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Journal of Environmental Radioactivity 135 (2014) 25e35

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate/ jenvrad

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

Lidia Fija1kowska-LichwaWrocław University of Technology, Faculty of Civil Engineering, Institute of Geotechnics and Hydrotechnics, Division of Engineering and EnvironmentalGeology, 50� 370 Wrocław, Wybrze _ze S. Wyspia�nskiego 27, Poland

a r t i c l e i n f o

Article history:Received 15 September 2013Received in revised form16 March 2014Accepted 17 March 2014Available online

Keywords:RadonShort-term radon concentration changesMineUnderground tourist routeVentilationAir exchange

E-mail address: Lidia.Fijalkowska-Lichwa@pwr.edu

http://dx.doi.org/10.1016/j.jenvrad.2014.03.0140265-931X/� 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

Short-term 222Rn activity concentration changes along the Underground Educational Tourist Route in theOld Uranium Mine in Kletno were studied, based on continuous measurements conducted between 16May 2008 and 15 May 2010. The results were analysed in the context of numbers of visitors arriving atthe facility in particular seasons and the time per day spent inside by staff and visitors. This choice wasbased on partially published earlier findings (Fija1kowska-Lichwa and Przylibski, 2011). Results for theyear 2009 were analysed in depth, because it is the only period of observation covering a full calendaryear. 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 mostvisible. Attention has been paid to three crucial issues linked to the occurrence and behaviour of radonand 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 metamorphicrock complex in the most radon-prone area in Poland. The facility has been equipped with a mechanicalventilation system, which is turned on after the closing time and at the end of the working day for thevisitor service staff, i.e. after 6 p.m.

Short-term radon activity concentration changes along the Underground Educational Tourist Route inthe Old Uranium Mine in Kletno are related to the activity of the facility’s mechanical ventilation. Itsinactivity in the daytime results in the fact that the highest values of 222Rn activity concentration areobserved 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 unfav-ourable working conditions, which persist in the facility for practically all year. The absence of appro-priate radiological protection (i.e. preventive measures like shortening working day, dosimetricmeasurements in the workplace) is a serious problem in the Kletno adit.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In many European countries, including Sweden, the Czech Re-public, Slovakia, Hungary, Great Britain, Spain, Denmark, Norway,Finland, Romania and Italy, there is an awareness that the occur-rence of increased concentrations of radioactive gas e radon e inunderground workplaces may have a detrimental effect on thehuman body. For this reason, these countries have adopted lawsfollowing guidelines from international organisations (ICRP, 1993;Åkerblom, 1999; IAEA, 2003) concerning chiefly the allowableannual limit of radon activity concentration, but also measurement

.pl.

techniques, measurement duration and the duration of exposure toradon and its progeny (Sainz et al., 2007; Kávási et al., 2009, 2010).

In Poland, the current law only requires that exposure to ionizingradiation from radon and its progenymust bemonitored in operatingunderground workplaces e coal mines (e.g. Skubacz and Bywalec,2003; Komosa et al., 2004; Skubacz and Mielnikow, 2004; Wysockaet al., 2005; Wysocka and Cha1upnik, 2009) and copper mines (e.g.Kisiel, 2007; Kisiel et al., 2010; Olszewski et al., 2005; Olszewski,2006). Unfortunately, the occurrence of this problem in other un-derground structures like tourist routes is disregarded both by theowners of such facilities and, most importantly, by local authorities.The reason is the lack of appropriate acts implementing the existinglaw (Ustawa, 2000). Despite the passivity of the organisationsresponsible for estimating and monitoring human exposure to

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e3526

increased levels of ionizing radiation in underground workplacesother than mines, measurements of radon activity concentration areyet performed. This should be mostly credited to researchersemployed by higher education institutions and scientific researchcentres all over the country (Przylibski, 1998, 1999, 2000a, b; 2001;Solecki et al., 2007; Tchorz�Trzeciakiewicz, 2008; Olszewski et al.,2005; Olszewski, 2006; Chru�scielewski and Olszewski, 2000;Chibowski and Komosa, 2001; Kozak et al., 2010; Przylibski andFija1kowska-Lichwa, 2010; Fija1kowska�LichwaandPrzylibski, 2011).

Long-term radon measurements, conducted at short intervals,have facilitated research into the behaviour of this gas. They havemade it possible to observe radon activity concentration changesduring 24 h or shorter periods, and the obtained results haveenabled a more accurate determination of an ionizing radiationdose from radon and its progeny than was possible with monthlymean measurements conducted by means of SSNTD. Such mea-surements may be also employed for monitoring geodynamicphenomena such as earthquakes, volcanic eruptions, etc. Similarresearch, using measuring devices suitable for long-term mea-surements with frequent data logging (every hour or day) has beenconducted in other countries including France (Perrier et al., 2004a,b, 2005, 2007; Perrier and Richon, 2010), England (Gillmore et al.,2000, 2001, 2002, 2011) and Spain (Sainz et al., 2007).

