Exposure and Radiation Protection of Uranium Mine Personnel

The nuclear fuel cycle starts with the mining of uranium ore — the basic raw material for nuclear fuel production. In Ukraine, this process is implemented by the underground method and technologically is not much different from iron ore mining in Kryvy Rig or in the Zaporizhzhya region.

Horror stories about the deportation to uranium mines as a “one-way ticket” for those sentenced to death in the Soviet Union are only rumors generated by the information on the unbearable GULAG conditions combined with the lack of knowledge of true radioactive properties of uranium ores.

At the same time, regarding radiation, uranium mining is hazardous and according to some sources, the most hazardous stage of the nuclear fuel cycle for workers. Severe physical conditions of underground work are accompanied by significant doses of exposure both external to gamma radiation, and internal to radon and its decay products, as well as to long-lived radionuclides of radium, thorium and uranium contained in uranium raw materials.

So, uranium mining is accompanied by radiation risks both for the mine workers themselves and for the public living in the zone of uranium site effects.

Due to direct contact with radioactive material, workers of uranium mines are classified as category A personnel. The activities of uranium sites, protection of personnel, the public and the environmental against radiation, as well as the peculiarities of social protection of uranium site personnel and the public due to radiation impact are regulated by the Law of Ukraine “On Uranium Ore Mining and Processing”.

The Ukrainian uranium mining industry is represented by two operating mines — Smolinska (about 1900 employees) and Ingulska (1600 employees) located in the Kirovograd Oblast. Both mines are included in the State Enterprise “Eastern Mining and Processing Plant” (SkhidGZK). In addition, SkhidGZK includes the Novokostiantynivska mine, where trial and commercial mining of uranium ore is ongoing as part of the development of capacities.

Organizationally, uranium ore mining is practically the same as in coal or iron ore mines. Mine workers go down the mine shaft by a hoist in the face, where they develop ore deposits (in Ukraine — by drilling and blasting method), which is transported to the shaft, by which they raise it to the surface.

Personal protection of mine workers against harmful production factors, as elsewhere, is provided by special work clothes, helmets, respirators, etc.

Main uranium deposits in Ukraine

In accordance with the requirements of standards and rules on radiation safety, workers who, according to the medical commission conclusion, have no adverse health conditions, were trained and have passed knowledge checks on radiation safety issues, instructions on their specialties are allowed to go underground. Miners exposed to radiation undergo medical examination before start of activities and periodically, at least once a year. Medical examination of mine workers is obligatory even in case of their dismissal.

Radiation Hazard Sources

Uranium ore mined at uranium sites contains all the elements of uranium-238 and uranium-235 decay chain, which are in radioactive equilibrium. The radiation background from uranium ore is linearly dependent on the uranium content and for uranium ores in Ukraine it is insignificant, since uranium-238 concentration in it is very low: in general, 1.5 kg per ton of ore.

However, Ukrainian uranium mines also have ore deposits with a rather high uranium content, where mine workers experience a rather significant effect of external gamma exposure from rocks, which requires additional protection.

Schematic structure of the Smolinska uranium mine. Source: Ministry of Energy and Coal Industry of Ukraine

Inert gas radon released during uranium ore mining is more hazardous. Its half-life is less than 4 days, during this period, short-lived progeny of radon are formed: polonium-218, plumbum-214, bismuth-214 and polonium-214.

These radionuclides bind with ore dust particles, which hang in the mine air and enter the organisms of miners through the respiratory system, then deposit in the respiratory tract and lungs. After a short half-life (less than half an hour), they form a sufficiently high exposure dose in lung tissues before removal. An exposure dose that will be received by a worker depends on progeny activity, both directly in the working zone air and in dust particles and their dispersion.

Long-term impact of progeny alpha- and beta-particles – polonium-218 and polonium-214 increases the risk of lung cancer – an occupational disease of uranium site workers.

In addition, workers in uranium mines are exposed to long-lived uranium series alpha radionuclides (LLUA) contained in dust, which depends on the uranium content in it, mining methods, and dust control measures.

Physiologically, aerosol particles of ore dust with a size of 20 microns and more mainly remain in the upper respiratory tract and are removed by coughing up in the first hours after work; dust particles of 5 microns reach the lower respiratory tract and lung alveoli and stay there.

The dose that will be received by a mine worker due to this depends on the solubility degree of the mineral itself in biological fluids, its size and specific radioactivity.

If mining is not conducted in high-grade uranium deposits (which is typical of most uranium deposits in Ukraine), the radiation from LLUA remains relatively small. The main thing is to properly control it.

