SUMMARY

The I²S-LWR is an innovative nuclear power plant design which still has the 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 scale.

The research in this document 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 are implemented in the 3D model through results and observations.

The 3D model is the principle focus of this research document. 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: 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 economic reasons.