In-core measurement methodology with optical fibers using Cherenkov radiation for transient induced power measurement in the CABRI experimental reactor

Abstract

This paper presents our experimental work to assess the capability to estimate the transient-induced power distribution in the CABRI experimental reactor using Cherenkov radiation. The CABRI reactor is designed to produce a power transient up to 21 GW within a time less than 100 ms in order to irradiate a test fuel pin in condition representative of a Reactivity insertion Accident in pressurized water reactors. The large response range and short response time required to follow the flux evolution during a complete transient makes classical means of detection, such as ionization or fission chamber, inoperative. For that purpose, we suggest to measure Cherenkov light produced within optical fibers. Indeed, Cherenkov light emission is linked to the local electron production, which is proportional to the local gamma flux through the Compton or pair production cross-section, the intensity of Cherenkov radiation is related to the photon flux intensity. The knowledge of the fission photons emitted by the reactor gives direct insight on the fission rate, hence a spatial power density distribution could be reconstructed thanks to the measure of the Cherenkov light at different point in the reactor.