  Rod bundle flows are commonplace in nuclear engineering, and are present in
light water reactors (LWRs) as well as other more advanced concepts.
Inhomogeneities in the bundle cross section can lead to complex flow phenomena,
including varying local conditions of turbulence. Despite the decades of
numerical and experimental investigations regarding this topic, and the
importance of elucidating the physics of the flow field, to date there are few
publicly available direct numerical simulations (DNS) of the flow in
multiple-pin rod bundles. Thus a multiple-pin DNS study can provide significant
value toward reaching a deeper understanding of the flow physics, as well as a
reference simulation for development of various reduced-resolution analysis
techniques. To this end, DNS of the flow in a square 5x5 rod bundle at Reynolds
number of 19,000 has been performed using the highly-parallel spectral element
code Nek5000. The geometrical dimensions were representative of typical LWR
fuel designs. The DNS was designed using microscales estimated from an advanced
Reynolds-Averaged Navier-Stokes (RANS) model. Characteristics of the velocity
field, Reynolds stresses, and anisotropy are presented in detail for various
regions of the bundle. The turbulent kinetic energy budget is also presented
and discussed