1.1. Choice of research object

TheUnderground Educational Tourist Route is situated in Lower-Silesian Voivodeship, K1odzko county, Stronie �Slaskie commune insouth-western Poland and in the south-eastern part of theWestern

Fig. 1. Location of the Underground Educational Tourist Route in the Old UraniumMine in Klof the Sudetes (A) and a map of Poland (B).

Sudetes (Fig. 1, Cymerman, 1991; Cymerman and Piasecki, 1994;Stupnicka, 1997; Janiec, 2003a, b; Cwojdzi�nski and Kozdrój, 2007).

The facility was first open to the public on 21 September 2002,under the name of the Underground Educational Tourist Route inthe Old UraniumMine in Kletno, but it is also known as the FluoriteAdit in Kletno. This informal name refers to mineralisation inthermal veins containing fluorite accompanied by quartz, hematiteand uranite (Cie _zkowski, 1989a, b; Gustaw, 2005).

The underground tourist route consists of workings of the dis-used uranium mine “Kopaliny” in Kletno operating in the 1950s.Earlier, since the Middle Ages, metal ores were mined in this area.After the termination of uraniummining, fluorite extraction startedin 1954 (Cie _zkowski, 1989a, b).

The underground tourist route is an enclosed system of workingsin the north-westernpart of themine. The entrance lies by the accessroad betweenKletno and Sienna, at the altitude of 773m. The systemconsists of six galleries, only two of which have a direct connectionwith the shaft. The total length of theworkings accessible for touristsis about 200 m (Fig. 2B). The height of the galleries varies from 1.7 to2.0m.Also, thewidthof theworkings is not the sameateverypoint ofthe route and it varies from 1.5 to 2.0 m (Gustaw, 2005).

The Underground Educational Tourist Route in the Old UraniumMine in Kletno was chosen for the research out of more than 70underground tourist facilities listed in the area of Poland, as itsatisfied all the requirements, i.e:

� accessibility (the route can be visited only with a guide),� a possibility of continuous monitoring of the measuring equip-ment (the facility opens and closes at designated times of the

etno on a geological sketch (based on Cwojdzi�nski and Kozdrój, 2007) of the Polish part

Fig. 2. Plan of the Underground Educational Tourist Route in the Old Uranium Mine in Kletno (based on Cie _zkowski and Krahl, 2001) with plotted places of performing mea-surements of 222Rn activity concentration (B) and a photo of SRDN�3 probe operating at measurement site 1 (A).

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e35 27

day: it is open daily from 10 a.m. to 6 p.m. except Mondays andThursdays),

� location within a radon-prone area (the crystallineLadek��Snie _znikMassif lying in the SE part of the Sudetes, rich inradium and uranium),

� the origin of the structure (an anthropogenic structure classifiedwithin the category of adits and mines),

� the lithology of the bedrock (a cracked rock massif in a tectoniczone within mica schists and gneisses containing from32 Bq kg�1 to 77 Bq kg�1 of 226Ra (Przylibski, 2005),

� the ventilation method (forced e the route is equipped withperiodically activated mechanical ventilation as natural air ex-change with the atmosphere is not efficient enough).

2. Material and methods

The key issue was to select measurement equipment suitable foruse in thenatural and technological conditionsof the structure.Whatturned out to be the best solution was building a device equippedwith a semi-conductor detector with relatively high sensitivity(LLD < 100 Bq m�3) and a small size (a single device weighs about3.2 kg). Theprototype is resistant to low temperatures, highhumidityand dust in the air. Moreover, it is powered by a double LSH�20battery (13Ah),which allows a12-month spanof virtually unmannedmeasurements (automatic data logging into microcomputer mem-ory). The used measuring devices are the product of collaborationbetween the Institute of Mining, Wroc1aw University of Technologyand the Institute of Chemistry and Nuclear Technology (ICHiTJ) inWarsaw. The operation of SRDN�3 probes, their structure and cali-bration, as well the results of calibration and field tests were given adetailed description by Przylibski et al. (2010).

Two SRDN�3 probes were placed along the underground touristroute in Kletno. In order to protect the measurement equipment,the measurement points (Fig. 2) were chosen in a way that madethem invisible to visitors. The probes were mounted on tripods, atthe height of about 1m above the floor of theworking (Fig. 2A). The222Rn activity concentration was recorded at 1-hour intervals,which enabled logging 24 results a day together with the values ofair temperature and relative humidity around the probe.

Determination uncertainty for SRDN�3 probes adopted afterdevice calibration at the 1d. The error ofmeasurement reaching 21e32% values of 222Rn concentration determination performed bySRDN�3 probes close to detection threshold, which is 96.5 Bq m�3

for SRDN�3 No. 2 and 94.8 Bqm�3 for SRDN�3 No. 3. In the order ofthousands Bq m�3 the determination uncertainty clearly decreases,reaching 7.5e9.5% of themeasurement value Przylibski et al. (2010).

