Modeling and Evaluating the Effective Use of Sheltering-in-place for Protection against a Radiological Release during a Nuclear Power Plant Severe Accident

Evacuation and sheltering-in-place are key protective actions during the early phase of a radiological emergency. Protective action strategies and decisions require balancing risks to ensure they provide more benefit than harm. While evacuations are generally safe, there are deterministic, long-term health consequences from prolonged displacement that outweigh the stochastic radiological health risk. In many cases, sheltering-in-place provides a viable alternative to evacuation, yet guidance and tools are lacking to aid decisionmakers on the best choice of action during an emergency caused by a nuclear power plant. Therefore, a method was developed to evaluate the effectiveness of sheltering-in-place and to explore ways to make better use of shelters during a radiological emergency. A model to estimate the radiological protection afforded by a typical residential shelter was developed and incorporated into a tool to examine the effectiveness of shelters during a hypothetical severe accident for typical BWR and PWR reactor designs and potential small modular reactor (SMR) design. The resultant analysis tool provides valuable insights into the parameters important to effective sheltering. Results demonstrate that typical residential homes can provide substantial dose reduction for an extended period of time following a significant radiological release. A sensitivity study was performed to identify important parameters and to inform how to implement sheltering-in-place for radiological emergencies involving different types of reactors and accidents with different radiological source terms. The model and results compared well to similar models and studies that also suggest shelters are more protective than previously understood. Additionally, contrary to the conventional shelter-in-place strategies, which recommend securing building ventilation, the results of this study suggest that sheltering strategies may benefit from a judicious operation of heating and ventilation systems for use in purifying indoor air to reduce inhalation dose.