ENEL
Società per azioni
Main Features of ECART
Enel Code for Analysis of Radionuclide Transport
ECART is a computer code of ENEL-EDF common property
Periodical revisions, updates and improvements are managed by
ENEL
Research Branch
Requests of information can be addressed to:
Flavio Parozzi - ENEL Research
via Reggio Emilia 39
20090 Segrate (Milano) - Italy
tel: +39-02-21.67.23.10
fax: +39-02-21.67.26.20
e-mail: flavio.parozzi@s1.cise.it
SUMMARY
SUMMARY.................................................................................................................................................... 2
INTRODUCTION TO ECART.................................................................................................................... 3
MAIN FEATURES AND CODE ARCHITECTURE ................................................................................ 3
BRIEF HISTORY OF THE CODE ....................................................................................................................... 3
CODE STRUCTURE AND MAIN ASSUMPTIONS ................................................................................................ 4
OVERVIEW OF THE THERMAL-HYDRAULIC MODELS ................................................................. 6
MAIN FEATURES .......................................................................................................................................... 6
CAPABILITY TO ANALYSE BOTH CONTAINMENT AND PRIMARY SYSTEM SCENARIOS ..................................... 6
CAPABILITY TO PROCESS EXPERIMENTAL DATA ........................................................................................... 7
OVERVIEW OF THE AEROSOL AND VAPOR MODELS ................................................................... 7
MAIN FEATURES .......................................................................................................................................... 7
TRANSPORT OF VOLATILE FISSION PRODUCTS .............................................................................................. 8
TRANSPORT OF AEROSOL PARTICLES ........................................................................................................... 8
OVERVIEW OF THE CHEMISTRY MODELS ..................................................................................... 10
RUNNING OF THE COUPLED MODULES ........................................................................................... 12
COMPUTER TIME REQUIREMENTS ............................................................................................................. 13
Tables
Figure 1: Schematic of the linking among the three main modules of ECART: ................. 5
Figure 2: Control volume model adopted for ECART code................................................ 7
Figure 3: Schematics of the transport phenomena considered by the Aerosol and Vapour
Transport Module in each control volume. ................................................................. 9
Figure 4: Example of log-normal aerosol particle size distribution and corresponding
discretization.............................................................................................................. 10
Figure 5: Example of the fitting function used to calculate the decay specific power
associated to an element, as a function of accident time and fuel irradiation time. .. 12
Figure 6: Example of ECART prediction of suspended masses of Caesium compounds
transported from the primary circuit into the containment, for a typical PWR small
break. ......................................................................................................................... 13
INTRODUCTION TO ECART
The realistic calculation of the radionuclide transport within a nuclear plant and the
release to external environment during an accident involving a severe damage of the fuel
rods requires an appropriate evaluation of the thermal-hydraulic conditions influencing
both the chemical equilibria among the involved chemical species and the radionuclide
retention phenomena. Also, the path followed by the radioactive stream before being
released to the environment through the potential containment leakages must be carefully
simulated in relation to the aerosol removal mechanisms which may occur in the presence
of heat structures and considering radionuclide scrubbing favoured by steam condensation
and bubbling through liquid sumps.
