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Organisation de Coopération et de Développement Économiques
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NEA/CSNI/R(2010)3

22-Jun-2010________________________________________________________________________________________________________English text only
NUCLEAR ENERGY AGENCYCOMMITTEE ON THE SAFETY OF NUCLEAR INSTALLATIONSNEA/CSNI/R(2010)3
Unclassified
OECD/NEA THAI ProjectHydrogen and Fission Product Issues
Relevant for Containment Safety Assessment
under Severe Accident Conditions
Final Report
10 June 2010

English text only

JT03285992

Document complet disponible sur OLIS dans son format d'origine
Complete document available on OLIS in its original format

NEA/CSNI/R(2010)3

ORGANISATION FOR ECONOMIC CO-OPERATION AND DEVELOPMENTThe OECD is a unique forum where the governments of 31 democracies work together to address the economic, social andenvironmental challenges of globalisation. The OECD is also at the forefront of efforts to understand and to help governments
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NUCLEAR ENERGY AGENCYThe OECD Nuclear Energy Agency (NEA) was established on 1st February 1958 under the name of the OEEC European Nuclear
Energy Agency. It received its present designation on 20th April 1972, when Japan became its first non-European full member. NEA
membership today consists of 28 OECD member countries: Australia, Austria, Belgium, Canada, the Czech Republic, Denmark,Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Korea, Luxembourg, Mexico, the Netherlands, Norway,
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The mission of the NEA is:–

to assist its member countries in maintaining and further developing, through international co-operation, the scientific,
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NEA/CSNI/R(2010)3

FOREWORDThe CSNI agreed in June 2005 to set-up an Expert meeting on the German proposal about the THAI
Project. The objectives of the THAI project were to carry out a series of experiments in the THAI
facility operated by Becker Technologies, Germany, in order to address open questions concerning the
behaviour of: a) hydrogen; b) iodine and c) aerosols, in a severe accident situation. The understandingof the respective processes is essential for evaluating the challenge posed on containment integrity(hydrogen) and for evaluating the amount of airborne radioactivity during accidents with core damage(iodine and aerosols). The Programme generated valuable data for evaluating the spatial distribution ofhydrogen in the containment, its effective removal by means of equipment such as Passive
Autocatalytic Recombiners, and slow hydrogen combustion. Concerning fission products the
programme has focused on iodine and aerosol interaction with Passive Autocatalytic Recombiners(PAR) with a quick look on wash down from walls through condensate film flow and impact of theiodine/ozone/ aerosol interaction on iodine volatility. An extensive analytical effort has accompanied
the experimental programme, mainly consisting of code calculations for pre-test assessments, result
evaluations and extrapolation to reactor situations.
This Project was finally established in 2007 and run until December 2009. The OECD/NEA THAI
project was supported by safety organisations, research laboratories and industries from Canada,
Czech Republic, Finland, France, Germany, Hungary, Korea, Netherlands and Switzerland. The THAI
Project programme was funded by contributions of signatories, the major one being from the hosting
country; the overall cost of the project amounted to 2.8 million Euros. As for any other OECD/NEA
Joint Project, the reports produced in the frame of the Project are restricted to the project signatories.
According to a general practice for Joint project, the Management Board of the THAI Project has
agreed that these reports will be disclosed for non-signatories after 31 December 2012 and could beobtained after this date upon request to the NEA secretariat.
However, in order to provide without any delay the CSNI with the main outcome of this OECD/NEA
joint project, the Management Board of the THAI Project has agreed to produce this special version of
the final report that can be open immediately to non signatories.

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TABLE OF CONTENTSFOREWORD.................................................................................................................................3
TABLE OF CONTENTS ..............................................................................................................4
EXECUTIVE SUMMARY ...........................................................................................................5
Background ................................................................................................................................5
Objective of the work.................................................................................................................5Work performed .........................................................................................................................6
Results and their significance.....................................................................................................6
Conclusions and recommendations............................................................................................71.

INTRODUCTION ..................................................................................................................82.

OBJECTIVES.......................................................................................................................10
2.1
2.2
2.3
2.4
2.5
2.6
2.7

3.

General objectives of the THAI project ........................................................................10
Particular objectives of the Helium/Hydrogen Material scaling (HM) tests .................10
Particular objectives of the Hydrogen Deflagration (HD) tests ....................................11
Particular objectives of the PAR performance tests ......................................................11
Particular objective of the test on metal iodide/PAR interaction ..................................11
Particular objectives of the test on PAR poisoning .......................................................12
Particular objectives of the Aerosol Wash-Down test...................................................12

EXPERIMENTAL FACILITY ............................................................................................13
3.1
3.2
3.3
3.4

Basic configuration........................................................................................................13
Supply systems..............................................................................................................14
Instrumentation..............................................................................................................14
Additional instrumentation............................................................................................15

4.

PERFORMED EXPERIMENTS..........................................................................................16

5.

ESSENTIAL RESULTS.......................................................................................................20
5.1
5.2
5.3
5.4
5.5
5.6

6.

Helium/Hydrogen Material scaling (HM) tests.............................................................20
Hydrogen Deflagration (HD) tests ................................................................................22
PAR performance tests..................................................................................................23
PAR test concerning metal iodides/PAR interaction (HR 31) ......................................25
PAR poisoning test (HR 32)..........................................................................................25
Aerosol Wash-Down test...............................................................................................26

CONCLUSIONS ..................................................................................................................28

REFERENCES ............................................................................................................................29
APPENDIX A: LIST OF PROJECT REPORTS.........................................................................30

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EXECUTIVE SUMMARY

Background
Progress in nuclear reactor containment safety research has led to a deeper understanding ofphenomena and processes that may occur during a severe accident. However, a number of safety
relevant gaps in this understanding exist due to limitations in the experimental data bases. Such gaps
are − among others − related to combustible hydrogen and to the behaviour of fission products, inparticular iodine and aerosols.
In the case of hydrogen, uncertainties show up mainly in the behaviour of deflagration flames, and in theperformance of Passive Autocatalytic Recombiners (PAR). Some concern exists about the validity ofmany previous hydrogen distribution experiments where helium was used as replacement for hydrogen.
The relevance to reactor safety is connected with the destructive potential of fast deflagrations.
In the case of fission products, a number of interaction processes with operating safety devices such as
PARs have not yet been investigated under realistic conditions which may either jeopardize theperformance of PAR systems or constitute an additional potential source term. Another important
issue related to fission product behaviour in the containment are transport processes which have notyet been investigated in sufficient detail by experiments like e. g. the wash down behaviour of fission
products from surfaces and possible retention in small pools, which in turn may result in delayedtransport of fission products into the sump.
At international level, large efforts have been undertaken for the evaluation and further development
of Lumped Parameter (LP) and Computational Fluid Dynamics (CFD) codes for the analysis andsimulation of severe accidents. However, the validity of these LP- or CFD codes has to be assessedagainst technical and large scale experiments representative for severe accident conditions. The needfor such experiments in the frame of an international programme is twofold; first, to enhance theconfidence in the performance of passive mitigation systems during severe accident scenarios andsecond, to establish a common database accessible by a large research community to support further
development and validation of LP- and CFD codes.
The OECD-THAI project was started in January 2007 under the auspices of the OECD Nuclear
Energy Agency to fill the above mentioned knowledge gaps, by delivering suitable data for evaluationand simulation of hydrogen and fission product interactions. The OECD-THAI project was supported
by safety organisations, research laboratories and industries from seven European countries andpartners from Canada and the Republic of Korea.
Objective of the work
The overall objective of the OECD-THAI project was to address open questions concerning the
behaviour of hydrogen, iodine and aerosols in the containment of water cooled reactors during severe
accidents. The understanding of the processes taking place during such events is essential forevaluating the challenge posed on containment integrity (hydrogen) and for evaluating the amount of
airborne radioactivity (iodine and aerosols) during severe accidents with core damage. The project was
aimed at generating valuable data for evaluating the spatial distribution of hydrogen in the5

