MODELLING THE EXPOSURE OF RESIDENTS OF A RADIUM-CONTAMINATED LIVING PLACE

Within the framework of the Swiss Radium Action Plan 2015-22, which aims to investigate and remediate sites contaminated by the radium used in the Swiss watch industry, a reference level of 1 mSv per y has been defined for the exposure of residents. An additional protection objective has been set for soil contamination, which should not exceed the value of 1000 Bq per kg 226Ra. Based on measurements on the study sites, the doses received by residents were calculated accordingly to the methodology, in both indoor and outdoor areas, taking into account external exposure and ingestion. The site diagnosis approach consists of a screening procedure based on a rapid measurement, followed, if necessary, by additional analysis to estimate doses. Sites where modelling indicates that the reference level or the complementary protection objective for soil contamination have been exceeded are subject to remediation. The application of the methodology based on these radiological criteria to 752 sites diagnosed until December 2020 indicates a rate of sites (buildings and outdoor areas) requiring remediation of ~16%. The annual doses to residents calculated by modelling are between 1 and 20 mSv per y for these sites.

REMEDIATION OF RADIUM LEGACIES FROM THE SWISS WATCH INDUSTRY

Discovery of radioactive radium contaminations in a former landfill site in Biel was made in 2014. Following this, it was decided to search for and remediate sites that had possibly been contaminated with radium as a result of its use in the watchmaking industry between 1920 and 1960. This work describe the general approach to identify survey and remediate affected sites. The methods is based on the concept of existing exposure situations as developed by the International Commission on Radiological Protection, and is supported by an action plan for radium 2015-2019 approved by the Federal Council in 2015. The plan comprises four steps: the search for potentially contaminated sites, the measurement and assessment of each site, the remediation of those sites where the public would be exposed to an annual dose higher than 1 mSv, and actions to secure the landfill sites. The arrangements for each step are described in the present article. The measurement and remediation procedures imply intrusions into the privacy of the inhabitants. This requires the public authorities to actively inform the population and to develop an effective and transparent means of communication. The actions developed for this are also described.

Variation in airborne 134Cs, 137Cs, particulate 131I and 7Be maximum activities at high-altitude European locations after the arrival of Fukushima-labeled air masses

The Fukushima-labeled air mass arrival, and later the cesium-134 (¹³⁴Cs), cesium-137 (¹³⁷Cs) and particulate iodine-131 (hereafter noted ¹³¹I_p) maximum levels were registered in Europe at different dates depending on the location. Most of those data were obtained at low-altitude sampling areas. Here, we compare the airborne levels registered at different high-altitude European locations (from 850 m to about 3500 m). The integrated ¹³⁷Cs activity concentration was not uniform with regard to the altitude even after a long travel time/distance from Japan. Moreover, the relation of integrated ¹³⁷Cs vs. altitude showed a linear decrease up to an altitude of about 3000 m. A similar trend was noticed for ¹³¹I_p (particulate fraction) while it increased above 3000 m. Comparison with ⁷Be activity concentration showed that, as far as the high altitude location is concerned, the ¹³⁷Cs and ¹³⁴Cs maximum concentrations corresponded to the ⁷Be maximum, suggesting downdraft movements from high tropospheric or stratospheric layers to be responsible for ^137,134Cs increase and peak values. This was also confirmed by high potential vorticity and low relative humidity registered during the peak values.

Cosmogenic (7)Be and (22)Na in ground level air in Switzerland (1994-2011)

We report monthly averages of weekly (7)Be and (22)Na concentrations in aerosol samples collected with high volume aerosol filters at 5 sampling sites in Switzerland from 1994 to 2011 ((7)Be) and from 2000 to 2011 ((22)Na). Monthly average concentrations of the two cosmogenic isotopes varied between 2600 and 4600 μBq/m(3) for (7)Be and between 0.2 μBq/m(3) and 0.5 μBq/m(3) for (22)Na. The (22)Na concentration in ground level air strongly increased from March to May, while a corresponding (7)Be increase was seen from March until July. The observed variations of the (7)Be and (22)Na activities together with the changes in the (7)Be/(22)Na ratio indicate input of stratospheric air between March and May, increased mixing of upper tropospheric air from June to August, and less exchange between the upper and lower troposphere in autumn and winter. Additionally, the 11-year solar cycle is clearly seen in the annual averages of the (7)Be concentrations.