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Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)

Editor
Michael G. Stamatelatos
Michael G. Stamatelatos
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Harold S. Blackman
Harold S. Blackman
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ISBN-10:
0791802442
No. of Pages:
2576
Publisher:
ASME Press
Publication date:
2006

The objectives of this study are to identify and evaluate alternative protective action recommendations (PARs) that could reduce dose to the public during a radiological emergency and to determine whether improvements or changes to the federal guidance would be beneficial. The emergency response strategies considered in this study are the following: (1) standard radial evacuation; (2) shelter-in-place followed by radial evacuation; (3) shelter-in-place followed by lateral evacuation; (4) preferential sheltering followed by radial evacuation; and (5) preferential sheltering followed by lateral evacuation. Radial evacuation is directly away from the plant; lateral evacuation is azimuthally (around the compass) away from the direction of the wind. Shelter-in-place is a protective action strategy in which individuals remain in their residence, place of work, or other facility at the time that a general warning is given. Preferential sheltering involves moving individuals to nearby, large buildings, e.g., high-school gymnasiums or courthouses, that afford greater protection than personal residences.

This study shows that there are benefits to sheltering if followed by lateral evacuation. However, if the lateral evacuation strategy cannot be implemented, then early radial evacuation is often preferable. The most appropriate PAR depends on the evacuation time estimate (ETE) and, therefore, it is desirable to reduce the uncertainty associated with the ETE.

Nuclear Regulatory Commission (NRC) guidance to commercial power plants currently allows for sheltering and/or evacuation as an emergency response to a serious nuclear accident. Frequently, however, licensees and states default to evacuation strategies and do not consider sheltering. Here we evaluate several alternative strategies to determine if standard radial evacuation is best or if other options could reduce the overall risk to the public.

We consider two source terms based on the NUREG-1150 study. These involve a rapid release of radioactive material into the atmosphere and a more gradual release. Two variations in timing have also been investigated, but are not reported here.

The evaluation was performed for a generic site, which uses a uniform population distribution and typical Midwest meteorological data (Moline, IL). Additional parameters that are varied in the study are the ETE (4-, 6-, 8-, and 10-hour ETEs are considered) and the duration of sheltering (2-, 4-, and 8-hr sheltering periods are considered). Additional sensitivity studies were performed to investigate nonuniform evacuation speed caused by traffic congestion, the time needed to reach a preferential shelter, and the effect of adverse weather conditions as opposed to favorable weather conditions. Adverse weather conditions are those for which precipitation occurs before the leading edge of the plume exits the 10-mile emergency planning zone (EPZ). Ultimately, emergency response strategies are ranked by their potential to reduce adverse health effects for residents within the EPZ.

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