PhD Defense | Floris Abrams | Towards more effective spatio-temporal schemes for soil remediation in response to large-scale nuclear emergencies affecting food and agriculture

Towards more effective spatio-temporal schemes for soil remediation in response to large-scale nuclear emergencies affecting food and agriculture

Although nuclear energy can be categorised as a safe and low-carbon energy source, two major  accidents (Chernobyl, 1986, and Fukushima, 2011) demonstrated the large-scale impact it may have on  neighboring communities. While immediate response plans to nuclear accidents are well established, the complex and resource-intensive recovery phase lacks adequate (inter)national guidance and tools. The recovery is especially important for agricultural areas, where food production needs to be returned  to normalcy. This research contributes to the development of tools within a spatial decision support system (sDSS) to improve the post-accident decision-making process about where, how, and when to  remediate agricultural land. This research illustrates the tools in two agricultural watersheds: the  Maarkebeek, located in Flanders (Belgium), and the Niida watershed, located in the Fukushima  prefecture (Japan). At the basis of the sDSS was a multi-criteria decision-aiding methodology (MCDA), which was found to be a good framework for supporting soil remediation on a local scale through  optimal remedial technology selection for a specific site and on a regional scale through optimal site  selection. However, we identified four major gaps in the reviewed case studies: (i) A lack of inclusion  of social criteria; (ii) A lack of early stakeholder engagement; (iii) A mismatch between weighting and  aggregation methodologies; and (iv) A lack of sensitivity analysis. To overcome (i) and (iv), a methodology to include linguistic scoring within ordinal qualitative scales as fuzzy numbers, for the evaluation of criteria or weight setting was proposed. The impact of an increasing amount of  uncertainty within the triangular fuzzy numbers (TFN) was studied, and it became clear that the impact  of uncertainty on decision-making power cannot be ignored. Proposing remedial plans using two  compromise programming methodologies for site selection and action selection results in a very complex spatial pattern for remediation. The clustering of individual entities into larger, homogeneous, actionable units can improve feasibility and reduce the cost of remediation, especially when  interventions are costly and technically challenging to perform. A spatio-temporal clustering approach  under a budget constraint was presented to determine homogenous clusters of polygons and interventions to reduce the cost of intervention while still attaining near-optimal effectiveness.

When remedial actions are converted into remediation trajectories, a sequence of multiple remedial actions in time, time is explicitly taken into account within the decision making. A column generation model was proposed that reconciles the economic and productive aspects of remediation for agricultural areas. The model’s main novelty is its ability to find optimal multi-period sequences or trajectories of remedial actions from a set of predefined remedial actions, where column generation is used to extend the candidate set of the remedial trajectories while keeping the computational complexity limited. The introduction of new trajectories with the column generation approach will, after 4700 iterations, further reduce the loss in productive years by 237 years and 20% of the accumulated productivity score.

An iterative framework called the CAMF approach (Cellular Automata-Based Heuristic for  Minimizing Flow) was used to model and reduce the off-site impacts of soil remediation in the Niida watershed. Spatially targeted afforestation of the 1000 best cells reduces the sediment quantity resulting  from the decontamination work by 15.4%, compared to 0.8% when the cells are selected randomly. Prioritizing topsoil removal interventions within the Maarkebeek watershed while accounting exclusively for off-site criteria results in a 267% increase in Cs-137 flux reduction efficiency in the first  year when compared to remedial schemes based only on on-site criteria.

Promotor:

• Jos Van Orshoven (KU Leuven)

SCK CEN mentors:

• Lieve Sweeck (SCK CEN)

• Johan Camps (SCK CEN)

Click here for a list of obtained PhD degrees.