Deterministic health effects can be prevented and the risk of stochastic health effects can be reduced by taking protective actions before or shortly after a release. These actions must be based on plant conditions and then refined subsequently based on environmental measurements. Operational intervention levels (OILs) are some calculated values (e.g., ambient dose rate or radionuclide concentration) measured by instruments or determined by laboratory analysis that correspond to a GIL or GAL. Through the use of the OILs, the environmental data are assessed primarily, which are quantities directly measured by the field instrument. Default OILs have been calculated in advance on the basis of the characteristics of severe reactor accidents. These default OILs are used to assess environmental data and take protective actions until sufficient environmental samples are taken and analyzed to provide a basis for their revision. This approach allows data to be quickly evaluated, and decisions on protective actions to be promptly made. A decision support system of the off-site emergency protective actions based on the OILs for nuclear emergencies was discussed in this paper. The system accesses the environmental data through the default OILs and the revisions of OILs. It is applied to Daya Bay Nuclear Power Plant. In the early release, according to the characteristic of the plant, the system provides the approach to calculate the default OILs based on the accident source terms described in Reactor Safety Study of USA. Also some real factors are considered, including the meteorological parameters. When sufficient environmental samples are taken and analyzed to provide a basis for their revision, the default OILs can be revised or recalculated by them. In the entire emergency planning zone, the environmental data will be assessed through the use of those OILs to provide the advice of protective measures.
