Long-lived Hybrid Incore Detector for Core Monitoring and Protection

The signal production mechanism in a rhodium (Rh) fixed in-core detector emitter relies primarily on the beta particles resulting from neutron absorptions in either of two Rh isotopes to produce an electric current. As the neutron transmutation process depletes the Rh isotopes, the signal output per unit neutron flux from an Rh detector emitter will decrease. A vanadium detector is primarily sensitive to neutrons, but with a somewhat slower reaction time as that of a Rh detector. The benefit of vanadium over rhodium is its low depletion rate, which is a factor of 7 times less than that of rhodium. Platinum detectors are very sensitive to gamma flux, but only mildly sensitive to neutron flux. Because the depletion rate of platinum is very small, it can be neglected. Generally, both gamma and neutron signals are proportional to the assembly power. The characteristics of a new detector are the long life time due to the low depletion of emitter materials and the capability of reactor protection as well as reactor monitoring. The new detector uses vanadium and platinum as the emitter materials to meet the long life time and reactor protection capability. Vanadium detector is used for reactor monitoring and platinum detector is used for reactor protection. To determine the number of emitter strings, a comparative study of the power peaking factor monitoring accuracy for various self-powered fixed in-core detector geometries was made, and the configuration of the optimal detector design was also established and verified. The design of a new detector consists of five-string vanadium detector elements, and three-string platinum detector elements. The detector assembly also contains a background wire for compensation of noise signal and a thermocouple for use in the post-accident monitoring system. This new hybrid detector can be used for both reactor Monitoring And reactor Protection (MAP)