Radiation: war with an invisible killer or a little more about radon

    Hello again. In the comments on the previous article, I promised to write about protection against radon and its DPR. Well, keep that promise.

    As I said in a previous article, radon poses a rather serious danger to people. It is especially great in some regions of the Earth, where radon from great depths is carried out on the surface along tectonic faults. And in these places, measures are vital to reduce its concentration in human housing.

    Ways of entering radon into the room

    Sources of radon in the bowels of the earth are rocks such as granites, syenites, clays and shales rich in uranium and its “daughters”, including radium-226. Radon is released (or as they say - exhaled) rocks and building materials through two main mechanisms: diffusion and recoil. The radon atom formed inside the solid containing radium must pass through the solid layer, before migrating to the gaseous medium, where it slowly migrates through the crystal lattice. Because of this, the “radon hazardous" is a fairly thin layer of dense solid substance, amounting to millimeters, but this thickness increases significantly - up to meters - if the material is porous or fractured. An alternative to the diffusion path of radon release is the mechanism associated with the fact that the radon nucleus receives a significant momentum during its formation, due to which it immediately overcomes a thin layer of the substance. The thickness of this layer is very small, but the recoil process, unlike diffusion, does not require time and does not depend on temperature. After radon enters the pore space of the soil or rock (regardless of the mechanism), it migrates relatively quickly and reaches the day surface. The release of radon in this way creates vast areas of the earth's surface with an increased background of radon concentration, coinciding along the contours with the zones where these rocks are located not deep from the surface.
    So, in the Leningrad Region, in a narrow strip of land 3-15 km wide, stretching from Kingisepp to the Syas River, outcrops of the so-called dictionemic schists of the Koporsky Formation are observed (the lower Ordovician is indicated in dark green on the map below). These shales are characterized by an abnormally high (up to 0.17%) uranium content, which is due to the active release of radon in this territory. The concentration of radon in the soil air here reaches at individual points 136$ kBq / m ^ 3 $and higher. Uranium-bearing dictionemic schists are also found in other places of the Leningrad region, as well as in Estonia.

    At the same time, local releases of radon in tectonically active zones are observed, marking faults, karst channels and other “radon conducting” structures. Over such "hot spots", the concentration of radon can sometimes exceed the background by hundreds and thousands of times, reaching tens of kilobecquerels per cubic meter.

    Typically, indoor radon concentrations are significantly higher than those observed outdoors. The main ways of its penetration into the room are as follows:

    • direct upward diffusion of radon from the bowels of the earth through microcracks and foundation pores;
    • penetration through underground communications, including with water and natural gas, as well as when burning solid fuel (coal, firewood);
    • emission of radon by building and facing materials of the house itself, and sometimes by objects in the house containing radium and thorium;
    • the intake of radon with outside air through the open windows of the lower floors, the ventilation of the basement, "sucking" ground-air enriched with radon.

    Building materials are the main source of radon in multi-story buildings. The most “radon hazardous” components of building materials are coal slag and alumina (bauxite), as well as phosphogypsum, used as a component of stucco mixtures, drywall and other facing materials. Ordinary sand and clay may also be radioactive. Granite is known for its radioactivity and the release of radon, used both in the form of crushed stone for concrete preparation, and in the form of facing plates and independent structural elements of buildings, for example, the foundation. Such a popular building material as red brick is rich in Radium-226. But it is porous and bulk materials that are most dangerous, since radon comes out of dense granite extremely reluctantly.

    The total power of radon entering a typical city apartment from the bowels of the earth and from building materials reaches 60 kBq / day. With outside air, depending on the number of storeys, it comes from a negligible amount on the upper floors to 10 kBq / day on the ground floor. Water and natural gas are usually much smaller sources of radon - up to 3-4 kBq / day, but in poorly ventilated small rooms of kitchens and bathrooms can quickly create very significant levels of radon. Thus, a survey of residential buildings in Finland gave the following values: with a tolerable level of radon in rooms 150-200$ Bq / m ^ 3 $, in the kitchen its EROA reaches 3, and in the bathroom - up to 8.5 $ kBq / m ^ 3 $! In the process of using the shower, the level of radon increases tenfold.

