Improvements in RFSP prediction capability for spatial control in Darlington reactors

The adjuster shim mode of operation was recently re-introduced at Darlington NGS, leading to prolonged operation with atypical reactivity device positions and flux shapes. It was recognized early on that accurate predictions of core parameters and transient effects during this new mode of operation would be important for reactivity management and licence compliance. The SIMULATE module of RFSP having bulk and spatial control reactivity capabilities was employed to supplement SORO-the steady state core tracking code used at Darlington NGS. There are multiple options available in the SIMULATE module of RFSP for simulating Reactor Regulating System (RRS) spatial control. Two of these are more realistic: Option 3, which is typically used for simulating spatial control in Candu 6 reactors; and Option 4-the 'Darlington' spatial control option. To support shim mode operation at Darlington, inputs to the 'Darlington' spatial control option were optimized to closely emulate RRS spatial control action at the station. This paper compares the accuracies of RFSP spatial control simulations of Darlington shim mode operation using the optimized D-card and the spatial control Option 3. The effect of shared Fully INstrumented Channels (FINCHs) on Darlington spatial control is discussed as well. (author)