Values of radon concentration measured in underground touristroute in Kletno are very different, as evidenced by the standarddeviation of the mean (SD). The adoption standard deviation (SD)as the measurement error (mean� SD) was not possible. Therefore,the measurement error (mean � SE) was taken as the standarderror of themean (SE). The average value of the measurement is thearithmetic mean (mean). The values of 222Rn with basic statisticalinformations were included in tables (Tables 1 and 2).

The continuousmeasurements of 222Rn activity concentration inthe air of the underground educational tourist route in Kletno wereconducted for two years, from 16 May 2008 to 15 May 2010.

An effective radiation dose was estimated in compliance withUNSCEAR guidelines (2000). According UNSCEAR (2000) recom-mendations radiation dose should be determined as the sum of twovalues (Eqs. (1) and (2)). First one is a dose coming from 222Rn andits progeny received through inhalation (Eq. (1)) and the secondone is a dose dissolved in as a result of the absorption of 222Rn andits progeny (Eq. (2)).

Et ¼ CRn�222$F$EiCF (1)

where:

Et e effective dose resulting from the absorption of 222Rn and itsprogeny through inhalation [mSv/h],CRn-222 e

222Rn activity concentration [Bq m�3],F e coefficient of radioactive equilibrium between 222Rn and itsdecay products [e]. The value of 0.4, recommended for this typeof structures. It is adopted if it was not measured directly(Gillmore et al., 2001; Kávási et al., 2010)EiCF e conversion coefficient per dose; adopted value of0.000009 mSv/Bq h/m3 UNSCEAR (2000).

Eb ¼ CRn�222$EbCF (2)

where:

Eb e effective dose resulting from 222Rn absorption and itsdissolution in blood [mSv/h],

Table 1Dose estimations for different exposure scenarios based on values of 222Rn activity concentration recorded at time when tourist route is open for visitors (10:00e18:00) at twomeasurement sites SRDN-3 No. 2 and SRDN-3 No. 3located in the Underground Educational Tourist Route in the Old Uranium Mine in Kletno.

SRDN-3No. 2

Meanvalueof 222Rnmean � SEa

StandarddeviationSD

Minimumvalueof 222Rnb

Maximumvalueof 222Rnc

Workhoursd

Mean value ofionizing radiationdose received during30 min time touristroute exploringmean � SEe ¼ (Et þ Eb)$0.5

StandarddeviationSD

Minimum value ofionizing radiationdose received during30 min time touristroute exploringf ¼ (Et þ Eb)$0.5

Maximum value ofionizing radiationdose received during30 min time touristroute exploringg ¼ (Et þ Eb)$0.5

Mean value ofionizing radiationdose receivedeach seasonof the yearmean � SEh ¼ e$d

StandarddeviationSD

Minimum valueof ionizingradiation dosereceived eachseason ofthe yeari ¼ f$d

Maximum valueof ionizingradiation dosereceived eachseason ofthe yearj ¼ g$d

Month [Bq m�3] [Bq m�3] [Bq m�3] [Bq m�3] [h] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv]January 5330 � 214 3580 190 13,945 184 0.01 � 0.0004 0.007 0.0004 0.03 1.8 � 0.07 1.2 0.07 4.8February 8147 � 299 4751 190 15,014 160 0.02 � 0.0006 0.009 0.0004 0.03 2.5 � 0.09 1.4 0.06 4.5March 4950 � 256 4271 113 21,854 184 0.009 � 0.0005 0.008 0.0002 0.04 1.7 � 0.09 1.5 0.04 7.6April 9559 � 385 5937 763 21,854 176 0.02 � 0.0007 0.010 0.001 0.04 3.2 � 0.13 2.0 0.25 7.3May 9209 � 397 6539 725 21,816 184 0.02 � 0.0007 0.010 0.001 0.04 3.2 � 0.14 2.3 0.25 7.6June 7736 � 276 4506 381 21,701 176 0.01 � 0.0005 0.008 0.0007 0.04 2.6 � 0.09 1.5 0.13 7.2July 3662 � 105 1751 534 10,277 184 0.007 � 0.0002 0.003 0.001 0.02 1.3 � 0.04 0.6 0.19 3.6August 3015 � 72 1198 572 7144 184 0.006 � 0.0001 0.002 0.001 0.01 1.0 � 0.02 0.4 0.20 2.5September 2627 � 87 1432 304 7488 176 0.005 � 0.0002 0.003 0.006 0.01 0.9 � 0.03 0.5 0.10 2.5October 4118 � 279 4580 113 21,128 184 0.008 � 0.0005 0.009 0.0002 0.04 1.4 � 0.10 1.6 0.04 7.3November 2238 � 165 2696 113 15,664 176 0.004 � 0.0003 0.005 0.0002 0.03 0.7 � 0.05 0.9 0.04 5.2December 2663 � 111 1856 113 8519 184 0.005 � 0.0002 0.003 0.0002 0.02 0.9 � 0.04 0.6 0.04 3,00

