IN DOOR RA DON IN SLOVENIA
by
Janja VAUPOTI^
Re ceived on Oc to ber 10, 2003; ac cepted on De cem ber 24, 2003
The Slovenian Ra don Programme started in 1990. Since then, ra don and ra don short-lived de cay prod ucts have been sur veyed in 730 kin der gar tens, 890 schools, 1000 ran domly se lected homes, 5 ma jor spas, 26 ma jor hos pi tals, 10 ma jor mu nic i pal wa ter sup ply plants, and 8 ma jor win er ies. Al pha scin til la tion cells, etched track de tec -tors, electret-based de tec tors and var i ous con tin u ously mea sur ing de vices have been used. On the ba sis of es ti mated ef fec tive doses, de ci sions were made on ap pro pri ate mit i ga tion. In to tal, 35 build ings have been ap pro pri ately mod i fied. The programme is dis played and re sults re viewed chro no log i cally and dis cussed.
Key words: in door ra don, work place, mea sure ment, dose es ti mates
IN TRO DUC TION
The first ra don mea sure ments in Slovenia were made by the Jožef Stefan In sti tute in 1969 in the, at that time ex plor atory, Žirovski vrh ura nium mine [1, 2]. Once the min ing com pany had es tab lished its own ra di a tion pro tec tion ser vice, the In sti -tute turned its at ten tion to un der ground mines of coal, mer cury, and zinc [3], karst caves [4-6], spas [7, 8], and a phos phate mill [9]. In door ra don sur veys started in 1985–86 when, in each of six ur ban and in dus tri al ized ar eas, 10-30 homes were se lected for mea sur ing – once in spring, au tumn and win ter – in stan ta neous air ra don con cen tra tion with al pha scin til la tion cells [10-12]. The vol ume of the re sults was not suf fi cient to es ti mate pop u la tion doses, but ad e quate to re cog nise the ra don prob lem in the coun try and hence to pro vide a good ba sis for pre -par ing a na tion-wide ra don programme. The programme pro posal was sent to the Health In spec -tor ate at the Min is try of Health, the gov ern men tal body re spon si ble for ra di a tion pro tec tion, for eval u -a tion. Af ter its -ap prov-al, -a sys tem -atic in door r-a don
sur vey was started in 1990. Firstly, kin der gar tens, schools, and homes, and then spas, hos pi tals, wa ter plants and win er ies were sur veyed. Ef fec tive doses of em ploy ees were es ti mated and used by the Health In spec tor ate as a cri te rion for un der tak ing mit i ga tion mea sures. A num ber of build ings with high ra don lev els have been ap pro pri ately mod i fied. In this re view, the re sults of the Slo vene Ra don Programme are pre sented and dis cussed.
THE PROGRAMME
The programme was car ried out in two steps. In the first pe riod, 1990–92, in stan ta neous in door air ra don con cen tra tion was mea sured in 730 kin der gar -tens [13-23] and 890 schools [19, 22-31] with al pha scin til la tion cells, and threemonth av er age ra don con -cen tra tion in 1000 ran domly se lected homes [32, 33] with etched track de tec tors. At the same time, we were in volved in ra don mon i tor ing in kin der gar tens in some neigh bour ing coun tries [14, 34-36]. In the sec -ond pe riod, 1994–2002, we fo cused our at ten tion pri mar ily on kin der gar tens and schools with el e vated ra don lev els. Ad di tional mon i tor ing, us ing a com bi -na tion of var i ous mea sur ing tech niques, pro vided data for dose es ti mates for the per son nel as well as for chil dren and/or pu pils, on the ba sis of which the Health In spec tor ate de cided whether mit i ga tion was needed or not. The Min is try of Ed u ca tion, Sci ence and Sport es tab lished the Slo vene Ra don Cen tre as the sci en tific and tech ni cal sup port for un der tak ing mit i ga tion mea sures. About 40 build ings have been Re view pa per
UDC: 614.876:504.06:550.835.2
BIBLID: 1451-3994, 18 (2003), 2, pp. 36-43
Au thor’s ad dress: Jo`ef Stefan In sti tute
P. O. Box 3000, SI-1001 Ljubljana, Slovenia
mod i fied and ra don lev els re duced [16] to be low 200-400 Bqm–3.
