Comparison of active and passive radon survey in cave atmosphere, and estimation of the radon exposed dose equivalents and gamma absorbed dose rates

Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces - the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11-6653 by Bq m-3 and 10-89,020 Bq m-3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process - convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Radon (222Rn) as a tracer in natural ventilation efficiency assessment in underground workings - an example of "St John Mine" tourist complex in Krobica (the Sudetes, SW Poland)

The authors characterize the use of ²²²Rn as an effective tracer of natural ventilation of an underground site where air circulates within a whole system of workings and ventilation intensity (the number of air exchanges in the space) is determined by atmospheric factors. A radon-related database containing results of measurements conducted at various intervals and at different stages of site accessibility was compiled. During 8 months of the calendar year ²²²Rn activity concentration exceeds the mean annual reference value established by Polish law (300 Bq/m³). These months correspond to periods with low intensity of natural ventilation of the workings and reduced efficiency of air exchange between the site and the atmosphere. They occur in autumn - in the second half of September, in October and November, and in May in spring, and persist for 7 to even 14 days. During these periods, the time spent inside the facility which is considered safe in terms of radiation protection is limited to an average of 6-8 h a day, i.e. from 6 a.m. to 6 p.m. in October, from 11 a.m. to 6 p.m. in November and from 11 a.m. to 5 p.m. in May. The length of a safe stay in the facility is determined by atmospheric factors, mainly the air and ground temperature. The concentrations of other gases in the atmosphere inside the facility comply with Polish mining regulations.

Activity concentrations and radiological hazard assessments of 226Ra, 232Th, and 40K in soil samples of oil-producing areas of South Africa

The specific activity of natural radionuclide in soil samples of the oil-producing areas of South Africa was measured using a High Purity Germanium detector. The activity of226Ra, 232Th, and 40K in the soil range from 16.5 ± 1.3 to 64.9 ± 3.1, 16.8 ± 1.5 to 88.6 ± 1.2, 135.2 ± 17.5 to 604.8 ± 13.4 Bqkg-1 for Mossel Bay; 14.3 ± 1.2 to 48.9 ± 8.2, 22.3 ± 1.4 to 45.1 ± 3.2, 237.7 ± 10.9 to 486.5 ± 40.1 Bqkg-1 for Cape Town; 10.5 ± 1.1 to 25.8 ± 3.2, 13.1 ± 1.9 to 44.3 ± 5.2, 140.2 ± 10.9 to 229.8 ± 12.8 Bqkg-1 for Nelson Mandela Bay and 5.6 ± 2.2 to 13.1 ± 2.9, 4.5 ± 2.5 to 14.1 ± 2.7, 62.7 ± 22.6 to 126.5 ± 21.2 Bqkg-1 for Msunduzi. Most soil samples' radiological hazards were within the world average.

Assessment of occupational exposure from radon in the newly formed underground tourist route under Książ castle, Poland

In the present study, 222Rn activity concentrations in a newly formed underground tourist route under Książ castle, Poland, were investigated for periods undisturbed and disturbed by construction works. This preliminary assessment is based on the almost 3-year long continuous measurements (28 Oct. 2016-02 Jul. 2019) done with an SRDN-3 instrument. In detail described are radon concentrations for periods of renovation (11 Aug. 2018-10 Oct. 2018), opening (15 Oct. 2018-10 Apr. 2019) and operation and monitoring (11 Apr. 2019-02 Jul. 2019) of the facility. It was observed that after the termination of construction work, when natural ventilation returned to the state preceding this work, the absolute values of radon activity concentration decreased. The mean annual radon concentrations were higher than the reference level of radon concentration in underground spaces recommended by IAEA, ICRP, and by the EU Council Directive for workplaces. They reached 1179 Bq/m3 and 943 Bq/m3 in 2017 and 2018, respectively. Cyclically recurring daily changes in radon concentrations occurred only in April and October (so-called transitional periods) and only outside the period of construction work. The results confirmed; however, that these changes need not be considered when planning the work in the tunnel. The minimum effective dose rate from radon exposure occurs in colder periods of the year, from November to the end of March, where the mean effective dose rate value was found to be 0.0003 mSv/h. In contrast, the maximum dose rate of 0.014 mSv/h was observed from April to August.