Analysis of Uncertainties Affecting Numerical Transport Models for a Potential Radioactive Waste Disposal Site

Abstract

Numerical models have been commonly used to study solute transport behaviours both in laboratory-and field-scale cases. However, numerical interpretation and predictions of solute transport are complicated by various uncertainties and therefore can be misleading and lead to incorrect understanding of solute transport behaviours in hydrogeological systems. Such uncertainties have been discussed with a case study of radionuclides transport at a potential site for disposal of Low-and Intermediate-Level radioactive Wastes (LILW) in southern China. Firstly, pre-modelling assumptions cause uncertainties for model performance and have a significant influence on the model output. Therefore, such assumptions and related factors should be thoroughly considered and minimized in laboratory experiments or investigated in the field. Secondly, difference in the calculated plumes caused by uncertainties in the development of conceptual models suggests that the hydrogeological conceptual model should be developed based on intrinsic understanding of the transport problems and relevant data collection. Thirdly, relative sensitivity (RS) has been calculated to analyse the parameter uncertainties. Results indicate that the uncertainties are tracer-, parameter-and time-dependent. Therefore, model uncertainties arising from parameters should be considered for each specific parameter with the specific period. Finally, prediction scenarios are associated with uncertainties in the model prediction stage. Results suggest that the uncertainties in scenarios of future transport conditions should be recognized prior to model prediction. This study illustrates some of the uncertainties that might affect numerical transport models and therefore will be a useful reference for application of solute transport models to assessment of contamination risks from a LILW disposal site.