Seismic Calculation And Safety Risk Assessment Of The Ventilation Equipments In Nuclear Power Plant

Nuclear power plant(NPP) is the place, in which the nuclear fission energy is applied to generate electricity. In the numerous equipments of NPP, the ventilation equipments are very important to ensure the normal operation of NPP. The most important function of ventilation equipments is to create a secure operating environment of equipments, control the emission of polluting gases and provide staffs with comfortable working environment. The normal operation of the ventilation equipment is one of the preconditions to ensure the safe operation of other equipments in NPP. The seismic performance of ventilation equipments has significant influence on the safety of NPP. During an earthquake, the normal operation of the ventilation equipment should be ensured. Therefore, it is necessary for further study of the seismic safety of nuclear power ventilation equipment.In this thesis, most of the current seismic theories and seismic codes for the ventilation equipments of NPP in China and abroad are compared and analyzed. The main seismic calculation methods for nuclear power equipment are introduced. Moreover, the principle and applicability of these methods are discussed. Furthermore, a thorough analysis for the seismic performance of ventilation equipments(including fan, motor, damper) in XX NPP under gravity loads, working loads and seismic loads is put forward by using finite element software ANSYS.The modal analysis and spectrum analysis are presented for a nuclear class fan by ANSYS APDL to obtain its natural frequencies and vibration modes, as such as the stress distribution and deformation of each part. It is shown that the fundamental frequency of the fan is away from the main earthquake frequency. It can be concluded that the resonance would not occur and the strength and stiffness of the fan can meet the requirements in the seismic codes.By a similar approach, the seismic performance of several parts, such as lug bolts, cover bolts, axial, key, rotor and cover, etc., in nuclear class motor are checked. It is proved that the seismic performance of each part of the motor satisfies the requirements of seismic code.Additionally, the floor response spectrums are transformed into artificial seismic waves through SIMQKE_GR program. Three methods, such as static method, response spectrum method and time history analysis method, are applied to calculate the seismic responses of the nuclear class damper. And the different calculation results are compared with each other.By above method, seismic behaviors of a number of ventilation equipments in XX NPP are calculated. According to these calculation results, a new risk assessment method is developed for the seismic safety of nuclear class ventilation equipments base on the seismic safety margin. Finally, several representative ventilation equipments in XX NPP are divided into different risk levels. A profound investigation of safety risk assessment for the seismic behavior of NPP is paramount significance for the design, construction and operation of NPP.