Nuclear Safety
NEA/CSNI/R(2021)8
August 2023
www.oecd-nea.org

OECD/NEA THAI-3 Project Final Reporton Fission Product Behaviour, Hydrogen
Mitigation, and Hydrogen Combustionin Water Cooled Reactors under Severe
Accident Conditions

NEA/CSNI/R(2021)8  1
Nuclear Energy Agency

NEA/CSNI/R(2021)8
Unclassified

English text only
2 August 2023

NUCLEAR ENERGY AGENCYCOMMITTEE ON THE SAFETY OF NUCLEAR INSTALLATIONS

OECD/NEA THAI-3 Project Final Report on Fission Product Behaviour,
Hydrogen Mitigation, and Hydrogen Combustion in Water Cooled Reactors
under Severe Accident Conditions

This document is available in PDF format only.

JT03523942
OFDE

Unclassified
This document, as well as any data and map included herein, are without prejudice to the status of or sovereignty over any territory,
to the delimitation of international frontiers and boundaries and to the name of any territory, city or area.

2  NEA/CSNI/R(2021)8
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OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  3

COMMITTEE ON THE SAFETY OF NUCLEAR INSTALLATIONS (CSNI)The Committee on the Safety of Nuclear Installations (CSNI) addresses Nuclear Energy Agency (NEA)
programmes and activities that support maintaining and advancing the scientific and technical knowledge
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The Committee constitutes a forum for the exchange of technical information and for collaboration
between organisations, which can contribute, from their respective backgrounds in research, development
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and safety R&D programmes of various sizes in order to keep all member countries involved in and abreastof developments in technical safety matters.
The Committee reviews the state of knowledge on important topics of nuclear safety science andtechniques and of safety assessments, and ensures that operating experience is appropriately accounted forin its activities. It initiates and conducts programmes identified by these reviews and assessments in order
to confirm safety, overcome discrepancies, develop improvements and reach consensus on technical issuesof common interest. It promotes the co-ordination of work in different member countries that serve tomaintain and enhance competence in nuclear safety matters, including the establishment of joint
undertakings (e.g. joint research and data projects), and assists in the feedback of the results to participatingorganisations. The Committee ensures that valuable end-products of the technical reviews and analyses areprovided to members in a timely manner, and made publicly available when appropriate, to support broader
nuclear safety.
The Committee focuses primarily on the safety aspects of existing power reactors, other nuclear
installations and new power reactors; it also considers the safety implications of scientific and technicaldevelopments of future reactor technologies and designs. Further, the scope for the Committee includes
human and organisational research activities and technical developments that affect nuclear safety.

OECD/NEA THAI-3 PROJECT FINAL REPORT4  NEA/CSNI/R(2021)8

Foreword
The Organisation for Economic Co-operation and Development (OECD) Nuclear Energy
Agency (NEA) launched the THAI-3 (Thermal-hydraulics, Hydrogen, Aerosols andIodine) project in 2016 as a follow-up to the THAI-2 project. The THAI-3 project aimed toinvestigate open questions on hydrogen and fission product issues, with special emphasison hydrogen passive autocatalytic recombiner performance, hydrogen deflagration
behaviour, fission product re-entrainment and resuspension behaviour under accident
conditions in the containment of water cooled reactors at the extended THAI+ plant at
Becker Technologies in Eschborn, Germany.
With an international partnership of more than 20 organisations from 16 countries, theexperimental database produced during the project provides valuable support for validationand further development of lumped parameter and computational fluid dynamics
approaches based severe accident codes.
Furthermore, the project contributed to the national competence and expertise in the fieldof reactor safety in NEA member countries and promoted international co-operation
between them.
The authors of the present project’s final summary report are:
S. Gupta, G. Poss, M. Freitag, E. Schmidt, M. Colombet, B. von Laufenberg, A. Kühnel
and G. Langer, all from Becker Technologies GmbH, and F. Funke and G. Langrock, bothof Framatome GmbH.
The report was reviewed by the project participants and approved by the NEA Committee
on the Safety of Nuclear Installations (CSNI) in December 2020.
Becker Technologies acknowledges the support provided by the NEA during execution of
the project. Furthermore, the financial support and technical input provided by all THAI-3
project partners is gratefully acknowledged.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  5

Executive summary
Background
Despite significant improvements in computer codes, there are still deficiencies inmodelling certain phenomena related to hydrogen and fission product behaviour during
severe accidents in containments of water cooled reactors. In this context, the realistic
boundary conditions employed in experiments to validate the concerned computer models
play a significant role by providing a reliable basis for containment safety analysis.
Uncertainties still exist in the modelling of slow hydrogen deflagration and passive
autocatalytic recombiner (PAR) performance behaviour under severe accident conditions.
Regarding fission product remobilisation behaviour, the outcomes of Fukushima Daiichi
accident analyses (e.g. the NEA BSAF and BSAF-2 projects) have revealed uncertainties
during the late phase of the accident, where small but long-term release of fission products
may play a vital role in determining the source term to the environment. The experimental
investigations carried out in the framework of the NEA THAI-3 project aim to resolve someof the remaining issues related to hydrogen and fission products with specific emphasis on
PAR performance, hydrogen deflagration behaviour, and fission product remobilisation
behaviour from water pools and surfaces. The aim of carrying out such coupled-phenomena
experiments in the framework of an international programme is twofold: to enhance
confidence in the performance of safety and mitigation systems during severe accidents;
and to establish a common database accessible by a large research community to support
further development and validation of lumped parameter (LP) and computational fluid
dynamics (CFD) codes.
The NEA THAI-3 project was conducted from 1 February 2016 until 31 July 2019 under
the auspices of the Nuclear Energy Agency (NEA). The project was supported by thesignatories from Belgium, Canada, China, the Czech Republic, Finland, France, Germany,
Hungary, India, Japan, Korea, Luxembourg, the Slovak Republic, Sweden, Switzerland andthe United Kingdom. Becker Technologies GmbH acted as operating agent.

Objective of the work
The overall objective of the NEA THAI-3 project was to address open questions concerning
the behaviour of hydrogen, iodine and aerosols under severe accident conditions in thecontainment of water cooled reactors. Understanding the processes taking place during
such events is essential to evaluating the challenge posed on containment integrity (due tohydrogen combustion) and for evaluating the amount of airborne radioactivity (iodine andaerosols) during such severe accidents with core damage and the associated source term.
The project also aimed to contribute to the validation and further development of advanced
LP- and CFD- codes used for reactor applications, e.g. by providing experimental data forcode benchmark exercises. Furthermore, the project aimed to maintain and extend thecompetence and expertise in the field of reactor safety in the NEA member countries andto promote international co-operation between these countries.

OECD/NEA THAI-3 PROJECT FINAL REPORT6  NEA/CSNI/R(2021)8Work performed
Tests were performed in the technical-scale THAI+ containment test facility, which consistsof the original THAI vessel (TTV), to which a smaller vessel, designated as a parallel
attachable drum (PAD), is interconnected by a lower and upper DN500 pipe. The facility
is operated by Becker Technologies GmbH in Eschborn, Germany, under the sponsorshipof the German Federal Ministry for Economic Affairs and Energy.
Within the NEA THAI-3 project, the following test series have been performed:
Hydrogen deflagration tests in two-vessel geometry (HD 40-45);

Hydrogen PAR tests (HR 46-50);

Soluble and gaseous fission product (CsI, iodine) release from a boiling pool (WH24 and WH-28, Iod-32);

Resuspension of iodine from decontamination paint by H2 deflagration (Iod-34);

Resuspension of aerosol deposits from surfaces by hydrogen deflagration (HD-46).

