 1.1 × 10-7 Bq/m3 or less, and the decontamination factor was 6.9 × 106 or greater. Most Cs remain in the digestate. No other ways of radioactivity leakage have been identified.

DETERMINING THE TRANSFER FACTORS FOR ESTIMATES OF THE RADIATION CONTAMINATION OF AGRICULTURAL CROPS.

The study aims to provide a basis for measures reducing the consequences of a nuclear accident in its late phase, when plant contamination occurs mainly through the root system. Samples of the above-ground biomass of crops and soil were taken in 2020 in the vicinity of the Temelín and Dukovany nuclear power plants (Czech Republic). The 137Cs activities were determined using gamma spectrometry, and the 90Sr activities were measured through beta radiation. From the obtained values, the radionuclide transfer factors (TFs) from soil to crop biomass were calculated. The average area activity of 137Cs in the soil around Dukovany and Temelín was 1700 and 2400 Bq m-2, respectively. The average area activity of 90Sr around Dukovany and Temelín was 211 and 184 Bq m-2, respectively. The TF 137Cs ranged from < 6.3 × 10-6 to 7.9 × 10-3, with a mean of 3.5 × 10-4 m2 kg-1, and the TF 90Sr ranged from 2.7 × 10-4 to 6 × 10-2, with a mean of 1.7 × 10-2 m2 kg-1.

EXPOSURE OF THE BIOGAS STATION OPERATORS WORKING WITH CONTAMINATED BIOMASS.

The article deals with evaluation of irradiation of an operator of a 1 MW biogas station (BGS), processing silage plant biomass contaminated by 137Cs and 134Cs. External irradiation and internal irradiation by the means of aerosol particles inhalation were considered. For calculation of the external irradiation, a BGS model was created in the MCNP. The calculated total committed effective doses received by the operator during annual handling of biomass contaminated by 1 kBq per kg of 137Cs or 134Cs were 34 or 69 µSv, respectively. Three scenarios of contamination were evaluated: freshly contaminated silage after model accident, silage right after the Chernobyl accident and at the current radiation situation in the Czech Republic.

Behaviour of 137Cs in forest humus detected across the territory of the Czech Republic.

The activity concentration of 137Cs in samples of coniferous forest humus collected across the territory of the Czech Republic in 1995 and 2005 was analysed, and it was found significantly correlated with the surface deposition caused by the Chernobyl accident. The effective (12.8 y) and environmental (22.3 y) half-lives of radiocaesium in humus were calculated and compared with those in spruce bark. The impact of important forest stand factors, that is, precipitation, content of organic matter, age of trees and pH, on the behaviour of 137Cs in humus was studied. It was observed that humus samples with a higher proportion of organic matter, higher pH(H2O) and pH(CaCl2) contained higher amounts of 137Cs. Conversely, with the age of trees, the activity concentration of 137Cs in humus is decreasing. Higher precipitation and humus acidity decrease the reduction rate of the 137Cs in humus. These stand factors increase bioavailability of 137Cs in humus. The transfer and retention of available 137Cs in biomass of organisms living in humus for a long time can satisfactorily explain the longer residence time of 137Cs in humus affected by the studied factors.

Ingestion intakes of 137Cs by the Czech population: Comparison of different approaches.

Ingestion intakes of 137Cs of the Czech population were calculated in two different ways - either from the measured activity of 137Cs in components of food in combination with statistical data about consumption rates or from retention of 137Cs in the human body obtained by whole body counting or calculated from daily urinary excretion of 137Cs. Data from the time period since 1986 to 2015 are used. The daily ingestion intake was about 25 Bq d-1 in 1986 and is around 0.1 Bq d-1 at present. Both approaches of ingestion intake calculation have their advantages and disadvantages. Ingestion intake calculated from 137Cs body content was assumed to be the most accurate as it requires fewer assumptions than the calculation from food consumption. However, calculation of 137Cs intake from food consumption is an important tool for prediction doses after the release of radionuclides into environment. The best agreement exceeding the intakes from urine measurement 5 times at maximum was achieved when intakes calculated from food also included products from the natural environment. Without this, the ingestion intake could be under-predicted seriously up to 6 times, especially in the longer time after the release of 137Cs into environment. Ingestion intakes up to 11 Bq d-1 in a group of people with significant consumption of game meat containing elevated activity of 137Cs activity were included as a special case. Various groups of foodstuffs had varying effects on the total committed effective dose from 137Cs. Dose estimates for the Czech population from 137Cs ingestion intake achieved 80 µSv in 1986 and not more than 2 µSv currently and were similar to those incurred by the population of neighbouring countries.

Radiocaesium levels in game in the Czech Republic.

The paper summarizes results of monitoring of (137)Cs activities in game species roaming in the woods over the territory of the Czech Republic for the time interval of 1986-2012. Geometric means and other statistical characteristics were estimated from the data sets on the assumption of log-normal distribution of the data from the time interval 2004-2012 where the character of data distribution had displayed no significant change. Geometric means (in Bq/kg) in meat were: wild boar 5.1, red deer 1.9, roe deer 0.77 and feathered game 0.14. The mean value in the less frequent game amounted to 0.36 Bq/kg. The geometrical standard deviation (GSD) widely varied from 1.6 to 21 for the studied species. Based on mass activity dependence on time, we assessed the effective and environmental half-lives of activity decline. For red deer and roe deer, the effective (137)Cs half-life was 2.9 and 3.2 years, and environmental half-life 3.2 and 3.6 years respectively. The effective half-life of (137)Cs in wild boar of 38 years was determined with large uncertainty and it shows constant influx of (137)Cs activity to the digestive tract of wild boars. A statistically significant season-based (137)Cs level was found in red deer and wild boar. Higher winter and spring activities of (137)Cs in wild boar are linked with decreasing access to naturally occurring food with lower (137)Cs content (chestnuts, acorns, and beech nuts), making boar grub around for ground-deposited food (often for mushrooms with higher activity). Higher winter activities of (137)Cs in red deer meat, most probably, are due to lower access to green diet in winter. The average annual committed effective dose for Czech population based on estimates of game species meat consumption between 2004 and 2012 was insignificant, only 0.03 µSv.