Modelling the atmospheric dispersion of radiotracers in small-scale, controlled detonations: validation of dispersion models using field test data

Abstract

A series of modelling exercises, based on field tests conducted in the Czech Republic, were carried out by the ‘Urban’ Working Groups as part of the International Atomic Energy Agency’s Environmental Modelling for Radiation Safety II, Modelling and Data for Radiological Impact Assessment (MODARIA) I and MODARIA II international data compilation and model validation programmes. In the first two of these programmes, data from a series of field tests involving dispersion of a radiotracer, 99mTc, from small-scale, controlled detonations were used in a comparison of model predictions with field measurements of deposition. In the third programme, data from a similar field test, involving dispersion of 140La instead of 99mTc, were used. Use of longer-lived 140La as a radiotracer allowed a greater number of measurements to be made over a greater distance from the dispersion point and in more directions than was possible for the earlier tests involving shorter-lived 99mTc. The modelling exercises included both intercomparison of model predictions from several participants and comparison of model predictions with the measured data. Several models (HotSpot, LASAIR, ADDAM/CSA-ERM, plus some research models) were used in the comparisons, which demonstrated the challenges of modelling dispersion of radionuclides from detonations and the need for appropriate meteorological measurements.

Urban working groups in the IAEA’s model testing programmes: overview from the MODARIA I and MODARIA II programmes

“…A series of field tests carried out in the Czech Republic formed the basis of several short-range atmospheric dispersion modelling exercises (Thiessen et al 2022), as described in section 2.1. Section 2.2 describes several mid-range atmospheric dispersion exercises based on monitoring data at locations in Slovenia and Canada.…”

“…Republic. These exercises are described in detail in a separate article in this issue (Thiessen et al 2022; see also Prouza et al 2010, Thiessen et al 2011, IAEA 2021, 2022in preparation). In each field test, a radiotracer ( 99m Tc or 140 La) was dispersed by means of a small explosion, and measurements of ground deposition of the radiotracer were made, as well as of detailed meteorological data before and during the dispersion event.…”

“…Participants did not directly model the explosions, but started with estimated dimensions of the initial cloud and partitioning of the source term within that cloud. As described by Thiessen et al (2022), model predictions for a given field test sometimes varied from each other with respect to the direction of the plume and the amounts of deposited activity. Such differences are potentially explained by differences in the models (e.g.…”

“…The Urban Areas Working Group of EMRAS II conducted three modelling exercises (Thiessen et al 2011, 2022, Periáñez et al 2016, IAEA 2021. The 1st modelling exercise was a short-range atmospheric dispersion exercise based on field tests involving dispersion of a radionuclide ( 99m Tc) by means of a small explosion.…”