There are several ways, in which inert gas radon is released from the parent rock and enters the air in the breathing zone of miners. First of all, when uranium ore contacts directly with the mine air. This happens most often when uranium ores are found in mine workings.

Large volume of radon is released within separating ore debris from the ore body: blasting, drilling, etc. As ore is loaded and transported by the mine to the surface, it continues to emit radon into the mine air.

Groundwater can also carry radon, so radon presence in mine water becomes another source of this gas and its progenyradiation. In SkhidGZK mine water, radon content can reach 60 kBq/l, which is a fairly high index (under a specific activity for drinking water safety index of not over 100 Bq/l).

Transport of uranium ore at Novokostiantynivska mine. Source: Kirovograd Regional Council

Repeated formation of aerosols of dust from mine workings and during contaminated equipment management is other significant exposure source. Considering this, only wet methods of drilling and transport of rock mass are used during uranium ore mining, which is an effective way of combating mine dust.

All of these radiation sources constitute the effective exposure dose for miners. According to many researchers, the main dose-forming factor (70%) is radon and its progeny.

According to L. Kovalevskyi, A. Operchuk and I. Los (2008), the upper limit of practical activity justification at uranium sites adopted at the international level and in Ukraine is the risk value equal to one death from cancer per 1000 workers per year.

 

Radiation Protection Equipment for Miners

In Ukraine, the entity (i.e. SkhidGZK) directly involved in mining activities and its separate divisions (mines) are responsible for radiation protection of personnel, in accordance with the Safety Requirements and Conditions (Licensing Conditions) for Uranium Ore Mining and Processing. Namely: compliance with the established dose limits, permissible levels for personnel; concentration decrease of radon and thoron and their other daughter decay products, as well as long-lived decay products of uranium and thorium radionuclides in the air of the working area; radiation monitoring at workplaces and industrial rooms, etc.

Trolley with the millionth ton of uranium ore mined at the Novokostiantynivska mine. Source: Kirovograd Oblast Council

The most effective way of protecting uranium mine workers is to provide an efficient ventilation system. The exposure of workers to radon daughter decay products depends on the rate of radon removal from the air of working areas. The efficiency of the ventilation system lies in minimizing the time spent by the radon saturated air in working areas, as well as maximizing the time spent by workers in the fresh air environment.

The mechanical mine ventilation is divided into primary and auxiliary. The primary ventilation directs clean air from the surface into the mine and brings it back to the surface through the mine workings of the mine field. The auxiliary ventilation systems distribute fresh air from the main channels to deeper and more remote working areas. Since the plans of mine workings are constantly changing, the auxiliary ventilation systems are also improved accordingly. It is important that the ventilation system renews the air from the surface, and not just provides mine air circulation, otherwise, this can lead to progeny concentration increase. The most efficient ventilation system for the mine field is the radical ventilation: when fresh air is supplied and exhaust air is discharged from different sides of the mine field.

Load-haul-dumper PFL-20. Such machines work at uranium mines of Ukraine. Source: SkhidGZK

However, in the Central Deposit of the Ingulska mine, according to hygienist Anatoliy Operchuk, such a ventilation system is impossible, since the mine field is located under the residential quarters of Kropyvnytskyi. The available circuit supplies fresh and evacuates exhaust air from the production site of the Central Deposit, which does not meet the requirements for normalizing the mine air directly at the main workplaces.

Another method for air normalization in uranium mines is the isolation of inactive mine workings to prevent the access of radon and its progeny to workplaces. It is implemented by filling the mined space with a hardening mixture (sand, clay and granulated slag), walling, which ensures tightness of mine workings and prevents the spread of radioactive gas (filled stope working).

For effective plugging pores and cracks, a coating of clean waste rock (on the floor) and shotcrete (on the walls) is used. It is possible to isolate radon dissolved in groundwater using: piping draining this water from active faces; cementing cracks that can leak or even freezing (if the mine is flooded).

Plan of the industrial site and underground facilities (shafts, entries and faces) of the Novokostiantynivska mine. Source: Ministry of Energy and Coal Industry of Ukraine

Although the level of personnel exposure to gamma radiation is lower than that to progeny and LLUA, protection against this exposure source should not be neglected. International experience recommended by IAEA, including, for example, gamma shielding engineering control tool such as shotcrete.

Such a simple method as maintaining general cleanness and good order in working areas also helps to reduce an exposure dose to gamma radiation. The use of personal protective equipment is also effective in reducing internal exposure. The use of respirators is obligatory.

However, during uranium ore mining by the drilling and blasting method as in Ukraine, a very large amount of fine dust with a particle size of 0.2-0.5 microns is released. Such dust fractions, according to A. Operchuk’s research, can penetrate through personal protective equipment into the respiratory tract of mine workers and reach the alveoli.

To ensure that the boundary values ​​of exposure doses for mine workers are not exceeded, dose and radiation monitoring is conducted according to the approved programs. Taking into account IAEA recommendations, in 1997, the effective dose limit of occupational exposure, including for miners, was set at 20 mSv/year (Radiation Safety Standards of Ukraine-97).

Limits of occupational exposure doses (NRBU-97)

Effective dose

20 mSv/year on average for 5 consecutive calendar years (100 mSv in total), 50 mSv in any other year

 

Annual equivalent dose for:

 

skin

500 mSv

hands and feet

500 mSv

lens

150  mSv/year

 

Dose monitoring is aimed not only at assessing occupational personnel exposure doses, but also at obtaining the data to assess the effectiveness of radiation protection measures. Upon the results of dose monitoring, the main dose-forming radiation sources and their contribution to the doses received by mine workers, effective dose-limiting devices, which can subsequently impact radioactive contamination levels and the like are identified.

In Ukraine, dose monitoring of mine workers is implemented by monitoring workplaces followed by the calculation of personal exposure doses. For this, mine workers are conventionally divided into similar exposure groups (SEG) or groups that work with similar radiation sources and perform similar work during the same periods.

For example, the Dose Monitoring Program of the SkhidGZK Ingulska mine provides routine, special operational and emergency dose monitoring. Routine dose monitoring of mine workers belonging to category A personnel is carried out once a week at the basic workplaces and twice a month at nonbasic ones. Special and operational dose monitoring is conducted in each specific case upon the order of the mine chief engineer, and emergency – at all stages of the mitigation of an emergency or abnormal situation to restore normal operation of the enterprise or decontamination completion.

The physicochemical laboratory of the Ingulska mine measures: dust concentration, gamma radiation power, alpha- and beta-contamination of industrial room surfaces, overalls, vehicles, scrap; equivalent equilibrium activity concentration of radon (EEACRn), thoron (EEACTn), total alpha activity and specific activity of radionuclides in the mine air, air of working areas and in the air of industrial rooms, etc.

Reference levels of radiation factors in the air of the working area in mine surface conditions (Dose monitoring program of the Ingulska mine):

Factors

Category А

Radon

42490 Bq/m3

EPOArn

1050 Bq/m3

EPOATn

77 Bq/m3

226Ra

0,042 Bq/m3

238U

0,15 Bq/m3

Long-lived alpha-active 238U radionuclides by specific alpha activity

0, 042 Bq/m3

The reference levels of the annual effective dose for category A and B personnel at the Ingulska mine are set at 12 mSv and 1.6 mSv, respectively. The dose for each employee is calculated in accordance with the “Guide for the calculation of personal exposure doses for SkhidGZK personnel and the public” (put into effect in 2008).

According to SkhidGZK official reports, the average annual dose load on mine personnel is recently:

Mine

2019 

2020 

Ingulska

5.81 mSv (29.05% of established annual limit)

4,60 mSv (23.01%)

Smolinska

6.34 mSv (31.7%)

6.09 mSv (31.%)

Novokostiantynivska

7.99 mSv (39.95%)

7.433 mSv (37.2%)

Of them, annual effective doses for personnel of the main occupations are:

Mine

2019 

2020 

Ingulska

from 1.70 to 11.91 mSv (to 59.6%)

from 1.34 to 9.58 mSv (to 47.9%)

 

Smolinska

from 0.79 to 14.06 mSv (to 70.3%).

 

from 0.583 to 10.252 mSv (to 51.3%).

Novokostiantynivska

from 3.58 to 12.28 mSv (to 64.4%).

from 2.92 to 13.79 mSv (to 68.9%)

In the uranium mining industry in other countries, it is also common practice for mine workers to use personal dosimeters. In this way, the radiation protection service receives the data on radon progenylevel and mine dust concentration in the breathing zone of each worker, as well as on his external exposure dose. This method has not been used at all in Ukrainian mines for a long time. In recent years, the “Program for personal dosimetry of radon, its progeny, uranium and long-lived alpha-nuclides at SkhidGZK facilities using personal dosimeters” is in force.

 

Radiation Protection Issues in Ukrainian Uranium Mines

According to many experts, the disadvantage of dose monitoring of uranium mines in Ukraine is the limited access to its results by inspection services, which casts doubt on the credibility of the assessment results of personnel exposure doses. Thus, V. Bogorad, E. Kadkin and A. Nosovsky consider the calculation of dose loads for category A personnel based on averaged indexes of working conditions for the main mining operations as an incorrect approach. “In this case, the real value of radiation situation parameters is underestimated and the real personnel dose at a particular workplace will be significantly higher”, the researchers write.

