Thermal modeling study for geologic borehole conceptual design

Abstract

Instituto de Pesquisas Energeticas e Nucleares (IPEN-CNEN/SP) is developing a strategy for safe, permanent disposal of disused sealed radioactive sources (DSRS) from industrial and medical applications within Brazil. The Institute is proposing modifications to the International Atomic Energy Agency (IAEA) Borehole Disposal of Sealed Radioactive Sources (BOSS) concept originally developed by the Nuclear Energy Corporation of South Africa. The current Brazilian modified design differs from the IAEA design in that the disposal zone is below 300 m versus 30 m of the boss concept, and will be used to dispose of a much larger number of DSRS. These modifications result in a considerable departure from the generic safety case established by IAEA. Therefore, a new safety case is required to assess radiological and thermal impacts among other considerations. Predictive modeling and simulations were performed to address impacts of the proposed borehole concept at the early design stage in order to provide timely improvements to the concept and a traceable rationale for decisions made throughout the program as required by the safety case. Preliminary objectives of the modeling effort were focused on evaluating the mechanical and thermal loads anticipated within the current Brazilian borehole disposal concept in order to assess potential material and design issues. This paper presents the thermal modeling predictions and performance results for the proposed BOSS design.