REACTOR: An Expert System for Diagnosis and Treatment of Nuclear Reactor Accidents

Abstract

REACTOR is an expert system under development at EG&G Idaho, Inc., that will assist operators in the diagnosis and treatment of nuclear reactor accidents. This paper covers the background of the nuclear industry and why expert system tech-nology may prove valuable in the reactor control room. Some of the basic features of the REACTOR system are discussed, and future plans for vali-dation and evaluation of REACTOR are presented. The concept of using both event-oriented and function-oriented strategies for accident diagno-sis is discussed. The response tree concept for representing expert knowledge is also introduced. I BACKGROUND The responsibilities of an operating crew of a commercial nuclear reactor can be compared with those of a medical doctor. During normal opera-tion, little care is required to monitor and main-tain the reactor. When an emergency occurs, however, quick and efficient diagnosis and treat-ment of the problem is essential. If the diagno-sis and treatment are effective, most incidents can be terminated without serious consequences. However, if the diagnosis is incorrect or the treatment improper, the consequences could be severe. A commercial nuclear power plant is a complex combination of systems. There are two types of reactors in commercial service--the Pressurized Water Reactor (PWR) and the Boiling Water Reactor (BWR). This paper discusses the PWR. The reactor core itself is contained in a large reactor vessel (see Figure 1). Control rods provide one mechan-ism for controlling the rate of the nuclear reac-tion. Heat is removed by the Primary Coolant System (PCS), which circulates water through the reactor vessel. Sufficient pressure to prevent boiling in the PCS is provided by the pressurizer. If a pipe break occurs in the primary coolant system (the so-called LOCA or Loss of Coolant Accident), the reactor is automatically shut down and the Emergency Core Cooling System (ECCS) pro-vides cooling water to the reactor core. Contin-ued cooling is required after shutdown to remove radioactive decay heat. Any radioactive materials which escape the PCS are contained in the