The issue of the current radiation protection system for workers in uranium mines is that it has practically not changed since its development in 1986, when the “Health and safety rules for the operation of uranium mines” were approved. The quality of exposure monitoring of workers in uranium mines is affected by the lack of personal dosimetry, since periodic monitoring of the working environment, according to A. Operchuk’s conclusions, does not guarantee calculation quality and reliability of effective exposure doses of workers at uranium mines.

In addition, ventilation circuits of underground mine workings are often arranged irrationally, ventilation partitions for redistribution of air flows are not constructed in time, inactive mine workings are not isolated. A fair amount of unfilled stope working, in addition to radon release, takes most of the fresh air forced by ventilation under the ground. There is the lack of reliable data for design of ventilation systems during construction of new cleaning units and choosing locations for workplaces and other mine workings.

“All of the above ultimately leads not only to an unreasonable increase/decrease of air supply from the main mine fans, but also to additional personnel exposure”,  A. Operchuk notes.

Experts present the statistics on the increase of lung cancer rate for underground personnel of uranium mines on average twice during 1991-2002. The death rate in 2008 was over 6 cases per 1000 category A workers, which corresponded to a dose of more than 100 mSv/year under a permissible limit of 20 mSv/year.

Operchuk’s studies state that according to the official data for 1997-2015 on personal exposure doses of workers in uranium mines of all cohorts, personal effective doses are much lower than the dose limit and reference levels. However, the real mortality rate due to occupational cancer prevails the predicted rates (one death per 1000 workers) for such doses and ranges from 3.54 to 7.67 cases per 1000 for different cohorts of underground personnel.

The registration of the cases of occupational oncological diseases by years. The occupational cancer rate tends to decrease slightly over the years. This phenomenon is associated with the introduction of more strict requirements for radiation protection of miners NRBU-97 and dose limit reduction for personnel from 50 mSv/year to 20 mSv/year, Source: A. Operchuk

So, miners actually receive higher doses than recorded, because the occurrence of oncological diseases linearly depends on the effective dose level and length of service under radiation effects. Although, additional exposure of uranium mine workers to radon at home cannot be excluded as one of the causes.

Anatolii Operchuk presents the data that, on average, the occupational cancer rate for workers in uranium mines in 1997-2015 was 11% of all diseases registered at uranium enterprises. At the same time, the occupational cancer rate in the Smolinska mine was 34% higher than in the Ingulska mine. This was explained by the fact that many miners working at this facility had previous work experience in uranium mines in other regions of the former USSR.

On average, occupational cancer was formed in uranium mine workers at the age of 59. The lower the age of work start, the greater cancer likelihood in the future.

Oncological diseases in Ukraine, Kirovograd Oblast and SkhidGZK mines located in the territory of the Kirovograd Oblast as of 2016 (relative indexes per 100,000 people).

Indexes

Total number of oncological diseases at the enterprise

Ingulska mine

Smolinska mine

Kirovograd Oblast

Ukraine

Total

499,7

776,5

900,0

411,2

328,6

Lung and upper respiratory tract cancer

164,7

64,7

100,0

54,8

37,9

Source: A. Operchuk

Thus, the maximum permissible dust concentration in the air of the working area in ​​uranium mines and personal exposure doses of mine workers require continuous monitoring and reduction. Moreover, medical supervision needs improvement, in particular, during admission to job, throughout employment and before retirement or upon dismissal, it is necessary to conduct a thorough medical examination of mine workers, with a mandatory X-ray functional assessment of respiratory system condition to identify possible presence or signs of occupational lung pathology and do not stop medical supervision until the end of the workers’ lives.

In addition, there is a need for engineering studies of protective measures related to radon monitoring and optimization of the radiation situation in general in design and commissioning of uranium mining enterprises.

Anatoliy Operchuk proposes to bring the methods to assess personal doses of miners in various mining operations into compliance with the requirements of the IAEA Basic Radiation Safety Standards and Euratom 2013/59/Directive, in particular in implementing personal dose monitoring.

Uranium mines currently provide 40% of the needs of the nuclear industry of Ukraine for raw materials for nuclear fuel taking our country to the 12th place in the world in terms of uranium ore production (as of 2019 year). The performance of this industry is highly dependent on personnel health. Therefore, radiation protection of miners should always remain a priority for both the management of enterprises and the state.

Uatom.org Editorial Board.