A method for design a linear heat rate ramp limit curve for thermal reactor fuel rods

Abstract

An increase in power during transient operating modes of reactors can lead to the depressurization of fuel rods due to the stress corrosion cracking mechanism. Expansion of fuel pellets due to increasing power induces tensile stresses in the cladding, which can initiate the formation and growth of corrosion cracks in the presence of aggressive fission products. Therefore, the plotted limit curve is primarily aimed at preventing circumferential stresses in the cladding from exceeding a certain maximum value during abrupt changes in power. The present article describes a system for performing multivariate statistical calculations of a single power increase to plot an envelope curve for the permissible area of fuel rod operation. The system uses the START-3A code to perform fuel rod calculations, which includes the ability to vary model and design parameters. The methodology for the calculated limit curve for a rapid increase in the power of a VVER-1200 reactor is presented with examples.