Especially for near-surface repository for disposal of the low- and intermediate-level radioactive waste, safety assessment in case of inadvertent human intrusion should be handled seriously. This is because this type of incident will possibly give rise to high acute, not chronic exposure dose even though its occurrence of likelihood could higher than rather deeper geological repository for disposal of high-level radioactive waste over long time span after closure of the repository. Recently well drilling scenario for the pumping groundwater from the aquifer near the repository, among other possible inadvertent human intrusion incidents, has been popularly evaluated for the worst case due to its relatively high possibility of occurrence in parallel with normal scenarios for the nuclide transport for post-closure safety assessment of the repository. Movement of nuclide plume both in the confined and unconfined aquifer under and over a radioactive waste repository is of importance especially around an extracting well. Through this study a simple comment regarding quantification between a pumping rate from the well drilled into the aquifer as well as quantification of the plume size flowing around the well is presented. Drawdown of the well which is the change of water level of the upper water surface of the aquifer due to well pumping makes a cone of depression. And capture zone in the aquifer which is formed around the well, by which the groundwater is removed out, is the groundwater volume or area in the aquifer that is considered to contribute the extraction of the well by pumping. Usually this capture zone does not encompass the entire aquifer thickness for the partially penetrating well, which means that not all the portion of flowing groundwater through the aquifer is drawn by the well. And this capture zone does not need to coincide with the volume of the cone. Furthermore, all the nuclide plume volume is not necessarily and completely mixed with the groundwater flowing the entire aquifer. Therefore, a strategical approach might be required to grasp the aquifer portion and the plume size influenced by pumping to evaluate rather accurate radiological consequences due to the well scenario avoiding overestimation and meaningless conservatism as well, which is especially very common in the mass balance modeling e.g., by GoldSim under assumption that all the groundwater volume from the aquifer near the well extracted by the well. Although the capture zone around the well should be determined both by use of global/local groundwater flow model in the aquifer but a simple analytical model could be sought. Capture zone analysis has been widely seen in the area of the design of groundwater remediation system. If for safety assessment of the subsurface repository the plume behavior in the aquifer under the repository should be well characterized and correctly modeled, then the current study is expected to be more or less helpful to develop a specific mass balance model for nuclide transport and groundwater flow for assessment of an abnormal well drilling scenario near the repository.

• Sung-Hoon Ji(Korea Atomic Energy Research Institute (KAERI))
• Dong-Keun Cho(Korea Atomic Energy Research Institute (KAERI))
• Youn-Myoung Lee(Korea Atomic Energy Research Institute (KAERI)) Corresponding author