Activation calculation for the dismantling and decommissioning of a light water reactor using MCNP™ with ADVANTG and ORIGEN-S

Abstract

Abstract. The decommissioning of a light water reactor (LWR), which is licensed under § 7 of the German Atomic Energy Act, following the post-operational phase requires a comprehensive licensing procedure including in particular radiation protection aspects and possible impacts to the environment. Decommissioning includes essential changes in requirements for the systems and components and will mainly lead to the direct dismantling. In this context, neutron induced activation calculations for the structural components have to be carried out to predict activities in structures and to estimate future costs for conditioning and packaging. To avoid an overestimation of the radioactive inventory and to calculate the expenses for decommissioning as accurate as possible, modern state-of-theart Monte-Carlo-Techniques (MCNP™) are applied and coupled with present-day activation and decay codes (ORIGEN-S). In this context ADVANTG is used as weight window generator for MCNP™ i. e. as variance reduction tool to speed up the calculation in deep penetration problems. In this paper the calculation procedure is described and the obtained results are presented with a validation along with measured activities and photon dose rates measured in the post-operational phase. The validation shows that the applied calculation procedure is suitable for the determination of the radioactive inventory of a nuclear power plant. Even the measured gamma dose rates in the postoperational phase at different positions in the reactor building agree within a factor of 2 to 3 with the calculation results. The obtained results are accurate and suitable to support effectively the decommissioning planning process.

Radiological Characterization and Safety during Decommissioning of aNuclear Reactor

“…-Identification of isotopic composition, contamination level in spent fuel, structures, and components -Identification of the nature and extent of remedial actions and decontamination methods -Facilitating the preparation for decommissioning Decommissioning project is divided into several phases to help personnel with learning and integrating their experience during work. This method assists with reduction of time while supporting safety and radiation protection, also, with additional information of radiological inspections, it contributes to the waste management process as it is required for waste characterization [1][2][3][4][5][6][7]. As a learnt lessons, it was found that to improve decommissioning project schedule, the removal of large components should be applied to ex-situ cutting as an alternative of in-situ cutting; that approach consist of [8][9]: Decontamination and removed component can be made outside the site by a service provider.…”