Post-test calculations on the QUENCH-14 bundle experiment with M5®
cladding material using ASTEC code
Dr. Petar Kaleychev – Technical University of Sofia, Bulgaria, bul. Kliment Ohridski 8, tel.
00359-895-58-61-16, e-mail: kaleychev@tu-sofia.bg
Dr. Juri Stuckert - Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1 76344
Eggenstein-Leopoldshafen
Dr. Heinrich Muscher - Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen
Keywords: QUENCH-14, M5®, ASTEC, oxidation, hydrogen production, validation
Introduction
The aim of this report is to present modelling results of the severe fuel damage experiment
QUENCH-14 using ASTEC code for analysis of severe accidents. This report results as a
consequence of the interest coming from both the Technical University - Sofia and Karlsruhe
Institute of Technology to prove the applicability of ASTEC for modeling of QUENCH
experiments. These activities are implemented in the frame of SARNET2 Mobility
Programme.
The QUENCH experiments investigate the hydrogen source term resulting from the water
injection into an uncovered core of LightWater Reactor (LWR) as well as the high
temperature behavior of core materials under transient conditions.
The QUENCH-14 experiment [1] investigated the effect of M5® cladding material on bundle
oxidation and core reflood.
Short description of the test facility and test scenario
The test section is enclosed by safety containment (Fig.1) with a wall thickness. In the forcedconvection mode, relevant for QUENCH-14, superheated steam from the steam generator and
superheater together with argon as a carrier gas enter the test bundle at the bottom. The argon,
steam and hydrogen produced in the zirconium-steam reaction flow upward inside the bundle
and from the outlet at the top through a water-cooled off-gas pipe to the condenser where the
remaining steam is separated from the non-condensable gases argon and hydrogen.
The test bundle is made up of 21 fuel rod simulators, each with a length of approximately 2.5
m, and of four corner rods. All test rods, excluding the rod in the bundle centre, are heated
electrically. The rod cladding of the heated and unheated fuel rod simulator is M5® industrial product made by AREVA [2, 3].
The total heating power available is 70 kW. The distribution of the electric power within the
two groups is as follows: about 40 % of the power is released into the inner rod circuit
consisting of eight fuel rod simulators (in parallel connection) and 60 % in the outer rod
circuit (12 fuel rod simulators in parallel connection).
Fig.1 QUENCH-14 - Test section with flow lines
The test bundle is surrounded by a 3.25 mm thick shroud, made of Zircaloy-4 with a 37 mm
thick ZrO2 fiber insulation and an annular cooling jacket.
There are four corner rods installed in the bundle. Insertion of four corner rods avoids an
atypically large flow cross section at the outer positions and hence helps to obtain a rather
uniform radial temperature profile. Two of them, i.e. rods “A” and “C” are made of a solid
rod at the top and a tube at the bottom and are used for thermocouple instrumentation. The
other two rods, i.e. rods “B” and “D” are particularly determined to be withdrawn from the
bundle to check the amount of ZrO2 oxidation at specific times.
The QUENCH-14 test phases were as follows:
Heatup to ~873 K. Facility check.
Phase I
Stabilization at ~873 K.
Phase II
Heatup with ~0.3-0.6 K/s to ~1500 K.
Phase III
Pre-oxidation of the test bundle in a flow of 3 g/s of superheated steam and 3
g/s argon for ~3000 s at relatively constant peak temperature of ~1500 K. Withdrawal of
corner rod B at the end.
Phase IV
Transient heatup with 0.3…2.0 K/s from ~1500 to ~2050 K in a flow of 3 g/s
of superheated steam and 3 g/s argon and withdrawal of the corner rod D ~30 s before
quench initiation.
Phase V Quenching of the bundle by a flow of ~41 g/s of water.
Model of the QUENCH-14 test facility implemented by the ASTEC code and the
calculation results
The QUENCH input deck developed at first by IRSN in 2001 and optimized as QUENCH-06
by KIT in 2004, was used as a base for the QUENCH-14 ASTEC simulations under ASTEC
v1.3R2 with its module DIVA. The old QUENCH-06 input file includes structures for
modelling the corresponding processes such as hydraulics boundary conditions, macro
components like heated rods, shroud and others as well as the description of the oxidation.
To adapt the QUENCH-06 input deck to the conditions of the QUENCH-14 experiment using
ASTECv2.0R2p2, changes in the style (ICARE syntax instead that of DIVA) were performed.
The M5 oxidation kinetics measured at KIT for the temperature range 1073 K – 1673 K was
used [2, 3]. Due to lack of corresponding experimental data for higher temperatures, the
existing oxidation kinetics for Zircaloy-4 was applied for temperatures above 1673 K.
Fig.2 Nodalisation scheme and temperature field, 3000 s