NEA/CSNI/R(2010)3

containment, its effective removal by PAR, and slow hydrogen combustion processes. Concerning
fission products and their interactions with operating safety devices such as PAR, the project focuses
on metal iodide/PAR interaction, PAR behaviour under adverse conditions, and aerosol wash-downfrom horizontal surfaces or small pools by condensate film flow.
The project contributes to the improvement and validation of simulation codes used for reactor
application and provides experimental data e.g. for International Standard Problems (ISP).
Furthermore, the project is aimed at maintaining competence and expertise in the field of reactor
safety in the OECD/NEA member countries and promotes international co-operation between its
member countries.
Work performed
The tests have been performed in the technical-scale, multi-compartment THAI containment test
facility (a 60 m³ stainless steel vessel 9.2 m high and 3.2 m in diameter) with exchangeable internals
for multi-compartment investigations. The vessel is designed for a maximum overpressure of 1.4 MPa
at 180°C and can withstand moderate hydrogen deflagrations. The facility is operated by Becker
Technologies GmbH at Eschborn, Germany, under the sponsorship of the German Federal Ministry of
Economics and Technology.
The facility is equipped with the necessary supply systems for steam, compressed air, nitrogen, oxygen,light gases (helium and hydrogen), aerosols and gaseous iodine, the latter also radioactive tracered. The
vessel walls can be heated and/or cooled to establish the desired thermal hydraulic conditions.
An advanced instrumentation and data acquisition system is installed to monitor the relevant physicalquantities with high spatial and time-related resolution.
Within OECD-THAI project, the following test series have been performed:
•
•
•
•
•
•

Helium/Hydrogen Material scaling (HM).
Hydrogen Deflagration (HD).
Hydrogen Recombiner (HR).
Interaction of Metal Iodides with Passive Autocatalytic Recombiner.
Passive Autocatalytic Recombiner Poisoning.
Aerosol Wash-Down (Scoping Test).

Altogether 70 tests have been performed.
In addition to the experimental work, an analytical workgroup was established in the frame of theOECD-THAI project, aimed at the evaluation of the test results for further development and validationof the predictive capabilities of advanced LP codes and CFD codes currently in use in the reactor
safety field. For this purpose, a number of experiments have been selected for blind and open post-test
calculations, some of them for an ISP.
Results and their significanceThe HM tests confirmed that for experiments investigating containment atmosphere flow dynamics
helium can be used as a substitute for hydrogen. Furthermore, calculations performed with various LPand CFD-codes exhibit a major progress in analytical modelling of stratification and mixing processes.
In the HD-tests, by systematic variation of initial pressure, initial temperature, steam content, burndirection and spatial gas distribution their influence on pressure build-up, temperature development,
flame front propagation and completeness of combustion was quantified. The data of selected tests
have been used for open and blind post-test calculations for the validation of combustion models.

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NEA/CSNI/R(2010)3

Significant progress in knowledge has been achieved on the behaviour of different PAR designs under
severe accident typical conditions. The data obtained for onset of recombination, recombination rateand ignition potential provide better insight on PAR behaviour under the thermal hydraulic conditions
investigated with ambient/superheated/saturated steam atmosphere and elevated initial pressure andtemperature in the test vessel. An increase in the investigated initial saturated steam content coupledwith an increase in the initial temperature level in the HR-test series does not have a significant
influence on recombination onset. Recombination rate increases with increasing pressure, and ignition
occurs at higher hydrogen concentrations (at PAR inlet) by increasing saturated steam content.
Oxygen starvation significantly reduces the recombination rate. A highly important result is that PAR
ignition potential is limited to a relatively small area of mixture compositions in the air-hydrogensteam ternary diagram capable to provide the high catalyst temperatures required for ignition.
The THAI experiment on metal iodide/PAR interaction demonstrated, that under realistic conditions
with catalyst plate temperatures of approximately 800°C a marked amount of Cesium Iodide (CsI) is
decomposed, producing gaseous iodine with conversion rates up to 3%, which is relevant for the sourceterm into the containment. The PAR had been exposed to CsI aerosol concentrations up to 4 g/m³.
The results of the experiment with the PAR exposed to excessive aerosol concentrations of insoluble
tin oxide (SnO2), highly hygroscopic and sticky lithium nitrate (LiNO3) droplets, steam and iodine
showed, that even under such challenging conditions, PAR recombination efficiency remained in therange of 50-70%. This is comparable to the results of other tests of the HR-series with the same
thermal-hydraulic conditions, but without aerosols and iodine. Also, the onset of recombination
occurred at the same PAR inlet hydrogen concentration as for comparable HR-tests. Apparently, theeffect of aerosols and iodine on PAR performance is not significant.
The results of the aerosol wash-down scoping test showed, that slightly inclined surfaces have been subject
to wash-down of CsI-particles in the time range of minutes to hours. The characteristic time of the transport
process and its completeness are dependent on the water flow rate and the surface characteristics (steel orpaint). Under low water flow rate, rivulets are formed, and the wash-down was incomplete. A shallow
puddle was acting as intermediate storage and decelerated the transport of CsI significantly.
Conclusions and recommendations
A broad spectrum of safety related issues has been addressed and was subject of the investigations
which could fill existing knowledge and data gaps. In case of PAR investigations, an almost complete
picture of its behaviour has been obtained and the results of the experimental program have provided
assurances of PAR performance under realistic conditions. The database developed in the frame of theOECD-THAI project has been and will be extensively used for improvement, further development andvalidation of CFD codes and Lumped Parameter codes applied in reactor safety analysis and thus, toimprove confidence in the available Lumped Parameter and CFD tools. The accompanying analyticalactivities of the project partners provided intensive analyses of the experimental data by pre- and posttest calculations performed.
Remaining open questions shall be addressed in future investigations. An OECD-THAI-II project isenvisaged to be started in late 2010.

7

NEA/CSNI/R(2010)3

1.

INTRODUCTION

Progress in nuclear reactor containment safety research has led to a deeper understanding of phenomena
and processes that may occur during an accident transient. However, a number of safety relevant gaps inthis understanding exists due to limitations in the experimental data bases. Such gaps are related to
combustible hydrogen and to the behaviour of fission products, in particular iodine and aerosols.
In the case of hydrogen, uncertainties show up mainly in the behaviour of deflagration flames, and in theperformance of Passive Autocatalytic Recombiners (PAR). Some concern exists about the validity ofmany previous hydrogen distribution experiments where helium was used as replacement for hydrogen.
The relevance to reactor safety is connected with the destructive potential of fast deflagrations.
In the case of fission products, a number of interaction processes with operating safety devices such as
PARs have not yet been investigated under realistic conditions which may either jeopardize theperformance of PAR systems or constitute an additional potential source term. Another important
issue related to fission product behaviour in the containment are transport processes which have notyet been investigated in sufficient detail by experiments like e.g. the wash down behaviour of fission
products from surfaces and possible retention in small pools, which in turn may result in delayedtransport of fission products into the sump.
In order to develop a high level of confidence that nuclear reactor containment systems andcomponents establish an acceptable level of safety, it is of utmost importance to understand theaforementioned phenomena and processes which may occur during a severe accident transient. At
international level, large efforts have been undertaken for the evaluation and further development of
Lumped Parameter (LP) and Computational Fluid Dynamics (CFD) codes for the analysis andsimulation of severe accident conditions. However, the validity of such LP or CFD codes can only beassessed against technical and large scale experiments reasonably representative of dominant accident
sequences or conditions. Additionally, as more and more passive safety systems are being installed incurrent reactors and also planned for future reactors, the aforesaid issues need to be coupled with
operation of passive safety systems in phenomena-oriented experiments. The need to carry out suchcoupled-phenomena experiments in the frame of an international programme is twofold; first, toenhance confidence in the performance of passive mitigation systems during severe accident scenariosand second, to establish a common database accessible by a large research community to support
further development and validation of Lumped Parameter and CFD codes.
In such a context, the OECD-THAI project was started in January 2007 under the auspices of the OECD
Nuclear Energy Agency to fill knowledge gaps and to deliver suitable data for evaluation and simulationof the hydrogen and fission product interactions mentioned above. The tests were performed in thetechnical-scale, multi-compartment THAI test facility (a 60-m³ stainless steel vessel 9.2 m high and3.2 m in diameter) with exchangeable internals for multi-compartment investigations. The THAI test
facility is operated by Becker Technologies, Eschborn, Germany. The vessel is designed for a maximum
overpressure of 1.4 MPa at 180°C and can withstand moderate hydrogen deflagrations.
From July 2007 until December 2009, more than 70 experiments defined and agreed with the projectsignatories during the Project Review Group meeting discussions held regularly along the three years
have been conducted successfully at the THAI containment research test facility in Eschborn, Germany.

