Reactor monitoring assembly

In a nuclear reactor core, this patent describes combined in-core flux detector and thermocouple assemblies. Each assembly comprises: an outer tube which is sealed at its upper end; an inner tube disposed within, and extending along the length of, the outer tube; neutron detector means disposed within the inner tube; means connected to the neutron detector means for displacing the neutron detector means along the length of the inner tube; and thermocouples disposed outside of the inner tube and enclosed within the outer tube. The thermocouples comprise one group of thermocouples which are spaced apart along the length of the outer tube, wherein the group of thermocouples of each assembly is connected to constitute a back-up coolant level monitoring means, and the assemblies are distributed over a selected region of the reactor core, with the locations of the group of thermocouples along the length of the outer tube being different from one assembly to another to provide a coolant level monitoring operation having a higher precision than could be achieved by one assembly alone