Calculation of the activity inventory of the CENM TRIGA MARK II reactor for decommissioning planninig

Abstract

This study aims to estimate the activity inventory of the Moroccan TRIGA MARK II research reactor components at the current time and at the end of cycle (EOF). The MCNP6.2 code was used to calculate the neutron flux distributions, which were used as inputs for CINDER’90 code to calculate the neutron-induced activity in the activated materials over time based on the reactor operating history. To ensure the highest possible accuracy of the activity inventory calculations, the MCNP model for the CENM TRIGA reactor was updated and improved using the reactor geometry and material composition details based on newly data acquired from CNESTEN. The validation of this updated model is achieved through reactivity calculations, where good agreement is demonstrated between the calculated core reactivity and excess reactivity measurements. Moreover, the reactor operating history required for burnup and activation calculations was analyzed and simplified based on several approaches to reduce the computational cost and time. The effect of the simplified approach on the neutronic parameters and activation calculations is investigated. It is demonstrated that the approach adopted does not affect the calculated core reactivity, and good correspondence is observed with the excess reactivity measurements. In addition, its effect on the activity of the long-lived activation products is negligible. At the end, the activity inventory of the in-core and reflector assembly structural components is presented at the current time, EOC, and after a cooling period of six months. The principal radionuclides contributing to the total activity are also presented.