Influence of the nodalisation/zoning by the ThAI – Iod 11 and Iod 12 tests
analysis with ASTEC code applications
Authors: Petar Kaleychev and Ivan Ivanov
Petar Kaleychev, Technical University of Sofia, Bulgaria, 1000 Sofia, 8, Kliment Ohridski Blvd.,
Block 12, tel. +359 895 586 116, Fax. +3592 965 2043, kaleychev@tu-sofia.bg
Ivan Ivanov: Technical University of Sofia, Bulgaria, 1000 Sofia, 8, Kliment Ohridski Blvd.,
Block 12
Keywords: Iodine, ThAI, ASTEC, severe accident, VVER
Introduction
The severe accidents management in the light water reactors and particular in the case of VVER1000 requires understanding the processes of iodine behavior and the interaction with thermal
hydraulics. Tests Iod-11 and Iod-12 have been implemented in 2004 and released for the
SARNET THAI Benchmark in 2010-2011 [1, 2].
In this report are presented results obtained by code ASTECv2.0 for the tests ThAI - Iod 11 and
Iod 12, in which are examined thermal hydraulics, hydrogen, aerosols and iodine (ThAI) in
multi-compartment reactor containment. As well in ThAI-Iod-11 the relative humidity of the
vessel atmosphere is high but no wall condensation occurs [1], in ThAI-Iod-12 wall
condensation is achieved by a controlled cooling of the walls [2].
Fig.1 THAI test facility
a) View with sections
b) Positions of the compartments
The main component of the facility is a cylindrical steel vessel of 9.2 m height and 3.2 m
diameter, with a total volume of 60 m³ (Fig.1a). The compartments of the facility in
correspondence to Fig.1b) are:





Dome compartment
Upper annulus
Lower annulus
Inner cylinder resp. central compartment (dead end zone)
Lower vessel part above sump, bottom compartment
 Sump compartment
At the lower end a sump compartment is attached. The vessel space is subdivided by an open
inner cylinder and a horizontal separation plane in the annular region with vent openings. The
outer cylindrical wall has cooling/heating jackets subdivided into three vertical sections. The
entire vessel is thermally insulated. In Fig.1b) are presented the injection positions for iodine,
helium and steam.
The test procedure of Iod-11 has 6 phases, beginning with two preparation phases.
 Test phase 1 (vessel preparation) of dry heating/cooling;
 Test phase 2 (test conditions) of setting of test conditions for the iodine measurement;
 Test phase 3 (stratified atmosphere) of iodine injection and measurement of iodine
distribution;
 Test phase 4 (transient conditions) of generating a mixed vessel atmosphere and
measurement of iodine distribution;
 Test phase 5 (mixed conditions) of measurement of iodine distribution;
 Test phase 6 (washing) of washing of iodine deposits from vessel walls.
The Iod-12 has 8 phases, as the first 5 are similar with these of Iod-11. The other 3 phases are:

Test phase 6 (rest period);

Test phase 7 of iodine resuspension in dome compartment by heating the walls;

Test phase 8 of washing.
THAI is a coupled-effects test facility that allows investigating of natural convection,
atmospheric stratification, heat exchange with solid structures, heat conduction and storage in
solid structures, steam condensation on walls and in the atmosphere and the transport of the
condensed water.
Model and results
An input deck (ID) for the code ASTECv2.0 (using the module CPA), distributed between
partners of SARNET and further developed in Technical University of Sofia (TUS) is used for
modeling of the thermal hydraulic and aerosol behavior in the containment parts for the both
tests - Iod 11 and Iod 12. Then are obtained results and comparison for the different node
numbers of the compartments as here are presented only the results for the test Iod 11. For this
purpose for ThAI - Iod 11 is made the division of the dome compartment to 4 nodes in Model-4
and 7 nodes in Model-7 (Fig.2) and subsequently are modeled the connections and the heat
exchange between them, as are take into the account the size of zones - absolute elevation of the
floor, floor area, volume of the zone, and absolute elevation of the zone center [3, 4]. The Model4 is simpler and clear as forms and sizes. In the Model-7 the real zones 1 and 7 are not cylinders,
but they are here recalculated as cylinders with same relevant volumes (Fig.2), where the zones
1, 2, 4 and 6 are cylinders filled with fluids and zones 3, 5 and 7 are empty cylinders filled with
fluids. The sizes of the zones in Model-7 are defined as are taking into account:

That the volumes of the 6 and 7 zones are equal to the real volume of the lower part of the
dome compartment.

