<p>The CANDU-900 reactor design is an improvement on the current CANDU-6 reactor in the areas of economics, safety of operation and fuel cycle flexibility. As power grids start to rely more heavily on nuclear, it will be imperative for future nuclear generating station designs to be able to adjust their output to suit the fluctuating demands of the grid. Additionally, the need to reduce global nuclear waste has motivated research into mixed oxide fuel with the goal of maximizing spent fuel repository capacity and reducing decay heat via transmutation of transuranic actinides. The objective of this thesis is to provide insight into the load following capabilities of the CANDU-900 reactor design for a transuranic mixed oxide (TRUMOX) fueled core.</p> <p>The three-dimensional fuel management code, RFSP-IST, was used to simulate a reactor operating history for week long load following operations in a generic CANDU-900 reactor. Daily refuelling operations as well as reactivity device movements supplementary to RFSP were performed using the RECORD RRS emulator program. Core snapshots were taken at periodic intervals using the SIMULATE module to observe and track various reactor parameters. Average liquid zone controller fills as well as core reactivity and channel power values were used to determine the controllability of the reactor for various load following depths.</p> <p>The results of the load following simulations show that TRUMOX fuel has superior load following capabilities to that of conventional NU fuel for practical operational scenarios in a CANDU-900 reactor. Load following operations could be performed for TRUMOX fuel down to 85% full power in a safe and controllable manner using only the liquid zone controllers to account for the xenon transient reactivity as compared to NU which could only be done down to 90% full power. For load following simulations that both fuel types were capable of performing in a controllable manner, the TRUMOX fuelled core maintained on average a larger safety margin between the average liquid zone controller fills and the established safety limits.</p> / Master of Applied Science (MASc)