Determination of Deformation Limit of Fuel Assembly Guide Tubes of the VVER 1000 Nuclear Reactor

The paper is focused on the control assembly of the VVER 1000 nuclear reactor. The multibody model of the control assembly of the VVER 1000 nuclear reactor was created in the alaska simulation tool. The multibody model is suitable for the investigation of its dynamic response in the course of a drop of the rod control cluster assembly. The influences of the pressurized water have to be introduced in the multibody model because the rods control cluster assemblies are falling in a limited space and water resistance is not negligible. Possible contacts of the falling rod control cluster assembly with adjacent structural parts inside the reactor are supposed. In case of emergency state the lifting system mechanism is set off and the rods control cluster assemblies can drop down through the protective tubes to the reactor core with fuel assemblies and stop the nuclear reaction. When the absorber rods reach the lower part of the core, they pass through the guide channel narrowing, which has the function of hydraulic shock absorbers for stopping the rods control cluster assemblies drop. Using the multibody model there were investigated limit curves of two parametrically set deformations of fuel assembly guide tubes, at which the absorber rods still reach lower part of the core. On the basis of results of the rod control cluster assembly drop simulations it is possible to state that the maximal deformations (they are in order of several millimetres) of fuel assembly guide tubes at given deformation curves fulfil the prescribed limits given for the nuclear power plants safety estimation.