Tools for harmonized data collection at exposure situations with naturally occurring radioactive materials (NORM).

Naturally occurring radioactive materials (NORM) contribute to the dose arising from radiation exposure for workers, public and non-human biota in different working and environmental conditions. Within the EURATOM Horizon 2020 RadoNorm project, work is ongoing to identify NORM exposure situations and scenarios in European countries and to collect qualitative and quantitative data of relevance for radiation protection. The data obtained will contribute to improved understanding of the extent of activities involving NORM, radionuclide behaviours and the associated radiation exposure, and will provide an insight into related scientific, practical and regulatory challenges. The development of a tiered methodology for identification of NORM exposure situations and complementary tools to support uniform data collection were the first activities in the mentioned project NORM work. While NORM identification methodology is given in Michalik et al., 2023, in this paper, the main details of tools for NORM data collection are presented and they are made publicly available. The tools are a series of NORM registers in Microsoft Excel form, that have been comprehensively designed to help (a) identify the main NORM issues of radiation protection concern at given exposure situations, (b) gain an overview of materials involved (i.e., raw materials, products, by-products, residues, effluents), c) collect qualitative and quantitative data on NORM, and (d) characterise multiple hazards exposure scenarios and make further steps towards development of an integrated risk and exposure dose assessment for workers, public and non-human biota. Furthermore, the NORM registers ensure standardised and unified characterisation of NORM situations in a manner that supports and complements the effective management and regulatory control of NORM processes, products and wastes, and related exposures to natural radiation worldwide.

A methodology for the systematic identification of naturally occurring radioactive materials (NORM).

Naturally occurring radioactive materials (NORM) are present worldwide and under certain circumstances (e.g., human activities) may give radiation exposure to workers, local public or occasional visitors and non-human biota (NHB) of the surrounding ecosystems. This may occur during planned or existing exposure situations which, under current radiation protection standards, require identification, management, and regulatory control as for other practices associated with man-made radionuclides that may result in the exposure of people and NHB. However, knowledge gaps exist with respect to the extent of global and European NORM exposure situations and their exposure scenario characteristics, including information on the presence of other physical hazards, such as chemical and biological ones. One of the main reasons for this is the wide variety of industries, practices and situations that may utilise NORM. Additionally, the lack of a comprehensive methodology for identification of NORM exposure situations and the absence of tools to support a systematic characterisation and data collection at identified sites may also lead to a gap in knowledge. Within the EURATOM Horizon 2020 RadoNorm project, a methodology for systematic NORM exposure identification has been developed. The methodology, containing consecutive tiers, comprehensively covers situations where NORM may occur (i.e., minerals and raw materials deposits, industrial activities, industrial products and residues and their applications, waste, legacies), and thus, allows detailed investigation and complete identification of situations where NORM may present a radiation protection concern in a country. Details of the tiered methodology, with practical examples on harmonised data collection using a variety of existing sources of information to establish NORM inventories, are presented in this paper. This methodology is flexible and thus applicable to a diversity of situations. It is intended to be used to make NORM inventory starting from the scratch, however it can be used also to systematise and complete existing data.

Do transient hydrological processes explain the variability of strontium-90 activity in groundwater downstream of a radioactive trench near Chernobyl?

The Chernobyl Pilot Site (CPS) was created in 2000 in order to study radionuclide migration processes to the geosphere from radioactive material of the Red forest buried in a trench. In this article, the data collected in the CPS up to 2015 are analyzed to identify the links between hydrological conditions and release of strontium-90 (90Sr) from the trench. Then, a flow-and-transport model is used for simulating distribution of 90Sr both in the unsaturated and saturated zones downstream of the trench. The results show that the 90Sr activity in groundwater is strongly transient in time, due to the high inter-annual variability of both the recharge rate and the groundwater level (some particularly wet winters resulted in saturation of the bottom part of the trench). In addition, the parameters that govern the sorption of 90Sr in trench material appear to vary significantly in space (the retardation factor ranges from 10 to 50 depending on the location). This spatiotemporal variability could hide some critical processes, e.g., related to a long-term trend, and needs to be characterized through an appropriate sampling frequency.

Combining geostatistics and simulations of flow and transport to characterize contamination within the unsaturated zone.

Characterization of contamination in soils or groundwater resulting from industrial activities is critical for site remediation. In this study, geostatistics and physically-based simulations are combined for estimating levels of contamination within the unsaturated zone. First, a large number of flow and transport simulations are run and their outputs are used to compute empirical non stationary variograms. Then, these empirical variograms, called numerical variograms and which are expected to reproduce the spatial variability of the contaminant plume better than a usual variogram model based on observations only, are used for kriging. The method is illustrated on a two-dimensional synthetic reference test case, with a contamination due to a point source of tritium (e.g. tritiated water). The diversity among the simulated tritium plumes is induced by numerous sets of hydraulic parameter fields conditioned by samples from the reference test case. Kriging with numerical variograms is then compared to ordinary kriging and kriging with an external drift: the results show that kriging with numerical variograms improves the estimates, all the more that few observations are available, underlining the interest of the method. When considering a relatively dense sampling scenario, the mean absolute error with kriging with numerical variograms is reduced by 52% compared to ordinary kriging and by 45% compared to kriging with an external drift. For a scarcer sampling, those errors are respectively reduced of 73% and 34%. However, the performance of the method regarding the classification into contaminated or not contaminated zones depends on the pollution threshold. Yet, the distribution of contamination is better reproduced by kriging with numerical variograms than by ordinary kriging or kriging with an external drift.