Furthermore, two HD tests (HD-36 and HD-38) and one HR test (HR-43) conducted in theframework of the THAI National (phase V) project have been shared with the NEA THAI-3
project partners at no additional cost.
Extensive analysis by partners in the framework of the Analytical Working Group (AWG)
accompanied the experimental programme.

Results
Hydrogen deflagration tests (HD 40-45) in multi-compartment geometry
The hydrogen deflagration test series investigated the effects of superimposed flow on
flame propagation. These effects are generally not considered in the existing models andneed to be quantified, creating experimental databases for further modelling efforts.
Furthermore, the tests addressed the effects of hydrogen deflagrations in a two-vessel
configuration, including stratifications of gas concentration and gas temperature. The peakpressures measured in all HD tests remained clearly below the adiabatic isochoric complete
combustion (AICC) pressures. The pressure increase gradient does not differ markedly forthe single vessel and the two-vessel configuration. Flame acceleration and combustion
modes similar to jet ignition were also observed in this test series.

Hydrogen passive autocatalytic recombiner tests (HR 46-50)
An operating PAR subjected to counter-current flow conditions as may typically occur inindividual compartments of the containment of a nuclear power plant was the subject ofinvestigation in tests HR-46 to HR-50 by using AREVA and NIS PARs. The countercurrent flow velocity was up to 1 m/s in the PAR outlet vicinity. The test results indicatethat the PAR with top cover on the chimney and lateral outlets provided effective means toprotect the PAR from intrusion of counter-current flow within the range of investigatedconditions. The impact of chimney height on PAR performance under counter-current flow
conditions was also quantified.

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Soluble fission product (CsI, Iodine) release from a boiling pool (WH-24, WH28, Iod-32)
Three tests were conducted to investigate wet resuspension or re-entrainment of aerosols(WH-24 and WH-28), and release of volatile gaseous iodine (Iod-32) from a water pool
under boiling conditions. As compared to test WH-24, which was conducted with demineralised water, test WH-28 was conducted with surfactants reducing the surface tensionof the water. The aerosol entrainment in the WH-28 test was about one order of magnitude
higher compared to test WH-24. Results from different particle measurement techniques
that
have
been
used
to
evaluatetheentrainment
intests
WH-24 and WH-28, indicate that the absolute entrainment is subject to an uncertainty bya factor of 2 - 5.
Test Iod-32 investigated the release of volatile iodine from a subcooled and boiling sump.
Under boiling conditions, the I2 concentration in the gas was higher by a factor of 100
compared to the end of the reference phase. However, this value has to be considered
carefully for reactor application as the conditions of test Iod-32 could influence this result.
The adsorption/desorption of I2 from the steel walls in the PAD gas atmosphere might
influence this result as well as the suspected stratification of the gaseous phase just above
the sump-gas interface, whose effect would be to underestimate the iodine gaseousconcentration in non-boiling conditions.

Resuspension of iodine from painted surfaces by hydrogen deflagration(Iod-34)
Test Iod-34 was aimed at studying the resuspension of iodine from painted surfaces by ahydrogen deflagration. The H2 deflagration induced a significant iodine release from thesurfaces to the gas phase. The iodine release fraction amounts to a range between 4 and
9%, considering experimental uncertainties of the initial iodine loadings on the painted andsteel surfaces. Out of the total resuspended amount, 50% of the iodine released by H2deflagration is in the form of gaseous organic iodide. The persistent iodine aerosol
concentration after deflagration indicates very fine particles. The release of iodine frompaint in aerosol form due to hydrogen deflagration is a new path for iodine containment
codes. The paint degradation probably also changes the conditions and the mechanism forthermal release of volatile organic iodide from paint. Modelling improvements towards
estimation of reliable release of volatile organic iodide from paint are considered necessaryfor extrapolating to deflagration-relevant temperatures. The investigated iodine releasemechanism due to H2-deflagration indicates complex behaviour (e.g. interaction of released
iodine with fresh or degraded paint) and the associated uncertainties may be subject tofuture experimental work.

Aerosol resuspension by hydrogen deflagration (HD-46)
The objective of test HD-46 was to study the resuspension of aerosols that have been
deposited on vertical, horizontal and containment typical step grating surfaces and thethermal decomposition of CsI particles by hydrogen deflagration. Among other effects,
resuspension may result in an increase in aerosol concentrations in the containment
atmosphere, which in turn may have an influence on the source term from containment to
the environment, if an accident management measure such as containment venting is
considered. The hydrogen deflagration resuspended about 4% of the previously deposited
CsI. The resuspended particles settled at much slower velocity due to the sub-micron rangeof particle sizes. The release of gaseous iodine by thermal decomposition of CsI particles
due to the high temperatures during hydrogen deflagration was measured in the range ofabout 2%.
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Analytical activities
An extensive analytical effort accompanied the experimental programme, consisting ofcode calculations to support test design, for pre-test assessments, result evaluation andextrapolation to reactor conditions. Data on fission product release from boiling pools andon fission product remobilisation from surfaces due to hydrogen combustion offer a unique
database to assess in containment airborne radioactivity during a severe accident. Data on
fission product release from boiling pools have been used in severe accident code
calculations of the Fukushima Daiichi Nuclear Power Plant accident in the assessment ofcontinued releases in the days following the accident.
Two code benchmark exercises have been conducted during the project. For this purpose,experimental data of a hydrogen deflagration test (HD-44) and of a hydrogen recombiner
test (HR-49) were selected for blind and open post-test calculations.

Conclusions and recommendations
The NEA THAI-3 project as a continuation of the THAI-2 project has extended theknowledge and data base of severe accident-related issues. As regards PAR, further data
about its behaviour under counter-current flow conditions have been obtained, whichallows for better assessment of hydrogen mitigation measures and implementation of
appropriate models in accident analysis codes. The tests regarding hydrogen deflagration
behaviour in the two-vessel geometry provide data for a sound safety-related assessmentof flame acceleration and pressure increase in multi-compartment geometry. The tests
concerning both molecular and aerosol-bound iodine release from a boiling sump provide
valuable data for the quantification of a potential accident source term. This refers also to
the resuspension of iodine from paint and the resuspension of pre-deposited aerosols in thecourse of a hydrogen deflagration. The database developed in the framework of the NEA
THAI-3 project has been and will be extensively used for improvement, further
development and validation of LP and CFD codes applied in reactor safety analysis,
increasing confidence in these tools.
Remaining open questions with a specific focus on the late phase of a severe accident will
be further addressed in upcoming projects. The issues proposed are related to investigations
on PAR performance, and PAR interactions with iodine oxides (IOx) and nuclear
background aerosol. With respect to hydrogen behaviour, experiments are planned on
combustion and flame propagation in a H2-CO containing atmosphere. Concerning source
term related issues, studies are planned on the retention of fission products in a water pool
under pool-scrubbing conditions and the IOx behaviour in containment atmosphereincluding interaction with “nuclear background aerosol” and the thermal stability of IOx.
The NEA THEMIS project is currently being conducted to consider the aforementioned
issues.

