Patent Number: 045405450
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a device for fixing fuel assemblies to a nuclear reactor core in a reactor pressure vessel of a boiling water reactor (BWR) for preventing fuel assemblies from upwardly rising and safely inserting a control rod into spaces between channel boxes of the fuel assemblies to promptly shut down the BWR on an occurrence of an emergency such as earthquakes. FIG. 1 shows a fuel assembly unit of a prior type inserted into an upper grid 20 secured to a reactor core, not shown. The unit generally comprises four fuel assemblies 1 as shown in FIG. 2. Each of fuel assemblies 1 is supported at its lower end by inserting the lower end into a hole provided on a fuel support 23 and at its upper end by the upper grid 20 and channel fasteners 22 which firmly interconnects the respective fuel assemblies 1 thereby to control or limit the horizontal movement or vibration of the fuel assemblies. In a BWR, though the irregular horizontal movement or vibration of the fuel assemblies is thus limited or suppressed, there is no specific means for limiting or suppressing vertical movement or vibration of the fuel assemblies. During the operation of a BWR, when an emergency such as large earthquake occurs, it is well known to insert a control rod having a cross shaped cross-section between the spaces defined by the channel boxes of the fuel assemblies as shown in FIG. 2 (a top plan view) to rapidly shut down the operation. However, in such case, the fuel assemblies move horizontally in an accelerated manner and flex or bend at their longitudinal central portions. These flexed or bent portions contact with the control rods now being inserted at the time of an emergency, thereby to generate a force for upwardly pushing the fuel assemblies 1, and this upward force is added to the vertical vibration of the fuel assemblies 1 which is caused by the earthquake. The upward force thus amplified may sometimes move upwardly the fuel assemblies 1 to a mechanically unstable position and may be damaged by the subsequent drop of the raised fuel assemblies. Therefore, in order to ensure the insertion of the control rod into the fuel assembly unit thereby to control the operation of a nuclear reactor, it becomes necessary to safely limit or suppress the vertical movement of the fuel assemblies. SUMMARY OF THE INVENTION An object of this invention is to provide an improved device for supporting fuel assemblies capable of preventing the fuel assemblies from rising upwardly upon the occurrence of an emergency such as an earthquake. Another object of this invention is to provide a device for preventing vertical movement of fuel assemblies when control rods are inserted therebetween, the device comprising locking means for engaging a reactor pressure vessel in operation of a nuclear reactor and disengaging smoothly therefrom when the fuel assemblies are removed from the reactor pressure vessel. According to this invention there is provided a device for securing a fuel assembly to a nuclear reactor pressure vessel comprising upper and lower tie plates for supporting the fuel assembly at its upper and lower end portions, spacers for supporting the fuel assembly at its intermediate points between the upper and lower tie plates, a channel box surrounding the fuel assembly, and a stationary handle attached to the upper tie plate. The device further comprises a movable handle attached to the stationary handle to be vertically slidable with respect thereto, a coil spring for always urging downwardly the movable handle, and hook members connected to the stationary handle to be rotatable in accordance with vertical movement of the movable handle such that the lower end of the hook member engages with an upper grid located in the reactor pressure vessel when the movable handle is lowered to a low position and disengages therefrom when the movable handle is lifted to an upper position.