Dose received during a work year[mSv/year]

>20 e >1.0 >60

SRDN-3No. 3

Meanvalueof 222Rnmean � SEa

StandarddeviationSD

Minimumvalueof 222Rnb

Maximumvalueof 222Rnc

Workhoursd

Mean value ofionizing radiationdose received during30 min time touristroute exploringmean � SEe ¼ (Et þ Eb)$0.5

StandarddeviationSD

Minimum value ofionizing radiationdose received during30 min time touristroute exploringf ¼ (Et þ Eb)$0.5

Maximum value ofionizing radiationdose received during30 min time touristroute exploringg ¼ (Et þ Eb)$0.5

Mean value ofionizingradiation dosereceived eachseason ofthe yearmean � SEh ¼ e$d

StandarddeviationSD

Minimum valueof ionizingradiation dosereceived eachseason ofthe yeari ¼ f$d

Maximum valueof ionizingradiation dosereceived eachseason ofthe yearj ¼ g$d

Month [Bq$m�3] [Bq$m�3] [Bq$m�3] [Bq$m�3] [h] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv] [mSv]January 2488 � 98 1644 208 6847 184 0.005 � 0.0002 0.003 0.0004 0.01 0.9 � 0.03 0.6 0.07 2.4February 3203 � 112 1778 130 8996 160 0.006 � 0.0002 0.003 0.0002 0.02 1.0 � 0.03 0.5 0.04 2.7March 2318 � 114 1897 208 1089 184 0.004 � 0.0002 0.004 0.0004 0.02 0.8 � 0.04 0.7 0.07 3.5April 6859 � 337 5011 403 20244 176 0.01 � 0.0006 0.009 0.0008 0.04 2.3 � 0,10 1.7 0.10 6.7May 2206 � 78 1306 169 6808 184 0.004 � 0.0001 0.002 0.0003 0.01 0.8 � 0.03 0.5 0.06 2.4June 2214 � 76 1247 208 7668 176 0.004 � 0.0001 0.002 0.0004 0.01 0.8 � 0.03 0.4 0.07 2.7July 2019 � 81 1346 325 8410 184 0.004 � 0.0002 0.003 0.0006 0.02 0.7 � 0.03 0.5 0.10 2.9August 1617 � 57 944 208 6535 184 0.003 � 0.0001 0.002 0.0008 0.01 0.6 � 0.02 0.3 0.07 2.3September 1484 � 74 1217 130 7902 176 0.003 � 0.0001 0.002 0.0002 0.01 0.5 � 0.02 0.4 0.04 2.6October 1900 � 54 992 130 5051 184 0.004 � 0.0001 0.002 0.0002 0.01 0.7 � 0.02 0.3 0.05 1.8November 1736 � 51 842 364 4777 176 0.003 � 0.0001 0.002 0.0007 0.009 0.6 � 0.02 0.3 0.10 1.6December 2088 � 72 1202 130 5598 184 0.004 � 0.0001 0.002 0.0002 0.01 0.7 � 0.03 0.4 0.05 1.9

Dose received during a work year[mSv/year]

±10 e £1.0 >30

Symbols: Et e effective dose resulting from the absorption of 222Rn and its progeny through inhalation [mSv/h], Eb e effective dose resulting from 222Rn absorption and its dissolution in blood [mSv/h], f, g e account respectivelyfor minimum and maximum 222Rn values [Bq m�3].

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Table 2Seasonal averages of 222Rn concentration occurred in twomeasurement sites SRDN-3 No. 2 and SRDN-3 No. 3 located in the Underground Educational Tourist Route in the OldUranium Mine in Kletno.

Mean � SE Standard deviation SD Minimum value of 222Rn Maximum value of 222Rn

[Bq m�3] [Bq m�3] [Bq m�3] [Bq m�3]

Season SRDN-3 no. 2 SRDN-3 no. 3 SRDN-3 no. 2 SRDN-3 no. 3 SRDN-3 no. 2 SRDN-3 no. 3 SRDN-3 no. 2 SRDN-3 no. 3

Spring 5809 � 118 2936 � 82 5489 3715 113 130 21,854 20,244Summer 1975 � 46 1081 � 27 2145 1225 113 130 1514 9699Autumn 2944 � 81 1860 � 26 3647 1199 113 130 21,701 7902Winter 5445 � 111 2510 � 47 5095 2128 113 130 21,854 11,769

Symbols: mean e arithmetic mean, SE e standard error.

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e35 29

EbCF e conversion coefficient per dose; adopted value of0.00000017 mSv/Bq h/m3 UNSCEAR (2000).