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List of abbreviations and acronyms
AERB

Atomic Energy Regulatory Board (India)

AICC

Adiabatic isochoric complete combustion

AWG

Analytical Working GroupBARC

Bhabha Atomic Research Centre (India)

BSAF

Benchmark Study of the Accident at the Fukushima Daiichi
Nuclear Power Station

BWR

Boiling water reactor

CFD

Computational fluid dynamics

COCOSYS

COntainment COde SYStem

CSNICommittee on the Safety of Nuclear Installations (NEA)

EPRI

Electric Power Research Institute (United States)

FTIR

Fourier-transform infrared spectroscopy

GRS

Gesellschaft für Anlagen- und Reaktorsicherheit (Germany)GS

Gas scrubber

HD

Hydrogen deflagration testHR

Hydrogen passive autocatalytic recombiner test

IRSN

Institut de Radioprotection et de Sûreté Nucléaire (France)

KAERI

Korea Atomic Energy Research Institute

KHNP

Korea Hydro and Nuclear Power Co., Ltd

KIT

Karlsruhe Institute of Technology (Germany)

LP

Lumped parameter

METUSA

Minimal encroaching turnable stream-wise anemometers

MMD

Mass median diameter

NEA

Nuclear Energy AgencyNIS

NIS Ingenieurgesellschaft MBH (Germany)

NUBIKI

Nuclear Safety Research Institute (Hungary)OECD

Organisation for Economic Co-operation and Development

PAD

Parallel attachable drum

PAR

Passive autocatalytic recombiner

PWR

Pressurized water reactor

QLR

Quick Look Reports

SSMStrålsäkerhetmyndigheten (Sweden)

THAI

Thermal-hydraulics, Hydrogen, Aerosols and Iodine

OECD/NEA THAI-3 PROJECT FINAL REPORT10  NEA/CSNI/R(2021)8
TTV

THAI test vessel

VTT

Teknologian Tutkimuskeskus VTT Oy (Finland)

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Table of contents
Foreword ................................................................................................................................................ 4
Executive summary ............................................................................................................................... 5
List of abbreviations and acronyms ..................................................................................................... 9
1. Introduction ......................................................................................................................................13
2. Objectives ..........................................................................................................................................18
3. Test configuration, test procedure and test results .......................................................................193.1. Test facility general overview ......................................................................................................19
3.2. Hydrogen deflagration (HD) tests ................................................................................................23
3.3. Hydrogen recombiner (HR) tests .................................................................................................26
3.4. Tests with aerosol release from a pool (WH-tests) ......................................................................29
3.5. Iodine release from a boiling pool – test Iod-32 ..........................................................................33
3.6. Iodine resuspension - test Iod-34 .................................................................................................36
3.7. Aerosol resuspension by hydrogen deflagration - test HD-46 .....................................................39
4. Conclusions .......................................................................................................................................60
4.1. HD experiments ...........................................................................................................................60
4.2. HR experiments ...........................................................................................................................61
4.3. Soluble and gaseous fission product (CsI, iodine) release from a boiling pool ...........................62
4.4. Resuspension of iodine from paint by hydrogen deflagration .....................................................63
4.5. Resuspension of aerosol deposits from surfaces by hydrogen deflagration ................................64
References .............................................................................................................................................65
Annex A. List of project reports .........................................................................................................68
Project deliveries.................................................................................................................................68
Technical Reports (TR) ......................................................................................................................69
Final project report..............................................................................................................................69

TablesTable 1.1. NEA THAI-3 signatories
Table 1.2. German Partners in the NEA THAI-3 Project
Table 1.3. Test matrix developed for the NEA THAI-3 project
Table 3.1. Test conditions as specified and measured for the HD test series
Table 3.2. Test conditions as specified and as measured for the HR test series
Table 3.3. Specified test conditions for the phases of test WH-28
Table 3.4. Specified test conditions in PAD
Table 3.5. Specified test conditions in TTVTable 3.6. Specified test conditions in TTVTable 3.7. HD-46: Specified test conditions in TTV

144
155
155
24
28
31
35
35
38
40

FiguresFigure 3.1. THAI+ configuration and dimensions of the system
Figure 3.2. Arrangement of the two-vessel facility within the THAI-building
Figure 3.3. HD-40 to HD-45 test configuration: Positions of igniters, supply systems, DN150 connection pipe and 3bladed fan
OECD/NEA THAI-3 PROJECT FINAL REPORT

42
43
44

12  NEA/CSNI/R(2021)8
Figure 3.4. HD-43, HD-22 and HD-36: Pressure transient
45
Figure 3.5. HD-43 to HD-45, HD-36, HD-22: Flame front propagation
45
Figure 3.6. HD-36, HD-43 to HD-45: Peak pressures for different initial flows as function of volumetric flow.
46
Figure 3.7. PAR unit (example NIS) and blower position. No blower was installed in HR-50.
47
Figure 3.8. NIS PAR 1/8 module used in test HR-46 with 1 m chimney (left) and in test HR-47 with 0.25 m chimney(right)48
Figure 3.9. ½ FR-380 size AREVA PAR unit used in HR tests HR-48 to HR-50
49
Figure 3.10. H2 depletion efficiency of NIS PAR tests HR-14, HR-15, HR-46, and HR-47
50
Figure 3.11. Recombination rate at the start-up of AREVA PAR tests HR-7, HR-8, HR-43, and HR-48
50
Figure 3.12. Depletion efficiency of AREVA PAR tests HR-7, HR-8, HR-43, and HR-48
51
Figure 3.13. WH-24, WH-28: Gas injections and gas releases
52
Figure 3.14. Primary bubbles leaving the downcomer during phases of low non-condensed volumetric gas flow, a3), a4)
and b1)52
Figure 3.15. Initial bubbles leaving the downcomer exit, phases a1), a2), a5), b2), b3), and b4.
54
Figure 3.16. Mass median diameter of particles as function of the superficial velocity, for boiling and subcooled poolconditions
535
Figure 3.17 Average bubble diameters at ImgLow (H = 0.675 m) and ImgUpp (H = 2.125 m) in comparison to THAI
tests WH7-WH15 measured 100 mm below the water surface
545
Figure 3.18. Iod-32: Gas injections and gas releases
556
Figure 3.19. Iodine concentrations in PAD atmosphere567
Figure 3.20. I2 masses in PAD sump, measured data, down-scaled COCOSYS pre-test design calculation by GRS, andexponential fit to measured data
567
Figure 3.21. Iod-34: Test configuration: Iodine injection, sump recirculation, online radiation detectors, large painted
surfaces and sampling stations
58
Figure 3.22. Iod-34: Photographs of painted coupons, comparison of surface degradation, before deflagration (left), after
deflagration (right)
98
Figure 3.23. HD-46 test configuration: CsI injection, horizontal gratings, laser extinction measurement, aerosol sampling
filter and impactor station
60

