DEVELOPMENT OF GUIDELINES FOR THERMAL LOAD MODELING

摘要

Conceptual design studies of Japanese commercialized fast reactors are now carried out as "Feasibility Study on Commercialized FR Cycle Systems". Aiming for economical improvement, these plants adopt innovative design, which leads to make thermal loads more severe. To certify the design concepts and validate structural integrity, research and development of Fast Reactor Structural Design Standard (FDS) for commercialized fast reactor components is now under way. Among them, a set of guidelines for thermal load modeling is under development to overcome above thermal problems. System thermal transient loads sometimes become critical for plant design. Prediction of these loads has difficulties because many influence factors exist. So that, two kinds of modeling methods are recommended. One is the multi-linear approximation method to envelop scatter of those factors. Another is a combination method of thermal hydraulic-structure total analysis and the Design of Experiments. This method can grasp relation between influence factors and induced thermal stress without conservative design factors. Furthermore, screening method prior to modeling is provided. In actual plants, high cycle fatigue failure sometimes occurred, due to thermal striping phenomenon. The guidelines also deal with the modeling method of thermal striping loads. For consideration of attenuation mechanism of temperature fluctuation, a frequency response function of thermal stress is utilized. This function enables us to evaluate sensitivities of thermal stress to frequencies of temperature fluctuation, constraint conditions of components etc.