Siseruumide radooni aktiivsuskontsentratsiooni uurimine Saaremaal Pärsama külas

Radoon on looduslik radioaktiivne väärisgaas, mis suurtes kontsentratsioonides on organismidele ohtlik. Seetõttu on oluline, et aasta keskmine aktiivsuskontsentratsiooni tase ruumide siseõhus jääks soovitatava piirnormi – 200 Bq/m3 piiridesse ning inimese aastane efektiivdoos alla 1 mSv. Oluline on jälgida radooni aktiivsuskontsentratsiooni talvisel kütteperioodil, mil toimub vähem ruumide õhutamist ning maapinnast eluhoonetesse liikuvat radooni koguneb rohkelt hoonete siseõhku. Ruumide siseõhku satub radoon peamiselt hoone aluses pinnases olevatest uraani sisaldavatest mineraalidest, kuid ka radoonirikkast tarbeveest või torujuhtmeid pidi maagaasiga. Üldiselt imetakse madala õhurõhu korral maapinnast rohkem radoonirikast gaasi välja, kuid erinevad ilmastikutingimused võivad seda korrapära moonutada, mida on ka käesoleva lõputöö raames teostatud mõõtmistulemuste põhjal näha. Tavaliselt teostatakse siseõhu radooni aktiivsuskontsentratsiooni mõõtmisi integraalsete meetoditega, kuid käesolevas töös teostatud mõõtmiste jaoks kasutati järjestikuseid punktmõõtmisi. Selline meetod võimaldab näha radooni aktiivsuskontsentratsioonide dünaamikat nii ööpäeva kui ka päevade lõikes. Selline lähenemine võimaldab täpsemalt hinnata erinevaid mõjureid radooni aktiivsuskontsentratsiooni väärtuste kujunemisel konkreetsete ruumide siseõhus. Saaremaal Pärsama külas 2023. aasta veebruarist kuni aprillini teostatud mõõtmised näitavad, et radoonisisaldus hoonete siseõhus on väga varieeruv ning sõltub välja paljudest erinevatest faktoritest. Hoonete esimestel korrustel, mille all asub ka kelder, on radooni aktiivsuskontsentratsioon madalam kui keldrikorrustel. Radoon peab esimesele korrusele jõudmiseks läbima keldrit ning suurem osa radioaktiivsest gaasist jääb keldrikorrusele püsima. Oluline roll on ka elumajade keskküttesüsteemidel. Keldris oleva keskütteahjuga köetavatel elumajadel on soodsamad tingimused radoonirikka gaasi imemiseks pinnasest. Lõputöö raames uuritud hoonetest võib probleemseks pidada objekte 2 ja 3. Objekti 2 keldrikorruse kahe kuu mõõtmiste põhjal leitud radooni aktiivsuskontsentratsiooni keskmine ületab soovitatavat siseõhu piirnormi. Objektil 3 on aga esimese korruse radooni aktiivsuskontsentratiooni tase kõrgem kui keldrikorrusel ning oletatav aastane efektiivdoos on lausa 4,8 millisiivertit. Kõrge radoonitase on tingitud asjaolust, et kelder on vaid poole elumaja all ning ruum, kus esimese korruse mõõtmised teostati, asub otse maapinnal. Seetõttu liigub radoon ilma keldrit läbimata otse eluruumidesse. Töös saadud tulemustele täpsema hinnangu andmiseks oleks vaja teostada Pärsama külas ka pinnaseõhu radoonisisalduse mõõtmisi, mida ajapuuduse tõttu seekord ei jõutud teostada. Töös uuritud elamute siseõhu radooni aktiivsuskontsentratsioonid on siiski suhteliselt tagasihoidlikud.

The aim of this thesis was to investigate the indoor radon activity concentration in Pärsama village on the island of Saaremaa, which is also the author's home village. In addition, an overview of radon is provided, and the measurement results obtained during the research are analyzed. Radon is a natural radioactive gas that is dangerous to organisms. In high concentrations, radon is carcinogenic and increases the risk of other health problems. Therefore, it is important that the annual average activity concentration level of radon in indoor air stays within the recommended limit of 200 Bq/m3, and that the annual effective dose for humans remains below 1 mSv. It is important to monitor the activity concentration of radon during the winter heating season, when there is less ventilation in buildings and radon from the ground accumulates in indoor air. Radon enters indoor air mainly from uranium-containing minerals in the soil beneath buildings, but it can also come from radon-rich tap water or from natural gas in pipes. Generally, more radon-rich gas is drawn out of the ground under low air pressure, but different weather conditions can distort this pattern, as can be seen from the measurements taken in this thesis. Usually, the indoor radon activity concentration is measured using integral methods, but for the measurements carried out in this thesis, sequential point measurements were used. This method allows for the dynamics of radon activity concentrations to be seen over both 24-hour periods and days. This approach allows for a more precise assessment of the different factors that contribute to the development of radon activity concentrations in specific indoor spaces. To investigate radon activity concentration, RadonEye Plus 2 radon monitors were placed on the basement and first floors of each building. For a more accurate overview, it is important that the measurement period is at least two months, and the measurements are carried out during the heating season, when rooms are less ventilated. The monitors were placed in buildings for two months - from February to April 2023. Measurements taken in the village of Pärsama show that the radon content in indoor air of buildings is highly variable and depends on many different factors. The radon activity concentration on the buildings first floor is usually lower than on the basement floors. Radon must pass through the basement to reach the first floor, and most of the radioactive gas remains in the basement. Residential buildings heated by a central heating furnace in the basement have more favorable conditions for drawing in radon-rich gas from the soil. Of the buildings studied in this thesis, objects 2 and 3 may be problematic. Based on measurements taken over two months on the basement floor of object 2, the average radon activity concentration exceeded the recommended indoor air limit. On object 3, the radon activity concentration on the first floor is higher than on the basement floor, and the estimated annual effective dose is as high as 4.8 millisieverts. The high radon level is due to the fact that the basement is only half under the residential building, and the room where the first-floor measurements were taken is located directly on the ground. As a result, radon moves directly into living spaces without passing through the basement. To provide a more accurate assessment of the results obtained in this thesis, measurements of radon content in soil air in Pärsama would also need to be carried out, which could not be done due to lack of time. Nevertheless, the indoor radon activity concentrations in the residential buildings studied in this thesis are relatively modest.