A hardwire technique developed for sub-criticality annunciation for PHWR

“Sub criticality” is a parameter of common interest and usage in reactor operation. A hardwired circuit for real time measurement of sub criticality is presented and it does not involve any data acquisition or estimation technique. The circuit was tested with different test inputs and the outputs were compared against the analytical solutions of reactor kinetic equation for the same. This reactivity meter is made for Indian PHWRs (Pressurized Heavy Water Reactor) for multi-decade operation from 10^-8 Full Power to final decade of power operation through 8 and half decades. However it can be tuned to use for any other reactor where flux shape can be considered as stationary. The scheme is very robust as its response to different kinds of test inputs are in very close agreement with analytical solutions. This system will aid reactor operator´s confidence and add to plant reliability and maintainability. The aim of this work is to have the system´s performance evaluated for multi-decade operation with single group solution, with the innovative electronic technique developed; subsequently the multi-group circuit enhancement is possible.