The Calculation of the Parameters of Buildings Protection from Radon
Received Date: August 16, 2021; Published Date: September 03, 2021
Radon-222 and its progeny can accumulate in the lower floor premises and harm the people respiratory organs. One of the challenges for the construction industry is to provide indoor radon concentrations that are not much different from its concentrations in the outdoor air. The article proposes an approach to ensuring the buildings radon safety by the passive protective technologies. Its essence is in the determination at the design stage of the required radon protection characteristics of the building underground shell, which performs load-bearing functions and at the same time limits the radon flux from the soil air
Keywords: Radon; Progeny; Walling; Flux; Equilibrium concentration
The danger of increased radioactive exposure for most people in the World is associated with accidents at nuclear fuel cycle plants or violations of the rules for handling radioactive substances. In fact, radon and its short-lived progeny (218Po, 214Pb, 214Bi and 214Po) form about 70% of the population radiation dose in countries with temperate climates and harm the people respiratory organs . Radon is a monatomic radioactive gas, it does not have stable isotopes and generated in the soil during the radium decay. The background radon concentration in the outdoor air is small, it rarely exceeds 10 Bq·m-3 and therefore radon does not harm human health. But under certain conditions, it is able to flow from the soil into the building and accumulate in the indoor air. Therefore, it is necessary to strive for the maximum, socially and economically justified decrease of radon concentration in buildings. Technical measures aimed at ensuring the minimum justified radon level in the building are implemented exclusively by construction means. Acceptable radon levels in buildings can be ensured through the rational design of underground walling, which perform the main load-bearing func tions. This technology for buildings protecting from radon is called passive. The calculation radon protection characteristics is carried out at the stage of building design using data on:
1. The dimensions of the underground walling elements and the radon diffusion coefficients in the walling materials.
2. Specific radium-226 activity and the radon emanation coefficient of the soil under the building.
3. The expected ventilation type and the air exchange frequency in the most deeply located rooms.
4. In the calculation of radon protective characteristics, the design scheme includes the soil, horizontal and vertical walling bordering on the soil, the upper floor and internal walls (Figure 1).
The calculation purpose is to assess the compliance of the radon concentration expected value (CRn) in the deepest rooms indoor air. This value should not exceed the national reference level (NRL), which is 150 Bq·m-3 in the United States and is about 250 Bq· m-3 in Russia [2,3].
The expected value of the radon concentration in the room is calculated by the formula
where q1 and q2 are the radon flux densities from the soil through the horizontal and vertical walling, respectively, Bq·m-2·s-1;
S1 and S2 are the areas of internal surfaces of horizontal and vertical walling, respectively, m2;
qi is the radon flux density into the room by the radon exhalation in the material of the i-th walling, Bq·m-2·s-1;
Si is the internal surface area of the i-th walling, m2.
The radon flux densities from internal structures can be calculated using the formula
where Сi is the radium activity in walling material, Bq·kg-1;
ρi is the walling material density, kg·m-3;
ki is the emanation coefficient value;
Di is the coefficient of radon diffusion in walling material, m2·s-1;
Li is the radon diffusion length in walling material, m;
hi is the walling thickness, m.
But the radon entry from internal surfaces is not the main source and with sufficient accuracy can be taken equal to 2.5 mBq·m-2 s-1 without calculating by (3). Most often, the radon entry from the soil through the vertical underground walling is negligible (q2 ≈ 0) since this structure does not interfere with the radon movement to the atmosphere. Then the density of radon flux from the soil
where PRn is the radon potential of the soil, Bq·m-3;
R is the radon resistance of horizontal walling, s·m-1.
The PRn value in (4) is calculated for the maximum values of CRa and ρs of soil at the building base, determined during engineering and geological surveys
where CRa is the specific activity of radium in the soil, Bq·kg-1;
ρ is the soil density, kg·m-3;
k is the radon emanation coefficient of the soil;
ε is the soil porosity.
An accurate experimental determination of PRn for the soil at the construction site is important, since this value is (with a small margin) the radon load on the underground building shell .
The required radon resistance value of the horizontal walling is determined by the formula:
where qmax is the ultimate radon flux density through the horizontal walling, at which the value of CRn will not be exceeded, Bq·m-2·s-1;
The total radon resistance of a n-layer structure is approximately equal to
where Ri is the radon resistance of the i-th structure layer, s·m-1;
λ = 2.1·10-6 s-1 is the radon decay constant.
Formulas (5)– (7) make it possible to move from the soil physical characteristics at the construction site to the dimensions of underground horizontal walling, which will ensure the building radon safety. The proposed approach to ensure the buildings radon safety on most soils, but at the high radium specific activity or air permeability of the soil, passive technologies turn out to be ineffective and it is necessary to use a soil depressurization system.
Conflict of Interest
No conflict of interest.
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