G. Szeiler

Dependence of radon emanation of red mud bauxite processing wastes on heat treatment.

Natural radioactivity content, radon emanation and some other physical characteristics of red mud were investigated, so that to identify the possibilities of the safe utilization of such material as a building material additive. Based on the radionuclide concentration, red mud is not permitted to be used directly as a building material, however, mixing of a maximum 20% red mud and 80% clay meets the requirements. The main aim of this work was to determine the dependence of the emanation factor of red mud firing temperature and some other parameters. The relevant experimental procedure was carried out in two different ways: without any additional material, and by adding a known amount of sawdust (5-35 wt%) then firing the sample at a given temperature (100-1000 degrees C). The average emanation factor of the untreated dry red mud was estimated to 20%, which decreased to about 5% at a certain heat treatment. Even lower values were found using semi-reductive atmosphere. It has been concluded that all emanation measurements results correlate well to the firing temperature, the specific surface and the pore volume.

Preliminary results from an indoor radon thoron survey in Hungary

More than half of the radiation dose of natural origin comes from radon. However, according to some surveys in certain cases, the radiation dose originating from thoron may be considerable. Among the factors disturbing the measurement of radon, the presence of thoron may also influence the measured radon value, making the estimated radiation exposure imprecise. Thoron has previously been surveyed, mainly in Asia; however, recent surveys for some European locations have found that significant thoron concentrations also need to be considered. In this survey, several types of commercially available SSNTDs (solid-state nuclear track detectors) capable of measuring both radon and thoron were placed at the same time in 73 houses and 7 workplaces in Hungary with 3-month exposition periods. In order to measure thoron, the distance of the detector sets was fixed as 15-20 cm from the walls. The radon concentration was measured with five types of SSNTDs: NRPB, NRPB SSI, Raduet, DTPS and DRPS. The first four types had relatively good accordance (within ± 10 %), but the results of the DRPS detectors were considerably lower when compared with other detectors for radon concentrations over 100 Bq m(-3). The thoron averages were provided by two different types of detectors: Raduet and DTPS. The difference between their average results was more than 30 % and was six times the maximum values. Therefore, the thoron measurement results were judged to be erroneous, and their measurement protocol should be clearly established for future work.

Systematic survey of natural radioactivity of soil in Slovenia

Soil samples, from 70 points uniformly distributed over entire Slovenia, were analysed for (40)K, (232)Th and (226)Ra using gamma spectrometry, and for (234)U and (238)U using alpha spectrometry. The following ranges and averages of activity concentrations (Bq kg(-1)) were obtained: 98-2600 and 800 ± 520 for (40)K, 9-170 and 77 ± 33 for (232)Th, 12-270 and 63 ± 44 for (226)Ra, 12-84 and 34 ± 19 for (234)U, and 11-90 and 34 ± 19 for (238)U. With respect to lithology, the highest average values for (40)K and (232)Th were found at clastic sediments containing clay and for (226)Ra on carbonate rocks. Based on the measured activity concentrations, terrestrial gamma dose rates were calculated. The total dose rate ranged from 15 to 260 nGy h(-1), with arithmetic mean of 110 ± 49 nGy h(-1), being the highest over carbonates.

Radiological Aspects of Red Mud Disaster in Hungary

One of the most severe industrial catastrophes happened in Kolontár, Hungary, on 4 October 2010. Red mud (bauxite residue) broke through the eroded wall of the red mud reservoir pond “Number X” and flooded the surrounding area. This led to the instant death of 10 people and the injury of more than 100 people. Red mud is enriched in radium and thorium isotopes; therefore, there is a chance that this flooding will increase radionuclide concentrations of soils and also in air. In this study we have examined the site to assess the realistic radiological risks. For the risk assessment the following parameters were determined: gamma dose rate, radon concentration, radionuclide concentration of red mud and air dust concentration. It was found that the radiation dose exposure resulting from red mud contamination was < 0.045 mSv y−1 (excluding radon), which can be considered negligible when compared to the average annual effective dose from natural sources (2.4 mSv y−1).

Radon emanation and exhalation characteristic of heat-treated clay samples

The exhaled radon originated from building materials corresponds to the indoor radon activity concentration. One of the most commonly used building materials is the brick made from clay by heat treatment. In this study, the radon emanation and radon exhalation features of clay samples are presented as a function of heat applied (100-950°C). The free radon exhalation was determined with the help of radon accumulation kit. The initial radon exhalation value continuously reduced owing to the increased temperature. In the case of the highest temperature treated sample, the measured exhalation was <1 % of the original. The tendency of the loss relates to the internal structure modification, which was also investigated (porosity, specific surface and superficial morphology by environmental scanning electron microscope snapshots). On the basis of the obtained result, it can be safely stated that strong correlation can be observed between the internal structural changes and the found exhalation profile.

Radiological investigation of the effects of red mud disaster

On 4 October 2010, the gate of a red mud waste dump of a Hungarian alumina factory was damaged and ∼800.000 m(3) of alkaline red mud flooded the vicinity of the dumps. Red mud samples were collected from the contaminated area and they were investigated from the radiological point of view. The activity concentrations were as follows: (232)Th: 264 (194-337) Bq kg(-1), (238)U: 265 (197-332) Bq kg(-1), (226)Ra: 180 (143-237) Bq kg(-1), (40)K: 283 (228-360) Bq kg(-1). As a function of the moisture content (0-28 %), the obtained radon emanation coefficients were relatively high (7.6-20 %) and, consequently, the radon exhalation also increased.