.. _section-12.9:

Interaction with Other SASSYS-1 Models
--------------------------------------

As mentioned in the introduction to this chapter, the voiding model
interacts directly with several other major modules in SASSYS-1. This
section will provide a more detailed discussion of these interactions.

The voiding model first makes use of information from another module by
accessing initialization data from the prevoiding calculation.
Quantities such as liquid sodium temperatures, pressures, and mass flow
rates are computed in the prevoiding module and passed to the voiding
model coding, once the prevoiding calculation has predicted that
initiation of voiding is imminent. The voiding model then begins
interacting with the transient heat-transfer module at the end of each
heat-transfer time step. The heat-transfer calculation provides the
cladding and structure axial temperature profiles required by the
voiding model (:math:`T_{e}` and :math:`T_{s}`, respectively). The voiding
model estimates these temperatures at the end of the new heat-transfer
time step by extrapolating the cladding and structure temperatures from
the ends of the previous two heat-transfer time steps. It then computes
the advanced time cladding and structure temperatures for each coolant
time step by interpolating between the temperatures at the beginning and
the end of the heat-transfer time step. During the course of the
heat-transfer time step, the voiding model computes the time-integrated
heat fluxes from the cladding (:math:`E_{e}`) and the structure
(:math:`E_{s}`) and supplies them to the transient heat-transfer
calculation at the end of the heat-transfer time step.

Reactivity feedback due to coolant voiding is provided by the voiding
model through calculation of a spatially smeared liquid sodium density
for each axial mesh segment. This density is passed to the point
kinetics module, where it is used to compute the sodium void fraction in
each segment. The reactivity change due to voiding is then computed from

(12.8‑1)

.. _eq-12.8-1:

.. math:: \rho_{c} = \sum_{I}^{}{\sum_{j}^{}{\left( \rho_{c} \right)_{jI}\alpha_{jI}}}

where

    :math:`\left( \rho_{c} \right)_{jI} =`  reactivity worth of sodium
    in axial segment :math:`j` of channel :math:`I` (input through variable :sasinp:`VOIDRA`)

and

    :math:`\alpha_{jI}` = average sodium void fraction in segment :math:`j` of channel :math:`I`.

Although the point kinetics module does not feed any information back
directly to the voiding model, it does supply the transient
heat-transfer module with information about the change in power, which
in turn affects the computation of the cladding temperatures, and so the
point kinetics model does indirectly influence the voiding model.