Study on safety gap between fuel channels in NHR200-II

This paper presents a novel method for estimating the safety gap between deformed fuel channels. The irradiation causes deformation of the fuel channel, which narrows the control rod channel, directly affecting the safety of the reactor. Investigating the critical safety gap between fuel channels can be utilized for safety assessments in design. Specifically, we first define the safety gap and three typical dropping cases. Next, we analyze the forces on the control rod, including flow resistance and channel resistance. Then, we establish a nonlinear dynamic model and simulate three dropping cases. Finally, we explore the influence of the friction coefficient and the fuel rod bundle. We find that the critical safety gap for the NHR200-II reactor is -5.0∼-3.1 mm (standard case) and -4.2∼-2.5 mm (arbitrary case), respectively. Our study provides a novel solution to accurately evaluate the effect of deformed boxed channels on the control rod’s dropping.