Adjuster Shim Operation at Darlington: Using Configuration-Specific Reference Maps

Abstract

The adjuster shim mode of operation has recently been re-designed and re-introduced at Darlington NGS. In order to facilitate compliance with channel-specific channel and bundle power limits, maps specific to each adjuster bank configuration have been defined and used in safety analyses. The Neutron Overpower Protection (NOP) reference map has also been re-defined for each adjuster shim configuration.In the context of low operating margins to channel and bundle power limits, this approach has allowed some optimization of safety and operational margins, and offers advantages for fuelling out of adjuster shim configurations. The paper presents some reactor core parameters during the latest period of shim operation (Feb. 2017) and during the shim commissioning test (July 2016). A few challenges associated with reactor operation using AA shim at Darlington are also presented.