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NEA/CSNI/R(2010)3

The following research areas have been addressed:• Helium/Hydrogen Material scaling (HM).
• Hydrogen Deflagration (HD).
• Hydrogen Recombiner (HR).
• Interaction of Metal Iodides with Passive Autocatalytic Recombiner.
• Passive Autocatalytic Recombiner Poisoning.
• Aerosol Wash-Down (Scoping Test).
The OECD-THAI project is supported by safety organisations, research laboratories and industries
from 7 European countries and partners from Canada and the Republic of Korea (See Table 1).
Table 1: OECD-THAI project partners with their country of origin
Participant Organisation
BT Becker Technologies GmbH (Operating Agent)
AREVA NP GmbH, Erlangen
GRS Gesellschaft für Anlagen-und Reaktorsicherheit mbH
RWTH Universität Aachen
RUB Ruhr- Universität Bochum
FZK Forschungszentrum Karlsruhe
IRSN Institut de Radioprotection et de Sûreté Nucléaire
NRI Nuclear Research Institute Rez plc
NUBIKI Institute for Electric Power Research
VTT Technical Research Centre of Finland
PSI Paul Scherrer Institut
NRG Nuclear Research and Consultancy Group, Petten
AECL Atomic Energy of Canada Ltd
KAERI Korea Atomic Energy Research Institute
KINS Korea Institute of Nuclear Safety

Country
Germany
Germany
Germany
Germany
Germany
Germany
FranceCzech RepublicHungary
Finland
Switzerland
Netherlands
CanadaKorea
Korea

In addition to the experimental work, an accompanying analytical workgroup was established in theframe of the OECD-THAI project, aimed at the evaluation of the test results for further development
and validation of the predictive capabilities of advanced LP- and CFD codes currently applied inreactor safety.
The data of all experiments have been processed, qualified and stored on a server accessible to thesignatory partners. Detailed experimental results and analysis for the user of the data is provided in
Quick Look Reports (QLR) and Technical Reports. The Management Board of the THAI Project has
agreed that these Quick Look Reports and Technical Reports will be disclosed for non-signatories
after 31 December 2012 and can be obtained after this date upon request to the NEA secretariat. These
reports are referenced to in Appendix A of this report.
Experiments performed in the HM test series were evaluated in a benchmark exercise organised by the
analytical working group in the frame of the OECD-THAI project. The experimental data include
detailed information on the turbulent exchange processes at the contact of the rising plume with thestratification interface, including PIV measurements of the velocity distribution. This information
confirms the observations made during the ISP-47 THAI test and provides a valuable support tocorresponding development and validation of turbulence models.
From the HD test series some tests are also used as a basis for the International Standard Problem
49 (ISP-49) on hydrogen deflagration. This ISP is organised in the frame of WGAMA activities of the
OECD/NEA Committee on the Safety of Nuclear Installations (CSNI). In total, three tests from the HD
test series have been selected for blind and post calculations along with three additional tests performedin the ENACCEF test facility in France. This ISP is envisaged to be concluded by mid July 2010.
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2.

2.1

OBJECTIVESGeneral objectives of the THAI project

The overall objective of the OECD-THAI project is to address open questions concerning the
behaviour of hydrogen, iodine and aerosols in the containment of water cooled reactors during severe
accidents. The understanding of the processes during such events is essential for evaluating thechallenge posed on containment integrity (hydrogen) and for evaluating the amount of airborne
radioactivity (iodine and aerosols) during severe accidents with core damage. The project is aimed at
generating valuable data for evaluating the spatial distribution of hydrogen in the containment, its
effective removal by Passive Autocatalytic Recombiners, and slow hydrogen combustion. Concerning
fission products and their interactions with operating safety devices such as Passive Autocatalytic
Recombiners, the project focussed on metal iodide/recombiner interaction, PAR behaviour underadverse conditions and aerosol wash-down from horizontal surfaces and small pools by condensate
film flow. An extensive analytical effort accompanies the experimental programme, consisting of code
calculations for pre-test assessments, result evaluation and extrapolation to reactor conditions.
The project contributes to the improvement and validation of simulation codes used for reactor
application by e.g. providing experimental data for International Standard Problems (ISP).
Furthermore, the project is aimed at maintaining competence and expertise in the field of reactor
safety in the OECD/NEA member countries and promotes international co-operation between its
member countries.
2.2

Particular objectives of the Helium/Hydrogen Material scaling (HM) tests

The majority of the available hydrogen distribution experiments have been performed using helium asa substitute for hydrogen in order to avoid safety problems in an experimental test facility. Theirresults have been applied to validate hydrogen distribution model calculations. However, helium andhydrogen differ in their material properties as follows: Ratios of density 2:1, diffusivity 1 : 1.1,
viscosity 2.3 : 1, heat conductivity 1 : 1.2, and specific heat 1 : 2.7. The effects of the different
properties on hydrogen distribution and mixing in complex situations (e.g. with condensation) can beassessed only by modelling. In the frame of the OECD-THAI project, an experimental investigation
was started with the aim to validate the above approach, respectively to identify any potential effect ofthe different properties on transport and mixing behaviour.
In order to validate the transferability of experimental findings with helium to H2 problems, twosimilar gas distribution and mixing experiments have been performed in the 9.2-m high, 60-m³ THAI
vessel: one with He (test HM-1), the other with H2 (test HM-2). The experimental procedure is slightly
simplified, but follows in principle that of the International Standard Problem ISP-47-Part 2 (THAI)[Fis05], which is considered to be very sensitive to gas distribution phenomena.
Apart from this, a further objective of the HM tests was to provide additional experimental data forcode validation. The experiment HM-2 was used as a base for a code benchmark. It consisted of twophases: In phase 1 an atmospheric stratification was established by injecting hydrogen near the halfheight of the facility. In phase 2 the stratification was gradually dissolved by a steam injection into the10

NEA/CSNI/R(2010)3

lower part of the facility. The experimental data of phase 1 were open to the participants of thebenchmark [Kan08b], for phase 2 “blind” calculations were performed.
2.3

Particular objectives of the Hydrogen Deflagration (HD) tests

The objective of the hydrogen deflagration experiments is to provide additional data for an improved
understanding of hydrogen combustion phenomena (since hydrogen deflagrations cannot be ruled out
completely even by use of PAR) and for the further development and validation of containment
system codes.
This requires experiments under conditions typical for severe accidents in a relatively large test facility
which allows combustion in upward and downward direction, since experimental data exist mainly forhorizontal flame propagation and/or small geometries which provide non-conservative data. In large
geometries, deflagrations occur faster than in small geometries due to e.g. increased turbulence
generation and therefore produce higher loads for the vessel and its internals. The systematic variationof the test parameters and test conditions, i.e. initial pressure, initial temperature, vertical temperature
gradient, hydrogen concentration (homogeneous and stratified), steam concentration (homogeneousand stratified), burn direction (upwards and downwards) help to determine the influence of theseparameters on combustion behaviour.
The experimental results of some selected tests have been used for open and blind post-test
calculations by various institutions of the participating member countries (ISP 49).
2.4

Particular objectives of the PAR performance tests

The particular objective of the PAR performance tests is to provide additional data about the
behaviour of Passive Autocatalytic Recombiners under accident typical conditions. Furthermore theexperimental data of past investigations are partially proprietary, i.e. not publically available.
Experiments to fill this gap have therefore been agreed upon. The experiments aim at the operation
behaviour of three PAR designs with focus on:-

Conditions for the start of catalytic reaction (onset of recombination).

-

Recombination rate, depending on hydrogen concentration, pressure, steam content.

-

PAR operation under lack of oxygen (oxygen starvation).

-

Conditions for ignition by PAR, resulting hydrogen deflagration in the vessel volume.

