Beyond a million years: Robust radiation shielding for high-level waste

A recent paper focused on gamma dose rates from unshielded high-level waste over periods exceeding 1 million years and demonstrated that this waste remains hazardous essentially indefinitely. This paper presents a novel perspective by focusing on the practical requirement of shielding to protect from this hazard. Using concrete as the reference material, this paper shows that the required thicknesses stabilize to several tens of centimeters at 1 million years and must remain robust for each individual spent fuel (SF) and vitrified high-level waste (VHLW) form essentially indefinitely, including relevant fragments. These new results provide an additional perspective on an enduring hazard that has been overlooked in discussions of the choice of fuel cycle and in the design and safety analysis of geological repositories. Further research and data needs are identified.