Patent Number: 050858254
Section: summary

FIELD OF THE INVENTION This invention relates to water cooled nuclear fission reactors of the so-called boiling water type. Boiling water nuclear reactors comprise a steam generating plant wherein reactor water coolant is circulated through a core of heat producing fissionable nuclear fuel to transfer thermal energy from the fuel to the coolant and produce steam. The steam is then used to drive turbines and other machinery employing steam, such as for electrical power generation. BACKGROUND OF THE INVENTION Due to the prodigious quantities of thermal energy produced by fissioning nuclear fuel, it is imperative to maintain the fuel core of commercial water cooled nuclear fission reactors submerged within heat transferring coolant water. The conveyance of heat out away from the energy producing fuel core by means of a fluid coolant is needed to preclude the possibility of hazardous conditions or reactor damage such as could occur with an overheating meltdown within the fuel core unit. Such a potentially destructive occurrence can result from a loss-of-coolant accident (LOCA) caused by an extensive breach of a major reactor coolant receptacle or conduit. To cope with this hypothetical accidental event, commercial water cooled nuclear fission reactors are provided with large reservoirs of water and dedicated safety injection systems(s) capable of supplying supplementary coolant water to the reactor vessel for cooling the fuel core and maintaining lower or normal operating temperatures. Typically, automatic safety measures are employed to activate and operate systems for supplying this supplementary coolant water as needed to the fuel core to replace or supplement the original coolant water lost due to some mishap. A different but additional safety measure commonly employed in commercial water cooled nuclear fission reactors comprises means to deal with any failure of the reactor control rods to effectively perform their designed fission regulating function. Nuclear reactor control rods, comprising elongated units containing neutron absorbing material such as boron or a compound thereof, are designed to be reciprocally movable into and out from the fuel core of fissionable material. The level of fission activity of the fuel material in a core of a reactor, and in turn heat produced, is determined or controlled by the amount of neutron absorbent advanced into or withdrawn from the fuel core with the control rod units. Moreover, the fission reaction of the plant can be rendered subcritical or terminated by inserting sufficient neutron absorbent material housed within control rods into the fuel core to deprive the fuel of the needed quantity of fission produced neutrons for maintaining the self perpetuating fission reaction, or so-called chain reaction, and in turn heat produced. However, in the event that the control rods fail to perform their intended role of governing and/or ceasing the fission reaction for any cause, mechanical, electrical or personnel malfunction, an auxiliary backup system is frequently provided for depriving the fuel core of the neutrons essential for maintenance of the heat producing fission reaction. Commonly this system comprises a supply of a water solution of a soluble boron or gadolinium compound, or so-called poison, which when introduced into the nuclear reactor vessel, merges with the reactor coolant and thus pervades the fuel core region to absorb the fission produced neutrons needed for continuing the fission reaction. Thus, in the remote event of any control rod failure, the poison solution is fed from a reservoir into the reactor vessel by suitable means on a signal of problem whereupon the fission reaction is terminated. A typical arrangement in commercial water cooled nuclear fission reactor plants for incorporating the foregoing standby safety systems which inject auxiliary coolant water to temper the fuel core temperature, or inject a neutron absorbing solution to deprive the fuel of neutrons, utilized an apt gas, such as nitrogen, for a propellant to drive the liquid water or boron solution from its source or reservoir through communicating conduits into the reactor vessel. Thus, auxiliary coolant water or poison solution is maintained within a closed vessel or tank under sufficient gas pressure to drive the liquid contents into the reactor vessel through an appropriate arrangement of conduits upon a manually or automatically actuated signal responding to a malfunction. SUMMARY OF THE INVENTION This invention comprises an improvement in a standby safety injection system for water cooled, nuclear fission reactor plants. The improvement of the invention enhances the injection delivery means, and includes a connecting of the reservoirs of two safety systems to provide an alternative auxiliary source of propelling gas for each system. Additionally this invention comprises a unique arrangement of control valves and fluid conduits joined with sensing means for initiating the standby safety injection units of either system into appropriate action for dealing with a reactor emergency or malfunction. OBJECTS OF THE INVENTION It is a primary object of this invention to provide an improved dual liquid standby safety injection system for nuclear fission reactor plants. It is an additional object of this invention to provide a liquid standby safety injection system for water cooled nuclear fission reactor plants having an alternative auxiliary source of propelling gas. It is a further object of this invention to provide a multiple liquid standby safety injection system for water cooled nuclear fission reactor plants having an improved gas propellant and application system that enhances performance as well as economic benefits. It is a still further object of this invention to provide a liquid standby safety injection system for water cooled nuclear fission reactor plants having an improved arrangement of fluid conveying conduits and flow controlling valves. It is also an object of this invention to provide improved multiple liquid standby safety injection systems for water cooled nuclear fission reactor plants providing for alternate application of coolant or neutron absorbent with a common source of propellant gas selectively applied or transferred, coupled with a unique arrangement of fluid transferring conduits and flow controlling valves combined with operating sensors.