That the volume of the zone 1 is the volume of the real dome compartment minus the sum of
the volumes of zones 2-7 and so, the sum of the volumes of all of the zones is equal to the
volume of the real dome compartment.
Fig.2 Dome compartment – Model-4 and Model-7
Fig.3 Model-4 – Nodes and junctions
For the junctions between nodes, from TUS in the ID are added the connection structures that
take into account the features of the connections as sizes, sections, etc (Fig.3). On the other hand
in the ID is added a code to present the heat exchange between nodes of dome compartment to
the others compartments in the facility as is take into the account the surface and height of the
zones.
For ThAI - Iod 11 in this report is made the comparison between Model-4 and Model-7 of dome
compartment, as are obtained variables for thermal hydraulic and aerosols. In the highest zones
by the both models, gaseous (Tg) and liquid (Tl) temperatures in the Model-4 are similar and
both are little higher (Fig.4) then these in Model-7 (Fig.5). This dependency is not valid only for
the lowest zones – Fig.6 and Fig.7. On the other hand the gaseous temperatures stand higher then
the liquid temperatures in Model-4 only in the lower zone, as is for the whole dome by Model-7.
Fig.4 Temperatures in highest zone
for Model-4
Fig.5 Temperatures in highest zone
for Model-7
Fig.6 Temperatures in lowest zone
for Model-4
Fig.7 Temperatures in lowest zone
for Model-7
The pressures of steam for all zones in the Model-7 (Fig.9 and Fig.11) are almost without
changes, in contrast to Model-4 (Fig.8 and Fig.10). The pressures of steam in the case of Model4 are higher in the upper zones and for all the zones they are higher then Model-7 except the
lowest zones where they are lower then Model-7. The total pressures (Ptot) is similar and almost
without changes in the compartments of the both models.
Fig.8 Pressure in highest zone
for Model-4
Fig.9 Pressure in highest zone
for Model-7
Fig.10 Pressure in lowest zone
for Model-4
Fig.11 Pressure in lowest zone
for Model-7
The results for mass gas of water in the cases of the Model-4 and the Model-7 are very close –
Fig.12 and Fig.13. The maximum achieved values of the water gas mass and mass flow trough
connection are in the same time interval for the both of cases, although the different number of
zones.
Fig.12 Water gas mass
for Model-4
Fig.13 Water gas mass
for Model-7
The number of nodes in the models of ASTEC is important for the precision of the output results.
As the increasing the number of nodes leads to results that are more correct and close to the
experimental results, consequently with Model-7 is achieving more detailed modeling and
analysis of the test in correspondence to Model-4 and then the results are more representative in
that case.
Conclusion
In the report are presented results concerning tests ThAI - Iod 11 and Iod 12 using the code
ASTECv2.0 as in this way are analyses the influence of the nodalisation. The obtained output
variables (pressures, temperatures, etc.) proofs that the increasing the node number strongly
influences the precision of the physical variables of the models. Generally the increasing the
number of nodes (increasing the number of volumes) leads to more correct results in a separate
volume, in correspondence to model with lower number of nodes.
The presented analysis and results presenting the applicability of ASTECv2.0 for modeling of
severe accident. The results are useful for presenting the possibilities for modeling and the
influence of nodding in the case of analyzing the multi-compartment vessels and the obtained
results of hydraulic and aerosol behavior are a base for developing of the recommendations
concerning safety management in the light water reactors.
References
[1] Weber G. Specification of the SARNET-2 WP8 THAI Benchmark. Part 1: MultiCompartment Iodine Test Iod-11. 8 July 2010.
[2] Weber G. Specification of the SARNET-2 WP8 THAI Benchmark. Part 2: MultiCompartment Iodine Test Iod-12. 14 March 2011.
[3] Ivanov I, P.Kaleychev. Technical University of Sofia – first analytical results on Iod-11
test by ASTEC v2.0. 2nd Meeting for SARNET WP8, ThAI Benchmark, 2010.
[4] Ivanov I, P. Kaleychev. Analysis of the results on Iod-11 test by ASTEC v2.0 in the period
October 2010-March 2011. SARNET WP8-ThAI Benchmark 3rd Meeting, 28 March 2011,
Bergen, Netherlands.