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Accuracy assessment of the annual average indoor radon concentration based on measurements of different duration

Periodic Reporting for period 1 - RadonACCURACY (Accuracy assessment of the annual average indoor radon concentration based on measurements of different duration)

Reporting period: 2018-11-01 to 2020-10-31

Radon is the most powerful source of natural radiation and dangerous carcinogen causing lung cancer. According to the recommendations of World Health Organization and EU Basic Safety Standards (EU BSS), the annual average indoor radon (AAIR) concentration should be limited to 300 Bq/m3. The national reference levels (RL) vary in different countries due to differences in regional levels of indoor radon and usually range from 100 to 300 Bq/m3. However, a reliable decision as to the compliance of estimated AAIR by test result with the RL remains an unsolved problem, since radon concentration in buildings has significant temporal variations (daily, weekly and seasonal) as seen in the Fig.1,2. This renders assessing the building compliance with radon safety criteria a serious challenge, and significantly complicates making an informed decision as to whether radon mitigation measures are needed. These unresolved issues greatly reduce the effectiveness of National Radon Action Plans established in Member States according to the requirements of the EU BSS.

The most reliable assessment of a building’s compliance with radon safety requirements can be obtained with measurements taken continuously for a period of one year. However, in most buildings the radon level is only about 30 Bq/m3, i.e. significantly lower than the RL. Measuring low activity with high accuracy using the long-term tests is time-consuming and costly. It is true that the shorter the test, the higher the AAIR uncertainty. However, even a high uncertainty of up to 200% would be satisfactory in most cases due to the generally low level of radon in buildings (for example, 30 + 60 < RL). Only in relatively rare cases, where the high uncertainty of the short-term test does not allow for a reliable assessment of radiation safety, a decision must be taken based on more accurate long-term measurements. Obviously, such a decision should be supported by certain quantitative criteria based on the known values of AAIR uncertainty, depending on the test duration. Despite this important requirement, none of the national regulations (the measurement protocol in USA, Israel, ISO and IAEA recommendations) provide an assessment of the AAIR uncertainty depending on the test duration.

Thus, the overall goal of the project is the assessment of the AAIR uncertainty based on the results of measurements with different duration and the development of rational (reliable) criteria for comparing the test result and RL. The overall goal of the project will be achieved as a result of implementing the following two research objectives:
1) definition of the values of the coefficient of temporal radon variation – K(t)
2) assessment of the influence of environmental factors on indoor radon behavior and determination the structure and values of the correction factor – k.
Both parameters are used in our first proposed radon control principle shown in Fig.3.
Objective 1. The coefficient K(t) determines by the innovative algorithm (Fig.3) using the results of annual continuous monitoring of radon in buildings with elevated radon. To search for such buildings, the “RadonTest” on-line system (www.radontest.online) was developed, and equipment based on the method of radon adsorption on activated charcoal was improved (Fig.4). This helped attract Israeli schoolchildren to conduct short-term (screening) tests in their homes (https://nbri.net.technion.ac.il/en/radon-project) with the support of TCSS (www.tcss.center). Thus, more than 14 schools located in different regions of Israel were covered, and more than 400 measurements (Fig.5) were carried out. These results are shown on the public radon map (https://radonmap.online/indoorradon) while ensuring confidentiality. The results of the mass survey made it possible to identify the required number of buildings with elevated radon. Then, after additional tests, the 12 most suitable buildings were selected for carrying out synchronous continuous monitoring of radon for one year. As a result, in 12 rooms (Fig.6) located in 9 different buildings, full annual monitoring was carried out, the results of which are shown in Fig.1,2. The values of the coefficient K(t) depending on the mode and duration of measurements in the experimental rooms (ER) are shown in Fig.7-9.

Objective 2. To assess the influence of various factors on the behavior of indoor radon, data of synchronous annual monitoring of the following environmental factors were also collected (see Fig.10): (a) air temperature and (b) humidity, (c) atmospheric pressure, (d) wind speed, (e) precipitation, (f) insolation (connection with cloudiness), (g) tidal forces (Earth's rotation speed or length of day), (h) seismic activity, (i) concentration of soil radon (under building), and (j) flux of soil radon inside the building. The study of the influence of the parameters (i) and (j) on the behavior of indoor radon was carried out in ER1 (Fig.6) in accordance with the measurement scheme shown in Fig.11. The results of annual continuous monitoring of soil and indoor radon in ER 1 with influencing factors are shown in Fig.12. The correlations between radon concentration in the ERs and influencing factors are shown in Fig.13. The correlations between indoor (ER1) / soil radon and influencing factors are shown in Fig.14.

It has been established that influence of (a)-(h) factors on the behavior of indoor radon is weak and irregular (Fig.13) in contrast to factors (i) and (j). However, both of last factors are not used in mass radon surveys due to the complexity, so the correction factor k=1. Thus, only way to assess the accuracy of AAIR is the algorithm presented in the Fig.3. In addition, the obtained values of K(t) in Israeli buildings are on average higher than for the Moscow region (Fig.9) which leads to the need to verify and clarify data by the accumulation of statistically representative of the array of calculated values of K(t). The actual action on this challenge is to conduct a large number (200-300) of annual continuous indoor radon monitoring in different countries, for example, Europe and America that will allow for the first time to create a basis for the rational regulation of indoor radon.

The obtained results can be exploited to improve the measurement protocol in order to more efficiently organize radon surveys and identify hazardous buildings. The project results are disseminated mainly through the created web-sites and web-pages (see links above), publications, presentations and reports at meetings with European and American experts, including grants and the organization of joint researches which develops and scales RadonACCURACY innovations.
i) the “RadonTest” on-line system (www.radontest.online) for organizing radon tests in any country, serving different laboratories and measurement methods with automatic processing and display of test results to the public radon map
ii) cost-effective and highly sensitive equipment for screening tests
iii) introduction and expansion of the application of the rational criterion for assessing the compliance of buildings with EU BSS requirements due to new values of K(t) in a tropical climate and unstable geology
iv) reduction of the costs for indoor radon tests
v) motivation for the organization of new cost-effective laboratories to deal mainly with screening tests
vi) radical increase of radon tests in Israel and other countries, and reduced radon risks of the public
The values of K(t) depending on the mode and duration of test in experimental rooms
Innovative rational principle of indoor radon control
Annual continuous monitoring of soil and indoor radon in ER 1 with influencing factors
The values of K(t) depending on the duration of test in experimental rooms
Annual continuous monitoring of the environmental factors affecting the indoor radon
New equipment for short-term measurements method based on activated charcoal
Scheme of measurement of soil radon in the ER 1 located in the basement
The results of short-term measurements by schoolchildren in Israel on the public radon map
Characteristics of the experimental rooms and buildings
The correlation between radon concentration in the ERs and influencing factors
Annual continuous monitoring of radon in the experimental rooms N 7-12
The values of K(t) depending on the mode and duration of test in Israel and Russia
Annual continuous monitoring of radon in the experimental rooms N 1-6
The correlation between indoor (ER 1) / soil radon and influencing factors