Patent Number: 047088443
Section: claims

1. In a nuclear reactor core, a plurality of combined in-core flux detector and thermocouple assemblies, each said assembly comprising: an outer tube which is sealed at its upper end; an inner tube disposed within, and extending along the length of, said outer tube; neutron detector means disposed within said inner tube; means connected to said neutron detector means for displacing said neutron detector means along the length of said inner tube; and a plurality of thermocouples disposed outside of said inner tube and enclosed within said outer tube, said plurality of thermocouples comprising one group of thermocouples which are spaced apart along the length of said outer tube, wherein said group of thermocouples of each said assembly is connected to constitute a back-up coolant level monitoring means, and said assemblies are distributed over a selected region of the reactor core, with the locations of said group of thermocouples along the length of said outer tube being different from one said assembly to another to provide a coolant level monitoring operation having a higher precision than could be achieved by one said assembly alone. 2. An arrangement as defined in claim 1 wherein in each said assembly thermocouples is provided with conductive leads and all of said conductive leads and said means connected to said neutron detector means extend out of said assembly via the lower end of said outer tube. 3. An arrangement as defined in claim 2 wherein in each said assembly outer tube is arranged to extend through the bottom of a reactor pressure vessel into the core of such reactor. 4. An arrangement as defined in claim 1 wherein said group of thermocouples of each said assembly is connected to constitute a back-up coolant level monitoring means. 5. An arrangement as defined in claim 4 wherein said plurality of thermocouples of each said assembly further comprises a first thermocouple connected to monitor the temperature of coolant exiting the reactor core and a second thermocouple connected to monitor that temperature in the event of failure of said first thermocouple. 6. An arrangement as defined in claim 1 wherein said plurality of thermocouples of each said assembly further comprises a first thermocouple connected to monitor the temperature of coolant exiting the reactor core and a second thermocouple connected to monitor that temperature in the event of failure of said first thermocouple. 7. An arrangement as defined in claim 1 in combination with a reactor including a pressure vessel and a core housed within said pressure vessel and containing a plurality of fuel rod assemblies, wherein each said flux detector and thermocouple assembly is located within a respective fuel rod assembly and is connected to the region outside of said pressure vessel via a single passage in the vicinity of the bottom of said pressure vessel.