Abstract: The pipe whip behaviour of a high energy pipe in a nuclear power plant under assumption of postulated ruptures was investigated by using the finite element method． A three-dimensional finite element model of the pipe and U-bolt restraint was built，the structural parameters of them were tested experimentally，the thrust force caused by jet flow was calculated based on the jet thrust equation，and the accuracy of the model was verified with reported experimental results． Then，the time traces of restraint force，displacement，velocity and the energy of the system were analyzed． Finally，the effects of overhang length，friction coefficient and clearance on the pipe whip behaviour of the pipe-restraints system were discussed． The research results show that the pipe oscillates with small amplitude after impacting on the U-bolt restraint，the impact velocity increases suddenly to a maximum val- ue，and then decreases rapidly to zero，and the impact force undergoes 150Hz periodic oscillation． The work done by thrust force is almost converted to strain energy． The vertical displacement of pipe increases with increasing o- verhang length，whipping force increases with increasing whipping friction coefficient and increasing primary clea- rance．

Key words: high energy pipe, pipe whip, U-bolt restraint, hypothetical rupture, thrust force