To estimate the values of radiation dose to which workers(mainly guides) and members of the public (visitors) were exposedin underground tourist route used partly published (Fija1kowska-Lichwa and Przylibski, 2011) results of radon activity concentra-tion measurements recorded on a hourly during a year. Conductedresults converted to real working timewhich guides (30minwithin8 h during a day for 269 days a year) and visitors (only 30min a day)spent inside the adit. The estimations for different scenarios ofradon exposure show table 1 (Table 1).

Fig. 3. Changes in 222Rn activity concentration observed during two-year-long moni-toring measurements, recorded on measurement site 1 (A) and 2 (B) inside the Un-derground Educational Tourist Route in the Old Uranium Mine in Kletno. Symbols: Theblack points represent the values of radon activity concentration logged at 1-hourintervals. The red line shows the course of observed 222Rn activity concentrationchanges represents by the moving average with a period of 30 days. (For interpretationof the references to colour in this figure legend, the reader is referred to the webversion of this article.)

3. Results and discussion

3.1. General description of radon concentration

The pattern of 222Rn activity concentration changes observedduring the two-year-long monitoring period is different for eachmeasurement site inside the studied structure (Fig. 3). At mea-surement site 1, the hourly values of 222Rn activity concentrationare in constant fluctuation. One can observe continuous drops(down to probe LLD ¼ 96.5 Bq m�3) and rises (from 7000 Bq m�3

even to 12000 Bq m�3) of radon activity concentration values(Fig. 3A). At measurement site 2, the range of 222Rn activity con-centration changes is clearly smaller. One cannot observe periodswhen radon concentrations at this measurement point were clearlylower or clearly higher than the mean value, which was a littlemore than 4000 Bq m�3 (Fig. 3B). Owing to this fact, further ana-lyses were performed for every hour of the measurements, con-ducted throughout the four seasons corresponding to the varyingvolume of visits to the facility in 2009, chosen as a representativeyear.

At measurement point 1 (SRDN�3 No. 2), high values of radonactivity concentration were recorded between 8 a.m. and 6 p.m.throughout the whole year (Fig. 4). They averaged from3400 Bq m�3 to 6000 Bq m�3 (Fig. 4). Quite stable low values ofradon activity concentration were recorded twice a day: frommidnight to 7 a.m. and from 7 p.m. to 11 p.m.. At measurementpoint 2 (SRDN�3 No. 3), one could also notice periods when therecorded values of 222Rn activity concentration were clearly loweror clearly higher than the others (Fig. 4). At this interval, the highestvalues of radon activity concentrationwere recorded in the daytimeand they varied from 2100 Bq m�3 to 2600 Bq m�3 (Fig. 4). Lowervalues of radon activity concentration were recorded frommidnight to 10 a.m. and from 7 p.m. to 11 p.m. and they stayed inthe range of 1800 Bq m�3e 2000 Bq m�3 (Fig. 4). A comparison ofthe obtained results shows that the highest values of radon activityconcentration at both measurement sites were recorded in thedaytime, i.e. when the staff and the visitors were present in the adit.The facility is equipped with a mechanical ventilation system

whose function is to lower the high concentrations of this radio-active gas inside the adit. However, as the results show, (Fig. 4) theventilation systemwas turned on in the hours when the facility wasclosed to visitors, i.e. after 6 p.m.. As a result, lower values of radonactivity concentration were recorded from 7 p.m. to 10 a.m., be-tween the closing and the opening of the facility (Fig. 4). It wasnoticed then that despite the 16 h of system operation per day, thereduction of radon activity concentration was very small, just be-tween 14% and 23%. Such a result proves both the low efficiency ofthe used system and its insufficient operation time.

mean±SE for measurement site No. 1 (SRDN-3 No. 2) mean±SE for measurement site No. 2 (SRDN-3 No. 3)

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The difference between the observed 222Rn activity concentra-tions inmeasuring sites No.1 andNo. 2may result from the distancebetween each points and the ventilation shaft. The first one islocated away from shaft, the second one closer it. Parallel, recordedin thesemeasuring points values of radon activity concentration arehigher at site No. 1, and smaller at site No. 2. This position ofmeasuring points can play an important role especially in autumnandwinter,where occurs natural air exchangewith the atmosphere.

A categorisation of 222Rn activity concentration, allowing for thetime of measurement, showed that one can distinguish periodswhen the values of radon activity concentration along the Under-ground Educational Tourist Route in the Old Uranium Mine inKletno are clearly higher or clearly lower than the annual meanvalues measured at each measurement point inside the facility, i.e.2000 Bq m�3 (SRDN�3 No. 2) and 4000 Bq m�3 (SRDN�3 No. 3).The annual mean close 2000 Bq m�3 is visible at measurement siteNo. 1 three times a year (Fig. 5). At measurement site No. 2 notedeach months mean values of 222Rn activity concentration aresmaller than the annual mean (Fig. 6).