In ad di tion, in the sec ond pe riod, the ra don sur -vey has been ex tended to other workplaces po ten tially ex posed to ra don. Thus, ra don was mea sured and ef -fec tive doses es ti mated for the em ploy ees of 26 ma jor hos pi tals [37], 5 ma jor spas [38], 10 ma jor wa ter -works [39], and 8 ma jor win er ies.
RA DON LIM ITS
Up to 2002, we fol lowed the ICRP rec om men -da tions [40] that ra don lev els should not ex ceed 200-600 Bqm–3 at home and 500-1500 Bqm–3 at workplaces. For the em ploy ees of kin der gar tens, schools, hos pi tals, spas, wa ter works and win er ies the first limit was taken into ac count be cause they are not de clared as ra di a tion work ers. In the be gin ning of 2002, the Slovenian gov ern ment is sued a gen eral law reg u lat ing ra di a tion pro tec tion [41], also de fin ing ra -don lim its for air. They are: 400 Bqm–3 in homes,
1000 Bqm–3 at workplaces, and 200 Bqm–3 in build
ings af ter mit i ga tion. In ad di tion, the Health In spec -tor ate uses the an nual ef fec tive dose of 2.5 mSv per year as the value above which pre cau tion ary mea sures have to be ini ti ated.
SLO VENE RA DON CEN TRE
The Slo vene Ra don Cen tre was es tab lished with the aim of de sign ing and ex e cut ing ra don mit i ga tion mea sures on an in ter dis ci plin ary ba sis. Ex -perts in ra don mea sure ment and do sim e try from the Jožef Stefan In sti tute and the Nova Gorica Poly tech nic worked jointly with ex perts in build ing en gi neer ing from the Na tional In sti tute of Con struc -tion and Build ing En gi neer ing. Firstly, ra don ex perts carry out thor ough mea sure ments of con -cen tra tions of ra don and ra don short-lived de cay prod ucts, as well as ra don equi lib rium fac tors and, in some cases, also the frac tion of un at tached ra don short-lived de cay prod ucts, by ap ply ing com bined and com ple men tary tech niques. The main ra don sources are iden ti fied. Af ter the re sults, to gether with ef fec tive dose es ti mates, are dis cussed at the Health In spec tor ate, a de sign for mit i ga tion is pre -pared by the con struc tion en gi neers and sent to the owner. Ev ery ma jor step in re mod el ling the build -ing is su per vised both by ra don and con struc tion en gi neer ing ex perts. In the end, ra don lev els are checked in or der to prove the suc cess of mit i ga tion [16]. The re port is sent to the Health In spec tor ate. Fol low ing this, yearly ra don check ing is re quired.
In 1997 a one week train ing course en ti tled “Di ag no sis and Mit i gating Ra don Prob lems in Build ings“ was or gan ised by the Slo vene Ra don
Cen tre and the Nova Gorica Poly tech nic. The or -gan is ers in vited em i nent ex perts from Rutgers Uni ver sity, the East ern Re gional Ra don Training Cen ter, New Bruns wick, USA, to in tro duce the main ra don mit i ga tion tech niques to at ten dees with dif fer ent pro files, such as health in spec tors, ra don ex perts, con struc tion en gi neers and oth ers in volved in ra don mat ters in Slovenia and neigh bour ing coun tries.
