[en] During the one-year study a conceptual upflow core plant design was developed and the downflow core plant reference design updated. A comparison was made between the two plant designs in critical areas of plant performance, safety, and licensing. The results of that comparison led to the recommendation to adopt an upflow core for the GCFR plant reference design. Although additional development and design efforts are required, the potential of residual heat removal by natural circulation alone offers a decisive safety and licensing advantage