Комплексные организационные и методические подходы к выводу из эксплуатации хранилищ РАО

Abstract

Purpose: Development of comprehensive organizational and methodical approaches to decommissioning of shallow radwaste (RW) repositories.
 Material and methods: The following researches were conducted during assessment of radiation and hygiene situation:
 - assessing the state of physical barriers of repositories (tanks) of solid and liquid RW;
 - assessing radiation situation at the repository site before and after remediation;
 - measuring specific activity of 90Sr and 137Cs in ground and subsurface water, core sample, soils, building structures.
 Methods: on foot gamma survey; gamma-ray spectrometric measurement of radionuclides in environmental samples using a stationary spectrometer; radiochemical extraction of radionuclides and their radiometry.
 Results: The surveys were performed in 2014–2016. They delivered data on gamma dose rate at the RW repository site, specific activity of 90Sr and 137Cs in ground and subsurface water, core sample, soils, building structures.
 The surveys showed that content of 90Sr in subsurface water varied from 0.25 to 0.4 Bq/kg, while content of 137Cs was below the detection threshold (0.01 Bq per sample). It was founded that distribution of 90Sr and 137Cs in soil (core sample) forming the top layer of the area is highly uneven. In some cases specific activity of soil exceeded 1000 Bq/kg (C-23 well at the depth of 2.75 m and C-24 well at the depth of 5 m). In all other cases specific activity of the core sample did not exceed 10 Bq/kg, and specific activity of soil was up to 50 Bq/kg which is over background values. The ambient dose equivalent rate at the site varied from 0.1 to 0.3 µSv/h.
 After remediation activities content of radionuclides in soil and subsurface water was at the levels of background values.
 More than 6700 measurements were performed (more than 2400 measurements of the ambient dose equivalent rate, more than 4100 measurements of beta-contamination of work surfaces and equipment, and more than 200 measurements of specific and volumetric activity of environmental samples). 
 Conclusions: This work allowed to substantiate technical solutions, procedure of RW accounting and control, using of shelters and mobile systems for radiation safety of the personnel and environmental protection.
 It was demonstrated that average external radiation doses for the workers involved in decommissioning activities did not exceed 0.7 mSv (variation from 0.16 to 1.7 mSv), while internal radiation doses varied from 0.35 to 3.3 µSv. 
 Density of beta-contamination of the site did not exceed 38 beta-particles/(cm2∙min) which corresponds to background values. The ambient dose equivalent rate of the site was within 0.09-0.15 µSv/h after the work has been done.