Observed that radon is accumulated in the stagnating air insidethe adit when the mean daily atmospheric temperature rises abovethe mean temperature inside the structure, which is about 6.5 �C.This phenomenon has been also observed in other structures anddescribed by Przylibski (1998, 1999, 2000a, b, 2001) as well asFija1kowska�Lichwa and Przylibski (2011). This trend is enhancedby deactivating the mechanical ventilation of the adit in the day-time, i.e. between 9 a.m. and 5 p.m. in spring and from 8 a.m. to 5p.m. in summer. Radon is removed from the structure only inautumn and winter, despite the inactivity of the mechanicalventilation between 10 a.m. and 4 p.m. in autumn and between 9a.m. and 4 p.m. in winter, and despite the low efficiency of thesystem when it is working, reducing the radon activity concentra-tion by only 17%e23%.

3.2. Seasonal values of radon concentration

The partially published results of long-term radon activityconcentration measurements conducted in the Kletno adit

confirmed that due to their seasonal character, radon activityconcentration changes coincide with changes in the number oftourists visiting the facility. (Fija1kowska�Lichwa and Przylibski,2011). For this reason, the change pattern of 222Rn activity con-centration obtained from the 2-year-long observations was ana-lysed for two periods with different visitor volumes. These were:the high season, corresponding to two calendar seasons: spring andsummer, and the low season, starting in autumn and continuinguntil winter. The year 2009 (from January 1 to December 31), as amore characteristic one, was chosen for the observation of short-term 222Rn activity concentration changes in particular calendarseasons (spring, summer, autumn, winter). The analysis was per-formed using the results obtained from two measurement sitesinside the facility. The values of annual 222Rn activity concentrationrecorded each season of the year show in Table 2 (Table 2).

In the spring (from 21 March to 21 June), the radon activityconcentrations recorded at each measurement site were compa-rable. At site 1, the values measured from midnight to 8 a.m. weremuch lower than those recorded during the next 15 h of the day(Fig. 7). Between 9 a.m. and 3 p.m. (measurement site No. 1) andbetween 9 a.m. and 2 p.m. (measurement site No. 2), there was amarked increase of 222Rn activity concentration. At this time in-terval, it oscillated between 4000 Bq m�3 and 9000 Bq m�3. Adecrease of the radon activity concentration values could beobserved between 6 p.m. and 10 p.m. (Fig. 7). At measurementpoint 2, the activity concentration recorded from midnight to 10a.m. remained at a stable average level of 2000 Bq m�3. Between 11a.m. and 5 p.m. however, there was a marked increase in radonactivity concentration up to 4000 Bq m�3. Between 6 p.m. and 11p.m., the activity concentrations dropped back to the initial averagevalue of 2000 Bq m�3 (Fig. 7).

An identical situationwas observed in the summer (between 22June and 22 September) of 2009. Also in that season, three char-acteristic periods were distinguished at both measurements pointsduring the day. In those periods, radon activity concentrationsinitially remained at a stable level, then sharply rose and thendecreased again after a few hours. Between midnight and 8 a.m.,radon activity concentrations stayed at a stable average level of

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R-3

]

mean mean±SE

Fig. 5. Monthly changes in 222Rn activity concentration recorded during one-year-long monitoring measurements at measurement site 1 (SRDN�3 No. 2) at the UndergroundEducational Tourist Route in the Old Uranium Mine in Kletno. Symbols: mean e arithmetic mean, SE e standard error.

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e35 31

1000 Bq m�3. A sharp rise in the value followed after 8 a.m. andcontinued until 5 p.m.. Between 6 p.m. and 11 p.m., radon activityconcentrations dropped to the level of 2000 Bq m�3 (Fig. 8). Theobserved situation confirms that in spring and summer there are noconvective air movements that would carry radon out of the Un-derground Educational Tourist Route in the Old Uranium Mine inKletno into the atmosphere. This is the reason why the highestvalues of 222Rn activity concentration occur here in the daytime,when visitors, and particularly the visitor service and maintenancestaff are present inside the facility.

Janu

ary

Febr

uary

Mar

ch

Apr

il

May

June

M

0

1000

2000

3000

4000

5000

6000

7000

222

m·qB[n

R-3

]

Fig. 6. Monthly changes in 222Rn activity concentration recorded during one-year-long mEducational Tourist Route in the Old Uranium Mine in Kletno. Symbols: mean e arithmetic

Likewise, autumn (from September 23 to December 21) andwinter (from December 22 to March 20) are seasons with distin-guishable times of the day when clearly higher radon activityconcentrations occur (Figs. 9e10).

