
PHYSICS OF ATOMIC NUCLEI Vol. 81 No. 8 2018
DAREUS SOFTWARE PACKAGE 1181
in positions of control elements. To this end, the
DAREUS software package has a special computa-
tional module for determining the functionals
required for the GARD program.
This makes it possible to significantly reduce the
calculated dynamic process modeling time, and, if
necessary, the bank of computed states of the reactor
can be quite easily supplemented.
Apparently, this approach is optimal for the com-
putational studies of specific solution reactors, in par-
ticular, the Argus RR.
2. GARD PROGRAM
The most important problem in analyzing the
dynamics of solution RRs is to formulate a complete
system of equations for the dynamics of RRs that link
up heterogeneous transient processes of neutron,
molecular, thermomechanical, thermodynamic, and
hydrodynamic phenomena [4]. An extensive list of
original works in this field is given in the cited paper.
Specific features of the dynamics of solution RRs
are largely determined by the phenomenon of radio-
lytic boiling of the core, which requires a correct
description of the mechanism of formation (nucle-
ation) of bubble nuclei in the core solution, the pro-
cess of transport of radiolytic gas and heat, and the
general behavior of vapor-gas bubbles under steady
and unsteady pressures and temperatures.
The regular and most widespread model of the
mechanism of formation of bubbles by ionizing parti-
cles is generalized in the bubble chamber theory [4]. In
this model, a charged particle passing through water
creates a thermal track, a region of high temperature
along the trajectory of this particle. The thermal track
rapidly expands causing a pressure wave and then
decays into discrete regions of water vapor and radio-
lytic gas under the influence of surface tension. In the
superheated water or water supersaturated with gas,
these gas microbubbles can be centers of further
increase in the gas phase volume.
The GARD program is specially designed for mod-
eling thermomechanical and hydrodynamic processes
in solution reactors, including pulsed ones, in both the
nominal and emergency modes.
The solution of the system of equations for the
dynamics of solution reactors mentioned above is
implemented in it. The program consists of a set of
computational modules describing the heterogeneous
transient processes of the physical phenomena listed
above, which are characteristic of solution reactors.
The GARD program sequentially calls the neces-
sary calculation modules on the basis of the pre-
defined thermohydraulic reactor model. In this case, a
complete and mutually consistent system of equations
of dynamics is formed, after solution of which new
thermophysical functionals are transferred to the KIR
program for further neutronic calculation. These
functionals include the temperature of the structural
materials of the reactor and the density of the core
solution. Note that, when the density of the core solu-
tion changes, its volume also changes, which leads to a
change in the fill level. This change is taken into
account in the neutronic calculation of the next state
of the reactor in order to obtain the reactivity value.
In the current version of the GARD program, in
addition to the standard modules specific to reactors
of any type, computational modules are implemented
in which the following physical processes are simu-
lated:
1. Formation of bubbles of radiolytic gas in solution
as a result of the interaction of fission fragments with
water molecules.
2. Diffusion of radiolytic gas from bubbles into the
core solution.
3. Motion (ascent) of bubbles and release of radio-
lytic gas into the cavity above the core.
4. Change in the pressure in the cavity above the
reactor owing to the release of radiolytic gas from the
core and change in the fill level because of changes in
the density of the core solution.
5. Processes of heat exchange in the core taking
into account the heat removal through different chan-
nels: gas discharge and heat exchange with the vessel
and water coolant of circuit I.
6. Processes of heat and mass transfer in circuit II
and change in the level in the volume compensator of
circuit II.
7. Processes of heat exchange in the vessel and the
reflector.
Computational modules of the GARD program
make it possible to adequately describe the physical
processes in the solution reactor, in particular, the
processes associated with the introduction of positive
reactivity (burst).
3. KIR PROGRAM
The KIR program [3] is designed to solve the inho-
mogeneous stationary and nonstationary equations
and the homogeneous neutron transport equation by
analogous Monte Carlo methods based on the calcu-
lated nuclear data in systems with three-dimensional
geometry.
In the KIR program, the nonstationary neutron
transport equation is solved by the Monte Carlo
method with the time dependences of the positions of
the control elements and the densities and tempera-
tures of the materials of the structural elements.
Delayed neutrons are taken into account (those whose
precursors accumulated by the beginning of the simu-
lated time process and those that are formed during
the process). Note that, in addition to the standard set
of neutron flux functionals, the program makes it pos-
sible to calculate the effective fraction of delayed neu-