During the '80s, in connection with the increased interest in Source Term problems and in
parallel with the large-scale experimental programs, several versions of computer codes
for Source Term analysis were released. In the same period, the need to have well-known
and well documented tools adapted to national studies, led to the development of
dedicated versions differing from the original ones. In this context, the Italian utility
ENEL built up an its own version of some STCP codes (Source Term Code Package) set
up for US NRC, paying particular attention to the aerosol transport modelling. TRAPMELT and NAUA, for instance, were improved and tested by ENEL on the basis of the
results of Marviken, LACE and DEMONA series of experimental tests on the aerosol
behaviour. These tools, together with other ENEL-adapted versions of this type of codes,
were successfully employed in the Italian Source Term studies for PWR and BWR plants,
and in the preliminary sizing verifications for the EU/CEA Phebus-FP and EU/JRC Ispra
STORM Projects.
ECART was born starting from those experiences. This new code was aimed at
representing the “container” of mechanistic radionuclide transport models developed in
the framework of experimental programs, able to couple aerosol/vapour transport with
thermal-hydraulic and chemical equilibria calculations, and taking into account, at the
same time, the need to have a computer code reasonably utilisable for plant analyses.
MAIN FEATURES AND CODE ARCHITECTURE
Brief history of the code
The work on ECART started at ENEL in 1989 with the valuable support of Synthesis,
which defined the code architecture and built up the Aerosol/Vapour Transport Module.
The first stand-alone version of this Module, in particular, was used in 1990 to run new
aerosol models, like those for steam condensation within pipeworks and particle dry
resuspension, developed in the framework of EU Reactor Safety Research Programs
1988-91 [Parozzi 1991; Borioli 1992].
In the following years, the Aerosol/Vapour Transport Module was continuously updated
in the framework of a wide validation campaign. This module, often quoted in literature
as the bulk of ECART itself [Wright 1994; Bowsher 1995], was widely used for research
purposes, like the STORM Project and the RCA Source Term Project of the European
Union [Eusebi 1992; Parozzi 1995b].
Since 1993, through an agreement between EDF-SEPTEN and ENEL related to joint
research actions on LWR severe accident studies, EDF started a significant financial and
technical contribution to the development and validation of ECART, involving its
Research and Development Division of Chatou: the Aerosol/Vapour Transport Module,
then, was submitted to a further revision in France by CNRS [Blawzdziewicz, 1995] and
was used on reference primary circuit transport problems for a detailed comparison with
the aerosol results given by MAAP [Hervouet 1995].
Still in the framework of EU Reactor Safety Research Programs 1988-91, ENEL carried
out a phenomenological research related to the chemical behaviour of fission products in
the gas stream after their release from the fuel and their dependence on parameters like
temperature, pressure and hydrogen-to-steam ratio [Borioli 1992]. On the basis of that
study, the Chemical Equilibria Module was set-up with a significant contribution of the
Industrial Chemistry and Chemical Engineering Department of Politecnico of Milano:
after a successful series of stand-alone tests on theoretical problems and chemistry
benchmarks, this ECART module was completed in 1994 [Biardi 1993].
At the Mechanical and Nuclear Constructions Department of University of Pisa, starting
from the experience on thermal-hydraulic analysis of nuclear accidents and FUMO
containment code modelling, the Thermal-Hydraulic Module was developed with a
significant support of Themas. A preliminary version of this module was completed in
1993 and successfully tested on a large series of theoretical problems and code
benchmarks on experimental situations [Oriolo 1995].
In 1995, the fully-coupled version of ECART was finally employed on typical PWR
severe accident scenarios and experimental benchmarks, like those on VANAM-M3 and
Phebus FPT0 [Ambrosini 1995; Paci 1996; Parozzi 1996; Salina 1996].
Code structure and main assumptions
ECART is designed to operate with three modules, linked together, but able to be
activated separately (Figure 1):

