Radioactive aerosols monitoring of the surface air near the Shelter object within 1998–2019

Abstract

The results of long-term monitoring (1998–2019) of radioactive aerosols (RA) in the surface air near the Shelter object (SO) during works on projects implementation on creation of the New Safe Confinement’s “Arch” (NSC) are presented. The composition of long-lived nuclides (LLN) in RA using for assessing the personnel radiation safety are included the following nuclides: Σα-LLN (238, 239, 240Pu, 241Am) and Σβ-LLN (137Cs, 90Sr+90Y, 241Pu). The average activity of Σ-LLN was about 17 mBq/m3 in the end of 1990th in the air near the SO. It was shown that the main decline of aerosol situation near the SO, when RA volumetric activity increased ten-fold as compared to the beginning of 2000s, was due to radioactive dust resuspension during technological works. First, during earthwork at building of foundation strips of the NSC in 2010. During this period, average annual volumetric activity of Σ-LLN was 80 mBq/m3 , and weekly maximum activity rose to 6 mBq/m3 for Σα-LLN and for ΣβLLN to 520 mBq/m3. Second, when dismantling concrete and metal structures of the Shelter object in 2016, average annual activity of Σ-LLN was 62 mBq/m3, and weekly maximum activity reached Σα-LLN — 18 mBq/m3 and Σβ-LLN — 1,400 mBq/m3. After the NSC commissioning the Σ-LLN volumetric activity in the air dropped to 0.8 mBq/m3 in 2019. It is shown that after 2010 in the RA of the surface air there is an increase in the activity of 137Cs, not associated with fuel particles, the average relative share of which in the beginning of 2000s was about 20%, in 2013 reached to 62%, and after 2017 was in the range of 50–55%.