More and more attentions have been paid to the impact of the earthquake on the reactor thermal hydraulics after the Fukushima accident. In order to figure out the seismic effect on the flow in primary loop, the natural circulation in primary loop of CPR1000 influenced by earthquake is modeled by learning from the study on natural circulation under ocean conditions. Natural circulation ability at earthquake, which includes longitudinal earthquake and transversal earthquake, is dynamically simulated by a program written with MATLAB, respectively. Besides, the safety of the system is discussed based on the calculated results.
The research results show that, once the longitudinal earthquake occurs, in the earlier stage of earthquake, the peak and valley values of the coolant mass flow rate decrease gradually and the amplitude will be a constant as time goes on because of flow fluctuation in seismic condition. On the contrary, as for transversal earthquake, the peak and valley values of the coolant mass flow rate increase gradually in the earlier stage of earthquake. However, the amplitude will be a constant as time goes on, just like that in the longitudinal earthquake.
For both of the two conditions, they have the same characteristics. The constant mentioned above grows up with the increase of the earthquake acceleration peak value and the period; the fluctuation period of mass flow rate is generally the same as the period of earthquake acceleration and the mass flow rate changes steadily; the average mass flow rate decreases slightly with the increase of the earthquake acceleration peak value and the period.
Both of the vibration period and the peak of seismic wave have disturbing effect on reactor coolant system natural circulation. And the increase of the peak of the earthquake acceleration as well as the period of the earthquake acceleration will reduce the natural circulation ability. In the range of research parameters, the system is considered to be safe according to the calculation results of core coolant temperature.