Aeroradiometric Measurements in the Framework of the Swiss Exercise ARM18 and the International Exercise CONTEX 2018

The measurement flights of the exercise ARM18 were performed between May 28th and June 1st, 2018. The exercise was organized by the National Emergency Operations Centre (NEOC) under coordination from the Expert Group for Aeroradiometrics (FAR). Representatives of KompZen ABC-Kamir participated both in the exercise and performed separate measuring flights. According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Beznau (KKB) and Leibstadt (KKL) and the nuclear facilities of the Paul Scherrer Institute (PSI) and the Zwischenlager Würenlingen AG (Zwilag) were surveyed. The measurements showed no artificial radionuclides outside of the plant premises. On request of German authorities, the measuring area was extended into German territory. In this area, a dose rate anomaly associated with 232Th activity in a mineral processing plant could be identified. The series of radiological background measurements over Swiss cities was complemented with measurements over Solothurn, Fribourg and Yverdon-les-Bains. The measurement in the vicinity of Yverdon-les-Bains was used to directly compare the evaluation software of the old ARM system (MGS32) to the proprietary software of the manufacturer of the RLL system (Mirion). The international exercise CONTEX18 was performed in the International Atomic Energy Agency (IAEA) Response and Assistance Network (RANET) framework between June 19th and 21st in northern Denmark, coordinated by the Danish Emergency Management Agency (DEMA). It provided the opportunity to measure an altitude profile over the North Sea with low airborne radon progeny concentrations. A clear difference to measurements over Swiss inland lakes was observed. This difference was used for investigating a potential method to compensate for the influence of airborne radon progeny on the measurement of 238U activity concentrations. The organisers of the exercise placed several sources of different radionuclides and activities in the exercise area, challenging the performance of airborne detection. A method using maxima of the man-made-gross-count(MMGC)-ratio to define points which should be inspected more closely was developed. The spectra of these points of interest were inspected in detail and led to the identification of 137Cs, 192Ir, 99mTc, 75Se and 111In sources. Measurements around Mont Vully on behalf of the University of Basel could not clearly locate small scale anomalies of 238U concentrations due to the field of view of the airborne measurements and depth of the peat layer containing elevated 238U concentrations. Measurements along a transversal showed expected results due to flight altitude and attenuation of photons by water bodies.