Flux Shape Confirmation - Darlington Unit 2 Return to Service after Refurbishment

Abstract

Unit 2 of the Darlington Nuclear Generating Station recently underwent refurbishment to extend the life of the station, culminating in a successful start-up in 2020. As part of the return to service activities, several physics tests of the newly refurbished unit were performed, including flux scans to confirm the vertical flux distribution using a Miniature Fission Chamber as Travelling Flux Detector. These measurements were performed at two Vertical Flux Detector (VFD) sites for two core configurations: with all 16 in-service Adjuster Absorbers (AA) inserted, and all AAs fully withdrawn. A novel technique was applied to supplement the flux scan data obtained with the TFDs: the current from 68 new vertical (pure Inconel) In-Core Flux Detectors (ICFDs) were collected and processed. By converting the collected currents to fluxes, the data from the ICFDs provided an additional point of comparison for pre-simulations and flux scan data. Flux data obtained from the traditional flux scans and the ICFD current measurements were in reasonable agreement with expectations and pre-simulations, demonstrating consistency between the physical reactor and design. This paper describes both types of flux shape measurements, post-processing and subsequent comparisons to multiple simulations.