(510f) Modeling Xenon Transport in Molten Salt Fueled Reactors

Modeling
Xenon Transport in Molten Salt Fueled Reactors

Valmor
F. de Almeida¹, Benjamin S. Collins¹, Robert K.
Salko¹, and Robert Z. Taylor²

¹Oak
Ridge National Laboratory, Oak Ridge, TN 37831-6181

²University
of Tennessee, Knoxville, TN

Abstract

There
exists a renewed interest in molten salt nuclear reactor (MSR)
technology in view of its favorable safety attributes, namely, 1) the
fuel is already in the liquid state (hence no fuel melt down
concerns), 2) operation near ambient pressure, 3) no fire or
explosion hazard, 4) with loss of pumping power, the fuel is drained
by gravity from the reactor’s core into storage tanks retaining the
fission products in the frozen salt. There are also economic
attributes that justify the revival of the molten salt reactor
development, and there are disadvantages and concerns that need to be
resolved before this reactor type can be adopted. Nevertheless, our
focus is in one aspect of any MSR design that must be implemented,
that is, the removal of volatile fission products during the
reactor’s operation. This is typically accomplished by contacting
the molten salt with an inert gas, e.g., He, either as cover
gas in the pump assembly or as entrained bubbles into the salt (or
both). Noble gases are typically removed from the salt in this
operation mode, in particular ¹³⁵Xe which is
the most notable thermal neutron absorber of the volatile fission
products. Ability to continuously remove volatile fission products is
a key enabling feature of high-burnup MSR’s and their economic
advantage over existing commercial reactors.

The
addition of a gas to a molten salt flow significantly complicates the
modeling and simulation of the coupled mass, heat, momentum, and
neutron transport in the presence of fission, transmutation and
decay. We are developing modeling and simulation capability for
coupled transport in MSR’s and this talk describes current efforts
to develop an integrated simulation tool. Our point of the departure
as far as data and model are concerned is the Oak Ridge National
Laboratory Molten Salt Reactor Experiment which operated in
1965-1969. We are specifically developing a model for the removal of
¹³⁵Xe by means of He bubbles in the LiF-BeF₂
salt mixture with soluble UF₄ fuel under reactor operation
conditions. The distinct difficulties faced at this point are: the
development of a non-isothermal, two-phase, volume averaged fluid
flow model with volatile mass transport from the liquid phase into
the gas phase, diffusion/dispersion, and generation of the fission
products in the liquid phase, and coupling of speciation to neutron
transport. The computational platform used is leveraging ORNL codes
from the Consortium for Advanced Simulation of Light Water Reactors
(CASL), a DOE Energy Innovation Hub.

This
talk will also provide an outlook of the additional modeling of redox
reactive fluid flows needed to account for corrosion of vessel
components and deposition of metallic fission products as interfacial
transport phenomena.