the Thermal-Hydraulic Module, providing the boundary conditions to the other
two modules;

the Aerosol and Vapour Transport Module, calculating the amount of
radionuclides that can be retained or released;

the Chemical Equilibria Module, evaluating chemical reactions occurring
among radionuclides.
The code applies to pure transport phenomenology (mass, energy, momentum transfer and
physico-chemical processes in whatever part of a nuclear power plant). As designdependent models are not included (e.g. core degradation, releases from fuel, safety
systems, etc.), the complete analysis of a severe accident requires the linking with other
suitable code packages.
The structure of ECART is designed to treat the thermal-hydraulic phenomena and the
radionuclide transport in an arbitrary flow system, that the user can subdivide into a series
of control volumes connected by flow junctions in an arbitrary way, and chosen on the
basis of considerations regarding geometrical features, thermal-hydraulic conditions and
relevant radionuclide phenomena. As shown in the following, the detail level of aerosol
and vapour transport analyses can be also decided by the user (i.e. the number of chemical
species, the number of aerosol size discretization bins, the occurrence of agglomeration
and the multicomponent description). These choices have obviously great influence on the
computing time.
Inside each control volume, a two-region model is adopted, being the liquid sump
separated from the atmosphere. Within each region, thermal equilibrium is always
assumed. Therefore, non-equilibrium effects related to superheated vapour injected in the
pool or subcooled water sprayed in the atmosphere are separately accounted for.
Also aerosols are assumed to be well-mixed inside the volumes. This assumption requires
that the amount of vapour and/or aerosol removed within the control volume is “small” in
relation to the total amount of material transported throughout the control volume itself. A
corrective action is provided for those volumes, like long pipes, having only a radial
mixing (concentration gradient along the pipe).
The direction and the rate of the flow can be directly assigned as input, together with other
thermal-hydraulic boundary data, or can be predicted by the thermal-hydraulic module.
The direction of flow can change with time, although the aerosol transport through
junctions is treated as one-dimensional (i.e. there is not simultaneous mixing through a
junction). Two-dimensional flows, however, required to simulate accident scenarios or
large-scale experimental situations where the natural convection currents could enhance
the mixing among the volumes, can be accounted for using two junctions to describe the
exchanges between two volumes. Recirculation phenomena promoted by density gradients
of the carrier gas at the inlet of large components (e.g. chimney-effect caused by hot gas
or hydrogen injection) are taken into account by aerosol models, in the absence of any
sub-nodalization, through the estimate of a “recirculation velocity” [Masnaghetti 1987].
THERMAL
HYDRAULICS
5
1
CHEMICAL
EQUILIBRIA
4
2
3
AEROSOL
TRANSPORT
Figure 1: Schematic of the linking among the three main modules of ECART:
1.
2.
3.
4.
5.
t-h boundary conditions for chemical equilibria;
selection of quantity of each chemical compound in gaseous phase;
species concentrations for updating chemical equilibria;
t-h boundary conditions for aerosol and vapours transport phenomena;
decay heat sources associated to transported fission products and aerosol
concentrations capable to modify gas physical properties.
OVERVIEW OF THE THERMAL-HYDRAULIC MODELS
Main features
The study of the thermal-hydraulics of primary system and containment during last
decades provided a plenty of possible options to simulate the thermal-hydraulic behaviour
of nuclear light water reactors. Specific modelling requirements are generally identified
for the simulation of DBAs or severe accidents and of primary system or containment
phenomena, suggesting different choices in the selection of models and of the level of
detail to be used in plant description.
Basing on previous experience in the development and application of models for
analysing the thermal-hydraulic behaviour of LWRs during postulated accidents
[Ambrosini 1987, Manfredini 1992, Ambrosini 1992, Ambrosini 1996] and considering
the peculiarities of the existing Aerosol and Vapour Module, the following characteristics
were agreed for the Thermal-Hydraulic Module:

capability of describing LWR thermal-hydraulic transients, with the degree of detail
required by the aerosol module, and of processing incomplete experimental data
providing the lacking information on local behaviour;

solution of mass, energy and momentum balance equations in order to provide for
realistic representations of flow and heat transfer;

transport simulation of the aerosol carrier gases expected within LWR plants under
accident conditions and usually employed in experimental test (steam, argon,
helium, hydrogen, carbon dioxide, carbon monoxide, krypton, nitrogen, oxygen and
xenon);

calculation of pool levels in the control volumes and evaluation of steam
suppression effects to support the aerosol scrubbing phenomenology;

steam condensation modelled by splitting bulk and wall condensation (influencing,
respectively, aerosol growth and aerosol diffusiophoretic deposition);

