Bruce 'B' core conversion

The Candu reactor is one of the few commercial power reactors with a small positive void coefficient. Supplementary, a postulated large break loss of coolant accident (LLOCA) in the primary heat transport system will cause the relocation of fuel towards the inlet end of channels. With the current Bruce 'B' Fuelling-against-Flow configuration, this will result in a moving of fuel bundles of low burnup to regions of greater neutron flux, introducing positive reactivity and increasing the power pulse. In order to improve LLOCA consequences and hence increase safety margins, Bruce 'B' units are being converted to a Fuelling-with-Flow scheme. This will result in reversal of the fuel burnup profile relative to the coolant flow direction, eliminating the positive fuel string relocation reactivity. This paper discusses the safety and implementation aspects of the core conversion that have been considered. (authors)