  Funded by the U.S. Department of Energy, the Nuclear Energy Advanced Modeling
and Simulation (NEAMS) program aims to develop an integrated multiphysics
simulation capability for the design and analysis of future generations of
nuclear power plants. NEAMS embraces a multiresolution hierarchy designing the
code suite structure to ultimately span the full range of length and time
scales present in relevant reactor design and safety analyses. Advanced
reactors, such as liquid metal reactors, rely on innovative component designs
to meet cost and safety targets. In order to span a wider design range,
advanced modeling and simulation capabilities that rely on minimal assumptions
play an important role in optimizing the design. Over the past several years
the NEAMS program has developed the integrated multiphysics code suite
(thermal-hydraulics, structural analysis and neutronics) SHARP aimed at
streamlining the prototyping of such components. For the simulation of fluid
flow and heat transfer, SHARP focuses on the high-fidelity end, aiming
primarily at turbulence-resolving techniques such large eddy simulation (LES)
and direct numerical simulation (DNS). The computational fluid dynamics code
(CFD) selected for SHARP is Nek5000, a state-of-the-art highly scalable tool
employing the spectral element method (SEM). In this manuscript, to be
published in a Von karman institute lecture series monograph on liquid metal
reactors, we review the method and its implementation in Nek5000. We also
examine several applications. We note that Nek5000 is also regularly employed
for intermediate-fidelity approaches such as Reynolds-averaged Navier-Stokes
(RANS) and for reduced-order models employing momentum sources or porous media,
especially when coupled to neutronics modeling.
