Examination of offsite radiological emergency protective measures for nuclear reactor accidents involving core melt

Abstract

Evacuation, sheltering followed by population relocation, and iodine prophylaxis are evaluated as offsite public protective measures in response to nuclear reactor accidents involving core-melt. Evaluations were conducted using a modified version of the Reactor Safety Study consequence model. Models representing each measure were developed and are discussed. Potential PWR core-melt radioactive material releases are separated into two categories, "Melt-through" and "Atmospheric," based upon the mode of containment failure. Protective measures are examined and compared for each category in terms of projected doses to the whole body and thyroid. Measures for "Atmospheric" accidents are also examined in terms of their influence on the occurrence of public health effects. For "Melt-through" accidents, few, if any, early public health effects are likely, and doses in excess of Protective Action Guides (PAGs) are "confined" to areas within 10 miles of the reactor.

Evacuation appears to provide the largest reduction in whole body dose for this category. However, sheltering, particularly when basements are readily available, may be an acceptable alternative. Both evacuation and iodine prophylaxis can substantially reduce the dose to the thyroid. For "Atmospheric" accidents, PAGs are likely to be exceeded at very large distances, and significant numbers of early public health effects are possible. However, most early fatalities occur within 10 miles of the reactor. Within 5 miles, evacuation appears to be more effective than sheltering in reducing the number of early health effects. Beyond 5 miles, this distinction is less, or not, apparent. Within 10 miles, early health effects are strongly influenced by the speed and efficiency with which protective measures are implemented. Outside of 10 miles, they are not.

The projected total number of thyroid nodules is not substantially reduced unless iodine prophylaxis is administered over very large areas (distances). The qualitative effects of weather conditions on the above conclusions are also briefly discussed.