The interaction of PAR operation and gas distribution in the vessel volume is an additional objective,in particular in combination with hydrogen deflagration initiated by PAR.
The data improved the understanding of PAR behaviour in general and also of the characteristics ofthe different PAR designs. Furthermore, the data were used as a basis for modelling PAR behaviour
and PAR-initiated deflagration.
2.5

Particular objective of the test on metal iodide/PAR interaction

The particular objective of this PAR test is to determine quantitatively the possible conversion of CsIparticles to gaseous iodine while passing through an operating PAR under realistic thermal hydraulicconditions. According to the French RECI experiments [Sab05], performed under laboratory
conditions high conversion rates have been observed. For the THAI test, more severe accident typicalconditions were established, and a commercial PAR, operated at high hydrogen concentrations (up to
8.5 vol %) to achieve high catalyst and gas temperatures was used. A high steam content wasestablished in order to exclude ignition of the hydrogen-rich gas by the PAR.
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Gaseous iodine, possibly produced from CsI aerosols by the operating PAR is of relevance for theradiological source term, since it is chemically more reactive, longer airborne than particles, and moredifficult to retain in filters.
2.6

Particular objectives of the test on PAR poisoning

The particular objective of this PAR test is to provide data about the start-up behaviour, recombination
rate and recombination efficiency (defined as % hydrogen conversion per pass) of commercial PARs
operating under extremely adverse conditions like high steam content at saturation state, relatively
high aerosol concentration both of soluble and non-soluble aerosols, presence of gaseous iodine as
catalyst poison, in order to assess the reliability of PAR operation under conditions as conceivable
during a severe accident.
2.7

Particular objectives of the Aerosol Wash-Down test

The particular objective of the Aerosol Wash-Down test is to explore some of the dominant influenceparameters and transport mechanisms on aerosol relocation by draining condensate. Predictive models
for wash-down as an integral part of a fission product transport model are required for best-estimatedaccident analysis and risk assessment. Such models do not exist at present.
The wash-down process is affected by complex interactions of geometry, thermal hydraulics,
aerosol particle and structural surface properties. The scoping aerosol wash-down test shall also
provide the basis for more extensive investigations on aerosol wash-down and contribute toexperience on related experimental methods, and outline the conditions for mechanistic transportmodelling. In addition to the scoping test in the THAI vessel, laboratory-scale tests were
undertaken to investigate specific details.

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3.

EXPERIMENTAL FACILITY

Described here is the basic configuration, including the basic instrumentation, of the test facility.
Additional instrumentation was installed specifically for each test group.
3.1

Basic configuration

The tests have been performed in the THAI containment test facility which is operated by Becker
Technologies GmbH at Eschborn, Germany, under the sponsorship of the German Federal Ministry of
Economics and Technology. Main component of the facility is a cylindrical stainless steel vessel of
9.2 m height and 3.2 m diameter with a total volume of 60 m³ (Fig. 3-1). The maximum admissible
overpressure is 14 bar at 180°C.

Fig. 3-1: THAI test vessel
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The vessel size allows to establish natural convection driven flow to study heat and mass transport
processes in sufficiently large scale, also in a multi-compartment geometry.
The vessel structures are made of stainless steel and are completely enveloped by a 120-mm rockwool
thermal insulation. The cylindrical part of the THAI vessel wall is double-walled and accommodates
the wall heating/cooling system. The cylindrical part of the inner vessel wall has a thickness of 22mm. The outer wall is made from 6-mm stainless steel; its outside is thermally insulated. At each of
the five levels at H = 2.1 m, 3.5 m, 4.9 m, 6.3 m and 7.7 m, four block flanges of 150 mm nominal
width and one 200-mm block flange are integrated into the cylindrical vessel wall.
3.2

Supply systems

The vessel is equipped with supply systems for steam, gases (hydrogen, helium, air, nitrogen, oxygen),aerosols (soluble, non-soluble, droplets), and iodine as described briefly in the following.
Steam supply
Steam is provided by a local 110-kW steam generator (8 bars, 170°C saturated steam). Once thepredetermined temperature and steam partial pressure has been achieved, steam feeding is stopped (ormarkedly reduced to compensate for condensation), and the vessel temperature is maintained by thevessel wall heating system which is used also for adjusting steam conditions either at saturation or atsuperheated state.
Gas supply
Hydrogen gas is taken from gas bottles, its pressure is reduced to a constant level of e.g. 6.5 bar; its
mass flow (e.g. 6 Nm³/h) is adjusted by a needle valve, measured by a float-type (rotameter) gauge,
and fed into the test vessel at various locations, depending on the test configuration. The same system
is used for helium injection.
Nitrogen and oxygen is also taken from gas bottles and injected into the vessel at various, test
dependant locations. Air is taken from the local compressed air supply system.
Aerosol injection
Non-soluble SnO2 aerosol is produced by means of a brushing device, in which SnO2 particles arebrushed in sufficiently small size from a solid SnO2 pellet, transported by nitrogen as carrier gas into
the vessel, and injected via a nozzle from top of the vessel. Soluble aerosol is injected as LiNO3
solution or as CsI solution, both together with nitrogen via nozzles as two-fluid jets
Iodine injection
The injection of gaseous molecular iodine (I2) into the THAI vessel consists of two steps, (1) the productionof I2 labelled with radioactive I-123 within a specially designed pressure vessel, the “iodine reactor”, and(2) the transfer of gaseous I2 from the iodine reactor into the THAI vessel with a carrier gas (either nitrogenor air) within a short period of time. The injection location varies with the test configuration.
3.3

Instrumentation

The standard instrumentation encompasses thermal hydraulic and gas composition instrumentation. It
is supplemented by special instrumentation depending on the specific test design and test objectives.

14

NEA/CSNI/R(2010)3

Feed mass flow measurements
Steam mass flow as well as compressed air mass flow is measured by a float-type gauge (Rotameter)
The mass flow of the gases hydrogen, helium, nitrogen and oxygen taken from gas bottles is measured
by float-type gauges. For test data evaluation, the integral of the gas mass flow measured with thisdevice is compared with the injected gas mass determined from the start and the end pressure of thegas bottles and compared with the pressure increase in the vessel.
Gas concentration measurement
Fifteen gas sampling lines continuously take gas samples from the PAR and from the vessel
atmosphere at different locations. The sampled gas is fed to a 15-channel gas concentration analyzer
which determines the concentration of hydrogen or helium in dry air by heat conductivity
measurement. Steam is removed by coolers and condensate traps upstream of the analyzers. Since inmost of the experiments the steam in the vessel atmosphere was at saturation state, the realconcentrations of hydrogen and oxygen in the vessel atmosphere could be determined by use of thesteam table for the partial pressure of steam at the temperature measured in the vessel.
Two channels of the measuring system are additionally equipped with oxygen concentration analyzers.
Temperature measurement
Calibrated 1.5-mm thermocouples for temperature measurement are positioned at each of the gas
sampling sites in the vessel and at other locations in the vessel atmosphere.
In addition, another 200 thermocouples are installed to measure the vessel wall temperature, the dataof which are provided in the Excel sheets of the respective test group.
Pressure measurement
The initial vessel pressure and the pressure increase due to gas injection is determined by two
absolute-pressure transducer and two high precision manometers.
3.4

Additional instrumentation

Additional instrumentation used in the respective tests is:
•
•
•
•

•
•
•
•
•
•
•
•

Gas flow velocity by vane wheels.
Flow velocity and velocity profile of He/H2-jet by Laser-Doppler Anemometry (LDA).
flow field by Particle Image Velocimetry (PIV).
A grid of “fast” sheathed thermocouples (outer diameter 0.25 mm), installed at 13 different
elevations in the test vessel to monitor flame propagation (“flame front arrival”) and flame
temperature during hydrogen combustion.
The transient deflagration pressure is monitored by four “fast” pressure transducers of thestrain gauge type.
Aerosol filter stations for aerosol concentration measurement.
Laser light extinction for on-line aerosol concentration measurement.
Cascade impactors for aerosol particle size distribution measurement.
Gas scrubbers for gaseous iodine concentration measurement.
Two Maypack filter stations for the discrimination of the iodine species in the vessel
atmosphere.
CsI concentration in the condensate by electrical conductivity sensors (on-line and off-line
measurement).
CsI aerosol and gaseous iodine deposition on surfaces by means of coupons.
15

NEA/CSNI/R(2010)3

4.