Fig.3 Axial temperature profiles, 3000 s
The temperature field description
The temperature fields for the central rod (U), one heated rod from inner ring (H1), one
heated rod from the outer ring (H2), two corner rods (C1 and C2), shroud and insulation are
presented both by ASTECv2.0R2p2 (Fig.2).
In correspondence to the results of the experiment, the highest temperatures before quenching
are calculated for in height of around 950 mm (Fig.2). In the end of the calculation at 7600 s,
the highest temperatures are calculated over the cooling jacket and insulation at height around
750 mm. On the other hand the visualization presents lacks of breakaway oxidation as in the
case of experiment [1].
Fig.4 Calculated axial final distribution

Fig.5 Hydrogen production
of cladding metal layer thickness
Axial temperature profiles
The axial temperature profiles at different times are presented for temperatures of the heated
rod, shroud, cooling jacket, unheated rod and corner rod (Fig.3).
The temperatures from the beginning of the calculation to the quench phase are similar for the
heated rod, the shroud, the unheated rod and the corner rod and they are higher in comparison
to the temperature of the cooling jacket. The highest temperature in this time period is
calculated for the heated rod in the height of about 950 mm (Fig.3) as in the case of the
experiment. Similarly, this is the height with the maximum temperatures for the shroud, the
unheated rod and the corner rod. The temperatures of the cooling jacket are lower than other
temperatures – and this just from the beginning of the calculation up to the beginning of the
quench phase.
After the beginning of quench phase the temperatures of the heated rod, shroud, the unheated
rod and the corner rod start to decrease in correspondence to the rapid changes in the water
level. After the quench itself, temperatures in higher parts of the heated rod, the shroud, the
unheated rod and the corner rod are still higher than temperature of the cooling jacket.
In the end of the calculation at 7600 s, the highest temperatures at levels down to 1 m were
calculated over the cooling jacket and the maximum is found at a height around 750 mm. In
the same time, at heights up to 1 m the temperatures of the heated rod, shroud, the unheated
and the corner rod remain higher in comparison to temperature of the cooling jacket.

Oxide thickness
The maximal oxide thickness calculated by ASTEC for the central unheated rod reaches about
630 µm at height of ca. 950 mm in comparison to 860 µm from experimental data at the same
height. The maximal layer thickness for inner ring rod at 950 mm is approximately the same
(around 650 µm) (Fig. 4). Finally, for the rod from the outer ring the maximal oxide thickness
is about 630 µm at the same height of around 950 mm. In the shroud the calculated oxide
thickness is about 650 µm. This result is similar to the experimental data of 590 µm, [1].

Hydrogen production
The results for the hydrogen masses obtained by ASTECv2.0R2p2 are very close to the
experimental data in the phases before quench (Fig. 5). Because of lack of M5® kinetic data in
the highest temperature range (1674 K – 2050 K) the existing was used data for Zircaloy- 4
were adopted. The calculated hydrogen production by ASTECv2.0R2p2 is around 32 g, in
comparison to the 40 g coming directly from the experiment.
The simulated hydrogen release values correspond very well to the data measured during the
pre- oxidation and transient phases of the test. Contrary to this, noticeable underestimation of
the hydrogen production was established for the quench phase. The possible reason for that is
lack of adequate models of such important phenomena as: hydrogen absorption and release by
cladding, oxidation of metallic melt formed between cladding and pellets, formation of quite
thick oxide layer at the inner cladding surface in the region of melt formation in the actual
version of the ASTEC code.
Conclusion
Thanks of the opportunity for joint research activities by SARNET2 Mobile Programme there
are obtained significant results concerning the ASTEC application for modelling and analysis
of the results of QUENCH-14 experiment.
The adapted input decks for QUENCH-14 and above all, the obtained results similar to
experimental ones, gives numerous examples for accurate modelling of the processes in the
QUENCH-14 experiment using the newest version of the ASTECv2.0R2p2 code. Quite apart
of this, some important aspects of the process as the position of the hottest zones and levels in
the test bundle, the generation of hydrogen in the different phases, the thickness of the oxide
layers could be well predicted.
References
[1] Stuckert J., M. Große, U. Stegmaier, M. Steinbrück. Results of Severe Fuel Damage
Experiment QUENCH-14 with Advanced Rod Cladding M5®, Karlsruhe Institute of
Technology, KIT SCIENTIFIC REPORTS 7549, 2010.
http://digbib.ubka.uni-karlsruhe.de/volltexte/1000018823
[2] J. Stuckert, J. Birchley, M. Grosse, B. Jaeckel, M. Steinbrück. Experimental and
calculation results of the integral reflood test QUENCH-14 with M5® cladding tubes. Annals
of Nuclear Energy 37 (2010) 1036–1047.
[3] M. Grosse. Comparison of the high-temperature steam oxidation kinetics of advanced
cladding materials. Nuclear Technology, vol. 170, Apr. 2010