Effectiveness of Various Shielding Materials for Mobile Microreactors

Unlike transportation casks, mobile microreactors also contain internal structures and a reflector. These components take a significant volume within the transportation conveyance, often assumed to be an intermodal container. Consideration of transportable shielding should be included in the early phases of the design process to ensure that there is sufficient spare volume in the intermodal container to accommodate transportable shielding. This work assesses the shielding efficiency of various common (lead and stainless steel) and less-common (tungsten, tungsten carbide, and tungsten boride) materials. The dose reduction for a given mass was found to be generally the same across all materials. However, the volume occupied by the shield can be greatly reduced for higher density materials such as tungsten. Also, the volume reduction afforded by a metallic beryllium reflector relative to graphite was found to be significant. A beryllium reflector frees up considerable volume to accommodate shielding. However, photoneutron production in beryllium by fission product gamma-rays requires neutron attenuation by the transportable shield. It was found that tungsten boride satisfactorily attenuated both gamma rays and photoneutrons.