Abstract
A research and development project is ongoing to convert the
currently operating High Flux Isotope Reactor (HFIR) of Oak Ridge
National Laboratory (ORNL) from highly-enriched Uranium (HEU
U3O8) fuel to low-enriched Uranium (LEU U-10Mo) fuel. Because
LEU HFIR-specific testing and experiments will be limited, COMSOL is
chosen to provide the needed multiphysics simulation capability to
validate against the HEU design data and calculations, and predict
the performance of the LEU fuel for design and safety analyses. The
focus of this paper is on the unique issues associated with COMSOL
modeling of the 3D geometry, meshing, and solution of the HFIR fuel
plate and assembled fuel elements. Two parallel paths of 3D model
development are underway. The first path follows the traditional
route through examination of all flow and heat transfer details
using the Low-Reynolds number k-e turbulence model
provided by COMSOL v4.2. The second path simplifies the fluid
channel modeling by taking advantage of the wealth of knowledge
provided by decades of design and safety analyses, data from
experiments and tests, and HFIR operation. By simplifying the fluid
channel, a significant level of complexity and computer resource
requirements are reduced, while also expanding the level and type of
analysis that can be performed with COMSOL. Comparison and
confirmation of validity of the first (detailed) and second
(simplified) 3D modeling paths with each other, and with available
data, will enable an expanded level of analysis. The detailed model
will be used to analyze hot-spots and other micro fuel behavior
events. The simplified model will be used to analyze events such as
routine heat-up and expansion of the entire fuel element, and flow
blockage. Preliminary, coarse-mesh model results of the detailed
individual fuel plate are presented. Examples of the solution for an
entire fuel element consisting of multiple individual fuel plates
produced by the simplified model are also presented.
