On-line decision aid for heatup, cooldown and emergency response based on reactor vessel integrity

The reactor vessel is the principal component in the nuclear steam supply system (NSSS) pressure boundary. It has irradiation embrittlement concerns not present for other components, and since it is a thick section steel body, nonductile failure modes are considered. These concerns are the basis for the 10CFR50 Rule restrictions on heatup and cooldown and for the Pressurized Thermal Shock screening criteria. Because of the critical nature of the vessel and resulting high degree of regulation, many conservatisms are placed on the limits which may become restrictive of operation. As an outgrowth of the analytical techniques used to evaluate the above concerns, an on-line system is evolving to provide the operator with direct information about the operating window available for the plant. This information is of value predominantly during heatup, cooldown and under a variety of off normal conditions affecting the vessel. This paper describes the information supplied to the operator, the applications and the use of this tool as a decision aid. The principal focus is on decision aids for the reactor operator that make it applicable as an on-line system