    As for the intake of radon with outside air, it is of course significant only if there are no other sources of radon or they are insignificant - for example, in wooden houses. Because along with the influx of radon from the outside into the room, the reverse process is also taking place - which helps to equalize the external and internal ERA of radon, and not the accumulation of radon inside.

    About the benefits of fresh air

    In the vast majority of cases, the concentration of radon in the open air is insignificant, so elementary ventilation is the simplest way to repeatedly reduce the radon's ERA. The external concentration of radon rarely exceeds unity and the first tens$ Bq / m ^ 3 $and airing quickly reduces it to these values. A well-thought-out building ventilation system, the use of exhaust ventilation in kitchens and bathrooms is one of the most effective ways to solve the radon problem. So, in the kitchen when using gas, turning on the hood usually completely prevents the increase in radon levels, while in the absence of the hood its level often grows rapidly.

    In the seventies, Sweden began to actively combat heat loss from buildings, and in this regard, the air exchange rate decreased by more than half. An unexpected and unpleasant consequence of this was an increase in radon levels by several times.

    True, intensive ventilation is not always useful - sometimes a powerful hood, leading to a drop in pressure in the basement, promotes the release of radon and sharply increases its concentration in the basements. Therefore, ventilation should be organized so that the hood is necessarily compensated by the influx. The organization of intensive ventilation of the space between the ground and the building being protected significantly reduces the concentration of radon in this zone and effectively prevents the penetration of radon from the soil into the building. The role of such a space can be played by an uninhabited or rarely visited basement or underground equipped in the basement.

    These drawings, like the one on the KDPV, are copied over many Russian-language sites.

    I could not find the source, but apparently, these are some official documents from the USA

    Barrier Against Radon

    The next protective measure, which is necessary to reduce the level of radon in the premises, is to create an impenetrable barrier to prevent it from getting there. As such a barrier can serve as a standard waterproofing foundation. However, the polyethylene film often used as a waterproofing material is unexpectedly very radon-permeable material. However, if we recall that radon is highly soluble in saturated hydrocarbons, and that polyethylene is actually a paraffin hydrocarbon with a very large molecular weight, the reason for this becomes clear. Waterproofing materials effective against radon are polymer-bitumen mastics and roll materials. There are two such barriers: one at the border between the ground and the building, and the other at the basement level.

    Radon emission from building materials is effectively prevented by painting, pasting the walls with special wallpaper (even ordinary paper wallpapers reduce radon emissions by 30%) by impregnating their surface with special compounds. An obstacle to radon is tile. By the way, porous and fractured materials are the most radionuclide, therefore preventing the formation of cracks (for example, in the foundation material) not only reduces the penetration of radon through the thickness of concrete, but also drastically reduces the release of radon from concrete itself. Of course, this also applies to the materials that make up walls and ceilings, the reduction of porosity and fracturing of which effectively reduces their emanating ability.

    Fighting Radon in Water and Gas

    A good way to reduce radon in water is to aerate it. It can be carried out by sparging air through a layer of water or vice versa, spraying water into air, passing water and air countercurrently through a packed column and other methods. This measure reduces the concentration of radon in water by at least an order of magnitude, and often more. As a rule, this operation is carried out by water at water treatment plants - but it does not exist if water comes from an individual well. The radon content in such water can reach 500-1000 Bq / l with an acceptable level of 60 Bq / l. Further purification of water from radon is possible using various adsorbents, for example, activated carbon, which is able to remove 99.7% of radon. The cleaning efficiency decreases over time due to the “aging” of coal, but the radon itself on the filter, of course, does not accumulate, since it quickly breaks up. Removal of radon is also a side effect of various ion-exchange and membrane filters. There are also specialized filtration plants for radon removal - from small ones, for one house or apartment, to those that can serve the whole city. Of course, an individual installation for water purification from radon should be installed outside the living room, and not directly in the kitchen under the sink, since otherwise the entire remote radon will end up in the air.