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1. Introduction

Over the past fifteen years, THAI experimental data have been continuously used for thevalidation and development of containment safety analysis tools with a specific focus on
severe accident conditions. Significant progress in measuring spatial hydrogen
distributions, slow hydrogen deflagration behaviour, performance of PARs under accident
conditions, and fission product distribution and interaction with operating safety devices
has been achieved with the THAI test facility. Improved models based on THAI
experimental data have demonstrated reliable simulations of complex experiments, e.g.
hydrogen distribution (NEA THAI HM-2 code benchmark), hydrogen combustion
behaviour (ISP-49), and hydrogen recombiner performance (NEA THAI-2 HR-35
benchmark).
Despite significant improvements in available computer codes, there are still deficiencies
in modelling certain phenomena. In this context, the realistic boundary conditions
employed in experiments to validate the concerned computer models play a significant roleby providing a reliable basis for containment safety analysis. Uncertainties still exist in themodelling of slow hydrogen flame propagation in compartmentalised geometries for which
not much experimental data at technical/large scale facilities are available in open
literature. In particular, the effects of superimposed flow conventions on the flame
propagation are generally not considered in the existing models and require quantificationof their influence and experimental database for further modelling efforts.
Code validation and development work based on previous THAI/PAR tests under naturalconvection flow conditions and varying containment atmosphere (e.g. O2 lean or O2 rich)demonstrated significant progress towards PAR performance analysis and their response to
severe accident conditions. Nevertheless, studies of representative accident sequencesindicate that performance of PARs might be affected by adverse flow conditions,e.g. counter-current flow. Therefore, an experimental database related to PAR onset andPAR performance (H2 recombination rate, H2 depletion efficiency) under counter-current
flow conditions is required to be investigated in order to enhance the predictive capabilities
of safety analysis tools.
Regarding open issues related to fission products, environmental measurements madeduring the Fukushima Daiichi Nuclear Power Plant accident revealed that a significant
amount of radionuclides was released into the environment. However, estimates of thisreleased amount proved uncertain not only due to limited knowledge about the accident
scenario but also because of uncertainties in quantifying fission product retention andrelease from water pools under accident conditions. Relatively larger uncertainties wereobserved during the late phase of the accident, where small but long-term release sourcesof fission products may play a vital role in determining source term to the environment.
The need for a more comprehensive understanding of fission product release from water
pools was emphasised by post-Fukushima analysis carried out by individual organisations
or in the framework of international projects, e.g. NEA BSAF (NEA, 2016). Particularinterest has centred on an experimental database for (soluble/non-soluble) aerosols as well
as gaseous iodine re-entrainment from water pools under different thermal conditions(e.g. subcooled, boiling), chemical boundary conditions and the characteristics of release
gas into the water pool (e.g. mass flow, non-condensable gas fraction). Another open issue
related to source term was to quantify the resuspension behaviour of aerosols and gaseousiodine pre-deposited over containment surfaces. Fission product resuspension may
influence the “delayed” source term from containment to the environment, in case of

OECD/NEA THAI-3 PROJECT FINAL REPORT14  NEA/CSNI/R(2021)8
containment breach or if an accident management measure such as containment venting is
considered.
To resolve the remaining open issues, the NEA THAI-3 project focuses on hydrogen andfission product issues with a special emphasis on PAR performance, hydrogen deflagration
behaviour, and fission product remobilisation behaviour from water pools and surfaces.
The need to carry out such coupled phenomena experiments in the framework of aninternational programme is twofold: to enhance confidence in the performance of passive
mitigation systems during severe accident scenarios and to establish a common databaseaccessible by a large research community to support further development and validation of
LP and CFD codes.
The NEA THAI-3 project was conducted from 1 February 2016 until 31 July 2019 under
the auspices of the OECD Nuclear Energy Agency. The tests were performed in thetechnical-scale THAI/THAI+ test facility (two stainless steel vessels, with total volume of
80 m³) with exchangeable internals for multi-compartment investigations. The
THAI/THAI+ test facility is designed for a maximum overpressure of 1.4 MPa at 180 °C
and can withstand moderate hydrogen deflagrations. Experiments were performed by useof representative aerosol, iodine and H2 concentrations and thermal hydraulic conditions.
Spatio-temporal fission product behaviour was studied by use of the radiotracer I-123.
The NEA THAI-3 project was supported by the signatories, i.e. safety organisations andresearch laboratories from 15 countries (see Table 1.1) and received technical contributions
from the German partners as listed in Table 1.2.
Table 1.1. NEA THAI-3 signatories
Signatories

Country

The Bel V

Belgium

The Canadian Nuclear Laboratory (CNL)The State Nuclear Power Software Development Centre (SNPSDC)The ÚJV Rež, a. s. Czech Republic

CanadaChina
Czech
Republic
FinlandFranceGermany

The Teknologian tutkimuskeskus VTT Oy
The Institut de Radioprotection et de Sûreté Nucléaire (IRSN) jointly with Electricité de France (EDF)
Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH
Becker Technologies GmbHThe Nuclear Safety Research Institute (NUBIKI), jointly with the MVM Paks Nuclear Power Plant Ltd.
The Atomic Energy Regulatory Board (AERB) jointly with the Bhabha Atomic Research Centre (BARC),
and the Nuclear Power Corporation of India Ltd. (NPCIL)
Nuclear Regulation Authority (NRA)The Korea Atomic Energy Research Institute (KAERI) jointly with Korea Hydro and Nuclear Power Co., Ltd(KHNP) and Korea Institute of Nuclear Safety (KINS)
Ministère de l’Enseignement Supérieur et de la Recherche (MESR)
Nuclear Regulatory Authority of the Slovak Republic (ÚJD SR)
The Strålsäkerhetmyndigheten (SSM)
Paul Scherrer Institut (PSI)
Office for Nuclear Regulation (ONR)

Hungary
India
Japan
Korea
Luxembourg
SlovakRepublic
SwedenSwitzerland
UnitedKingdom

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  15

Table 1.2. German Partners in the NEA THAI-3 Project
Project partners

City

Becker Technologies GmbH (operating agent)

Eschborn

Framatome GmbH

Erlangen

RUB Ruhr-Universität-Bochum

BochumGesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH

CologneKarlsruhe Institute of Technology (KIT)

Karlsruhe

The operating agent was supported by Framatome’s Radiochemical Laboratory, Erlangen,Germany, to operate the iodine instrumentation, to perform chemical analyses, and toevaluate and assess the iodine results.
The contributions provided by GRS, RUB and KIT included design calculations and posttest calculations with the respective codes.
Table 1.3 provides the details of the test matrix designed to improve insight into issues
related to hydrogen and fission products. In addition to the experimental work, anaccompanying analytical working group (AWG) was established with voluntary technicalcontributions from project partners in the framework of the NEA THAI-3 project. The
AWG aimed at performing design calculations, the evaluation of the test results for further
development, blind and open code benchmarks, and validation of the predictive capabilities
of advanced LP- and CFD codes currently applied in reactor safety. For this purpose,experimental data of a hydrogen deflagration test (HD-44) and of a hydrogen recombiner
test (HR-49) have been selected for blind and open post-test calculations in the frameworkof NEA THAI-3 benchmark exercises (Freitag and Sonnekalb, 2018), (Freitag andSonnekalb, 2019).
Furthermore, two HD tests (HD-36 and HD-38) and one HR test (HR-43) conducted in theframework of the THAI National (phase V) project have been shared with the NEA THAI3 project partners at no additional cost (Gupta et al., 2017), (Freitag et al., 2016), (Freitag
et al., 2017c).
Table 1.3. Test matrix developed for the NEA THAI-3 project
Test
series/Test
no.
1

Test series/test
designation

No.
of
tests

HD Tests (HD 40 - 45): Hydrogendeflagration and flame propagation in twocompartment system

62

HR Tests (HR 46 - 50): Recombiner
behaviour5

OECD/NEA THAI-3 PROJECT FINAL REPORTObjectives

Influence of convective flows on flame propagation.
Influence of scale on flame acceleration effects.
Influence of two-compartment configuration on deflagration
behavior.
Influence of stratification of gas concentrations andtemperature.
Comparison to single-compartment tests.
Behaviour of two different commercial PAR units undercounter-current and natural convection flow
conditions.
To validate codes on the available experimental database
and to evaluate the influence of counter-current flow
on PAR performance.
To evaluate the influence of the chimney height onto theself-induced PAR flow under counter-current flow.
Comparison to single-compartment tests.