PERFORMED EXPERIMENTS

In this chapter, the specified tests of the experimental programme with their test parameters and test
conditions are compiled.
Table 2 shows the test parameters of the two HM-tests (hydrogen/helium mixing).
Additional tests HM-3, HM-4 and HM-5 have been performed with test conditions different to thoseof HM-1 and HM-2 in order to measure flow field parameters by use of particle image velocimetry(PIV). The results of these tests are described in detail in [Kan08a, Kano8b].
Table 3 shows the test parameters of the HD-tests.
The test matrix of the HR experiments is compiled in Table 4.
The metal iodide/PAR interaction experiment (HR 31) encompasses three tests, since two tests could
not be completed as planned due to unexpected, but important results: In the first test, an unintended
ignition occurred, in the second test the outlet grid of the PAR was blocked by aerosols. The test
parameters of the three tests are compiled in Table 5.
Table 6 shows the test parameters for test HR 32.
Table 7 shows the test procedure, test parameters and test conditions of the aerosol wash-down test.
Table2: Test parameters of HM experiments (hydrogen/helium material scaling)

Testparameter/test no.

light gas Temperature Temperature Pressure Pressure Steaminjected
initialend (mean)
initialend
injection

HM-1

He

22°C

50°C

1.01 bar

1.43 bar

25 g/s

HM-2

H2

22°C

50°C

1.01 bar

1.44 bar

24 g/s16

Table 3: Test HD-experiments (hydrogen deflagration)
Vertical flame propagation as function of temperature, hydrogen and steam content, and burn direction
Variation of fluid and wall temperature and2Hydrogen concentration (premixed)
Po = 1 bar, 25°C, no steam

6% H 2 : HD-4

7.5% H 2 , 1.14 bar: HD-5

6% H 2 : HD-1R

7% H 2 : HD-6 8% H 2: HD-2R , HD-12

Po = 1.5 bar, no steamt = 25°C

upwardst = 25°C

downwards

t = 140°C

upwardst = 140°C

downwards

ignition limit: HD-13/-14
6%H 2 : HD-20

9% H 2 : HD-3

10% H 2 : HD-7

9% H 2 : HD-11 10% H 2 : HD-8 11% H 2 : HD-9

12% H 2 : HD-10

11 tests

10% H 2 : HD-17
9% H 2 : HD-21 10% H 2 : HD-18

12% H 2 : HD-19

Variation of steam concentration (pre-mixed)

17

Po = 1.5 bar, t = 90°C
upwards

10% H 2no steam: HD-15

25% steam: HD-22(74°C dewpoint)
P steam = 0.375 bar

downwards

12% H 2no steam: HD-16

25% steam: HD-23(74°C dewpoint)
P steam = 0.375 bar

47% steam: HD-24(saturation)
P steam = 0.7 bar
5 tests

Vertical flame propagation in a stratified atmosphere
Po = 1.5 bar
upwards

top
90°C/saturation (47% steam)bottom 30°C/saturation (3% steam)
top 10% H 2bottom 10% H 2*

top 12% H 2bottom 10% H 2

HD-25

top 12% H 2bottom 6% H 2
top 12% H 2bottom 6% H 2

HD-27

top 6% H

HD-29*= originally specified to be 10% H ; this mixture, however, turned out too lean for downward combustion.
2

2

bottom 12% H

HD-28
2

5 tests

NEA/CSNI/R(2010)3

downwards

HD-26

NEA/CSNI/R(2010)3

Table 4: Test matrix HR experiments (hydrogen recombiner)
Test objectives

Test parameters
25°C, dryp = 1.0 bar

p = 1.5 bar

Numberof Tests

Onset ofrecombination

Recombinatio
n rate

3

x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

86°C, 60% steam
25°C, dry

1
5

74°C, 25% steam

7

90°C, 47% steam

3

97°C, 60% steam3

p = 2.2 bar

25°C, dry4

p = 3.0 bar

108°C, 34% steam
25°C, dry
117°C, 60% steam

1
1
2

18

Oxygenstarvation

Ignition
potential

x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x

NEA/CSNI/R(2010)3

Table 5: Initial test conditions of HR 31 experiment (metal iodide/PAR interaction)
Test

Pressure bar

HR-31

Steam concentration vol % Temperature °C

specified measured specified

Measured

specified measured

1.34

71

135

1.376

70

140

Table 6: Test parameters of test HR 32 (PAR poisoning)

Phase 1: Pre-condioning( pre core damage)Phase 2: Release phase(  core damage phase)step 1: H2-release
step 2: H2-release
Aerosol release SnO2
LiNO3 w/o waterPhase 3: PAR operation continuing(  post core damage phase

Duration
specifiedachieved
3-5 h
5h

Release rate
specifiedachieved

1000 s2600 s2600 s2600 s>1h0.17 g/s
0.24 g/s
not spec.
not spec.

1000 s2600 s2600 s2600 s4.7 h0.17 g/s
0.26 g/s
0.26 g/s
0.34 g/s

Table 7: Test conditions of Aerosol Wash Down test
Duration

Phase 1
Precond.
Phase 2
Aerosol
injection
Phase 3Aerosoldepos.
Phase 4
CouponremovalPhase 5
Washdown

specif.
24 hachiev.
25.3 hTemp. gas

Temp. wall

specif.
130°C

achiev.
133°C

specif.
135°C

achiev
138°C

49 min 50 min h 130°C

133°C

135°C

138°C

20 h

24.3 h

130°C

133°C

135°C

138°C

3h

4.5 h

transient transient transient transient

23 h22.9 h

90°C

90°C

90°C

19

85°C

horiz. surface
loading
specif. achiev.

2< 150 80 g/m
2g/m

NEA/CSNI/R(2010)3

5.

ESSENTIAL RESULTS

This chapter gives an overview about the most important results of the OECD-THAI experimental
programme. Diagrams are of illustration character only; quantitative data can be found in therespective Quick-Look Reports and Technical Reports listed in Appendix A.
5.1

Helium/Hydrogen Material scaling (HM) tests

In the Helium/Hydrogen Material scaling (HM) test series, two identical tests (with respect to initialconditions and parameters) were run − one with helium, one with hydrogen − in order to investigate inwhich way helium can be used as a replacement for hydrogen in experimental studies on containment
thermal hydraulics. It was shown in the experiments that comparable atmospheric distributions,pressure and temperature levels can be obtained if the volumetric concentrations of hydrogen andhelium are comparable. This conclusion is based on volumetric light gas concentrations up to 40%
according to the experimental parameter ranges. The thermal-hydraulic processes in the containment
atmosphere, in particular the stratification and mixing phenomena are primarily governed by thedensity differences in the atmosphere. Since both hydrogen and helium have much smaller molecularweights as compared to air or steam, the differences in the molecular weights of these light gases give
only very small contributions to the atmospheric density differences, provided that similar volumetricconcentrations are established. Other differences in physical properties, like diffusivity, thermal
conductivity or heat capacity, are of little influence. From this observation it can be concluded thatexperiments on containment atmosphere flow dynamics using helium instead of hydrogen can provide
meaningful data for identification of flow phenomena and code validation.
Fig. 5-1 gives as example the light gas concentration distribution history during the experiment,
demonstrating the development of the concentration stratification as well as the erosion and mixing
process.

20

NEA/CSNI/R(2010)340

He concentration vol%(related to steam-N2-He mixture )35

30

208 DCH87M00

201 DCH83F10

215 DCH79H10

202 DCH75F10

210 DCH72B10

205 DCH72M00

214 DCH69H10

209 DCH66B10

203 DCH63F10

207 CCH60M00

212 ACH57H10

204 ACH46H10

213 CCH46M00

206 ACH31H10

211 BCH16B06

25

20

15

10

5

0
0

600

1200

1800

2400

3000

Time

3600

4200

4800

5400

6000

6600

s

Fig. 5-1: Helium concentration transients at different elevations of the test vessel
The HM tests were also used to more deeply investigate atmospheric stratification and mixing
processes similar to those previously observed in connection with the NEA/CSNI International
Standard Problem ISP-47 on Containment Thermal Hydraulics [All07]. The most important process
was the erosion of a light gas stratification layer by means of a buoyant steam plume rising frombelow. More detailed measurements near the stratification interface, including PIV velocity
measurements, confirm the experimental findings of ISP-47. In the frame of the benchmark exercise,intense analytical work in connection with the HM tests was done, which resulted in significantly
improved test simulations by means of Lumped-Parameter and CFD codes. Technical details of theanalytical work are presented in [Sch08, Sch09, Sch10].
Table 8 shows the participants of the benchmark.
Table 8: Participants of the HM-2 Benchmark
Participant
Bentaib
Burkhardt
Schwarz
Lee
Duspiva
VisserKyttäläRoyl
Kim
KostkaLiang

