Performance of Prompt- and Delayed-Responding Self-Powered In-Core Neutron Detectors in a Pressurized Water Reactor

An assembly of self-powered in-core neutron detectors has been tested for 6 yr over four fuel cycles in the Oconee 2 pressurized water reactor. The assembly contained both prompt-responding ytterbium and delayed-responding rhodium detectors. Two ytterbium detectors were paired with two rhodium detectors in the assembly. The experiment was conducted to define the long-term performance characteristics of the ytterbium detectors. The results show that the radiation sensitivity of the ytterbium detector, after an initial decrease of 15 to 20%, regenerates with exposure, becoming more sensitive than at the beginning.