IN STRU MEN TA TION OF THE SLO VENE RA DON CEN TRE
The Ra don Cen tre pos sesses var i ous mea sur -ing de vices for dif fer ent pur poses of sur vey. They are:
– Al pha coun ters IGMA and PRM 145 with a
set of dif fer ent size cal i brated al pha scin til la tion cells
[1, 13] (RACI, AMES, Jožef Stefan In sti tute, Slovenia),
– E-PERM Sys tem [42]: electret-based
short-term and long-term de tec tor cham bers (Rad Elec. Inc., USA),
– Etched-track de tec tors pro vided by
Forschungszentrum Karlsruhe and eval u ated at Forschungszentrum Karlsruhe, Ger many [43],
– AlphaGuard PQ2000 multiparameter ra don
mon i tor (Genitron, Ger many),
– Sys tem 30 com bined con tin u ous ra don gas
and ra don daugh ter mon i tor (Scintrex, Can ada), – RTM 2010-2 ra don and thoron gas mon i tor
(Sarad, Ger many),
– EQF 3020 and EQF 3020-2 [44] ra don and ra don prog eny mon i tor sys tem with sep a rate mea sure ment of at tached and un at tached de cay prod -ucts (Sarad, Ger many),
– Barasol [45] ra don mon i tor sys tem (ALGADE, France),
– Spec tra 5011 al pha spec trom e ter (Sarad,
Ger many),
– Doseman ra don per sonal do sim e ter (Sarad,
Ger many),
– Radim 5 ra don mon i tor (Plch – SMM,
Czech Re pub lic), and
– Gamma spec trom e try of sam ples of build ing
ma te rial and soil is per formed by the Me dium and High En ergy De part ment at the Jožef Stefan In sti -tute.
and ra don shortlived de cay prod ucts to be ob -served. The val ues of the equi lib rium fac tor and the frac tion of un at tached ra don short-lived de cay prod ucts, the two pa ram e ters play ing a cru cial role in ra don do sim e try, can also be ob tained.
In or der to com ply with the Qual ity As sur -ance/Qual ity Con trol re quire ments, all mea sur ing de vices have been reg u larly checked at the intercomparison ex per i ments or ga nized an nu ally by the Slovenian Nu clear Safety Ad min is tra tion at the Min is try of the En vi ron ment, Spa tial Plan ning and En ergy [46-48]. We also par tic i pated in the in -ter na tional in-tercomparison ex per i ments held in 1991 in Badgastain (Aus tria) and 1997 in Pribram (Czech Re pub lic). In ad di tion, al pha scin til la tion cells are cal i brated monthly with 226RaCl
2 so lu tion
pur chased from NIST (Na tional In sti tute of Stan dards and Tech nol ogy US, Stan dard Ref er ence Ma -te rial 4953D) [1, 49] and in about 10% of rooms etched track and electret de tec tors were ex posed in du pli cate.
RA DON LEV ELS
Kin der gar tens and schools
Dis tri bu tions of the in stan ta neous in door air ra don con cen tra tions in 730 Slovenian kin der gar -tens and 890 schools [15, 25] are shown as lognor -mal plots in fig. 1 and as iso-con cen tra tion con tours in fig. 2. In the karst re gion in the south ern part of the coun try, ra don em a nates from deep soil lay ers through fis sures and then en ters build ings through cracks and faults in the floor slabs, thus en hanc ing in door air ra don con cen tra tions. On the other hand, in door ra don con cen tra tions are lower in the north-east ern part of Slovenia be cause the wa ter sat u rated clay lay ers of the sed i men tary strata pre -vent move ment of soil gas con tain ing ra don.
