Degradation of TRU waste in a geological disposal facility may cause the formation of a nitrate plume. A Nitrate Evolution model due to mineral reactions, microbial activity, and metal corrosiON (NEON) has therefore been developed to evaluate the chemical behavior of a nitrate plume and assess its potential to impact on radionuclide migration and the safety case for geological disposal of TRU waste. The NEON model includes the redox reactions of nitrogen, as nitrate, nitrite and ammonium ions, and their reaction with groundwater, minerals, microorganisms, including the microbial mediated nitrogen cycle, and metal corrosion products. Small scale laboratory experiments can be reproduced satisfactorily, however, it is necessary to demonstrate the applicability of the NEON model on scales relevant to the geological disposal of TRU waste. In the current study, an industrial analogue of a nitrate plume from the pollution of groundwater from nitrate fertilizers used on Ikuchi Island in Hiroshima Prefecture, Japan was selected to test the applicability of the NEON model. Concentration profiles of nitrate and ammonium ions in the groundwater were successfully reproduced over the hundreds of meters scale demonstrating the applicability of the NEON model in evaluating the chemical behavior of a nitrate plume derived from the geological disposal of TRU waste.

  In this study, an applicability of the modified Cam clay model to the buffer material under salt water conditions was examined. Consolidated-undrained triaxial test was conducted using NaCl solution and artificial seawater. Based on the consolidated-undrained triaxial compression test results and the existing consolidation test results, the difference in the mechanical behavior of the buffer material under distilled water and saltwater condition was clarified. In particular, there was a difference in the unloading behavior in the consolidation test. Through reproducibility analysis of these experimental data, it was confirmed that the mechanical behavior of the buffer material can be roughly reproduced by setting the swelling index according to the salt concentration.

  Geological disposal of radioactive wastes requires the large amounts of fundamental technical knowledge throughout the project such as the investigation of geological environment, facility construction, operation and closure. Monitoring is carried out to collect site-relevant information for the creation of an environmental database, to assist in the decision-making process, to provide information for the various stakeholders, etc. We summarized the current technical level and problems of the groundwater monitoring in the world. Through the research and technology development so far, the technologies have been developed for drilling borehole in the geological environment survey prior to monitoring and the selection of the monitoring site. On the other hand, the following technical developments are remaining issues: long-term operation method of monitoring equipment, retrieving method of monitoring equipment after long-term operation, transport method of backfill material for borehole sealing, technical basis for the sealing performance when the borehole-protective casing and strainer tube are left. Thus, to plan for the groundwater monitoring, preliminary studies on long-term operation of monitoring equipment and abandonment of monitoring borehole are necessary.