Emergency Classification Level Automatic Judgment and Warning System Based on Emergency Action Level of Nuclear Power Plant

Abstract

The emergency plan is an indispensable part of the safety of nuclear power plants. It generally includes four Emergency Classification Levels, each of which corresponds to a set of emergency response actions. Emergency Classification Level (ECL) is one of a set of names or titles established for grouping off-normal events or conditions of nuclear power plants according to: ①potential or actual effects or consequences, and ② resulting onsite and offsite response actions. The ECLs established by U.S. NRC, in ascending order of severity, are ①Notification of Unusual Event, ②Alert, ③Site Area Emergency and ④ General Emergency. In China, the corresponding ECLs are ① Emergency Standby, ② Plant Emergency, ③Site Emergency and ④Off-site Emergency. To determine the emergency classification level of nuclear power plants, the concept and methodology of Emergency Action Level(EAL) is proposed by NRC. EAL is a pre-determined, site-specific, observable threshold for an Initiating Condition(IC) that, when met or exceeded, places the plant in a given emergency classification level. EAL statements may utilize a variety of criteria including instrument readings and status indications; observable events; results of calculations and analyses; entry into particular procedures; and the occurrence of natural phenomena. According to the methodology proposed by NRC, the specific IC/EALs have been studied and developed by each nuclear power plant in China. As the IC/EALs contain complex threshold and logic, it is difficult for emergency response personnel and decision makers to give the quick judgment of emergency classification level manually. It is necessary to build an emergency classification level automatic judgment and warning system based on emergency action level for each nuclear power plant. A complete solution of this system is present in this paper. The core issues such as data model, trigger mechanism of threshold and logical control process are deeply discussed. Fundamentally, a set of computerized data model is designed and built to describe characteristic of IC, EAL, ECL and other concepts or elements. Access to automatic data and manual data of nuclear power plant is also considered in these data model. Further, the trigger mechanism of threshold in the system is designed to include two layers in which the first layer is used to trigger the numerical conditions and second to trigger the time conditions. Different warning information is also designed to correspond to these two layers. Referring to the basic principle of circuit logic gate, the system gives a similar logical control process. Beginning with one or more parameters, the logical control flow eventually moves towards the specific ECL via the combination of threshold trigger controllers and logic gates. The above core issues discussed provide basic models and principles for system implementation. Based on the basic models and principles, a complete ECL automatic judgment and warning system based on EAL is developed and established. The paper introduces the basic framework and modules of the system briefly. And the important functions and components such as database, threshold trigger module, automatic judgment and warning module and so on are discussed in detail and in depth. The system has been applied in depth at Qinshan Nuclear Power Base and other nuclear power plants in China. It is indicated that the system is fast and accurate in emergency exercises by providing timely and effective information of ECL judgment and warning for emergency response personnel and decision makers.