|NEWS AND INFORMATION
|Year : 2021 | Volume
| Issue : 3 | Page : 171-173
Salient features of IAEA-TECDOC-1951: Protection against exposure due to radon indoors and gamma radiation from construction materials - Methods of prevention and mitigation
Editor, RPE; Ex. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Submission||20-Dec-2021|
|Date of Acceptance||20-Dec-2021|
|Date of Web Publication||04-Jan-2022|
D D Rao
Editor, RPE; Ex. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Rao D D. Salient features of IAEA-TECDOC-1951: Protection against exposure due to radon indoors and gamma radiation from construction materials - Methods of prevention and mitigation. Radiat Prot Environ 2021;44:171-3
|How to cite this URL:|
Rao D D. Salient features of IAEA-TECDOC-1951: Protection against exposure due to radon indoors and gamma radiation from construction materials - Methods of prevention and mitigation. Radiat Prot Environ [serial online] 2021 [cited 2022 Jun 28];44:171-3. Available from: https://www.rpe.org.in/text.asp?2021/44/3/171/334785
International Atomic Energy Agency has brought out this publication to provide guidance on the prevention and mitigation of indoor radon exposure and also discussed gamma exposure due to construction materials. Radon is a chemically inert, naturally occurring radioactive gas generated by the radioactive decay of 238U and 226Ra, which are present in rocks, soils, and building and construction materials. Some types of rock have higher than average uranium and radium contents. Radon is transported from soil and rocks by convection and diffuses into the upper layers of soil and then into the atmosphere. Radon is drawn into buildings due to wind action and pressure differences induced by air densities. Soil gas infiltration is recognized as the most important source of radon in dwellings and other buildings. Other sources of radon include building and construction materials and water extracted from wells, but they are of less importance. In some areas of the world, particularly in countries with certain geology and long and cold winters, some houses can have very high levels of radon. The United Nations Scientific Committee on the Effects of Atomic Radiation has observed that, for most people, radon is the largest source of radiation exposure throughout their lifetime. The World Health Organization has estimated that the proportion of lung cancer linked to radon lies between 3% and 14%, depending on the average radon concentration in the country and the method of calculation.
This publication describes methods for reducing the entry of radon into dwellings and other buildings (i.e., preventive measures for new buildings and corrective actions for existing buildings). The publication contains practical information on the types of measurement that need to be considered to demonstrate compliance with established national reference levels for exposure to radionuclides in building and construction materials.
Chapter 1 contains introduction, background, scope, and structure. Chapter 2 is on building foundations, ventilations, and construction materials that release radon. There are generally four types of building foundations, namely (1) slab-on-grade, (2) crawl space, (3) basement with footings, or (4) basement with load-bearing slab and wall construction. Details on each type of foundation along with diagrams are provided. There are also three common types of ventilation system used to ventilate dwellings: (a) natural draught ventilation; (b) mechanical exhaust air ventilation system; and (c) mechanical supply and exhaust air ventilation system having different influences on indoor radon accumulation or ventilation. There are discussions on air exchange rates and the related formulae with numerical examples. Diagrams are given for each type of ventilation and the necessary exhaust systems.
Chapter 3 is on radon mitigation strategies in existing buildings. Generally, there are three approaches to radon mitigation: depressurization of the ground beneath the building, over-pressurization inside the building or in the ground beneath the building, and isolation. Before designing and installing the measures to reduce the ingress of radon into the building, an expert is needed to review the measurements that have been made of the radon levels in the building, carry out diagnostic tests to determine entry points for radon into the building, and make an assessment of the type of foundation and the construction of the building to determine the most appropriate mitigation methods to be installed in the building. Detailed explanation with schematic diagrams of buildings, mathematical formula, and numerical examples is provided for radon mitigation exercises in the existing buildings.
Chapter 4 is on mitigations of exposures from radon release from the water supply. If water containing dissolved radon is used in the household, it can be a source of elevated radon levels and sometimes very high concentrations of indoor radon. This is primarily an issue for buildings where the water supply is drawn from a private borehole in an area enriched with radium in the bedrock. Water from local water companies is usually sufficiently aerated in the storage, preparation, and distribution process. Dissolved radon in water can also become airborne during heating and splashing of water indoors (cleaning and cooking). The finer the water is divided, i.e., the smaller are the drops, and exposed to the air, the more of the dissolved radon gas can become airborne. Thus, radon concentration resulting from the household water will be highest in the kitchen, laundry room, and bathroom. As a rough indication of the household's water contribution to the radon concentration in a relatively small indoor space, it is a generally accepted that 1000 Bq/l of radon in the water contributes to 100–200 Bq/m3 of radon in indoor air, if the water consumption is 1 m3/day. The formula for the calculation of radon exhalation from the water into a building is given along with numerical examples. Radon emanation to indoor air is estimated as 60%–70% for a shower bath, 30%–50% for common bath, and about 95% for dishwashing.
Chapter 5 is on radon prevention strategies in new buildings. Preventive measures for new buildings are generally implemented through national building codes. The national building authority may also specify whether the preventive measures are required in all new buildings, or whether they are only used in particular regions of the country that have elevated average levels of radon in buildings. The main types of preventive measures are: (a) inclusion of a continuously impermeable membrane designed to isolate the building from the ground over the whole floor area of the building and (b) the provision of soil depressurization or subfloor depressurization of the building. At the same time, it is important to seal all possible entry paths through a concrete slab floor into the building. Detailed explanation of all the possible methods, along with schematic house diagrams, is provided.
Chapter 6 is on the effectiveness of the assessment. Any designed and installed radon mitigation system needs to be evaluated for its effectiveness immediately after the installation. This might be a part of the contract with the company carrying out the mitigation work. The system has to be periodically re-evaluated by means of measurement. The publication also discusses the postmitigation obligations and guarantee from the construction companies.
Chapter 7 is on building and construction materials. Building and construction materials can contribute significantly to gamma exposure of the occupants. In particular, the components of the concrete used for the inner walls of the building may contain high levels of naturally occurring radioactive materials (NORMs). To prevent these situations, the regulatory body is required to establish specific reference levels for construction materials, based on an annual effective dose to the representative person that is not greater than 1 mSv (para. 5.22 of GSR Part 3). The requirements of EU Directive 2013/59 Euratom also stipulate a reference level for construction materials based on an annual effective dose of 1 mSv from construction materials. Concrete, aggregate (ballast), and sand are the three main stone-based construction materials of major interest when it comes to NORM content in construction material of buildings. To ensure compliance with the requirements of GSR Part 3 on annual effective dose from construction materials, it is essential that all building and construction materials are tested before entering the market. For verification of compliance, there is a need to measure NORMs in materials to be used for the new built. SSG-32 provides recommendations on a process to determine compliance of building and construction materials containing radionuclides of natural origin with the reference level. The process includes the determination of the activity concentrations of radionuclides of natural origin, followed by the determination of an activity index. An example of an activity index that could be considered by the national authority is given by an equation. For the determination of construction materials' activity index or content of NORM radionuclides, the measurement is to be performed with a gamma spectrometer on a representative sample of appropriate size.
In situ dose rate measurement of gamma radiation of a 10-min duration can be made in the middle of the room. This measurement includes gamma rays from radon daughter decay, so radon measurement is also necessary because the reference level of 1 mSv/a is related to the construction material only. If the resulting dose exceeds 1 mSv/a, a further measurement is advised. This needs to include a radon concentration measurement with a calibrated integrated (instant) radon instrument.
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Conflicts of interest
There are no conflicts of interest.