Affiliation
IRSN Institut de Radioprotection et de Sûreté Nucléaire
RUB Ruhr-University Bochum
GRS Gesellschaft für Anlagen- und Reaktorsicherheit mbH
KINS Korea Institute of Nuclear Safety
NRI Nuclear Research Institute Rez plc
NRG Nuclear Research and Consultancy Group, Petten
VTT Technical Research Centre of FinlandFZK Forschungszentrum Karlsruhe
KAERI Korea Atomic Energy Research Institute
NUBIKI Institute for Electric Power Research
AECL Atomic Energy of Canada Ltd
21

Programme
ASTEC
COCOSYSCOCOSYSMELCORMELCORFLUENTFLUENTGASFLOWGASFLOWGASFLOWGOTHIC

Type
LP
LP
LP
LP
LP
CFD
CFD
CFD
CFD
CFD
CFD

NEA/CSNI/R(2010)3

5.2

Hydrogen Deflagration (HD) tests

In the Hydrogen Deflagration (HD) test series, the upward and downward propagation of flames inpremixed or stratified air-steam-hydrogen atmospheres was investigated. In the tests, by systematic
variation of initial pressure, initial temperature, steam content, burn direction and spatial gas
distribution, their influence on pressure build-up, temperature development, flame front propagationand completeness of combustion was quantified.
Higher initial temperatures (up to 140°C), which are more typical for severe accidents conditions, leadto lower peak pressures (because of the lower density/energy inventory in the gas mixture) and also
give rise to more steady flame front propagation and a more complete combustion. They cause slower
upward and faster downward flame propagation because of changes in buoyancy forces. Upward
flame propagation is supported by buoyancy; it proceeds at comparatively low hydrogen concentration
with higher velocity and shows convex flame surfaces; downward flame propagation shows lower
velocities and more flat flame surfaces and does not occur below a hydrogen concentration of
8.7 vol% even in this large facility.
A high steam content (48 vol %, at saturation state) in the combustible gas mixture leads to an
irregular (“erratic”) combustion both for upward and downward burn direction with lower flame
velocities and lower peak pressures as compared to “dry” mixtures. Fig. 5-2 shows as an example thecontours of a propagating flame in a premixed atmosphere without steam, Fig. 5-3 shows those of acomparable test (same initial conditions) with high steam concentration (48 vol %, at saturation state).
The difference in flame front propagation − steady vs. erratic − is clearly visible.
9 100

9 100
8 400

8 400

7 700

7 700

7 000

7 000

6 300

6 300

5 600

5 600

4 900

4 900

4 200

4 200

3 500

3 500

2 800

2 800

2 100

2 100

1 400

1 400

igniter
700

700

Fig. 5-2: Test without steam: Flame
front propagation as isochrones

Fig. 5-3: Test with 48 vol % steam: Flame
front propagation as isochrones
22

NEA/CSNI/R(2010)3

In the tests with initially stratified atmosphere and upward burn direction, after the initiation of the
combustion process a large scale convection was generated, which displaces hydrogen-rich mixture
into hydrogen-lean, originally non-burnable mixture, which then becomes burnable.
Fig. 5-4 shows the flame contours of a test with stratified atmosphere (well-burnable mixture in theupper part of the vessel, non-burnable mixture in the lower part) and downward burn direction. In thisexperiment, the downward combustion does not produce much displacement of well-burnable mixture
ahead of the flame downwards, and combustion stops once the flame enters into the non-burnablemixture.

Fig. 5-4: Flame front propagation as isochrones:
Test with lean mixture at vessel bottom; downward burn direction
5.3

PAR performance tests

In the Hydrogen Recombination (HR) test series, the performance of three PAR designs has been
investigated in a hydrogen-air-steam test atmosphere with free, unrestricted convection. Emphasis has beenlaid on the following topics: onset of recombination, hydrogen recombination rate, oxygen starvation, andignition potential.
In total 30 experiments were conducted in the PAR performance test series. These tests (separate
effect tests) were dedicated to the investigation of PAR performance under varying parameters
including ignition potential by a PAR under certain thermal-hydraulic conditions.
Two special integral tests (PAR-fission products interaction) had been designed to test PAR behaviour
under accident typical experimental atmosphere: HR 31 investigated the potential of an operating PAR
to convert particulate iodine (CsI) to gaseous iodine, which is of substantial relevance for theradiological source term, and HR 32 investigated the influence of adverse conditions on PAR
operation, exposing the PAR to high aerosol concentration and gaseous iodine during the start-up
phase. These two tests are described separately in chapter 5.4 and 5.5.
The data obtained for onset of recombination and for hydrogen recombination rate confirm andbroaden the existing data base as follows: Saturated steam conditions (in combination with increased
23

NEA/CSNI/R(2010)3

temperature) have no significant influence on recombination onset in comparison to dry conditions.
Having overcome the onset threshold, hydrogen recombination rate develops almost proportional tohydrogen concentration. Higher pressure results in higher recombination rates (at the same hydrogenconcentration); the effect of steam is small.
Significant progress in knowledge has been made in the field of oxygen starvation. A surprisingly highsurplus of oxygen (compared to the stoichiometric O2:H2 ratio of 1:2) is required for unimpaired PAR
performance: A minimum oxygen surplus factor Φ (2 • cO2/cH2) between 2 and 3 for unimpaired PAR
performance has been determined from the test data. For smaller values of Φ, H2 recombination rate,
PAR efficiency and catalyst temperatures drop drastically. For Φ = 1 (stoichiometric O2:H2 ratio) thehydrogen recombination rate falls below 50% of its value for unimpaired PAR operation.
The HR test series markedly improved the level of knowledge on ignition potential by PAR. A PAR
loaded by high H2 concentration (sufficient O2 surplus provided) ignites the present H2-air-steam
atmosphere in a reproducible way and initiates a hydrogen deflagration which develops from the PAR
outlet opening. Ignition is directly correlated with the PAR catalyst material temperature which
depends on the H2 concentration present at the PAR inlet.
Combining the findings on minimum H2 concentration for ignition by PAR and those on minimum
oxygen surplus required for unimpaired PAR performance (and hence for maximum catalyst
temperature which, again, is correlated with ignition), a relatively small area in the hydrogen-air-steam
ternary diagram can be defined to which ignition by PAR is confined. Reduced O2 concentration in
the air at the PAR inlet (from e.g. PAR operation prior to ignition) further narrows down this“potential ignition area by PAR” in the ternary diagram as indicated in Fig. 5-5. This important findingon ignition by PAR should be introduced into future accident modelling and PSA studies.

Fig. 5-5: Ternary diagram (example):
Area of possible ignition by PAR (green shaded), resulting from HR test findings
24

NEA/CSNI/R(2010)3

5.4

PAR test concerning metal iodides/PAR interaction (HR 31)

The test HR 31 considers a phase in the accident in which steam and hydrogen release has alreadyoccurred and PAR units are working. Locally in the containment, high hydrogen concentrations (8 to 9
Vol %) and a steam inerted atmosphere may prevail. The removal of hydrogen under these conditions
results in temperature levels at the catalytic surfaces higher than 800°C and produces hightemperatures in the gas volume of a PAR unit. Under such operating conditions, suspended CsI andother iodide particles are transported with the convective gas flow through PARs and can be converted
into volatile iodine. Even low conversion rates of a few percent can increase the concentration of
gaseous iodine and may influence the iodine source term into the containment.
The RECI laboratory experiments carried out by IRSN in France [Sab05]. showed that conversion
rates of up to 60% can be achieved under conditions favourable for the decomposition of metal iodides(e.g. temperature > 900°C, fine particles < 1 µm, residence time > 0.5 s). A test with more accidenttypical thermal hydraulic conditions has been designed performed in the THAI facility with acommercial PAR.
Test specifications and boundary conditions, in particular high temperatures (which require highhydrogen concentrations and, hence, steam inertisation) of the catalytic foils have been chosen for thisexperiment to maximise CsI conversion.
PAR inlet hydrogen and steam concentrations have been set to approximately 8 vol % and 60%
respectively, hence limiting the catalyst plate temperatures to approximately 800°C, in order to avoid
ignition. Particle sizes (Sauter diameter) between 0.5 and 0.7 µm and residence times in the range of
0.15 s were achieved. Conversion rates in the range of 1 to 3% were found in the experiment. For
similar test conditions with respect to particle size, temperature of catalyst foils and residence time, in
the RECI experiments conversion rates in the order of 5% were found.
5.5

