Research On Seismic Toughness Assessment And Toughness Enhancement Methods For Nuclear Industry Plants

In recent years,China’s demand for clean energy is increasing day by day.However,nuclear energy in China accounts for less than 5% of the energy supply.At the same time,China’s external demand for nuclear fuel is as high as 75% year-round,far exceeding the international alert line of 50%.It is foreseeable that a large number of nuclear industry facilities will be built one after another in the future.Based on various considerations such as strategy,safety,environment and social impact,a large number of nuclear industry facilities are sited in the inland western region of China,which has been in a seismically active period since the Wenchuan earthquake of 5.12.In this paper,an existing nuclear industrial plant in the western region of China,built in the 1960 s,is taken as the research object,and its seismic toughness is evaluated first,and the seismic toughness rating is obtained.Based on this,three approaches of seismic damping,column top seismic isolation and dissipation integration are adopted to improve the toughness of the nuclear plant.Finally,through incremental dynamic analysis,the vulnerability and damage probability of the original plant structure and the toughness upgraded structure under the action of ground shaking are studied,and the collapse resistance of each structural system is evaluated.The main research contents are as follows:(1)Using the existing nuclear industrial plant as the research object,SAP2000 was used to establish its elasto-plastic analysis model to evaluate the structural response of 11 ground shaking under the action of fortified and rare earthquakes,and to evaluate the seismic toughness level of the structure,and to identify the main controlling factors of the seismic toughness level of the existing nuclear industrial plant.The results show that: the displacement and acceleration responses of the existing nuclear plant are large,resulting in a high probability of damage to both structural and nonstructural members;the structural and acceleration-sensitive nonstructural members control the overall repair cost more obviously,and the overall repair time is determined by both structural and acceleration-sensitive nonstructural members,so the displacement and acceleration responses need to be controlled simultaneously to greatly improve the seismic toughness of the existing nuclear plant.The seismic toughness level of the existing nuclear plant is greatly improved.(2)Combining the structural layout characteristics and special production requirements of nuclear industry plants,the damping,column-top isolation and dissipation integration measures were adopted to improve the toughness of the structure.The impact of various toughness improvement measures on the seismic toughness level of the structure from the point of view of collapse resistance was analyzed through the vulnerability analysis of the damping structure,column-top isolation structure,dissipation integration structure and the original seismic structure under the action of actual ground vibration.The results show that the upper roof structure has the smallest probability of exceeding each performance state when the ratio of maximum displacement to span λ is used as the judgment criterion,followed by the column-top isolation structure and the damping structure,and the original seismic-resistant structure has the largest.In the case of the lower reinforced concrete row structure,when the maximum inter-story displacement angle is used as the criterion,the probability of the damping structure exceeding each performance state is the smallest,followed by the dissipation-integrated structure and the column-top seismic isolation structure,and the original seismic structure is the largest.(3)The collapse resistance safety reserve factor CMR was adopted as an index to quantify the collapse resistance of the structure,and the safety reserve factor between the seismic design capacity of the existing nuclear plant and the actual collapse resistance of the seismic-absorbing structure,the column-top isolation structure and the dissipative integrated structure under different ground shaking was studied.The results show that the CMR values of the existing nuclear plant structure,the seismic-absorbing structure,the column-top isolation structure and the dissipative integrated structure are 1.675,3.850,2.025 and 2.075,respectively,and their improvement compared with the existing nuclear plant structure is29.9%,20.76% and 20.89%,respectively,and the seismic-absorbing structure has a better safety reserve against collapse.