Automatically scramming nuclear reactor system

#The invention generally pertains to nuclear reactor systems, and more specifically, to automatically scramming nuclear reactor systems.

#There are over four-hundred nuclear power plants worldwide, providing nearly twenty percent of the world's electricity. Nuclear power plants function much like power-generating plants that are fueled by coal or oil. That is, either type of power plant generates heat. The heat is used to heat water and produce steam, or to heat a gas. The steam or the gas, as the case may be, drives one or more turbines which in turn generate electricity. The difference, of course, is that heat is generated at a nuclear power plant by nuclear reactions (i.e., induced fission) instead of by burning coal or oil.

#Induced fission takes place in the reactor. The fuel for the reactor is provided by a suitable radioactive material (e.g., uranium-235 or plutonium-239) typically formed into either rods or “pebbles” that are arranged within the core of the reactor. As the fuel fissions, neutrons are released which bombard the nuclei of the other fuel atoms in the core of the reactor. The bombarded nuclei absorb the neutrons causing the nuclei to become unstable and split, releasing one or more neutrons which bombard the nuclei of yet other fuel atoms, and so on. The split atoms release energy in the form of radiation and heat.

#Illustrative and presently preferred embodiments of the invention are illustrated in the drawings, in which:

#FIG. 1 is an illustration of a nuclear power plant;

#FIG. 2 is a cross-sectional view of one embodiment of an automatically scramming nuclear reactor system;

#One embodiments of an automatic scramming system 10 according to the present invention is shown in FIG. 2 as it may be used in a nuclear power plant 12 (FIG. 1). Briefly, the nuclear power plant may be of conventional design (with the exception of the presence of the invention) and may involve a fission reactor 14 for producing heat. A coolant 22 is provided to the core 16 of the reactor 14 and absorbs the heat produced during induced fission. The heated coolant 22 flows out of the reactor 14 and is passed through a heat exchanger 23. Water 24 is also provided to the heat exchanger 23 and absorbs the heat from the heated coolant 22 to produce steam 26. The coolant 22 can then be recirculated through the reactor 14, and the steam 26 is used to drive one or more turbines 28, which operate a generator 30 to generate electricity 32. Of course in another embodiment, the coolant 22 may be used to drive the turbines 28 directly. In any event, if the flow of coolant 22 through the reactor 14 is insufficient to cool the core 16 of the reactor 14, however, the reactor 14 must be shut down before it overheats.

#According to the teachings of the present invention, an automatically scramming nuclear reactor system 10 (FIG. 2) may comprise a core 16 having a coolant inlet end 42 and a coolant outlet end 44. A cooling system 20 (FIG. 1) operatively associated with the core 16 of the reactor 14 provides the coolant 22 to the inlet plenum 53 through the coolant inlet end 42 of the core 16. As the coolant 22 flows through the core 16 of the reactor 14, it absorbs heat. The cooling system 20 removes the heated coolant 22 from the outlet plenum 54 through the coolant outlet end 44 of the core 16, and maintains a pressure differential (Δp) between the coolant inlet end 42 of the core 16 and the coolant outlet end 44 of the core 16 during a normal operating condition of the nuclear reactor system 10. A guide tube 50 (FIG. 2) having a first end 51 and a second end 52 is positioned within the core 16 so that the first end 51 of the guide tube 50 is in fluid communication with the coolant inlet end 42 of the core 16, and the second end 52 of the guide tube 50 is in fluid communication with the coolant outlet 44 end of the core 16. A control element 18 is positioned within the guide tube 50 and is movable within the guide tube 50 between a lower position 19′ and an upper position 19 under the influence of the pressure differential. That is, the control element 18 is raised to the upper position 19 when the flow of coolant 22 is sufficient to cool the core 16 of the reactor 14 (e.g., a safe pressure differential is established) so that induced fission occurs during normal operation. If the flow of coolant 22 is insufficient to maintain the reactor 14 at a safe operating temperature (e.g., the pressure differential drops below the safe pressure differential), the control element 18 automatically falls under the action of gravity to the lower position 19′ and shuts down the reactor 14.

#The automatically scramming nuclear reactor system 10 may be operated as follows according to the teachings of the invention. The cooling system 20 provides coolant 22 to the core 16 of the reactor 14 at a first pressure (p1). The heated coolant 22 is then removed from the core 16 at a second pressure (p2). The first pressure is greater than the second pressure during a normal operating condition of the nuclear reactor system 10. The control element 18 is held above a scramming position 19′ (e.g., in position 19) during the normal operating condition of the nuclear reactor system 10 by the pressure differential (Δp) between the first pressure and the second pressure. When the pressure differential drops below a safe pressure differential, the control element 18 automatically falls under the action of gravity to the scramming position 19′ to shut down the reactor.