allowance for counter-current flow conditions at junctions;

capability of evaluating wall heat transfer taking into account wall thermal
conductivity changes due to aerosol deposition and radioactive decay heat sources;

possibility of characterising heat structure surfaces with local hydraulic parameters
having strong influence on aerosol deposition and resuspension mechanisms (i.e.
hydraulic diameter, local fluid velocity and Reynolds number, etc.).
Capability to analyse both containment and primary system scenarios
The assumption of complete stratification adopted in ECART control volumes is fairly
well suited for severe accident containment analyses, but has some limitations in
simulating primary system conditions. These limitations are accepted considering that,
under core melt-down conditions, single-phase flow (superheated steam-hydrogen
mixture) or stratified flow (formation of water sumps in cold components) is likely to
occur within the reactor coolant system.
A complete solution of the problem, obviously, would require flow regime maps and
constitutive laws for interfacial area and heat transfer under the various regimes.
However, this kind of accident scenarios, expected to be of minor importance in terms of
radiological consequences (e.g. TMI accident or steam generator tube rupture), would
imply removal mechanisms of fission products differing from those mainly influencing
the source term associated to the severe accidents normally considered for probabilistic
safety assessments.
External Spray
Door
Heat Sink
Blowdown
jet
Deentrainment
Evaporation
Liquid
Film
Junction
Figure 2: Control volume model adopted for ECART code.
Capability to process experimental data
The capability to process incomplete experimental data to supply the lacking information
consists in imposing the value of pressure, temperatures and void fraction in outer
environments located upstream or downstream a given junction or to assign flow rates
through particular fluid injection or removal devices, according to different possible
choices (e.g., tables of flow as a function of time, pressure or level).
OVERVIEW OF THE AEROSOL AND VAPOR MODELS
Main features
The Aerosol and Vapour Transport Module is based primarily on the validation and
development work carried out for US NRC codes, and the knowledge coming from the
participation in ATT-Marviken V, LACE, and DEMONA experimental programs
[Parozzi 1988a; Parozzi 1988b]. The more recent results and models produced in the
frame of the European Union Reactor Safety Research Programs, like the dry physical
particle resuspension or the multicomponent description, are included [Borioli 1992;
Parozzi 1995b]. Although ECART adopts the classical well-mixed assumption to describe
the transport within each control volume, the deposition and resuspension phenomena can
be described by dividing each control volume into sub-regions, where local thermalhydraulic conditions (temperature, gas flow velocity, etc.) can be taken into account. In
this way, removal mechanisms associated to small pipes can be detected, without using
too short time steps and ad-hoc running the aerosol equation.
As already shown in Figure 2, each control volume can simulate the presence of liquid
water at the bottom. A BWR suppression pool, large water tanks of advanced LWRs or
time-varying sumps caused by steam condensation can be then modelled. Within each
control volume, all phenomena that can be responsible for retention or re-entrance of
radionuclides are taken into account using the same criteria (Figure 3).
Transport of volatile fission products
Because of their negligible latent heat, condensation and evaporation of volatile species
onto and from airborne particles and structure surfaces are dynamically calculated by
diffusion equations. Conversely, steam-water phase changes can be either calculated by
the Thermal-Hydraulic Module or assigned as input data.
The condensation and evaporation onto and from airborne particles promotes aerosol
growth or shrink, while the presence of a liquid phase in an aerosol deposit can inhibit its
resuspension.
Irreversible sorption of I2, HI, CsOH and Te vapours onto internal surfaces is also
modelled by adopting the usual deposition velocity approach.
Transport of aerosol particles
ECART works with discretized size distributions both for airborne and deposited particles
(Figure 4) and always uses mono-component basic aerosol equations to compute the
evolution of aerosol particles. The number of size bins is an input choice. Ordinary
differential equations solvers with implicit integration methods allow to save computing
time and prevent from numerical instabilities.
Optionally, in order to give a multicomponent description of both airborne and deposited
particles, the code can individually track the transported species in each size bin,
accounting for all transport mechanisms. In more detail, the current particles mass in each
size bin is distributed among the involved chemical species following all the particle
transport phenomena accounted by the code (sources, particle growths or shrinking,
depositions, resuspensions, etc.). The computational correctness and the stability of this
algorithm, that represents the only available possibility to manage the multicomponent
behaviour of aerosols with large catalogues of species, was tested through theoretical tests
simulating typical LWR primary circuit conditions [Kourti 1995].
To simulate asphericity of aerosol particles, an aerodynamic shape factor (accounting for
different resistance to motion of the actual particles if compared to the mass-equivalent
sphere) and a collision shape factor (accounting for the increased effective collision crosssection) are adopted as size-dependent by the code.
Agglomeration of suspended particles is based on the three classical mechanisms, usually
modelled in this type of codes: :

