Tornado-induced Load On Envelope-damaged Main Powerhouse Of Nuclear Plant Conventional Island With Consideration Of The Internal Structures

Tornado is a kind of small-scale meteorological phenomenon,which can cause severe damage to buildings and infrastructures.Tornado-induced loads should be considered in nuclear plants and thermal power plants designing.For the conventional island in nuclear plant,it is mentioned in current code that the envelope damage is acceptable.However,available formula to calculate tornado loads of envelope-damaged conventional island is not given by the code.To investigate the tornado-induced load on the envelopedamaged main powerhouse,the envelope damaging process was simulated by the method of Computational Fluid Dynamics(CFD).The tornado-induced load on envelope-damaged powerhouse was analyzed and as a result,the reduction coefficient was concluded to calculate the tornado-induced load on the envelopedamaged main powerhouse.The main work contents are as followings :Numerical tornado field was simulated by using CFD method,and the simulation result was analyzed.By comparing the numerical results with Rankine vortex theory,the tangential velocity and pressure drop profile showed good agreement,which proved the reliability of numerical model.Subsequently,the effect of swirl ratio on tornado characteristics was studied.The result showed that as the swirl ratio increases,the maximum tangential velocity and pressure drop gradually decrease.The corresponding core radius increases and the profile of vortex core turns from funnel to cylinder.One-way fluid-structure interaction method(FSI)was applied to simulate the envelope damaging process of the powerhouse and the mechanism of tornado attacking angle as well as internal structure influencing the damage of envelope structure was revealed.The damaged forms caused by different attacking angles were compared and the influence of internal structures on damaged form was studied.The study showed that the damaging process generally consists of 3 steps: windward roof damage,windward wall damage,leeward wall and other sides damage.The damage rate of the main powerhouse is lower because of internal structures.The tornado-induced load on envelope-damaged powerhouse was analyzed.As a result,the most disadvantageous form of envelope destruction and the tornado-induced load reduction coefficient was concluded.The study showed that a decrease of 41% of tornado-induced load on the main structure is caused by envelope damage.Affected by internal structures,the internal and net pressure of envelope structure is lower,however,the tornado-induced load on the main structure is higher.