Abstract
The thimble tube, which is made of Zircaly-4, is one of the main components of a PWR fuel assembly. The thimble tube has an important role as a structural member of the skeleton. Another role of the thimble tube is to guide a rod cluster control assembly (RCCA) for insertion during the reactor operation. The function has to be assured not only in normal operation but in a seismic event. In a horizontal seismic event, the fuel assembly vibrates laterally, which gives bending moment to the thimble tube. In addition, axial compression force acts on the thimble tube in a vertical seismic event. The integrity of the thimble tube has to be maintained while this force and moment act. Mitsubishi has confirmed by the elastic stress analysis that the stress of the thimble tube has been lower than the limit value requested for the seismic event. The stress evaluation method is based on the ASME code. The ASME code also describes the limit analysis which is available when the predicted stress is beyond elastic region of the material. In the analysis, the material is assumed to be elastic-perfectly plastic, and the maximum load that the structure can carry is calculated but the load is one direction. In our previous paper, the strength limit of the thimble tube with material plasticity was analyzed considering the bending moment and axial compression force at the same time. The analyses were performed with parameters of material properties. According to the analysis results, the practical strength limit by the analysis with the actual elastic-plastic material was larger than the one with the elastic-perfectly plastic material. This paper describes the experimental verification for the strength limit analysis model of the thimble tube with material plasticity under bending moment and axial compression force. The experiments are conducted to investigate the thimble tube’s strength at room temperature and the elevated temperature, 343oC. The simulation analyses for the experiments are performed by the 3 dimensional model with elastic-plastic material. According to the comparisons with the experiments, the analysis results show good agreement with the experiment results at both room temperature and 343oC. Based on the comparison, the analysis model is verified and can be effective for the strength prediction of the thimble tube.
