Abstract
Dose rate calculations are important for judging the shielding performance of transport casks for radioactive material. Therefore it is important to have reliable calculation tools. We report on measured and calculated dose rates near a thick-walled transport and storage cask of ductile cast iron with lead inserts and a Co-60 source inside. In a series of experiments the thickness of the inserts was varied, and measured dose rates near the cask were compared with SCALE/MAVRIC 6.1.3 and SCALE/MAVRIC 6.2 calculation results. Deviations from the measurements were found to be higher for increased lead thicknesses. Furthermore, it is shown how the shielding material density, air scattering and accounting for the floor influence the quality of the calculation.
Highlights
The calculation of dose rates behind multiple shielding layers of material is highly relevant for radiation shielding assessment tasks within package design approval procedures
The goal of the study was to determine the accuracy of dose rate calculations for thick-walled transport and storage casks using two versions of SCALE/MAVRIC
The results of our SCALE 6.1.3 model fit well the results described in an earlier study of the same cask, where analyses identify the variability of the group wise modelling of the Co-60 source as one significant parameter causing the observed deviations to the measurements and the MCNP-results presented in [3]
Summary
The calculation of dose rates behind multiple shielding layers of material is highly relevant for radiation shielding assessment tasks within package design approval procedures. It is important that the underlying calculation methods work as accurate as possible and that they are validated against experimental data. A series of experiments was performed and evaluated by WTI (Wissenschaftlich-Technische Ingenieurberatung GmbH) allowing to check the accuracy of such calculation tools Due to the high source activity of about 1 TBq, dose rates could be measured accurately even for the highest lead thickness. In order to ensure homogeneous shielding properties of the cast iron wall and the lead between source and detector these structures were checked for material errors, e.g. cavities, by gamma radiography before the experiments were carried out. The real cast iron and lead density were measured after the measurement series had been conducted
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