Patent Number: 047088443
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to assemblies for monitoring various operating parameters within a reactor core, including, in particular, the neutron flux distribution throughout the core and the core exit coolant temperature. During the operation of a nuclear reactor, it is necessary to constantly monitor a variety of operating parameters, including the neutron flux throughout the reactor core, the core exit coolant temperature, and the coolant level within the reactor pressure vessel. Heretofore, these operations have been performed by a variety of monitoring devices which extend through the reactor pressure vessel at various locations. Of course, each penetration of the reactor pressure vessel requires a high quality, reliable seal. Furthermore, it is common practice to utilize thermocouples for the various monitoring operations, particularly for monitoring the core exit coolant temperature. It is known that thermocouples are prone to failure and that their replacement is a difficult and time consuming operation. SUMMARY OF THE INVENTION It is an object of the present invention to reduce the number of locations at which the connections for such monitoring devices must pass through the pressure vessel of such a reactor. A further object of the invention is to reduce the frequency with which the thermocouples of such monitoring devices must be replaced. A further object of the invention is to provide an effective backup coolant level monitoring system for such reactors. Yet another object of the invention is to provide spare thermocouples which are installed at the same time as the primary thermocouples. The above and other objects are achieved, according to the present invention, by the provision of a combined in-core flux detector and thermocouple assembly for a nuclear reactor comprising: 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 a plurality of thermocouples disposed outside of the inner tube and enclosed within the outer tube. According to preferred embodiments of the invention, a group of the thermocouples enclosed within the outer tube are spaced apart along the length of the tubes and are electrically connected to constitute a backup coolant level monitoring system. Since the primary coolant level monitoring system utilized in many reactors is of the pressure sensitive type, a significant advantage of the present invention is that it provides a coolant level monitoring system operating according to a different principle so that any condition causing failure of one system is unlikely to simultaneously cause failure of the other system. According to a further feature of the invention, one of the thermocouples constitutes the normally operative core exit coolant temperature sensor, while a second one of the installed thermocouples is connected to take over this function if the normally operative coolant temperature thermocouple should fail. According to a particularly advantageous feature of this invention, all of the mechanical and electrical connections for the monitoring elements of the assembly can be brought out of the pressure vessel via a single passage which is preferably located in the vicinity of the bottom of that vessel.