Reactivity Coefficients in Darlington Unit 2 Reactor after Refurbishment

Abstract

Unit 2 reactor of the Darlington Nuclear Generating Station recently underwent refurbishment and was successfully restarted in April-May 2020. Accurate measurements of the reactivity coefficients for the fresh core were completed for the Liquid Zone Control system, as well as for Primary Heat Transport and Moderator system temperatures. Excellent agreement with expectations and pre-simulations using MNCP was found for the bulk LZC reactivity, also confirming the slight overestimation of the LZC coefficient when using the current full- DRAGON generated incremental cross-sections in the RFSP model.

For PHT and moderator temperature coefficients of reactivity, comparisons of measurements with pre-simulations are presented, followed by an example of the impact of the negative PHT/fuel temperature coefficient on core behaviour during a stepback and shutdown from 100%FP.