PAR poisoning test (HR 32)

Test HR 32 considers an early phase of an reactor accident where PAR units are exposed to saturated
steam environment favouring formation of a condensate layer and deposition of aerosol mixture (inert+ hygroscopic) on catalyst foils along with exposure of catalyst foils to gaseous iodine flowing
through the PAR unit. In such a situation, the efficiency of a surface to act as a catalyst will be subject to
a competition between the rate of decrease of the free catalytic surface and the hydrogen and oxygen
recombination reaction.
In the experiment, two different aerosols were injected separately: solid SnO2 particles were injected(together with nitrogen) from top of the vessel, a LiNO3 solution was injected via two nozzles (together
with nitrogen) as small droplets near the vessel bottom into the inner cylinder. The resulting aerosolconcentration, i.e. the sum of the solid SnO2 particles and the hygroscopic LiNO3 particles was relatively
high in the range of 1.5 g/m3 to 2.5 g/m3 during the main PAR operating phase.
Hydrogen injection started at a release rate of 0.17 g/s for 16 min; at this time, aerosol and iodine injections
were started and the hydrogen release rate was increased to 0.26 g/s for another 44 min. Recombination
onset was observed 25 min after start of hydrogen injection.
The injection of gaseous iodine (catalyst poison) resulted in a mean iodine concentration in the vessel
atmosphere of about 0.5 10-3 g/m3 during the main PAR operating phase.
Under these challenging test conditions, PAR recombination efficiency remained in the range of
50 − 70 %, which is comparable to other tests of the HR series with the same thermal-hydraulic conditions,but without aerosols and iodine and an artificially slightly increased oxygen concentration (recombination
efficiency 60–70%). Also, the onset of recombination occurred at the same PAR inlet hydrogenconcentration as for the comparable HR tests, Fig. 5-6. Apparently, the effect of aerosols and iodine on
PAR performance is not significant.

25

NEA/CSNI/R(2010)3

100
90
80

Recombination efficiency

Comparable test w/o aerosols, iodine
70
60
50
Test HR 32
40
30
20
10
start ofrecombination

0

Hydrogen concentration
Fig. 5-6: Test HR-32: Recombination efficiency and onset of recombination for test
HR 32 and for a comparable HR test without aerosols and iodine
5.6

Aerosol Wash-Down test

Fig. 5-7 shows the progression of different phases and the resulting pressure history during the test.
The pressure increase from t = −25.1 to t = −24.3 h is due to the injection of CsI-aerosol solution
together with air as carrier gas. At time t = −24.3, aerosol injection has been stopped and aerosols areallowed to be deposited on the surfaces in a dry vessel atmosphere.
Steam injection is started (wash-down phase) at time t = 0 h and pressure starts to increase. Before
starting the steam injection i.e. between t = −4 h and t =0 h, a flange was opened to remove thedeposition coupons. Cooling of the middle and lower vessel walls was started at time t = −2.50 h inorder to ensure maximum condensation on the vertical vessel walls. During this wash-down phase,steam mass flow rate was adjusted to 14 g/s (considering cooling power available for the vessel
jackets) to achieve vessel wall temperatures of 80˚C, which results in complete condensation of theinjected steam in a quasi-stationary condition.
The CsI aerosols deposition on the horizontal surface that includes plate sections and the puddle wasquantified by means of the coupons The aerosol horizontal surface loading measured with deposition
coupons was of the order of 80 g/m2. The specific surface loading of the vertical walls was 11 %,compared to 89% for the horizontal surfaces.
Slightly inclined surfaces are subject to aerosol wash-down in the time range of minutes to hours. The
measurements of CsI concentration in the condensate flow from the plate- and puddle sections show
the highest values at the beginning of the water flow. The concentration in the plate runoff water decreases
26

NEA/CSNI/R(2010)3

rapidly and reaches low nearly-constant levels after 2.5 hours. The concentration in the puddle runoff water
decreases much slower and shows enhanced values even after 23 hours of washing time. The puddle water
acts as an intermediate storage of aerosol material, which leads to a considerable delay in the wash-downtransport.
Laboratory experiments performed in parallel showed, that the characteristic time of the transport
process is shorter and the wash down more complete for high water flow rates on stainless steel
surfaces. For identical test conditions (aerosol surface loading, water flow rate), the painted surface
exhibited a higher wash down efficiency as compared to the stainless steel surface. The difference of
the wash down process on stainless steel and painted surfaces was found to be associated with theformation and dissolution mechanisms of rivulets across the surface.
Aerosol
injection(~ 49 min)2

072 BPA21H16

Coupons
removal1,9
1,8

Aerosoldeposition phase
phase

Pressurebar

1,7

Aerosol
washdown phase
phase

1,6
1,5
1,4
1,3
1,2
1,1
1
-25,00-20,00-15,00-10,00

-5,00

0,00

Time

5,00

10,00

h

Fig. 5-7: Aerosol Wash-Down Test: Test phases

27

15,00

20,00

25,00

NEA/CSNI/R(2010)3

6.

CONCLUSIONSThe experimental data obtained from the different series of tests demonstrated the capabilities of the
THAI facility in producing high-quality, high-resolution data on gas mixing/stratification issues, slowhydrogen deflagration, Passive Autocatalytic Recombiners and their interaction with fission products,
and fission product wash-down in a large-scale geometry. The database developed in the frame of theOECD-THAI project has been and will be extensively used to validate and improve Lumped
Parameter and CFD tools available and under development for containment analysis. The analyticalactivities performed by project partners provided very complete analyses of the experimental data by
carrying out pre- and post-test calculations of the test series performed. The enhanced tools validated
against experimental data will provide a more reliable approach to safety relevant issues in evaluationof the containment response and the planning of accident management measures.
A broad spectrum of issues has been addressed. The investigations have filled existing knowledge
gaps to a large extent. As an example, in case of the PAR investigations, an almost complete picture of
their performance under accident typical conditions has been obtained. The results of the experimental
program have provided assurances of PAR performance under realistic conditions. However, not all
open questions could be resolved; they remain open and have to be addressed in future investigations.
Some of these investigations are part of a planned OECD-THAI II project, for which −among others−
further experiments about a special hydrogen combustion phenomenon, PAR behaviour, and iodine
volatilization and transport are planned to be investigated. This project is envisaged to be commenced
in late 2010.

28

NEA/CSNI/R(2010)3

REFERENCES[All07]

H.-J. Allelein et al.: International Standard Problem ISP-47 on Containment Thermal
Hydraulics. Nuclear Energy Agency, Committee on the Safety of Nuclear Installations,Final Report NEA/CSNI/R(2007)10, 2007.

[Fis05]

K. Fischer et al.: International Standard Problem ISP-47 on Containment ThermalHydraulics, Step 2: ThAI, Volume 2: Comparison Report of Blind Phases I-IV. Becker
Technologies GmbH, Eschborn, Report Nr. BF-R 70031-2, June 2005.

[Kan08a]T. Kanzleiter et al.: Technical Report Helium/Hydrogen Material Scaling Test HM 1.
Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical Report No.
1501326 – HM-1 TR Rev. 1, January 2008.

[Kan08b]

T. Kanzleiter, K. Fischer: Quick Look Report Helium/Hydrogen Material Scaling Test
HM-2. Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical
Report No. 1501326 – HM-2 QLR, March 2008.

[Sab05]

J.C. Sabroux et al.: Iodine Chemistry in Hydrogen Recombiners, EUROSAFE 2005,
Brussels, November 2005.

[Sch08]

S. Schwarz: Comparison and Evaluation of Experimental Data and Blind Calculations of
OECD/NEA THAI Test HM-2, GRS, Technical Note TN1-08, December 2008.

[Sch09]S. Schwarz et al.: Benchmark on Hydrogen Distribution in a Containment Based on the
OECD/NEA THAI HM-2 Experiment, NURETH13, N13P1088, Kanazawa, Japan,
September 27 – October 2, 2009.

[Sch10]S. Schwarz et al.: Blind and Open Calculations of OECD/NEA THAI Test HM-2, GRS,Technical Note TN1-10, April 2010.

Notes:
By decision of the THAI Project Management Board the HM series report are available to nonsignatories without waiting for the non-disclosure deadline.
References to Project Report are listed in Appendix A.

