Calculation Of Blowdown Thrust Force Due To The Rupture Of Main Pipe In Nuclear Power Plant

The main steam, main feed water pipe are important parts of nuclear power plant. The main pipe, which are running at high temperature and high pressure, may rupture because of the occurrence of earthquake, fatigue stress and other reasons. As a result, the fluid will eject from the pipe with high speed, which causes huge blowdown thrust force. At the same time, the long and soft pipe will start moving. This phenomenon is called "pipe whip". It is worth noting that the pipe whipping may cause serious damage to surrounding structures and equipments, and seriously threaten the safety of staffs around. More importantly, it may influence the safety of the nuclear power plant and cause unbearable secondary disasters. In order to conduct targeted research on "pipe whip" problem and take appropriate protection measures at a later time, it is essential to study the blowdown thrust force caused by the pipe rupture that may occur under extreme conditions. Specifically, the blowdown thrust force is an important and critical input variable in the analysis of "pipe whip" problem, which should attract great attention.The key to calculate the blowdown thrust force is to calculate the fields of velocity, density and pressure of the fluid after the pipe rupture. The fluid in the pipe may possibly exist in three states——subcooled water, saturated-superheated steam or saturated steam-water mixtures, whose characteristics are different from each other. As a result, the methods of calculating the blowdown thrust force depends strongly on these three fluid states. In this paper, these three states are distinguished and specific methods are individually developed. Correspondingly, numerical analysis on typical examples are quantitatively presented. The blowdown thrust forces for different situation are calculated and further compared with the value obtained through the American standard——ANSI/ANS-58.2-1988. It is mainly indicated that(1) When the fluid is subcooled water, the blowdown thrust force is calculated by the theory of water hammer. The relative error is less than2%when comparing with the value from the "ANSI"(2) When the fluid is saturated-superheated steam, the theory of adiabatic and constant-area flow of perfect gas is used to describe the flow of the fluid. Besides, isentropic flow upstream and critical flow at the exit is assumed. The blowdown thrust force is calculated by this theory and further compared with the value from the "ANSI" It is shown that the relative error is less than5%when ?L/D?2while more than5%when ?L/D>2. Since coefficient ?L/D in engineering practice is mostly less than1.0, this method is still practically useful. In addition, the impact of pipe section collapse on the blowdown thrust force is discussed. It is revealed that this impact can't be ignored. (3) When the fluid is saturated steam-water mixtures, the blowdown thrust force iscalculated by the MOODY model. The relative error is less than5%when comparingwith the value from the “ANSI”.