Sta tis tics of kin der gar tens and schools ex ceed ing the Slovenian ra don limit of 400 Bqm–3 are sum ma
rised in tab. 1. Al to gether, thor ough ra don mea sure -ments were car ried out and an nual ef fec tive doses of the per son nel and chil dren/pu pils es ti mated in 123 build ings (45 kin der gar tens and 78 schools) with ra don lev els above this limit. On the ba sis of the mea sured ra don con cen tra tion, equi lib rium fac tor be -tween ra don and its prog eny and du ra tion of ex po sure pe ri ods ef fec tive doses to these per son nel and chil dren may be es ti mated. Here and in other parts of this pa -per the quoted ef fec tive doses re ceived are es ti mates. In kin der gar tens, of the 2700 per sons (260 work ers
Fig ure 1. Log-normal dis tri bu tion of in door ra don con cen tra tions in kin der gar tens and schools
Fig ure 2. Ra don isoconcentration con tours in kin -der gar tens and schools (in Bqm–3)
Table 1. Statistics of kindergartens and schools exceeding the Slovenian radon limit of 400 Bqm–3
Kindergarten School
Total number of buildings 730 890
Rn concentration above
400 Bqm–3 (6.2%)45 (9.0%)78
Total number of children/pupils 65,600 280,000
Number of children/pupils in buildings with Rn concentration exceeding 400 Bqm–3
2700
(4.1%) (5.7%)16,000
Number of workers in buildings with Rn concentration
exceeding 400 Bqm–3 260 270
Maximum Rn concentration 5600 Bqm–3 4680jBqm–3
Arithmetic mean 133 Bqm–3 168 Bqm–3
Geometric mean 58 Bqm–3 82 Bqm–3
Total number of modified
buildings (35.5%)16 (24.0%)19
No action (ignored requirement
of health inspectors) (9.0%)4 (17.0%)13
Rn concentration during working hours below 400 Bqm–3
–jmitigation measures not request
25
and 2440 chil dren) 470 re ceived ef fec tive doses of more than 2.5 mSv per year. In schools, of 16,000 per sons con sid ered (270 work ers and 15,730 pu pils), 750 re ceived more than 2.5 mSv per year. In one of the high ra don level schools, with oc cu pants re ceiv ing more than 6 mSv a year, chro mo some ab er ra tion anal -y ses were per formed [27]. Up to the end of 2002, 16 kin der gar tens and 19 schools have been suc cess fully mod i fied.
Typ i cal di ur nal vari a tions of ra don con cen tra -tion in a school, with over night max ima and min ima in the af ter noon of the work ing day, are shown in fig. 3. This type of data on di ur nal vari a tions is very im -por tant in de tailed dose anal y sis.
Homes
In 1994, 3 month ra don con cen tra tions were mea sured in 1000 ran domly se lected homes dur ing the win ter, us ing etched-track de tec tors. Val ues ranged from 7 to 1890 Bqm–3, with a me dian of 54 Bqm–3. In
4.5% of homes the value ex ceeded 400 Bqm–3 [32,
33].
All peo ple con cerned about ra don lev els in their home or work ing place can ask the Slo vene Ra don Cen -tre to carry out mea sure ment at their ex pense. In last five years about 250 mea sure ments were per formed.
Spas
Fif teen rooms of 5 ma jor spas were sur veyed for ra don. Ra don was an a lyzed in air and drink ing wa ter [38]. Be cause of very ef fec tive ven ti la tion, air ra don con cen tra tions ev ery where are kept be -low 250 Bqm–3. There fore, un der the pres ent op
-er a tional con di tions and work ing re gime th-ere is no con cern about the ra don ex po sure of per son nel.
Wa ter works
Fifty two workplaces, at tended tem po rarily by about 40 per sons, in 10 ma jor drink ing wa ter sup -ply plants were sur veyed. Ra don in air and ra dium (226Ra) in wa ter were an a lyzed [39]. Both in stan ta
neous and 3month av er age air ra don con cen tra -tions were low at the ma jor ity of places, al though up to 5 kBqm–3 was re corded at some. Be cause of
short at ten dance times, ra don ex po sure at these places is not high, as ev i denced from fig. 4, show ing an nual ef fec tive doses of each em ployee cal cu lated ac cord ing to the ICRP-65 meth od ol ogy [40].
