Development of serpent-based methods for I2S-LWR depletion modeling and sensitivity studies
Ramey, Kyle Michael
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The I2S-LWR is an innovative nuclear power plant design with the power level and size of conventional large LWRs. While other new reactor designs use exotic coolants or are very small in size with unconfirmed claims of scalability, the I2S-LWR design promises safer operating and shutdown features in a package with proven economic power level. The research in this thesis analyzes the I2S-LWR core design using 2D and 3D Serpent models. Work completed using the 2D model is used to verify the accuracy of uncertainties reported by Serpent and provide guidance for moving forward with the 3D design. Serpent-reported uncertainties are compared to observed uncertainties from replica runs and also symmetric groupings. In moving toward creating a 3D model, the 2D model results are compared with an industry code. Knowledge derived from these endeavors is implemented in the 3D model through results and observations. The 3D model and depletion methodology is the principal focus of this thesis. It is described in detail and its depletion of a first core using a candidate core loading pattern is evaluated based on power performance. The depletion analysis uses temperature feedback for the fuel, IFBA, and coolant as well as density variation for the coolant. For a design using only four fuel enrichments, the achieved power peaking factors are better than expected at the quarter assembly level: FdH stays below 1.25, Fz stays below 1.45, and Fq stays below 1.7 for the entire fuel cycle. While the equilibrium core design for this study has a target average burnup of 348 EFPD, this first core operates for a slightly longer period of time (438 EFPD or about 15 months) for the economic reason of increasing the discharge burnup of the fuel discharged after the first cycle.