16  NEA/CSNI/R(2021)8
Table 1.3. Test matrix developed for the NEA THAI-3 project (Continued)
Test
series/
Test
no.
3

Test series/test
designation

No.
of
tests

WH-Tests (WH-24 and WH-28): Reentrainment of fission products fromwater pools

2

4

Test Iod-32: Volatile Iodine releasefrom boiling water pool
Test Iod-34: Iodine resuspension byhydrogen deflagration

1

Test HD-46: Aerosol resuspension andthermal decomposition by hydrogendeflagration

1

5

6

1

Objectives

Quantify the re-entrainment of soluble fission product CsI fromwater pools at elevated temperature.
Investigate the effect of surface tension on the re-entrainmentof CsI from the pool.
Contribute to the validation and further development ofdedicated empirical or semi-mechanistic models ofadvanced LP- and CFD codes.
Quantification of gaseous iodine release from a boiling waterpool for different boiling rates and different pH-values.
Quantification of resuspension of iodine from painted surfaces
pre-loaded with iodine in a representative manner byhydrogen deflagration.
Degradation of paint by H2-deflagration.
Quantification of CsI-aerosol resuspension and its thermal
decomposition to gaseous I2 in high-temperatureenvironment of a hydrogen deflagration.

The experimental data obtained from the different test series demonstrated the capabilityof the THAI/THAI+ facility to produce high quality, high resolution data on the issues
mentioned in Table 1.3. The tests provide a better physical understanding and data for thevalidation and further development of analytical tools related to:The phenomenology of hydrogen deflagration in a two-vessel geometry withinteracting flame fronts. The tests provide a comprehensive database for further
development and validation of combustion models implemented in containment
system codes. Test conditions and parameters were defined considering severe
accident thermal hydraulic conditions. For the tests, initial conditions were set to
1.5 bar pressure, 90 °C temperature, 10 vol.-% H2 concentration and 25 vol.-%steam concentration in premixed gas atmosphere, and up to 12 vol.-% hydrogenconcentration in stratified atmosphere. The test parameters that varied were burndirection (upward or downward), initial turbulence, initial gas flow velocities andsteam- and temperature stratification.

The behaviour of two commercially available PAR units (AREVA and NIS) under
different flow conditions, e.g. counter-current flow, superimposed natural andforced convection, chimney height effect. The parameters that varied were pressure
and temperature. The test series evaluate the influence on PAR performance of thedifferent initial flow conditions as may exist in a multi-compartment geometry,
including onset of recombination, recombination rate and H2 depletion efficiency,
effect of initial pressure and temperature on PAR performance.



The re-entrainment of dissolved CsI from a heated/boiling pool by injection of airand steam/air mixtures using a down-scaled DN 100 downcomer pipe in the test
WH-24. Droplets with dissolved CsI evaporate in a superheated atmosphere, andparticles are measured (for concentration, size distribution) with various
techniques. Particle re-entrainment from a flashing pool, induced by vented
depressurisation, is investigated. In test WH-24, de-mineralised water was used andin test WH-28 a surfactant was added to reduce the surface tension of the water.
The corresponding test Iod-32 was performed with gaseous iodine being released
from a heated/boiling pool.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  17

The resuspension of iodine from painted surfaces through the impact of a hydrogendeflagration, where the vessel surfaces and the installed painted surfaces were preloaded with gaseous iodine, was the subject of test Iod-34. Hydrogen deflagrationinduces a short but strong impact through high temperatures and high atmosphericflow speeds. Iodine measurements in the test vessel were to be performed todetermine the rate and efficiency of I2 deposition on painted surfaces, the speciationof the released iodine (iodine in aerosol form, molecular iodine, organic iodide),and the degradation of the paint.



Test HD-46 studied the resuspension by hydrogen deflagration of aerosols that havebeen deposited on vertical and horizontal surfaces and containment typical step
gratings. Furthermore, the test investigated the release of gaseous iodine by thermal
decomposition of CsI particles due to the hydrogen deflagration. Both are ofinterest for long-term fission product behaviour and, hence, for the radiologicalsource term.

For the majority of the experiments, design calculations were performed by the operating
agent for the detailed determination of test conditions, test parameters, and test proceduresand for the detailed design and configuration of the instrumentation and other experimental
equipment.
Numerous analytical activities with respect to the tests are documented in the respective
reports and publications. The AWG of NEA THAI-3 project organised two code
benchmark exercises; one based on the hydrogen deflagration test HD-44 and the second
based on PAR performance test HR-49. The code benchmark exercise for HD-44 and HR49 tests included both Blind-phase and Open-phase calculations, the results of which are
documented in the respective comparison reports, namely (Freitag and Sonnenkalb, 2019)and (Freitag and Sonnenkalb, 2018). In addition to HD-44 and HR-49, other tests from thehydrogen deflagration and PAR performance test series have also been used extensively bya majority of the project partners for code-model validation purposes.
For the fission product re-entrainment tests (WH-24, WH-28 and Iod-32), and fission
product resuspension tests Iod-34 and HD-46, post-test calculations were performed by thepartners and some of results were reported at the AWG meetings, e.g. by IRSN, GRS, VTT.
The THAI re-entrainment experimental results also provided feedback in an IRSN analysis
performed to study the impact of aerosol re-entrainment from pressure suppression poolson the source term of the Fukushima Daiichi Nuclear Power Plant accident with ASTEC.
The experimental results obtained in the framework of the present experimental programme
have helped to achieve the goals of the NEA THAI-3 project, namely to improve
confidence in available LP- and CFD-tools for containment analysis. The enhanced tools
validated against experimental data will provide a more reliable approach for the analysisof the containment response during accidents and the planning of accident management
measures.
The data of all the performed experiments have been processed, qualified and stored on aserver hosted by the NEA and are accessible to signatory partners. Detailed experimental
results and analyses are provided in Quick Look Reports (QLR) and Technical Reports.
The Management Board of the THAI-3 Project has agreed that these QLR and Technical
Reports can be disclosed for non-signatory NEA countries after 31 July 2023 and may beobtained after this date upon request from the NEA Secretariat. These reports are compiled
in Annex A of this report.

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2. Objectives

The overall objective of the NEA THAI-3 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 for evaluating the challenge posed on containment integrity (by hydrogen
combustion) and for evaluating the amount of airborne radioactivity (iodine and aerosols)
during such severe accidents with core damage. The project generated valuable data forevaluating the hydrogen deflagration behaviour in a multi-compartment geometry withinteracting flame fronts and its effective removal by PARs. Concerning fission products,
the project focused on the resuspension of iodine from a painted surface and aerosols
deposited on surfaces including containment typical gratings by a hydrogen deflagrationand on the release of volatile iodine and soluble aerosol from a boiling pool. Extensive
analytical effort accompanied the experimental programme consisting of code calculations
to support test design for pre-test assessments, result evaluation and extrapolation to reactor
conditions.
The project contributed to the validation and further development of advanced LP- and
CFD codes used for reactor applications by for example, providing experimental data forcode benchmark exercises. Furthermore, the project contributed to maintain competence
and expertise in the field of reactor safety in the NEA member countries and to promoteinternational co-operation between its member countries.

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3. Test configuration, test procedure and test results

This section describes the standard configuration and basic instrumentation of the test
facility, the specific configurations and additional instrumentation of each test series, andthe test procedures and results specific to each test series.

3.1. Test facility general overview
3.1.1. Two-vessel facility THAI+
The two-vessel facility consists of the original THAI test vessel (TTV), to which a smaller
vessel, designated as parallel attachable drum (PAD), is interconnected by a lower and an
upper DN500 connection pipe, Figure 3.1. The arrangement of the two-vessel system
within the THAI building is depicted in Figure 3.2.
The total gas volume of the facility amounts to about 80 m³. The specifics of the two vessels
are described below and more details of the THAI+-facility are provided in the respective
Technical Report (Freitag et al., 2016).
The THAI building includes a restricted area in accordance with the respective radiologicalprotection regulations for tests for which a radioactive iodine tracer I-123 is used.

