Patent Number: 050733346
Section: claims

1. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system with a space defined directly above the guide tube being surrounded by upper ends of the wrapper tubes,  a control rod disposed coaxially with said control rod guide tube;  an electromagnet disposed above said control rod in the nuclear system;  drive shaft means connected to said electromagnet for moving said electromagnet axially of said control rod guide tube over a predetermined distance;  temperature-sensitive magnetic material forming the upper end of each of the wrapper tubes,  the temperature-sensitive magnetic material of the wrapper tubes disposed entirely above the level at which the upper end of said control rod guide tube is located in the nuclear system, said upper ends of the wrapper tubes formed of the temperature-sensitive magnetic material each having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet, and the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point;  said temperature-sensitive material and said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned in said space surrounded by the upper ends of the wrapper tubes and the temperature thereof is below its Curie-point,  the magnetic circuit being broken when coolant flowing in the nuclear system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube.  a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system,  a control rod disposed coaxially with said control rod guide tube;  an electromagnet disposed above said control rod in the nuclear system;  drive shaft means connected to said electromagnet for moving said electromagnet axially of said control rod guide tube over a predetermined distance;  a respective extension tube of temperature-sensitive magnetic material extending coaxially from an upper end of each of the wrapper tubes, and the extension tubes surrounding a space directly above said control rod guide tube in the nuclear system,  each said extension tube disposed entirely above the level at which the upper end of said control rod guide tube is located in the nuclear system, and having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet, and  the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point;  said temperature-sensitive material nd said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned within said space surround by the extension tubes and the temperature thereof is below its Curie-point,  the magnetic circuit being broken when coolant flowing the nuclear system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube.  a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system with a space defined directly above the guide tube being surrounded by upper ends of the wrapper tubes,  a control rod disposed coaxially with said control rod guide tube;  an electromagnet disposed above said control rod in the nuclear system;  drive shaft means connected to said electromagnet for setting said electromagnet at a predetermined position during normal operation of the nuclear system and for moving said electromagnet axially of said control rod guide tube over a predetermined distance;  ferromagnetic material forming the upper end of each of the wrapper tubes,  the ferromagnetic material of the wrapper tubes disposed entirely above the level at which the upper end of said control rod guide is located in the nuclear system, and said upper ends of the wrapper tubes formed of the ferromagnetic material each having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet;  a respective extension tube of temperature-sensitive magnetic material extending coaxially from the upper end of each of the wrapper tubes with a space defined directly above said guide rod control tube being surrounding by the extension tubes, each said extension tube disposed adjacent said predetermined position, and the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point;  said temperature-sensitive material and said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned in said space surrounded by said extension tubes and the temperature thereof is below its Curie-point,  the magnetic circuit being broken when coolant flowing in the reactor system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube. 2. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: 3. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: