The Calculation of the Parameters of Buildings Protection from Radon

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 [1]. 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 (C_Rn) 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;

q_i 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;

S_i 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 С_i is the radium activity in walling material, Bq·kg^-1;

ρ_i is the walling material density, kg·m^-3;

k_i is the emanation coefficient value;

D_i is the coefficient of radon diffusion in walling material, m²·s^-1;

L_i is the radon diffusion length in walling material, m;

h_i 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 P_Rn is the radon potential of the soil, Bq·m^-3;

R is the radon resistance of horizontal walling, s·m^-1.

The P_Rn value in (4) is calculated for the maximum values of C_Ra and ρ_s of soil at the building base, determined during engineering and geological surveys

where C_Ra 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 P_Rn 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 [4].

The required radon resistance value of the horizontal walling is determined by the formula:

where q_max is the ultimate radon flux density through the horizontal walling, at which the value of C_Rn will not be exceeded, Bq·m^-2·s^-1;

The total radon resistance of a n-layer structure is approximately equal to

where R_i 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.

None.

No conflict of interest.

1. Darby S, Hill D, Auvinen A, Barros-Dios JM, Baysson H, et al. (2005) Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. Br Med J 330(7485): 223–227.
2. Radiation safety standards (NRB-99/2009) Ministry of Justice of Russia.p.225.
3. US Reducing Radon in New Construction of 1 and 2 Family Dwellings and Townhouses (CCAH 2020) AARST Consortium on national radon standards.
4. Shubin I, Bakaeva N, Kalaydo A, Skrynnykova A (2019) The radiation safety of the designing constructions in radon-hazardous areas E3S Web of Conferences 01019 CATPID-2019 Vol. 138.