3.1.2. THAI test vessel
The THAI vessel (TTV) is 9.2 m high, has a volume of 60 m³, an inner diameter of 3.2 m,
and a sump compartment of 1.7 m³ with an inner diameter of 1.4 m. The vessel ismanufactured from austenitic steel 1.4571 (DIN EN 10088-3 X6CrNiMoTi17-12-2 ≈AISI/SAE 316Ti) with complete thermal insulation. The cylindrical part of the vessel walls
is a double walled steel structure with 22 mm inner wall thickness, a 16.5 mm thermal oil
gap and 6 mm outer wall thickness and is subdivided in three vertical sections that can beheated or cooled separately. Heating of a section by means of thermal oil is possible up to
160 °C. The (static) maximum overpressure is 14 bar at 180 °C (design value). Completeor partial removable internal steel structures allow the performance of multi-compartment
tests or the installation of specific hardware for testing, e.g. PARs, elevated water pools.
Comprehensive process equipment is available e.g. for steam supply (up to 37 g/s at 170°C,
8 bar), compressed air, injection gases like H2, N2, He, water/solution spray injection,
aerosol generation and injection, and the injection of I2 (both as gas and liquid) labelledwith radiotracer I-123, including the respective equipment for volume flow control andmeasurement.

3.1.3. PAD test vessel
The PAD has a similar design and the same design specifications as the THAI vessel, but
is smaller in volume (V = 18 m³) and inner diameter (ID = 1.6 m), and is slightly higher(H = 9.7 m). The auxiliary and supply systems of the PAD correspond to that of the TTV.
The PAD is instrumented like the TTV, but with a smaller number of sensors.
Upper and lower pipe segments (inner diameter 0.5 m) with the same design specifications
as the TTV and PAD connect the two vessels.

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3.1.4. Instrumentation
For the tests described in this report, comprehensive instrumentation for thermal
hydraulics, iodine, aerosol and gases is installed. The standard instrumentationencompasses thermal hydraulic and gas composition instrumentation. It is supplemented
by special instrumentation depending on the specific test designs and test objectives.

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 this device is compared with the injected gas mass determined from the startand the end pressure of the gas bottles and compared with the pressure increase in thevessels.

Gas concentration measurement
Up to 25 gas sampling lines continuously take gas samples from the vessel’s atmosphereat different locations. The sampled gas is fed to a 25-channel gas concentration analyser
system that determines the hydrogen or helium concentration in dry air. In case ofexperiments with steam, steam is removed by coolers and condensate traps upstream of theanalysers. Up to six of the 25 lines for hydrogen/helium concentration measurement are
additionally equipped with oxygen sensors. Concentration of hydrogen/helium and oxygenis then determined in dry air. For those experiments for which the steam in the vessel’s
atmosphere was at saturation state, the real (“wet”) concentrations of hydrogen/helium andoxygen in the vessel atmosphere could be determined by use of the steam table for thepartial pressure of steam at the temperature measured in the vessel. Otherwise relative
humidity measurements are used in the vessels to determine the partial pressure of steam.

Temperature measurement (“slow thermocouples”)
Up to 150 calibrated 1.5-mm thermocouples are installed in the TTV and PAD for
temperature measurement in the vessel atmosphere with an accuracy of ± 0.3 K for atemperature range 0 °C to 130 °C.
In addition, another 300 thermocouples are installed to measure the wall temperatures of
the TTV and PAD.

Temperature measurement (“fast thermocouples”)
To monitor the PAR catalyst temperature, flame front propagation and flame temperatureduring hydrogen combustion, “fast” sheathed thermocouples (outer diameter 0.5 mm) areused. As the arrival of the flame front at the individual thermocouple causes a steep
temperature signal rise, the time points of flame front arrival can be determined with anuncertainty smaller than 0.01 s.

Pressure measurement (“slow”)
The initial vessel pressure and the pressure increase due to gas injections or gas atmosphereheating are determined by four pressure transmitters and a digital high-precision
manometer. The measurements with pressure transmitters are cross-checked with a highprecision manometer (accuracy ± 10 mbar). Also recorded is the absolute atmosphericpressure with a barometer inside the experimental hall.
OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  21

Pressure measurement (“fast”)
The transient of the deflagration is measured with fast piezoresistive pressure transmitters(Keller PAA-M5 HB), using a sampling rate of 1 kHz. The signals of these transducers
show a slight temperature influence and therefore are referenced to the “slow” transducer
with respect to zero-point deviation and identical pressure decrease after the deflagration
event.

Flow velocity measurement
Flow rate at PAR inlet
In order to determine the H2 recombination rate of a PAR, the H2 concentration at the PAR
inlet, at the PAR outlet and the volume flow through the PAR are to be measured. The latteris achieved by a turbine flow metre (“vane wheel”) installed in the inlet flow channel. The
vane wheel transducer applied has a lower threshold value for start-stop of vane wheel
rotation of approx. 0.25 m/s and a measuring accuracy of ± 0.1 m/s.

METUSA
A unique measurement device (minimal encroaching turnable stream-wise anemometers:
METUSA) is installed in the upper connection pipe that makes it possible to determine thevolumetric flow being exchanged between the two vessels. It consists of two rotatableflanges that envelope an 885 mm long DN 500 pipe section into which six vane wheels are
installed. Each of the 30 mm  vane wheels is installed at a different pipe radius between
the centerline and pipe wall. Additionally, all the vane wheels have been installed at
different angles and axially over a distance of 100 mm in order to minimise the flow
disturbance. By turning the pipe section by 360°, each of the vane wheels run along a
circular path. The summation of the six circular paths, each being 30 mm thick, makes it
possible to accurately calculate the velocity distribution inside the pipe. During hydrogendeflagration tests, the vane wheels were pulled out of the gas space before triggering theignition in order to protect the vane wheels from being exposed to high temperatures.

3.1.5. Aerosol measurements
To determine aerosol concentration and particle size distribution, different methods havebeen established.

Integrating filter (WH-24 and WH-28)
A metal fibre filter is installed in the PAD exhaust line to integrally collect all salt/CsI
particles leaving the PAD vessel. Five filter cartridges are operated in consecutive manner
during the twelve measurement phases of test WH-24, and during thirteen phases in test
WH-28, respectively. When a measurement phase is finished, the particular filter cartridge
is leached two times into 5 L of decalcified water after dismantling. Leaching liquids areanalysed after the test for salt/CsI content.

Bulk filters
Measurement of the aerosol mass concentration is performed with bulk filters. The filters
are weighed before and after the experiment. From gas sample volume flow, the samplingtime and mass of the retained particles, a mean aerosol concentration can be calculated forthe sampling period. In tests with very low aerosol concentration, chemical analysis is used
to determine the aerosol loading.

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Gas scrubbers (WH-24 and WH-28)
Two gas scrubbers are installed to measure the aerosol concentration in the gas space. Even
though the aerosol concentration at the gas scrubbers only gives information about the local
concentration, the aerosol concentration is quasi-stationary during the individual periods ofconstant gas injections into the sump or during the depressurisation phases.

Cascade impactor
Furthermore, low-pressure cascade impactors are available to determine the particle size
and the particle size distribution. The impactors separate ten particle size classes. The massof each particle class collected during the sampling period is determined by weighing or
chemical analysis.

3.1.6. Iodine measurements
The measurement of iodine is mainly based upon the use of detectors for iodine labelledwith the radiotracer I-123, samples from gas scrubbers and Maypack filters, or online
monitoring of deposition coupons.