In autumn, such a situation was observed only at measurementsite 1. From 10 a.m. to 4 p.m., the values recorded in this section ofthe facility rose from themean level of 2700 Bqm�3 to 3500 Bqm�3

(Fig. 9). For the rest of the day, the radon activity concentrationstayed at an average level of 2900 Bq m�3. The obtained resultsconfirm the low efficiency of the mechanical ventilation system

July

Aug

ust

Sep

tem

ber

Oct

ober

Nov

embe

r

Dec

embe

r

onth

mean mean±SE

onitoring measurements at measurement site 2 (SRDN�3 No. 3) at the Undergroundmean, SE e standard error.

mean ±SE for measurement site No. 1 (SRDN-3 No. 2) mean ±SE for measurement site No. 2 (SRDN-3 No. 3)

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

11:0

0

12:0

0

13:0

0

14:0

0

15:0

0

16:0

0

17:0

0

18:0

0

19:0

0

20:0

0

21:0

0

22:0

0

23:0

0

Hour

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

222

m·qB[n

R-3

]

Fig. 7. Hourly values of 222Rn activity concentration in spring recorded at two measurement sites along the Underground Educational Tourist Route in the Old Uranium Mine inKletno.

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e3532

used in the facility. Its operation enables reducing the values ofradon activity concentration only by about 17%.

In winter, there were characteristic hours during the day withclearly higher or lower values of radon activity concentration atboth measurement points (Fig. 10). At measurement point 1, muchhigher radon activity concentrations were recorded between 9 a.m.and 4 p.m., while at point 2 e slightly later, from 11 a.m. to 4 p.m..Between 9 a.m. and 4 p.m., radon activity concentration values rosefrom 5000 Bq m�3 to 6700 Bq m�3 (Fig. 10). Between 11 a.m. and 4p.m., they reached 2600 Bqm�3e 3000 Bqm�3 (Fig.10). For the rest

mean±SE for measurement site No. 1 (SRDN-3 No. mean±SE for measurement site No. 2 (SRDN-3 No.

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

222

m·qB[

nR

-3]

Fig. 8. Hourly values of 222Rn activity concentration in summer recorded at two measuremKletno.

of the day, the radon activity concentration remained at quite astable level with an average value of 5200 Bq m�3 at measurementpoint 1 and 2300 Bq m�3 at point 2. In winter, activating the me-chanical ventilation of the adit reduced the recorded values ofradon activity concentration by 23%.

The ventilation system currently used in the facility is not effi-cient enough, because the mean annual values of radon activityconcentrations recorded in the Kletno adit are from two to fourtimes as large as the values recommended by international orga-nisations (Table 2; IAEA, 2003; ICRP, 1993).

2) 3)

11:0

0

12:0

0

13:0

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0

18:0

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0

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0

22:0

0

23:0

0

Hour

ent sites along the Underground Educational Tourist Route in the Old Uranium Mine in

mean±SE for measurement site No. 1 (SRDN-3 No. 2) mean±SE for measurement site No. 2 (SRDN-3 No. 3)

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

11:0

0

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15:0

0

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0

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0

23:0

0

Hour

0

500

1000

1500

2000

2500

3000

3500

4000

4500

222

m·qB[

nR

-3]

Fig. 9. Hourly values of 222Rn activity concentration in autumn recorded at two measurement sites along the Underground Educational Tourist Route in the Old Uranium Mine inKletno.

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e35 33

3.3. Dose assessment

The conducted measurements of radon activity concentrationand their analysis considering the number of visitors to the facilityin each of the four seasons of 2009 have indicated that the largestexposure to ionizing radiation in the adit occurs in the daytime,when the facility is open to visitors. This is due to natural factors(advection) and, most of all, to deactivating the mechanical venti-lation of the structure during the opening times. The unconsideredusage of the mechanical ventilation system in the adit results in the

mean±SE for measurement site No. 1 (SRDN-3 No. mean±SE for measurement site No. 2 (SRDN-3 No.

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

0

1000

2000

3000

4000

5000

6000

7000

8000

222

m·qB[

nR

-3]

Fig. 10. Hourly values of 222Rn activity concentration in winter recorded at two measuremeKletno.

fact that the facility is visited by tourists in the conditions ofincreased exposure to radiation. This is particularly disadvanta-geous from the point of view of radiological protection of peopleemployed in the facility, including their safety and health at work(Ustawa, 2000).

In 2009, the Underground Educational Tourist Route in Kletnowas open to visitors for 8 h a day, from 10:00 to 18:00 daily exceptMondays and Thursdays. The facility was closed for 8 days eachmonth. In 2009, the visitors to the underground tourist route wereserved for 30min 16 times a day, for 269 working days per calendar

2) 3)

11:0

0

12:0

0

13:0

0

14:0

0

15:0

0

16:0

0

17:0

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18:0

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20:0

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21:0

0

22:0

0

23:0

0

Hour

nt sites along the Underground Educational Tourist Route in the Old Uranium Mine in

L. Fijałkowska-Lichwa / Journal of Environmental Radioactivity 135 (2014) 25e3534

year. Themean annual dose of radiation from radon and its progenyreceived by the guides working according to a planned schedulewas bigger than 20 mSv/year. This value was slightly higher thanthe annual radiation dose of 20 mSv/year allowed by the Polish law(Ustawa, 2000). The estimation for different scenarios of radonexposure included in Table 1 (Table 1).

