BASIC CONSIDERATIONS AND ASSUMPTIONS FOR GUIDANCE ON OFFSITE EMERGENCY INSTRUMENTATION

2.1Protective Action Decision Making

For protective actions to be most effective, the selection from available alternatives must be made at the most opportune time. This act of making a decision can be expedited if the decision maker is provided with criteria for determining that a decision should be made, i.e., the PAGs.^xx Other criteria for choosing among the available protective action alternatives must be determined by the planner because these criteria are usually site dependent. The decision making process can be further expedited if the information received by the decision maker is directly comparable to the criteria.

The primary value of radiation measurements is to provide information for use by the decision maker for verifying if the protective action taken, based on projected radiation levels, was correct or if protective action recommendations are necessary for additional areas. For example, local meteorological or topographical conditions may cause the offsite radioactive plume to behave different from the projections based on the onsite plant data, e.g., localized areas of higher radiation levels or actual plume boundaries which differ from those projected by the calculational models. The amount of data provided must be adequate to make the most effective decision. Only necessary data need be taken and evaluated, because consideration of extraneous data will contribute to delay of the decision making and will waste resources that may be scarce during an emergency.

The systematic acquisition of data from offsite field measurements and conversion to information for use in the decision making process is diagramed in Figure 1. Also the application of this approach in deciding whether to shelter or evacuate a population to prevent an inhalation exposure to radioiodine is presented in Figure 1. (The same principle can be applied to the use of field measurements for verification of whole body exposure.) The use of field monitoring data to revise protective action decision making could follow this scenario. Assume that prior to the airborne release of radioactivity from a serious nuclear power plant accident, protective actions are being taken to evacuate the population in all directions within two miles of the plant site and five miles down wind from the site in a sector covering approximately 68 degrees. A population center located approximately 10 miles from the plant site is not included in these protective actions. When the actual release occurs, field measurements near the site boundary indicate that the projected whole body dose and path of the plume are in error due to a release that is much larger than anticipated and defects in the meteorological models used in the projection. Based on these data, the revised whole body dose at the population center is estimated to exceed 1.0 rem. Revised protective actions to evacuate or shelter persons within this population center can be made; depending on the time available and needed to carry out the action as well as other considerations (e.g., estimated duration of the release, weather conditions, meteorological forecasts). Although it is not illustrated in Figure 1, this approach can also be used to determine the time within which the measurements must be made in order to verify that the protective actions will be effective. This is accomplished by comparing the time required to make the field measurements, processing the data, interpreting the information, and communicating the decisions with the time available prior to implementing the protective action.

The EOC is considered a focal point for gathering information, making decisions, and communicating with the facility and organizations (e.g. local, state or Federal) involved in a nuclear accident. The first off-site organizations to be involved are local, followed by State, Federal and other organizations. The first protective action decisions should be based on a projected dose pattern provided by the nuclear facility.

An outline of an effective data-to-information conversion system (modified to meet local constraints) can be developed by the planner from the guidance provided in this report for each class of PAGs. The offsite emergency field measurement requirements for a specific emergency plan can also be identified. These specific measurement requirements and instrumentation needs must, of course, be responsive to the local planning situation including the hypothesized type and size of the radionuclide release for the Emergency Planning Zones (EPZ)^xxi under consideration.

*Please see attached Image – Figure 1.*

Figure 1. Illustration of the Systematic Conversion of Radiological Measurements to Information of the Decision Making Process for Protective Action Planning