Power distribution measuring system employing gamma detectors outside of nuclear reactor vessel.

摘要

A system for measuring the power distribution in a reactor core (14) includes a plurality of gamma detectors (78) disposed outside of the reactor vessel (12) which houses the reactor core (14). The gamma detectors (78) correspond in number to the number of instrumentation tubes (50) in the fuel assemblies (16) in the reactor core (14) to be sampled. A first plurality of separate flow branches (82) connect the instrumentation tubes (50) with the gamma detectors (78) for routing the flow of coolant from the instrumentation tubes (50) to the gamma detectors (78) so that the gamma detectors (78) can measure the <1><6>N decay gamma activity in the respective instrumentation tubes (50) of the fuel assemblies (16). A second plurality of separate flow branches (84) connect a cold leg (74) of the reactor coolant system (66) with the gamma detectors (78) for routing the flow of coolant from the cold leg (74) to the gamma detectors (78) so that the gamma detectors (78) can measure the background gamma activity in the respective instrumentation tubes (50) of the fuel assemblies (16). Control valves (86, 88) interposed in the first and second pluralities of flow branches (82, 84) are operable to select communication of one or the other of the flows of coolant to the gamma detectors (78) from either the instrumentation tubes (50) or the cold leg (74). <IMAGE>