Brownian (Smoluchowski);

Gravitational (collision between particles having different settling velocities);

Turbulent, shear and inertial (Saffman and Turner).
Particle growth due to bulk vapour/steam condensation is modelled taking into account
the Kelvin effect (the condensation of steam is inhibited for particles having radii smaller
than the critical radius), while particle deposition and resuspension onto and from surfaces
is computed as the sum of several phenomena [Borioli 1992]:

inertial impaction from turbulent flow (Liu-Agarwal);

diffusion from turbulent flow (Davies);

diffusion from laminar flow (Gormley-Kennedy);

thermophoresis (Brock-Talbot);

gravitational settling (Stokesian and non-Stokesian);

centrifugation in curved pathways (Stokesian and non-Stokesian) accounting
the trapping effect within bent pipes;

diffusiophoresis (Schmitt-Waldmann);

dry physical resuspension (force-balance correlation).
In water sumps, the formation of bubbles and their evolution (growth, asphericity, breakup and rise velocity) are calculated on the basis of experimental data, while particle
scrubbing is modelled accounting for inward and condensing steam, gravitational settling,
particle diffusion and centrifugation.
STEAM
VAPORS
DEPOSITION
SURFACES
PHYSICAL RESUSPENSION
LAMINAR DEPOSITION
TURBULENT DEPOSITION
THERMOPHORESIS
GRAVITATIONAL SETTLING
WATER
SUMP
AEROSO L
GROWTH
CENTRIFUGAL DEPOSITION
DIFFUSIOPHORESIS
SUMP
BUBBLING
AEROSOLS
Figure 3: Schematics of the transport phenomena considered by the Aerosol and Vapour
Transport Module in each control volume.
Number of particles
0.01
0.10
1.00
Particle radius [m]
Figure 4: Example of log-normal aerosol particle size distribution and corresponding
discretization
OVERVIEW OF THE CHEMISTRY MODELS
To set-up the Chemical Equilibria Module, it was necessary to identify the chemical
species that can originate, under reference PWR severe accident conditions, in the gas
stream after the release of the elements from the fuel. To meet this objective, a wide set of
sensitivity calculations, exploring the dependence of the chemical speciation on gas
temperature, pressure and hydrogen-to-steam ratio, was performed with SOLGASMIX
code [Borioli 1992].
The Chemical Equilibria Module contains information for the most representative
chemical species selected with that method (Table 1) and the solver algorithm is based on
Gibbs free energy minimisation at constant pressure and temperature of the system: this
allows the calculation of the equilibrium composition of the mixture in terms of molar
fractions for the gaseous phase and in terms of the moles for the condensed phase. In
order to manage the formation and evolution of radionuclide species within LWR primary
circuits, this module is dimensioned for environments characterised by temperatures in the
range from 1000 to 2500 K with pressures up to 15 MPa [Biardi 1993].
Within the ECART architecture, the possible reactants and reaction products considered
by the Chemical Equilibria Module are the carrier gas components, with the exception of
nitrogen and noble gases, and most of the transported species which are airborne as gases
or vapours. To match with the phase change models of the Aerosol and Vapour Transport
