Use of Fission Chambers for Monitoring Neutron Flux for the First Start-ups of the Refurbished Bruce a Reactors

Abstract

As BF₃ and ³He counters are inoperable in the high gamma fields inside the calandria of a refurbished reactor, a design using in-core fission chambers to monitor neutron flux over the range 10^-14 to 10^-6 full power was adopted for the first start-ups of the refurbished Bruce A Units 1&2 in 2012.Three 1 inch diameter fission chambers were installed in a temporary tube in the view port to monitor neutron flux during manual fuel loading and the first approach to critical of each unit.Although there were issues related to low fission chamber sensitivity and noise pickup during fuel loading, the system performance satisfied neutron monitoring requirements for fuel loading and responded in accordance with theoretical predictions during the first approach to critical of both units.