Neutron-coupled thermal hydraulic calculation of BWR under seismic acceleration

In the BWR subjected to an earthquake, the oscillating acceleration attribute to the seismic wave may cause the variation of the coolant flow rate and void fraction in the core, which might result in the core instability due to the void-reactivity feedback. Therefore, it is important to properly evaluate the effect of the seismic acceleration on the core stability from a viewpoint of plant integrity estimation. In the present study the numerical code analyzing the behavior of nuclear power plant under the seismic acceleration is developed based on the three-dimensional neutron-coupled thermal hydraulic code, TRAC-BF1/SKETCH-INS. The coolant flow in the core is simulated with introducing the oscillating acceleration attributed to the earthquake motion into the motion equation of the two-phase flow as external fore terms. The analyses are performed on a real BWR4-type nuclear power plant (Peach Bottom no.2) with the sinusoidal acceleration and the acceleration obtained from the response analysis to the E1 Centro seismic wave of Imperial Valley earthquake. The behaviors of the core and coolant are calculated in the various parameters of acceleration. The effects of the frequency, amplitude and direction of the oscillating acceleration are discussed. (author)