Module, supersaturation conditions of the predicted vapours are accepted. The databases
of the Chemical Equilibria Module are also used by ECART to determine the
temperature-dependent saturation pressures of all volatile species.
Table 1: Catalogue of the chemical species available in ECART.
Species
Ag
AgI
B
BI3
B2O3
Ba
BaI
BaI2
BaO
BaOH
Ba(OH)2
C
Cd
CdI
CdI2
CdO
Cd(OH)2
CdTe
CH4
Cr
CrI
CrI2
CrO
Cr2O3
Cs
CsBO2
CsI
CsO
CsOH
Cs2
Cs2CrO4
Cs2MoO4
Cs2O
Cs2(OH)2
Cs2Te
Cs2TeO3
Cs2ZrO3
Fe
FeI2
FeO
Fe2I4
Fe2O3
Fe3O4
H
HBO2
HI
H2O
H2Te
H3BO3
I
I2
Silver
silver iodide
Boron
boron triiodide
boron sesquioxide
Barium
barium monoiodide
barium iodide
barium oxide
barium hydroxide
barium dihydroxide
Carbon
Cadmium
cadmium monoiodide
cadmium diiodide
cadmium oxide
cadmium dihydroxide
cadmium telluride
Methane
Chromium
chromium monoiodide
chromium diiodide
chromium oxide
chromium sesquioxide
Caesium
caesium borate
caesium iodide
caesium monoxide
caesium hydroxide
diatomic caesium
caesium chromate
caesium molybdate
caesium oxide
caesium dihydroxide
caesium telluride
caesium tellurite
caesium zirconate
Iron
iron iodide
iron oxide
iron iodide
iron sesquioxide
iron tetraoxide
elemental hydrogen
boric acid
hydrogen iodide
Water
hydrogen telluride
boric acid
elemental iodine
molecular iodine
Evap.
cond.
Chem.
reactive
yes
yes
yes
no
yes
yes
no
yes
yes
no
yes
no
yes
no
yes
yes
no
no
no
yes
no
yes
no
no
yes
no
yes
no
yes
no
no
yes
yes
no
no
no
no
yes
yes
yes
no
no
no
no
no
no
yes
no
no
no
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
Table 1 - Catalogue of the chemical species available in ECART (cont'd).
Species
In
InI
InTe
In2O
In2O3
In2Te
MnI2
MnO
Mn2O3
Mn3O4
MoO2
MoO3
NG
Ni
Ni(CO)4
NiI2
NiO
O
OH
PA
PM
PS
RbI
RbOH
Ru
RuO2
RuO3
Sb
SbTe
Sb2
Sb2O3
Sb2Te3
Sb4
Sn
SnH4
SnI2
SnO
SnO2
SnTe
Sr
SrI2
SrO
SrOH
Sr(OH)2
Te
TeO2
Te2
Zn
ZnO
ZrI4
ZrO2
Indium
indium monoiodide
indium telluride
indium suboxide
indium sesquioxide
diindium telluride
manganese diiodide
manganese oxide
manganese sesquioxide
trimanganese tetraoxide
molybdenum dioxide
molybdenum trioxide
noble gases
nickel
nickel carbonyl
nickel iodide
nickel monoxide
elemental oxygen
hydroxyl
aggregate
aggregate
aggregate
rubidium iodide
rubidium hydroxide
ruthenium
ruthenium dioxide
ruthenium trioxide
antimony
antimony monotelluride
diatomic antimony
antimony trioxide
antimony tritelluride
tetraatomic antimony
tin
tin tetrahydride
tin iodide
tin monoxide
tin dioxide
tin monotelluride
strontium
strontium iodide
strontium oxide
strontium hydroxide
strontium dihydroxide
tellurium
tellurium dioxide
diatomic tellurium
zinc
zinc oxide
zirconium tetraiodide
zirconium dioxide
Evap.
cond.
Chem.
reactive
yes
yes
no
no
no
no
no
no
no
no
yes
yes
no
yes
no
no
yes
no
no
no
no
no
yes
no
yes
no
no
yes
no
no
no
no
no
yes
no
yes
yes
no
yes
yes
yes
no
no
yes
yes
yes
no
yes
no
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
no
yes
yes
yes
yes
yes
yes
no
no
no
yes
no
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
RUNNING OF THE COUPLED MODULES
The coupling among the three modules is explicit. As the Thermal-Hydraulic Module and
the Aerosol and Vapour Transport Module are advanced with different time steps,
