PSI - Issue 22

António Curado et al. / Procedia Structural Integrity 22 (2019) 386–392 António Curado et. al / Structural Integrity Procedia 00 (2019) 000 – 000

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3

1 N ∑ x i N i=0

ARC=

(1)

The parameters contained in (1) are the following: x i is the sensor i-order reading, and N is the total number of radon readings during the measurement period. 2.1. Calculation of Indoor effective dose on an annual basis (IED) To convert the Average Radon Concentration (ARC), in Bq.m -3 , into the Indoor Effective Dose (IED), on an annual basis, it is required to apply a radon dose conversion factor of 9 nSv per (Bq.m -3 .h) -1 . Moreover, for indoor analysis an equilibrium factor (F-factor) of 0.4 is adopted, according to Chen (2005), Chen et al. (2010) and ICRP (2007). The referred equilibrium factor (F-factor) reflects the relationship between indoor radon concentration and its progeny. An F-factor of 1 represents similar values for radon and respective progeny. In general, an F-factor of 0.4 is appropriate to describe the radioactive decay of radon into its progeny for residential buildings or similar. The formula to determine the Indoor Effective Dose (IED), on an annual basis, based on Average Radon Concentration (ARD) as defined in Chen (2005), Chen et al. (2010) and ICRP (2007), is computed according to (2): IED (mSv)=AARC ( Bq.m - 3 ) × 0.4 × AO (h) × 9(nSv(Bq.m - 3 .h) - 1 ) (2) As shown in (2) AARC depicts the Annual Average Radon Concentration in the radioactivity units of Bq.m -3 , and AO depicts the Annual Occupancy (AO) in hours. As recommended by the International Commission on Radiological Protection (ICRP) the public dose threshold concerning exposure to radiation is one mSv/year — Chen (2005), Chen et al. (2010) and ICRP (2007). The ICRP threshold of one mSv a year is defined as a limit laid out in order to prevent the so-called deterministic effects derived to radiation exposure (demise or malformation of somatic cells), and to restrict the chance of stochastic effects (cancer or cancer development). ICRP projects that radiation doses that overtake one mSv/year will determine the application of safeguarding measures for people of the public and remediation measures for the buildings where the limits are exceeded — Chen (2005), Chen et al. (2010) and ICRP (2007). In order to evaluate radon risk, the IED value will be calculated for the case study occupancy schedule (ground floor office) stipulated according to Section 1. For the referred occupancy schedule, the whole AO is computed according to (3): AO (h)=11 months year × 4 weeks month × 5 days week × 7 hours day =1540 h (3) Consequently, if an IED limit of 1 mSv is considered, on the basis of (2) the correspondent value for AARC can be determined cf. (4): AARC ( Bq.m - 3 ) = 0.4 × 1540 (h) × 9(nSv(Bq.m - 3 .h) - 1 1 (mSv) = 180 Bq.m - 3 (4) This result (180 Bq.m -3 ), obtained according to (4) indicates the value for the annual average radon concentration of 180 Bq.m -3 which meets the occupational exposure limit, when the office occupation schedule defined according to Section 1 is considered. 3. The Portuguese legislation on radon mitigation The Portuguese regulation concerning protection against ionizing radiation exposure is in force since April 3, 2019 - Decreto-Lei n. o 108/2018 (2018). This legislation derives from the transposition of Directive 2013/59/Euratom — Euroatom (2018).