Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Nuclear Engineering

Major Professor

Ronald E. Pevey

Committee Members

Lawrence W. Townsend, Laurence F. Miller


The purpose of this research was to create computer models to expedite the core design of the International Reactor, Innovative and Secure (IRIS), specifically, so that it may employ burnable absorbers to achieve a longer cycle length and enhanced safety while minimizing the use of soluble boron. The IRIS is a next-generation, integral pressurized water reactor (PWR) being designed by an international consortium led by Westinghouse Electric. Two series of comparison benchmarks, defined by Westinghouse, were completed to validate computer models of representative pin cell, assembly, and whole core geometries. The models were created using the collision probability code HELIOS and a conversion utility to pass cross sections to NESTLE, a nodal diffusion code. Gadolinium and erbium were chosen as the two best qualified elements to be employed as burnable absorbers. Research was performed to create burnable absorber configurations for assemblies that minimize reactivity swing over their expected lifetimes. These optimal assembly designs were then loaded into a simple full reactor geometry to emulate a two-batch core, and the critical soluble boron letdown curves were calculated. While both gadolinium and erbium cores met the requirements for maximum soluble boron levels, neither configuration satisfies all thermal hydraulic safety margins. Future work will address the optimization of core loadings so that these safety margins are met. This work will contribute to establishing an attractive, safe, and economic core design for the IRIS long cycle.

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