2020 Volume 27 Issue 1 Pages 3-11
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.
