Conceptual Design of a Nuclear Microreactor Transportation Cask

Abstract

Nuclear microreactors are a rising technology with the potential to be fueled at a central facility and transported to the operation site, which would mark the first attempt to transport a fueled commercial reactor in the US. A standard Type B cask may be adapted to transport a fueled microreactor core, passing the normal condition tests and hypothetical accident condition tests, demonstrated using a sample microreactor core design with heat pipes. An adequate shutdown reactivity margin (k_{eff} < 0.95) can be maintained using the control drums and shutdown rods except if the heat pipes are broken open and flooded with water. Shielding the gamma radiation so that the dose rate at a distance 2 m from the outer surface of the cask remains below 0.1 mSv/h requires 57 tons of lead, including 14 cm of radial shielding, 10 cm of solid axial shielding, and 14 cm of axial shielding through which the heat pipes pass. Decay heat can be effectively removed using thermal fins on the outer surface of the cask to maintain a surface temperature below 85C. Lead shielding melts during hypothetical accident thermal tests, which suggests that the lead must be properly protected from puncture or, better, replaced by depleted uranium (which has higher density and melting point) in further work. Redwood impact limiters and stainless steel 316 shims are sufficient to keep the vessel and heat pipes intact under the condition that the clearance holes through which the heat pipes pass through the lead shield have at least 0.21 mm of clearance. The normal and hypothetical accident conditions thermal tests and the hypothetical accident condition free drop and radiation tests were feasible with this standard Type B cask design.