Abstract: OILs are measurable radiation parameters which are related to the generic intervention level of the specific action for public protection. OILs can be used to provide recommendations on emergency protective actions through comparison with environmental monitoring data. After Fukushima nuclear accident, emergency preparedness and response of nuclear power plants in China focuses on the issues of multi-unit accident. Based on the methods of calculation and revision of OILs suggested by IAEA, methods of calculation OILs for multi-unit accident were established, and the corresponding decision support system was also designed and implemented. The system provided a complete process for use of OILs including the function of data management, data query, calculation, revision and decision on protective actions, which can be used for both single-reactor and multi-reactor accident. The system has been applied in Qinshan, Ningde, Sanmen, Taishan and Yangjiang NPPs in China.

Key words: OIL, protective action, decision support system, light water reactor, multi-unit accident