depending on their own convergence criteria, a proper logic of synchronism is adopted.
The thermal-hydraulic problem is firstly solved over the time interval between two
synchronous conditions (of the order of the lowest Courant limit in the nodalization),
often adopting short time steps. The aerosol-vapour and chemical equilibria calculations
follow, with implicit integration methods allowing time steps usually longer than the
thermal-hydraulics ones: this technique gives the possibility to smooth out the data related
to flow rates and pressures calculated by the Thermal-Hydraulic Module in the case of
oscillations due to limited instabilities.
In the coupling, the influence of high airborne aerosol concentrations on the gas physical
properties (apparent density and viscosity) is taken into account. Decay heat can be
accounted for the most powerful elements undergoing transport processes (Kr, Rb, Sr,
Mo, Ru, Ag, Sn, Sb, Te, I, Xe, Cs and Ba) through time-dependent  and  specific power
correlations (Figure 5) deduced for typical LWRs [Parozzi 1995a].
The Chemical Equilibria Module updates the gaseous phase composition whenever
significant changes in temperatures, pressures or vapour species amounts are calculated by
the other modules. Possible phase changes, however, are dynamically accounted for in the
diffusive model employed by the Aerosol and Vapour Transport Module (Figure 6).
1E+9
400 days
[W•days/kg]
1E+8
600 days
1200 days
1800 days
1E+7
1E+6
1E+5
0.0E+0
5.0E+5
1.0E+6
1.5E+6
2.0E+6
Time after shutdown [s]
Figure 5: Example of the fitting function used to calculate the decay specific power
associated to an element, as a function of accident time and fuel irradiation time.
CsOH
1E+5
CsI
1E+4
Cs
1E+3
1E+2
Suspended mass [g]
1E+1
Cs2Te
1
CsO
0.1
Cs2
1E-2
1E-3
1E-4
1E-5
1E-6
Cs2O
1E-7
1E-8
1E-9
1E-10
11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 21000
Time [s]
Figure 6: Example of ECART prediction of suspended masses of Caesium compounds
transported from the primary circuit into the containment, for a typical PWR small break.
Computer Time Requirements
The ECART code can be compiled with Microsoft FORTRAN Power Station (with no
DEBUG option) and executed with a PC 486 or Pentium under DOS control. In these
environments, the CPU time required for complete reactor coolant system transients turns
out to be some tenths of hours, depending on the scenario, the nodalization and the
number of models activated. The code has also successfully installed and used on other
computers, such as IBM Power PC (RISC) workstation and IBM-9021/740 mainframe,
with a performance of about 5 times as fast for the former and 13 times as fast for the
latter.
These computing times are not excessively long if compared with the times taken by other
mechanistic severe accident codes, and it is likely they will be reduced introducing
optimisation criteria and improvements in the numeric.
REFERENCES
[Ambrosini 1987]
W. Ambrosini, G. Fruttuoso, M. Mazzini, F. Oriolo, “FASTRAP : a Very Fast-Running
Code for the Analysis of Special Transients and SB-LOCAs in PWRs”, ANS Anticipated
and Abnormal Transients Topical Meeting, Atlanta (USA), April 1987.
[Ambrosini 1992]
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