Neutronic Analysis of Critical Configurations in Geologic Repositories: I—Weapons-Grade Plutonium

Conditions for criticality by uranium deposition in water-saturated geological formations

“…Combining the mass transport analysis with the results of the neutronics analysis, which has been performed partially in this study, some important points for selecting a site for criticality safety can be suggested. These include (1) iron existing in the host rock reduces the likelihood of criticality significantly; (2) low host rock porosity is preferred for criticality safety; (3) the conservatism could change when comparing heterogeneous geometries for different fracture apertures, in other words, the planar fracture geometry applied in the previous CSA for geological disposal [6][7][8][9][10][11]15] would not necessarily yield conservative results against the homogeneous uranium deposition because the k eff for heterogeneous geometry can be smaller than that for homogeneous one in case of larger width of fracture aperture; and (4) the importance of the mass of the deposition increases when it is smaller. To make these more reliable and specific, further studies in the neutronics and mass transport are crucially important.…”

“…Corresponding to these two questions, CSA consists of two parts: the neutronics analysis for evaluating critical mass of TFM [4] and the analysis for transport and deposition of TFM in the near and far fields [5]. For the first part, in the CSA for YMR, various neutronics models were developed [6][7][8][9][10][11][12][13] by considering compositions of TFM, groundwater, rocks, and geometries of TFM depositions for various conditions in Nevada tuff rock.…”

“…In the previous studies for repository criticality safety such as [6][7][8][9][10][11]15], the planar fracture model was used for representing heterogeneity of C 2014 Atomic Energy Society of Japan. All rights reserved.…”