Monte Carlo based investigation of a universal two-component albedo neutron dosimeter in a deep geological disposal system for high-level nuclear waste

Albedo neutron dosimeter utilizes the property of the human body to moderate incident high energy neutrons, which are scattered and reflected as thermal and low energy neutrons that can be measured by thermoluminescence detector (TLD) with high sensitivity. The current study is devoted to the assessment of possible utilization of the albedo neutron dosimeter as a personal monitoring device in a deep geological disposal system for high-level nuclear waste. When a nuclear waste package is transported to its final disposal position in a deep geological repository, such as in a horizontal emplacement drift in a rock salt mine, the question about the appropriate calibration factor of the albedo neutron dosimeter arises. Neutrons backscattered by the surrounding host rock layers might contribute significantly to the composition of the radiation field and in turn influence the response of the neutron detector. To account for different radiation field compositions, a field calibration technique providing field-specific calibration factors was applied in the current study. The field calibration of an albedo neutron dosimeter in a deep geological repository was performed with Monte Carlo method. The radiation field was simulated by a shielding cask loaded with a 252Cf neutron source that is placed in a horizontal drift of a rock salt mine. Calibration factors were calculated at various distances to the shielding cask. In the investigated case, the neutron radiation field in a geological repository can be assigned to the calibration factor N1, which is recommended for reactors and accelerators with heavy shielding.