沸騰水型原子炉の地震時制御棒挿入解析モデルの開発

概要

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In the seismic design of the boiling water reactor, we need to estimate the dynamic insertion behavior of control rods into the core region to secure the safety of the reactor under seismic events. In particular, estimation of the insertion time is one of the most important design tasks affecting the scrammability of the reactor. We developed a numerical analysis model to predict the control rod insertion time under seismic events using multibody dynamics. The effect of the interaction force between the control rod and the fuel assemblies is considered in three-dimensional contact analysis. This interaction force causes resistance force acting on the control rod under insertion. The hydraulic control unit and the control rod drive, which provide the control rod with driving force, were modeled in the concentrated parameter system considering dynamic characteristics, such as the inertance of the working fluid in the scram piping and the capacitance of the working gas in the accumulator. The numerical analysis can simulate the realistic insertion behavior of the control rod by coupling these models together and using an interactive process to calculate how they interact. The validity of the numerical analysis model was confirmed by comparing the analytical results with the experimental ones. The results of our analysis showed that the numerical analysis model provides good agreement with the insertion time of the control rod.