Optimizing the Placement of Burnable Poisons in PWRs

The principal focus of this work is on developing a practical tool for designing the minimum amount of burnable poisons (BPs) for a pressurized water reactor using a typical Three Mile Island Unit 1 2-yr cycle as the reference design. The results of this study are to be applied to future reload designs. A new method, the Modified Power Shape Forced Diffusion (MPSFD) method, is presented that initially computes the BP cross section to force the power distribution into a desired shape. The method employs a simple formula that expresses the BP cross section as a function of the difference between the calculated radial power distributions (RPDs) and the limit set for the maximum RPD. This method places BPs into all fresh fuel assemblies (FAs) having an RPD greater than the limit. The MPSFD method then reduces the BP content by reducing the BPs in fresh FAs with the lowest RPDs. Finally, the minimum BP content is attained via a heuristic fine-tuning procedure. This new BP design program has been automated by incorporating the new MPSFD method in conjunction with the heuristic fine-tuning program. The program has automatically produced excellent results for the reference core, and has the potential to reduce fuel costs and save manpower.