29

NEA/CSNI/R(2010)3

APPENDIX A: LIST OF PROJECT REPORTS

These reports are restricted to the project signatories, however, the Management Board of the THAI Project
has agreed that these Quick Look Reports and Technical Reports will be disclosed for non-signatories after
31 December 2012 and can be obtained after this date upon request to the NEA secretariat.
Reports in alphabetical and chronological order[Fis08]K. Fischer: Comparison of Experimental Data and Blind Calculations of Test HM 2.
Becker Technologies GmbH, Eschborn, OECD/NEA-THAI Project, Technical Report
1501326-HM-2 CMR, May 2008.

[Gup09a]S. Gupta et al.: Quick Look Report: Hydrogen Recombiner Test HR-31, CsI-PAR
Interaction Test. Reactor Safety Research Project 150 1326, OECD/NEA THAI Project,
Report No. 150 1326–HR-QLR-5, Becker Technologies GmbH, Eschborn, Germany,
September 2009.

[Gup09b]

S. Gupta et al.: Quick Look Report: Hydrogen Recombiner Test HR-32, PAR Poisoning
Test. Reactor Safety Research Project 150 1326, OECD/NEA THAI Project, Report No.
150 1326–HR-QLR-6, Becker Technologies GmbH, Eschborn, Germany, October 2009.

[Gup09c]

S. Gupta, G. Langer: Quick Look Report: Aerosol Wash Down Test. Reactor Safety
Research Project 150 1326, OECD/NEA THAI Project, Report No. 150 1326 QLR-AW,
Becker Technologies GmbH, Eschborn, Germany, December 2009.

[Kan07]

T. Kanzleiter, K. Fischer: Quick Look Report Helium/Hydrogen Material Scaling Test
HM-1. Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical
Report No. 1501326 – HM-1 QLR, August 2007.

[Kan08a]T. Kanzleiter et al.: Technical Report Helium/Hydrogen Material Scaling Test HM 1.
Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical Report No.
1501326 – HM-1 TR Rev. 1, January 2008.

[Kan08b]

T. Kanzleiter, K. Fischer: Quick Look Report Helium/Hydrogen Material Scaling Test
HM-2. Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical
Report No. 1501326 – HM-2 QLR, March 2008.

[Kan08c]

T. Kanzleiter et al.: Technical Report Helium/Hydrogen Material Scaling Test HM 2.
Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical Report No.
1501326 – HM-2 TR, February 2008.

[Kan08d]

T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-2R and
HD-12. Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical
Report No. 1501326 – HD-QLR 1, April 2008.
T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-1R, HD4, HD-7, HD-8 and HD-10. Becker Technologies GmbH, Eschborn, OECD/NEA THAI
Project Technical Report No. 1501326 – HD-QLR 2, April 2008.

[Kan08e]30

NEA/CSNI/R(2010)3[Kan08f]

T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-15, HD16, HD-17, HD-18, HD-19, HD-20 and HD-24. Becker Technologies GmbH, Eschborn,
OECD/NEA THAI Project Technical Report No. 1501326 – HD-QLR 3, May 2008.

[Kan08g]

T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-25, HD26, HD-27, HD-28 and HD-29. Becker Technologies GmbH, Eschborn, OECD/NEA
THAI Project Technical Report No. 1501326 – HD-QLR 4, August 2008.

[Kan08h]

T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-22 andHD-23. Becker Technologies GmbH, Eschborn, OECD/NEA THAI Project Technical
Report No. 1501326 – HD-QLR 6, September 2008.

[Kan08i]

T. Kanzleiter, G. Langer: Quick Look Report Hydrogen Deflagration Tests HD-3, HD-5,
HD-6, HD-9, HD-11, HD-13/14 and HD-21. Becker Technologies GmbH, Eschborn,
OECD/NEA THAI Project Technical Report No. 1501326 – HD-QLR 5, November
2008.

[Kan09a]T. Kanzleiter, G. Langer: Hydrogen Deflagration Tests in the THAI Test Facility. Reactor
Safety Research Project 150 1326, OECD/NEA THAI Project Technical Report No. 150
1326–HD-1, Becker Technologies GmbH, Eschborn, Germany, February 2009.

[Kan09b]

T. Kanzleiter: Quick Look Report: Hydrogen Recombiner Tests HR-1 to HR-5, HR-27
and HR-28 (Tests without steam). Reactor Safety Research Project 150 1326,
OECD/NEA THAI Project Report No. 150 1326–HR-QLR-1, Becker Technologies
GmbH, Eschborn, Germany, February 2009.

[Kan09c]

T. Kanzleiter: Quick Look Report: Hydrogen Recombiner Tests HR-6 to HR-13, HR-29
and HR-30. Reactor Safety Research Project 150 1326, OECD/NEA THAI Project Report
No. 150 1326–HR-QLR-2, Becker Technologies GmbH, Eschborn, Germany, August
2009.

[Kan09d]

T. Kanzleiter: Quick Look Report: Hydrogen Recombiner Tests HR-17 to HR-26.
Reactor Safety Research Project 150 1326 OECD/NEA THAI Project, Report No. 150
1326–HR-QLR-3_r1, Becker Technologies GmbH, Eschborn, Germany, October 2009.

[Kan09e]T. Kanzleiter: Quick Look Report: Hydrogen Recombiner Tests HR-14 to HR-16.
Reactor Safety Research Project 150 1326, OECD/NEA THAI Project Report No.
150 1326–HR-QLR-4, Becker Technologies GmbH, Eschborn, Germany, October 2009.

31

NEA/CSNI/R(2010)3

THAI Test numbers referenced to reports

HM Tests (Hydrogen/Helium Material scaling )
Test
No.
HM 1
HM 2
HM 3
HM 4
HM 5

Documented in
Quick-Look Report
1501326 QLR-HM-1/August 2007
1501326 QLR-HM-2/February 2008

Technical Report
1501326-HM-1 TR/January 2008
1501326-HM-2 TR/February 2008
1501326-HM-1 TR/January 2008

Final Report
1501326FR-1/FR-2,
April 2010

HD Tests (HydrogenDeflagration)
Test
No.
HD 1R
HD2R
HD 3
HD 4
HD 5
HD 6
HD 7
HD 8
HD 9
HD 10
HD 11
HD 12
HD 13
HD 14
HD 15
HD 16
HD 17
HD 18
HD 19
HD 20
HD 21
HD 22
HD 23
HD 24
HD 25
HD 26
HD 27
HD 28
HD 29

Documented in
Quick-Look Report
1501326 HD-QLR-2/April 2008
1501326 HD-QLR-1/April 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-2/April 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-2/April 2008
1501326 HD-QLR-2/April 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-2/April 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-1/April 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-5/August 2008
1501326 HD-QLR-6/September 2008
1501326 HD-QLR-6/September 2008
1501326 HD-QLR-3/May 2008
1501326 HD-QLR-4/August 2008
1501326 HD-QLR-4/August 2008
1501326 HD-QLR-4/August 2008
1501326 HD-QLR-4/August 2008
1501326 HD-QLR-4/August 200832

Technical Report

Final Report

1501326-HD-2 /January 2010
(incl. results of HD 22 and HD 23)

1501326
FR-1/FR-2,
April 2010

NEA/CSNI/R(2010)3

HR Tests (Hydrogen Recombiner)
Test No.

Documented inTechnical Report

HR 1
HR 2
HR 3
HR 4
HR 5
HR 6
HR 7
HR 8
HR 9
HR 10
HR 11
HR 12
HR 13
HR 14
HR 15
HR 16
HR 17
HR 18
HR 19
HR 20
HR 21
HR 22
HR 23
HR 24
HR 25
HR 26
HR 27
HR 28
HR 29
HR 30

Final Report

1501326 HR-QLR-1/February 2009

1501326 HR-QLR-2/August 2009

1501326 HR-QLR-4/October 2009

1501326 FR-1/FR-2, April 2010

1501326 HR-QLR-3/October 2009

1501326 HR-QLR-1/February 2009
1501326 HR-QLR-2/August 2009

HR 31

1501326 HR-QLR-5/September 2009

1501326 FR-1/FR-2, April 2010

HR 32

1501326 HR-QLR-6/October 2009

1501326 FR-1/FR-2, April 2010

AW

1501326 AW-QLR/December 2009

1501326 FR-1/FR-2, April 201033