Potential Source Apportionment and Meteorological Conditions Involved in Airborne ¹³¹I Detections in January/February 2017 in Europe

Abstract

Traces of particulate radioactive iodine (I) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 μBq m except at one location in western Russia where they reached up to several mBq m. Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of I resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related toI use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

Chemical and radioanalytical investigations of 106Ru-containing air filters from Vienna in fall 2017: searching for stable element anomalies

“…Two unusual incidents of radionuclide releases occurred in 2017. In January/February of that year, an unusually long episode of 131 I was observed [ 3 ]. In fall 2017, European monitoring stations reported an unusual and unprecedented detection of radioruthenium in air [ 4 ].…”

Atmospheric modeling and source reconstruction of radioactive ruthenium from an undeclared major release in 2017

“…The concentrations reported were in the range of several microbequerels per cubic meter to more than 100 mBq/m 3 (1). As for the 131 I detection event in January/February 2017 (2), no elevation in gamma dose rate was reported by measurement networks around known nuclear sites in Europe. While this makes a major accidental release scenario unlikely, analyzing only activity measurements in the air, for which the observed values are usually weekly averaged, cannot identify either the origin or the magnitude of the release.…”

“…Variational inverse modeling methods (11–16) are a variant of Bayesian methods since they draw on the Bayes formula but consist only of estimating the optimal solution and not obtaining the probability density function of the estimated source parameters. A variational method was applied to identify the origin of 131 I detected in Europe between January and February 2017 (2). As no information on the source was available, several potential releases sites were considered to reduce the size of the inverse problem.…”

Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017

“…Today, the memberships have grown to laboratories in 22 countries (while the name was kept), and the Ro5 is still an informal arrangement on a laboratory level and between scientists. In January 2017, the Ro5 alerted its members regarding the widespread detection of airborne 131 I in Europe (1). In October 2017, an unprecedented release of ruthenium-106 ( 106 Ru; T 1/2 = 371.8 d) into the atmosphere was the subject of numerous detections and exchanges within the Ro5.…”