The distribution of radiation dose inside the undergroundtourist route in Kletno shows that it does not depend on seasonalchanges. The highest exposure to ionizing radiation from radonshould be expected both in warm months (April, May and June),when visitor numbers are the highest, and in cold ones (Januaryand February), when these numbers clearly decrease. However, ithas been noticed that ionizing radiation doses undergo short-termchanges. Regardless of the season, both the guides and the visitorsreceive the maximum radiation dose between 11 a.m. and 5 p.m.,which is linked to the insufficient ventilation of the structure. Theventilation system is turned off in the daytime, which results in thefact that exposure to ionizing radiation is the highest at the timewhen the adit is open to visitors.

4. Conclusions

The Underground Educational Tourist Route in the Old UraniumMine in Kletno is a place where occur short-term radon activityconcentrations changes. The observed changes have clearly irreg-ular character and they depend on the activation or deactivation ofthe mechanical ventilation of the structure. Large daytime fluctu-ations of radon activity concentrations in the Kletno adit are visiblein each of the four calendar seasons corresponding to tourist sea-sons with the varying number of visitors to the facility. The highestvalues, regardless of the season, are recorded when the facility isopen to visitors, i.e. from 10 a.m. to 6 p.m. The patterns of short-term radon activity concentration changes observed at particularmeasurement sites in spring and summer are similar to those inautumn and winter. However, in spite of these similarities, thereare clear differences in the absolute values of radon concentration.

Natural process of radon removing from underground structureoccurs only in autumn and winter. Turn off the mechanical systemof object ventilation during a daytime does not affect the process ofconvection. In order part of the year radon is accumulated in thestagnating air inside the adit. It is related to the mean daily atmo-spheric temperature and the inactivity of the forced ventilation.Increase of mean daily atmospheric temperature above the meantemperature inside the structure, which is about 6.5 �C causes alsoincreasing of 222Rn activity concentration inside. This relationshipswere described by Fija1kowska�Lichwa and Przylibski (2011).

Currently used the ventilation system is not efficient enough. Itsoperation enables lowering values of radon activity concentration byno more than 23% of the mean value, i.e. down to the level of3000Bqm�3 atmeasurement site1 (SRDN�3No.3) and1500Bqm�3

at site 2 (SRDN�3 No. 2). Even so, these values are considerablyhigher than the allowable threshold limit of 500 Bq m�3e

1000 Bq m�3 recommended for such underground workplaces byinternational organisations: the International Atomic Energy Agency(IAEA), the International Commission on Radiological Protection (ICRP)and the European Commission (EC) (IAEA, 2003; ICRP, 1993).

The system of mechanical ventilation used in the studiedstructure does not operate properly as it is activated at the wrongtimes (after closing the facility for visitors). It means that activatingthe system does not lead to lowering radon concentration insidethe facility in the part of the day (10 a.m. e 6 p.m.) when touristsand, more importantly, the staff employed to serve them and doother jobs inside the structure are present there. The ill-consideredmechanical ventilation of the structure, inadequate to the workingconditions in the facility, does not prevent, and even increases the

risk of radiation exposure, particularly for the staff. Staying in thefacility during a 30-minute tour results in receiving an ionizingradiation dose averaging 0.004 e0.02 mSv. For visitors, the time ofthe tour (spent inside the structure) is too short (30 min) to putthem at risk of receiving a radiation dose exceeding the allowableannual limit of 1 mSv/year set by the Atomic Law (Ustawa, 2000;Regulation of the Council of Ministers, 2005). The situation of theworkers employed at the underground tourist route in Kletno,analysed through the prism of a year’s work, even for a short, 30-minute stay inside the structure is disadvantageous in light of thecurrent Polish law (Regulation of the Council of Ministers, 2005).According to this law, the allowablemean annual effective radiationdose received by the staff employed in the conditions of exposureto ionizing radiation must not be higher than 20 mSv/year(Regulation of the Council of Ministers, 2005). In the Kletno adit,this level is exceeded in year. For this reason, the manager of theunderground tourist route should classify the workers employed atthe facility according to the size of the received ionizing radiationdose as category A (individual dose > 6 mSv/year) or category B(individual dose > 1 mSv/year) workers (Chap. 3, Art. 17, par. 1 and2, Ustawa, 2000). Such categorisation would enable taking appro-priate action to improve the workers’ safety and health at work(Chap. 3, Art. 17, par. 6, Ustawa, 2000). In the light of the mentionedlaw, such action is obligatory for all employers (Chap. 3, Art. 26, p. 1and 2, Ustawa, 2000).

Acknowledgements

The author would like to thank professor Tadeusz AndrzejPrzylibski for helpful discussion and constructive comments.

The article was financed from statutory resources of the Insti-tute of Mining Engineering, Wroc1aw University of Technology,assigned for the research: Comparison of radon content ingroundwaters in the K1odzko-Z1oty Stok granitoid intrusion andgranitoids of the Tatra crystalline structure. Commission No.B20028.

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