Over recent years more and more studies have been published on the harmfulness of NORM materials, and there has been no unified recommendation (regulation) on the restriction of their use until recently, yet the European Basic Safety Standard known as EU-BSS (Council directive 2013/59/EURATOM, European Basic Safety Standards) emphasizes the restrictions related to these materials by monitoring the radioactivity index (I) of materials. Additionally, a reference level applying to indoor external exposure to gamma radiation emitted by building materials, in addition to outdoor external exposure, shall be 1 mSv per year.
The importance of the utilization of by-products and residue streams has grown over recent decades due to the concern about the sustainability of the human environment; of course, the use of residues sometimes provides better financial solutions. In recent years, some studies are focused on the utilization of industrial waste residues (e.g., waste glass, concrete waste) in concrete or mortar to improve some (Li, 2008; Gutiérrez, et al., 2015;
Sas, et al., 2015a; Kovács, et al., 2017).
Manganese clay is the residue of manganese mining, it is not classified as a by-product as it is listed as a secondary raw material. About 2.8 million tons of the residue of manganese ore mining clay has been deposited on the land surrounding the Úrkút manganese mine.
However, in case of reusing of by-product in building material industries, several studies have been conducted mainly focusing on gamma dose; While, measuring only the gamma dose is not suitable as the majority of radiation dose is provided by radon and its progenies (Somlai, et al., 1997; Somlai, et al., 2006). Therefore, it is necessary to include the radon exhalation (as measuring only the radionuclides concentration is insufficient) as a monitoring tool in the processing used in the building industry to derive a useful radon exhalation data; Following recent studies (Kávási, et al., 2012; Sas, et al., 2015a) on utilization of clay as a building material, heat treatment used as a radon exhalation treatment tool in this study.
The quantity and quality of additives usable in building materials have long been set out by strict regulations. The radioactivity of materials usable in building materials is regulated explicitly by the standards of only relatively few countries. However, some have been established for many years: Hungary the regulation setting out the radioactivity limit of building materials has been in effect since 1960 (no. 26/1960 Directive of Hungarian
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Ministry of Construction). Due to other major components of manganese clay (Seil &
Heiligman, 1928) it is potentially useful in brick productions. Thermal treatment (firing) is the basic treatment method of brick-making and this has implications on the amount of radon emitted.
In this study, in addition to the internal physical features changes, the radon emanation characteristics of manganese clay were measured at different temperatures identifying the optimum firing temperature in order to minimize radon exhalation and provide useful data for later modelling and also for construction companies, and information for authorities on the maximum amounts of additives.
35 1.8. Background of the Study
The Úrkút Manganese mine was on attention for the first time in middle 2002, doing a regular radioecological measurements along with the new national regulation about radon concentration in workplaces and underground mines. It makes a big opportunity for Hungarian researchers to have some related experiment and studies. Regarding to the properties of the mine as an underground mine, in 2002 the first study was conducted to figure out, if there is a health risk for workers who exposure to radionuclides in the mine during working time based on the standards and regulations at that time; It was indicated that, the only direct potential hazard health can be the accumulated Radon in the air;
Therefore, increasing the ventilation rate was suggested as a solution, but increasing the ventilation flow rate to the rate that could guarantee the low radon concentration was not possible due to the Hungarian regulation; On the other hand, increasing the air flow could cause distribution of dust on the mine environment what could cause other health problem.
Then, it was suggested to increase the working shifts, as a result, the health risk of exposure to radon could be reduce as workers would expose to radon for a shorter period. Following the first study second one was conducted between 2003 and 2006 focusing on seasonal fluctuations effect on dose estimation and equilibrium factor. The third study had started between 2006 and 2010 about geological role on radon concentration in mine, it was indicated that changes in mining circumstances may cause an increase in radon concentration, and it was found that radon in underground water may not have any influence on the radon concentration in the mine and measuring radon emanation and exhalation of the rhodochrosite and black- shale. Regarding the Tamás Vigh study and suggestion it could be possible to meet the regulation in Úrkút underground mine.
In 2013, Vigh et al., investigated the activity concentration of three natural occurring radioisotopes (U-238, Ra-226, K-40) in black shale (Vigh, et al., 2013).
During years, the average radon concentration was keeping below 1000 Bq·m-3 by improving mitigation system in Úrkút manganese mine; However, decreasing working hours and improving mitigation could be a practical solution until 2013 when Europe established a new regulation to keep radon concentration in dwellings and work area below of 300 Bq·m
-3. According to the timeline of the European Basic Safety Standard, all EU members should apply the requirements by starting 2018. Reducing radon concentration to below the recommended level, can be a new challenge for the work area (such as underground mines
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and caves) due to their limitation. Therefore, in this study to follow new European regulation, it was tried to find out the problems and solutions for underground workplaces (Case study: Úrkút manganese mine). The first step to control radon concentration at an environment is to recognize the source of the radon. By following, optimization of ventilation can be other way of reducing the radon concentration, however, a good measurement device and a long-term monitoring are required to plan the best way of reducing radon in workplaces.
In this thesis, it has been tried to apply the EU basic safety on an underground mine as case study manganese mine to be possibility of a guide for other similar workplaces. In the first phase, a regular long-time radon concentration measurements by using passive and active method and difference devices to compare performance of devices under the mine condition and trying a new intelligent system (TESLA TSR2), in the second phase following the last study to get an overview of radon concentration a material analyses have been done to find the main source of radon in the mine. Additionally, a long-term dosimetry was doing and finding the behaver of attached and unattached particles on the received dose by workers based on the radon source. In the third phase it has been tried to develop and optimized ventilation system based on the regulation. In the fourth phase it tried to find attached and unattached rate for working hours and not working hours and the traveling distance of particles and the effect of radon. In the last phase it has been tried to figure out the possibility of reusing by-product of the mine as building material by heat treating and active coal additive treatment.
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