    Mainly, the goal of water purification from radon is to prevent it from entering the room. As for the use of water with radon inside, boiling it in an open container instantly reduces the concentration of radon in it to almost zero, so do not drink raw water from the tap.

    The simplest and most effective way to reduce the content of radon in natural gas is exposure. A month of storage in the gas storage almost completely destroys radon in the gas. The problem with radon arises either when gas is supplied to the network directly from the production site, or when radon enters the storage itself in addition to gas.

    Air purification from radon and DPR

    All the above measures are good when the house is just under construction. But in the existing housing, little can be done except for the forced ventilation of the basement. But maybe you can try to organize air purification? After all, as we have already seen, radon is readily sorbed.
    Yes, there is such an option. And first of all, it is advisable to remove not radon itself from the air, but its much more harmful DPR. They are present as active plaque on aerosol particles and beta decay gives these particles a positive charge. This is what we use.
    The first option is the use of HEPA filters or the so-called Petryanov tissue. This material is entangled polymer fibers, which tend to accumulate a negative charge, and this electrification is caused by the fact that such a filter with high efficiency captures the smallest aerosol particles whose sizes are many times smaller than the filter pores (there are other mechanisms, but this is important to us) . A positive charge of aerosol particles coated with active plaque promotes electrostatic adhesion to the filter fibers. To effectively capture radon, the performance of the filtration unit should be such that the time during which the filter pumps a volume of air equal to the volume of the room exceeds the time of complete exchange of air in the room.

    The second option is electrostatic precipitators. As in the method of trapping radar DPR, which I described in a previous article when I talked about home methods for assessing the level of radon in a room, active deposition of radon DPR occurs on a negatively charged electrode. A prerequisite for the successful operation of the electrostatic precipitator is the potential of the trapping electrode, which is within certain limits - about 1000-5000 V. A lower voltage is inefficient, a higher one leads to recharging of dust particles and their repulsion from the electrode. Incidentally, we observe this on the example of the Chizhevsky chandelier, the ceiling over which is covered with a layer of stubborn dust. By the way, fans of the Chizhevsky chandelier are very fond of mentioning that it purifies the air of radon. So no, it doesn’t.

    I’ll give an interesting description of the successful experiment on air purification from radon by the electrostatic method, conducted by begin_end .
    We conducted research on the electrostatic filtration of radar DPRs - it is the Chizhevsky chandelier that is not suitable, since the potential for such an installation is above 5 kV. If the voltage is too high, dust particles do not settle on the electrode, but on objects nearby.
    Electrostatic filter in the form of a -5kV electrode with a tablet act. coal reduces activity in a 200l barrel from 1988 Bq / m3 to 67 Bq / m3 (almost 30 times) in 6 hours. Of course, the experience in the barrel is only trial, it does not have high significance.

    When tested in a room of 59m3 (p. 317), it was possible to reduce the concentration of the DPR from 89 Bq / m3 to 28 Bq / m3 in 8 hours (3.2 times, however, 28 Bq / m3 is close to the lower boundary of the determination of the RAA-10 device; efficiency the work of the method is difficult to evaluate at such a low initial concentration, and a room with a high level in our area cannot be found).
    I will also refer to the begin_end post devoted to the problem of air purification from radon.

    In conclusion, I should add that the effectiveness of such cleaning should increase significantly with the introduction of a “flow driver” - a fan pumping air past the trapping electrode.

    * * *

    Radon ERAA in rooms usually significantly exceeds that in the open air. Since a person spends most of his life in rooms, it is advisable, and in many cases vital to take measures to reduce air pollution by radon and its DPR.

    The degree of complexity and effectiveness of these measures is different, but there is one quick and worthless method - to open the window.

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