Patent Number: 039403106
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The field of this invention is nuclear reactors which use a coolant fluid under pressure, such as light water (H.sub.2 O). 2. Description of the Prior Art U.S. Pat. No. 3,462,345 to Felix S. Jabsen discloses a nuclear reactor in which several fuel elements and individual control rods are provided in the reactor vessel. The individual control rods are longitudinally adjustable in the region of the fuel elements and are movable hydraulically in the guide tubes of the fuel elements, using the reactor coolant and a pump arranges outside the reactor vessel. For the purpose of moving the control rods hydraulically in the guide tubes, the pump generates suction or low pressure in a space provided at the cover of the reactor vessel by means of a suction line which leads from the lid of the reactor vessel to the pump. The pressure line is also connected to the lower part of the reactor vessel. The problem with this arrangement disclosed in the U.S. Pat. No. 3,462,345 is that if a break occurs in a suction line, this would cause a withdrawal of the control rods from the guide tubes, thereby jeopardizing the safety of the nuclear reactor. SUMMARY OF THE INVENTION The object of this invention is to provide an arrangement for the hydraulic operation of control rods within the reactor vessel such that withdrawal of the control rods is prevented in event of trouble, such as a break in the pressure line carrying the reactor coolant, thereby avoiding damage to the nuclear reactor. The nuclear reactor of this invention uses a coolant fluid under pressure and comprises: a reactor pressure vessel; a core disposed within the reactor pressure vessel; one or more fuel elements disposed within the reactor vessel; one or more control rods disposed adjacent to the fuel elements within the reactor vessel; one or more guide tubes, each guide tube having a control rod disposed longitudinally therein, the control rods being movable hydraulically within the guide tubes; a pump disposed outside of the reactor vessel for maintaining the coolant fluid under pressure; and a pressure line carrying coolant fluid under pressure from the pump to the reactor vessel. The high pressure end of the pressure line is connected to the lower end of each guide tube, thereby generating high pressure at the lower end within the guide tube for operating the control rod within the guide tube to support the control rod and move the control rod out of the guide tubes and away from the core, with the result that in the event of a break in the pressure line and a loss of pressure, the control rods are inserted further into the guide tube. Thus, the arrangement of this invention utilizes high pressure, rather than low or a suction pressure, to support the control rods. A high pressure control valve is located outside the reactor vessel at a point accessible for maintenance and is used to control the control rods of the fuel elements. Several high pressure control valves may also be used to control the control rods within the reactor vessel so that not all control rods of the fuel elements are moved at the same time. A flow control connector is brought through the lid of the reactor vessel in a pressure tight manner and a flexible connection is provided between the high pressure control valve and the flow control connector. If more than one high pressure control valve is used, the plurality of valves may be distributed on the outside periphery of the flow control connector so that a compact, space-saving design is achieved. Inside the reactor vessel, the pressure line branches into a plurality of feed lines. These feed lines from several fuel elements lead into one flow control connector. A guide adapter is used between the flow control connector and the guide tubes of the fuel element or elements, with a flexible connection between the guide adapter and the guide tubes. The purpose of this design is to compensate for manufacturing and installation tolerances and to avoid harmful forces in assembly. The feed lines are flexibly coupled to each other. In order to obtain an indication of the position of the control rods within the guide tubes, the pressure exerted by the coolant being fed to the lower end of the guide tube is measured and then the pressure loss over the length of the upper guide tube is measured.