Communicating results and uncertainties of radioecological modelling – a transdisciplinary workshop
Authors: Kogiomtzidis Anna Lina , Hormann Volker , Walther Clemens 
Published: September 2023

Abstract. Compared with geological structures, many processes and fluctuations in the biosphere take place on much shorter timescales and are difficult, often nearly impossible to predict over long periods of time. Consequently, modelling results are subject to tremendous uncertainties. While German regulations require biosphere modelling for dose estimations as part of the site selection procedure for a nuclear waste repository, they also recognize those uncertainties by stating that the calculated dose estimates are not an actual prognosis of the effective dose used in practical radiation protection but merely an indicator for the safety of the repository (BASE, 2022, p. 6). In addition to the complex technical aspects, this
subtle but important distinction might pose an additional difficulty in
understanding the meaning of dose modelling results and their uncertainties
when presented to an interested public. Within a transdisciplinary online workshop on safety indicators in nuclear
waste management, relevant aspects for communicating dose estimates and
uncertainties were evaluated. As the target group, the Citizens' Working Group
(CWG) of the TRANSENS research project was chosen. TRANSENS is a transdisciplinary project addressing socio-technical questions concerning
the disposal of nuclear waste (TRANSENS, 2023). As an “extended peer community”, the CWG is an important part of the transdisciplinary research
approach (Seidl et al., 2021). Currently, the group consists of 14 citizens
with a diverse distribution of age, profession and degree of (scientific)
education. By design, citizens with no stakes and no particular expertise
concerning nuclear waste or radioactivity were recruited. However, the
members of the CWG acquired ever-increasing knowledge about the subject in
over 2 years of regular meetings and workshops within the project. Thus,
the CWG can be seen as a proxy for members of the public with high interest
in nuclear waste disposal but potentially without distinct scientific
education. The workshop took place over two days as a virtual meeting and covered the
full modelling chain from the confinement providing rock zone to the biosphere. Here, mainly results concerning the radioecological modelling
will be presented. As a central element we investigated the use of an interactive web tool to
illustrate the effects of parameter uncertainties on dose estimates. The web
tool, created specifically for this workshop, consists of some slide
controls, allowing the user to select values from a given range for four
parameters relevant for biosphere modelling. From the selected parameter
combination, a dose estimate based on the biosphere model described in the
German regulations (BASE, 2022) is calculated and displayed. Additionally, a
probability is displayed for each combination, which results from (not
necessarily scientifically accurate) underlying probability distributions
assumed for each parameter. This rather abstract numerical value, which
varies over many orders of magnitude, is in addition visualized by a density
plot. The user is asked to rate the information regarding dose value and
probability on a scale from “very concerning” to “very reassuring” in an input form at the lower end of the screen. After an introductory presentation on the concepts of effective dose and
radioecological modelling, the participants had time to try out the web tool
in breakout rooms of three to four people followed by a free discussion on
various aspects connected to the tool. Afterwards, the CWG members were asked
to collect decisions that need to be made when designing such a tool
together with available options (e.g. “Which colour should the slide
controls have” → “red, green, blue …”). For inspiration, two
alternative designs were shown as examples. A subsequent multiple-choice survey found that the employment of explanatory
information boxes, the indication of (legal) references values and the
annotation of the dose axis were perceived as the most important aspects
within the group. Each of these questions was then revisited in a silent
discussion collecting advantages and disadvantages for multiple options on
how to address these issues. In the last part of the workshop, the effective dose was compared to two
other safety-related indicators resulting from modelling calculations
(porosity of the backfill material and radionuclide concentration in
groundwater). For this purpose, the participants were asked to discuss to
what extent each of the three indicators matched a number of desirable
features identified in a previous part of the workshop. The workshop was planned, conducted and evaluated by a team of engineers and
natural scientists with support of CWG's coordination team offering
psychological and social–scientific expertise as well as experience from a
number of previous workshops with the CWG.