Channel over power trip unit (COPTU) for TAPP 3 and 4

500 MWe PHWR reactors are loosely coupled reactors. Therefore the neutron flux measurement is done by several self-powered neutron detectors (SPND) distributed through out the reactor vessel instead of single out of core detector. A representative reactor power from these detector signals is generated to control the mechanical shut down devices of the reactor. The amplified SPND signals are isolated, filtered and validated by detecting the health of SPND signal viz. low insulation, signal-snapping etc. This has also to account for deterioration of detector sensitivity and also their positional disparity. The representative neutron signal (VN) is then matched with actual reactor power i.e. thermal equivalent (VTH) and accordingly corrected with correction factor Kcf (VN/V TH). The ultimate equivalence of neutron signal is instantaneous neutron signal multiplied by Kcf and this is compared against set value for generating the reactor trip. The entire design has been carried out on fail safe criteria and is realized through analog devices and relays. (author)