Scintillation detectors
Three lead-shielded NaI scintillation detectors outside the test vessels are focused tomonitor the I-123 radiation inside the vessel. They indicate the evolution of the iodine
activity either on iodine deposition coupons (stainless steel or decontamination paintcoated) or in the gas phase. Usually, a standard geometry configuration of detector,
shielding (focus) and deposition coupons is used and evaluated based upon calibrated
geometries. The measurement is quasi-continuous and typically every 30 s a count rate isrecorded during transient phases. During less transient phases, i.e. in later stages of Iod-32,
the output of a count rate is slowed down as far as every 10 min.

Gas scrubbers
Measurement of gas-borne iodine concentrations is based on the gas scrubber (GS)technique, with up to eight gas scrubbers. To avoid long gas sampling lines often associatedwith significant iodine losses, these gas scrubbers are installed inside the vessels at various
positions. Absorber solution is fed into and removed from the gas scrubbers from outside
the test vessel repeatedly during a test, so that concentration evolutions with time can be
determined. After sampling (scrubbing) for several minutes at a gas flow rate 0.5–1 l/min,the absorber is recovered, cooled down and measured by I-123 γ-counting and by UV-VIS
spectroscopy. Sampling times vary between 2 min and 30 min, with increasing tendency inthe course of a test to account for the depletion of gas-borne iodine by deposition onto
surfaces and for the short half-live (13.2 h) of I-123.

Maypack filters
Two Maypack filter sampling stations are available to discriminate gas-borne iodine inmolecular iodine (I2), gaseous organic iodide and iodine in aerosol form. Each Maypack
device consists in general of one quartz filter to retain aerosols, two filters to retain gaseous
I2, and two charcoal filters (KI-impregnated) to retain organic iodides. This enumeration
defines at the same time the flow direction.

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Laser absorption system (LASI)An additional iodine measurement is performed by iodine specific light absorption, which
provides a continuous, in-line and non-intrusive measurement of gas-borne iodine. The
532 nm wavelength laser is emitted by a laser diode located outside of the PAD. The beam
is mirrored so that it passes the vessel’s diameter four times, resulting in a total opticalpathway of 12.6 m. The light absorption at 532 nm is sensitive to molecular iodine (I2),with minimum cross-sensitivity to the remaining gas mixture, which consists predominantly of N2, O2, H2O and argon.

3.2. Hydrogen deflagration (HD) tests
The objectives of the hydrogen deflagration test series HD-40 to HD-45 are to provide more
knowledge and experimental data on the influence of convective flows on the flame
propagation of hydrogen combustion and the relevance of scale for flame acceleration
effects as a function of the hydrogen concentration. Furthermore, tests should address theeffects of hydrogen deflagrations in a two-vessel configuration including stratifications ofgas concentration and/or gas temperature. These data are required for model development
and code validation purposes taking into account “multi-compartment effects”.
To achieve these goals, appropriate hydrogen deflagration tests are performed in the twovessel THAI+ test facility. In large geometries, deflagrations may proceed faster due to, forexample, increased turbulence generation and therefore may produce higher loads for thevessel and its internals.
Details of test series HD-40 to HD-45 are provided in the respective Technical Report(Freitag et al., 2019).

3.2.1. Test configuration
The test configuration for tests HD-40 to HD-45 with the gas injection positions, theinternal blower and the igniter positions is shown in Figure 3.3.
The blower was operated to establish a (low-velocity) circulating flow within the TTV andthe PAD prior to ignition in forward direction, i.e. gas is sucked from the PAD vessel andblown into the sump compartment and consequently through the lower connecting pipe into
the TTV.
Remotely controlled arc igniters are installed in the sump compartment at an elevation of
H = 0.5 m and close to the vessel head at H = 9.1 m of the TTV. In all tests only one igniter(either top or bottom) is operated. The integral energy delivered during the igniter operation
time of 1s is about 10 J.

3.2.2. Test procedure
Table 3.1 summarises the specified initial test conditions for the tests HD-40 to HD-45. All
tests were performed at 1.5 bar initial pressure. Steam, temperature and hydrogenconcentration gradients were established in the two-vessel configuration for tests HD-40 to
HD-42 under similar conditions as in tests HD-26 to HD-28, performed in the TTV alone
in the framework of the NEA THAI project (NEA, 2010). Tests HD-43 to HD-45 were
performed under similar initial conditions as HD-36, which was performed in the THAI+
test facility in the framework of the German national THAI program (Freitag et al., 2017a),but without the large blower, i.e. without initially superimposed gas convection. Prior toignition, the blower was started for tests HD-43, HD-44 and HD-45 to produce an initial
flow in the vessels and in the interconnecting pipes. The mixture was ignited at the TTV

OECD/NEA THAI-3 PROJECT FINAL REPORT24  NEA/CSNI/R(2021)8
sump compartment in all tests except HD-45 where the mixture was ignited at the top of
the TTV. One additional pre-test was performed during which the influence of the blower
on the flame propagation was quantified without operation of the blower. The test was
performed with ignition at the bottom of the TTV, similarly to test HD-36.
Table 3.1. Test conditions as specified and measured for the HD test series
Test ID

HD-40(spec)

HD-40(meas)
HD-41(spec)

HD-41(meas)
HD-42(spec)
HD-42(meas)
HD-43(spec)
HD-43(meas)
HD-44(spec)
HD-44(meas)
HD-45(spec)
HD-45(meas)
Pretest(meas.)

Test Parameter
Temp.
Initial gas
flow
[°C]
90 top none30
bottomObjectives

cH2[vol.-%]
12
top
6 bottomcst[vol.-%]
47 top3
bottomIgniter

11.9 top
6.0
bottom6
top
12 bottom

45 top2
bottom47 top3
bottom89 top34
bottom90 top30
bottomnone

TTVbottomnone

TTVbottom

6.2 top11.4
bottom10
top
10 bottom

44 top4
bottom87 top34
bottomnone

TTVbottom47 top3
bottom90 top30
bottomnone

TTVbottom

10.0 top
9.5
bottom10

45 top3
bottom25

89 top32
bottom
90

none

TTV
bottomlow

TTVbottom

10

26.0

88.8

0.61 m3/s

TTVbottom

10

25

90

high

TTV
bottom

10.2

25

89

1.2 m3/s

TTVbottom

10

25

90

high

TTV top

10

25.3

89.9

1.2 m3/s

TTV top

9.95

25.3

88.5

none

TTV
bottomTTVbottomStratified conditions in 2-vessel system
Potential jet ignition effect in positive H2-concentration gradient
Effect of stratification in 2-room compartment on flame propagation
Comparison to HD-27 (TTV only) and HD-38

Effect of negative H2-concentration gradient in 2-room compartment
on flame propagation
Comparison to HD-28 (TTV only) and HD-40
Variation of jet ignition effect, interaction of flame fronts

Potential jet ignition effect in homogenous H2-concentration
Effect of stratification in 2-room compartment on flame propagation
Comparison to HD-26 (TTV only), HD-40, and HD-41

Influence of initial convection in 2-room facility; comparison to HD-22(TTV only), HD-36

Influence of high initial convection in 2-room facility; comparison to
HD-36 and HD-43

Influence of high initial convection in 2-room facility; comparison to
HD-36 and HD-43
Influence of igniter position HD-44

Evaluation of influence of blower
Comparison to HD-36 (TTV bottom ignition)

The test procedure for the HD test series consisted of a preconditioning phase, during which
the initial conditions were established, followed by the main test phase. Both vessels weredried up and the remaining condensate from previous tests was removed before the tests.
To achieve the desired initial thermal hydraulic conditions, the vessel walls were heated tothe desired target temperatures. Steam, air and hydrogen injections were performed
according to the pre-calculated amounts to generate the desired mixture at the specified
temperature and pressure conditions in the vessels.
The main test phase started with the triggering of the igniter at time t = 0 s.

