Extremely high radon activity concentration in two adits of the abandoned uranium mine 'Podgórze' in Kowary (Sudety Mts., Poland)

Measurements of radon activity concentration were conducted for a period of 6 months, from April to September 2011, in the air of two adits constituting part of the disused uranium mine 'Podgórze' in Kowary. Adits no. 19 and 19a in Kowary had been chosen owing to the occurrence within them of the highest documented radon concentrations in Poland, With levels higher than a million Bq m^-3. The main goal of this study was to characterize the level of ²²²Rn activity concentration registered in selected workings of this underground space, investigate ²²²Rn changes and their characteristics over selected periods of time (an hour, a day, a month, six months) and determine the effective doses, which provided the basis for estimating the risk of exposure to increased ionizing radiation for employees and visitors to the mine. The highest values of ²²²Rn activity concentration inside the adits occurred at the time when visitors, guides and other members of the staff were present there. The recorded values of radon activity concentration, regardless of the time and the month when the measurement was performed, remained at an average level of 350-400 kBq m^-3. These values were far above the limit of 1.5 kBq·m^-3 recommended by international guidelines. The maximum values ranged from 800 to more than 1000 kBq·m^-3. Radon activity concentration changes occurred only in periods determined by 7-h cycles of connecting and disconnecting the mechanical ventilation. For about 7 h after activating the ventilation system, between 7 a. m. and 2 p. m., and after closing the adit, between 7 p. m. and 2 a. m., ²²²Rn activity concentrations decreased to levels even as low as 100 kBq·m-3. However, as early as 3-4 h after disconnecting the ventilation system, there was a sharp rise in the values of ²²²Rn activity concentration, to the level higher than 800 kBq·m-3. The risk of receiving a radiation dose higher than the national standard of 1 mSv/year by members of the public occurred as soon as after spending 1 h inside the workings. The minimum monthly effective radiation dose received by every employee in the tourist adit no. 19 in Kowary was higher than 1/5 (4 mSv) of the annual effective dose allowed by Polish law (20 mSv/year). In the non-tourist adit no. 19, the minimum monthly radiation dose was more than 3 times as high as the allowed value of 4 mSv. Due to the highly disturbing and unfavourable, from a radiological protection point of view, conditions inside the disused uranium mine 'Podgórze' in Kowary, the mine manager decided to increase the efficiency of the designed mechanical ventilation system and launch measurements of radon activity concentration in the workplace.

Radon as a tracer of daily, seasonal and spatial air movements in the Underground Tourist Route "Coal Mine" (SW Poland)

The surveys of radon concentrations in the Underground Tourist Route "Coal Mine" were carried out using passive and active measurement techniques. Passive methods with application of Solid State Nuclear Track Detectors LR115 were used at 4 points in years 2004-2007 and at 21 points in year 2011. These detectors were exchanged at the beginning of every season in order to get information about seasonal and spatial changes of radon concentrations. The average radon concentration noted in this facility was 799 Bq m(-3) and is consistent with radon concentrations noted in Polish coal mines. Seasonal variations, observed in this underground tourist route, were as follows: the highest radon concentrations were noted during summers, the lowest during winters, during springs and autumns intermediate but higher in spring than in autumn. The main external factor that affected seasonal changes of radon concentrations was the seasonal variation of outside temperature. No correlation between seasonal variations of radon concentrations and seasonal average atmospheric pressures was found. Spatial variations of radon concentrations corresponded with air movements inside the Underground Tourist Route "Coal Mine". The most vivid air movements were noted along the main tunnel in adit and at the place located near no blinded (in the upper part) shaft. Daily variations of radon concentrations were recorded in May 2012 using RadStar RS-230 as the active measurement technique. Typical daily variations of radon concentrations followed the pattern that the highest radon concentrations were recorded from 8-9 a.m. to 7-8 p.m. and the lowest during nights. The main factor responsible for hourly variations of radon concentrations was the daily variation of outside temperatures. No correlations were found between radon concentration and other meteorological parameters such as atmospheric pressure, wind velocity or precipitation. Additionally, the influence of human factor on radon concentrations was noticed. As human factor, we consider open entrance door during restorations works carried out inside the underground facility. Comprehensive surveys of radon concentrations in the Underground Tourist Route "Coal Mine", which included hourly, seasonal and spatial measurements, have revealed that radon can be the excellent tracer of air movements inside the underground facilities that are not equipped with mechanical ventilation system. The main external factor that affects hourly, seasonal and even spatial changes of radon concentrations inside Underground Tourist Route "Coal Mine" is the variation of outside temperature. The maximum effective dose received by employees during 2000 working hours in a year was 5.8 mSv y(-1) and the minimum was 3.5 mSv y(-1). Tourist guides, who usually spend underground about 1000 h y(-1), received effective dose from 1.7 mSv y(-1) to 2.3 mSv y(-1). According to Polish Law, employees, receiving effective dose for occupational exposure higher than 1 mSv y(-1) but below 6 mSv y(-1), are allocated to category B of workers and the level of radiation in their place of work should be controlled and continuously monitored. The radiation monitoring system in the Underground Tourist Route "Coal Mine" does not exist. None of Polish tourist routes or caves has installed radiation monitoring system although effective doses received by employees, in some of them, exceed values defined by law. Effective dose received by tourist during one trip was lower than 0.001 mSv y(-1) and risk of cancer induction was lower than 0.00001%. The probability, that tourists inside the Underground Tourist Route "Coal Mine" receive effective dose exceeding allowable annual limit for members of the public of 1 mSv y(-1) does not exist. The Underground Tourist Route Coal Mine is a safe place for tourists from radiological point of view.

Short-term radon activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno (Sudety Mts., SW Poland)

Short-term (222)Rn activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno were studied, based on continuous measurements conducted between 16 May 2008 and 15 May 2010. The results were analysed in the context of numbers of visitors arriving at the facility in particular seasons and the time per day spent inside by staff and visitors. This choice was based on partially published earlier findings (Fijałkowska-Lichwa and Przylibski, 2011). Results for the year 2009 were analysed in depth, because it is the only period of observation covering a full calendar year. The year 2009 was also chosen for detailed analysis of short-term radon concentration changes, because in each period of this year (hour, month, season) fluctuations of noted values were the most visible. Attention has been paid to three crucial issues linked to the occurrence and behaviour of radon and to the radiological protection of workers and visitors at the tourist route in Kletno. The object of study is a complex of workings in a former uranium mine situated within a metamorphic rock complex in the most radon-prone area in Poland. The facility has been equipped with a mechanical ventilation system, which is turned on after the closing time and at the end of the working day for the visitor service staff, i.e. after 6 p.m. Short-term radon activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno are related to the activity of the facility's mechanical ventilation. Its inactivity in the daytime results in the fact that the highest values of (222)Rn activity concentration are observed at the time when the facility is open to visitors, i.e. between 10 a.m. and 6 p.m. The improper usage of the mechanical ventilation system is responsible for the extremely unfavourable working conditions, which persist in the facility for practically all year. The absence of appropriate radiological protection (i.e. preventive measures like shortening working day, dosimetric measurements in the workplace) is a serious problem in the Kletno adit.