Hos pi tals
In stan ta neous and 1-month av er age air ra don con cen tra tions were mea sured in 186 rooms of 26 ma jor hos pi tals, with the em pha sis on base ments [37]. Ra don lev els were mostly low, fig. 5, but in 7 rooms el e vated ra don con cen tra tions were ob served, in one case up to 15 kBqm–3, with a pro nounced di ur
-nal vari a tion, fig. 6. Dose es ti mates were made for 1025 per sons. Em ploy ees in the above men tioned 7 rooms re ceived from 2.1 to 7.3 mSv an nu ally, while an nual ef fec tive doses for oth ers are shown in fig. 7. Fig ure 3. Typ i cal di ur nal
vari a tion of ra don con cen -tra tion in a school
Win eries
In stan ta neous and longterm av er age air ra -don con cen tra tions in 8 ma jor win er ies, tab. 2, were be low the Slovenian in ter ven tion limit of
400 Bqm–3. Only in one win ery did ra don lev els
ex ceed this limit, but only dur ing the pe ri ods of ven ti la tion shut down, fig. 8. These pe ri ods do not af fect the ra don ex po sure of per son nel, be -cause no body is pres ent at that time.
Fig ure 6. Di ur nal vari a tion of ra don and de cay prod uct con cen tra tion in a hos pi tal main -te nance shop
Fig ure 7. An nual ef fec tive doses re ceived by em ploy ees av er aged for each hos pi tal
CON CLU SION
Var i ous liv ing and work ing en vi ron ments in which ex po sure to ra don and its short-lived de cay prod ucts may be ex pected were in cluded into the in -door ra don sur vey in Slovenia. In 5 ma jor spas based on ther mal and min eral wa ter, ef fec tive ven ti la tion keeps ra don con cen tra tions low, mostly be -low 250 Bqm–3, and no ra di a tion pro tec tion con
-cern is needed. The sit u a tion is sim i lar in 8 ma jor win er ies with un der ground fa cil i ties, in which el e -vated ra don con cen tra tions (the high est value of 3500 Bqm–3) were found only dur ing the pe ri ods of
ven ti la tion shut down, when workplaces are not oc cu pied. In some of the 15 ma jor wa ter works, el e
-vated ra don lev els (the high est con cen tra tion was 2600 Bqm–3) have been found, but the at ten dance
time is short and the re sult ing ef fec tive dose is low. Nev er the less, lon ger main te nance work should be care fully planned. Of 186 rooms sur veyed in 26 ma jor hos pi tals, only in 7 rooms did the ra don con cen -tra tion ex ceed 400 Bqm–3, with the high est value of
2800 Bqm–3 in a base ment main te nance shop. Con
-cen tra tions higher than 400 Bqm–3 have been found
in 45 kin der gar tens (of to tal 730), 78 schools (of to -tal 890), and 42 homes and/or flats (of to -tal 1000).
Spe cial at ten tion has been paid to pub lic build ings such as kin der gar tens and schools with el -e vat-ed ra don l-ev -els in which ad di tional thor ough mon i tor ing, us ing so phis ti cated and com ple men -tary mea sur ing de vices, was im ple mented. Based on the re sults of this mon i tor ing, ef fec tive doses were es ti mated and used by the Health In spec tor ate as the cri te ria for de cid ing whether mit i ga tion is needed or not. In or der to as sure an in ter dis ci plin -ary ap proach to ward mit i ga tion, the Slo vene Ra don Cen tre in which ex perts on ra don mat ters and con struc tion en gi neer ing work to gether was es tab -lished. In to tal, 35 build ings have been suc cess fully mit i gated. The fun da men tal and ap plied re search in the Ra don Cen tre is strongly in ter re lated. Re sults of the first are im me di ately trans ferred into prac tice, and for prob lems en vis aged in ev ery day mon i tor -ing, sci en tific so lu tions are sought. Hence, we use the ad van tage of per form ing fun da men tal re search in real build ings, not in model houses, and thus try to si mul ta neously at tain a high sci en tific level and prac ti cal value of our fun da men tal re sults.
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Jawa VAUPOTI^
RADON U ZATVORENIM PROSTORIJAMA SLOVENIJE