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3.2.3. Test results
Deflagration pressure increase behaviour of the 2-vessel system
Slightly lower peak pressures were observed for tests in the 2-vessel THAI+ geometry thanfor tests in the single vessel (TTV only) with the same initial conditions, Figure 3.4. Thisapplies for well-mixed tests (compare HD-36 and HD-22, Figure 3.4) as well as for tests
with a positive H2-concentration gradient. This finding can be attributed to higher heattransfer in the two-vessel geometry due to a higher surface-to-volume ratio, namely 2.2 forthe two-vessel geometry, and 1.67 for the single vessel (Freitag et al., 2017a).
The pressure increase gradient did not differ markedly for the single vessel and the twovessel configuration. However, pressure increase behaviour was markedly influenced by
the operation of the blower, which produces a significantly steeper pressure increase.
All peak pressures remained clearly below the AICC pressures.

Jet ignition effect
Jet ignition is characterised by a three-step process:1. Flame propagation in the ignition compartment: Due to volume expansion, unburnt
mixture is displaced into the downstream compartment. Downstream of theinterconnecting opening, the jet produces high turbulence within the downstream
compartment.
2. Ignition of the downstream compartment: Once the jet passing the interconnecting
opening turns into a flame jet, the inventory of the downstream compartment is ignited
instantaneously and the subsequent extremely strong pressure increase might not be
relieved by openings further downstream.
3. Post combustion in the ignition compartment: The overpressure in the downstream
compartment produces a backflow into the ignition compartment, thereby increasing
turbulence, which intensifies the combustion of the residual H2, producing a steep pressure
increase also in the ignition compartment.
Step 2 requires only a few milliseconds, as has been observed also for a relatively large
downstream compartment of 80 m³ with 11 vol.-% H2 in both ignition and downstream
compartments, 25 vol.-% steam in the ignition compartment, and 35 vol.-% steam in thedownstream compartment (Kanzleiter, T., 1992).
Such a pronounced jet effect was not observed for the present test series. The reason may
be as follows: In tests performed by Kanzleiter (Kanzleiter, T., 1992) and otherexperimenters, the downstream compartment with relief opening remained unpressurised
during step 1. Hence, gas transport into this compartment was restricted only by theinterconnecting opening, whereas in the present tests both compartments where pressurisedat the same time, inhibiting the gas transport into the downstream compartment. During
combustion, no pressure difference between the two vessels was observed, i.e. the twovessel geometry behaved in this respect like a single vessel. This applies also for test HD-45
with the ignition position at the top of the TTV. This ignition position was regarded to be
most favourable for a jet ignition effect.

Flame front propagation
Flame front propagation in the TTV, the PAD and the upper connection pipe is depicted astime/travelled distance-function for well-mixed tests in Figure 3.5. For tests HD-40 to
HD-42 with H2, with steam and temperature stratification, an exact determination of a flame
OECD/NEA THAI-3 PROJECT FINAL REPORT26  NEA/CSNI/R(2021)8
front is not possible due to pronounced flame instabilities and erratic flame propagation.
The fast flame travel was remarkable in the PAD for the tests with an ignition location at
the TTV’s bottom. The reason is the flame acceleration in the lower connection pipe, which
creates additional turbulence in the yet unburnt mixture in the lower part of the PAD.
For test HD-36 (same initial conditions as test HD-43, but without initial flow) an
extremely fast downward travelling flame was observed inside the upper half of the PAD,
which can be regarded as jet ignition.
The apparent negative elapsed time in the upper part of the TTV, Figure 3.5, can be
explained by the fact that the elevation of 11 m represents the centreline of the upper
connection pipe, in which for tests HD-43 and HD-44 the flame travelled from the PAD to
the TTV. For test HD-45, with ignition located at the TTV’s top, the flame travelled much
faster within the upper connection pipe to an elevation of 11 m than downward in the TTV.

Influence of initial flow on peak pressure
The different initial flow conditions established for the premixed tests were as follows:

HD-36: no initial flow

HD-43: = 0.61 m³/s



HD-44: = 1.2 m³/s

HD-45: = 1.2 m³/s but with ignition location at the TTV top

The evolution of peak pressures for these tests is depicted in Figure 3.6. Since these tests
had slightly different initial H2-concentrations, the peak pressures were extrapolated to a
H2 concentration of 10.2 vol.-% (HD-44) using the slope of the AICC for an initial pressureof 1.5 bar and an initial steam content of 25 vol.-%. For an H2-concentration of 10.2 vol.%, an initial volume flow increases peak pressures linearly if ignition is triggered at the
TTV vessel’s bottom. For ignition at the TTV’s top, a slightly smaller peak pressure isobserved, Figure 3.6.

3.3. Hydrogen recombiner (HR) tests
Test results on PAR behaviour have been acquired so far by exposing the PAR to initiallystagnating flow conditions. Further experimental investigations that address the influenceof containment typical flow conditions on the performance of PARs were considered to beof high relevance for the development and validation of severe accident analysis codes.
In the test series HR-46 – HR-50, the onset and performance of two different commercial
PAR units under counter-current flow were investigated. In particular, the tests investigatedwhether the exposed flow influences the internal PAR behaviour, e.g. its self-induced
chimney flow and the recombination efficiency of the catalytic materials.
Details of the test series HR-46 – HR-50 are provided in the respective Technical Report(Freitag et al., 2017a).

3.3.1. Test configuration
The THAI+ configuration consist of the THAI test vessel (TTV) and the smaller parallel
attachable drum (PAD), which are connected by two pipe segments of DN 500, Figure 3.1.
For tests HR-46 to HR-50, all standard internals (inner cylinder and four lateral condensate
trays) were removed from the TTV except all condensate gutters, which collect wallcondensate in both vessels.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  27

Further details about the THAI+ test facility and the instrumentation are given in section
3.1. Added to the basic configuration were the following components:

Large axial blower
To produce an initial flow inside the vessels and the interconnecting pipes, a large axial
blower was installed for tests HR-46 to HR-49 atop of the TTV sump compartment, Figure
3.7. During all the tests of the series, the blower was operated in reverse direction, hence
gas was sucked from the TTV sump compartment and accelerated into upward direction.
By this, either a counter-current or co-current flow could be superimposed on the naturalconvective flow produced by the PAR. No blower was installed for test HR-50.

Passive autocatalytic recombiners
For the tests, PAR units provided by AREVA (now Framatome GmbH) and NIS
Ingenieurgesellschaft mbH were used.
The tests HR-46 and HR-47 were conducted with a 1/8 module NIS PAR, Figure 3.7 andFigure 3.8. The catalyst arrangement consists of 11 perforated stainless steel cartridges
filled with palladium-coated porous ceramic pellets with a diameter of 4-6 mm. Due to theirporosity, the pellets have a very large inner surface that favours catalyst reaction.
In tests HR-48 – HR-50, an AREVA PAR (model FR-380) was installed, Figure 3. The
capacity of the PAR unit was scaled down to match the size of the test facility by reducing
the number of catalytic foils to approximately 50% of the original number, and by insertinga vertical partition wall to reduce the active PAR flow cross section accordingly. In thepresent PAR unit, 19 stainless steel foils coated with porous platinum catalyst werearranged with 10 mm spacing in the lower part of the PAR housing. In all tests, only one
PAR unit (either NIS or AREVA) was installed inside the PAD.

3.3.2. Test procedure
Table 3.2 summarises the specified and measured initial conditions of tests HR-46 to HR50 performed in the THAI+ facility. The initial thermal hydraulic conditions of tests HR46 to HR-48 and HR-50 were set identically to the conditions of tests HR-7 and HR-8,
which were performed in the TTV test facility during the OECD-NEA THAI project(Kanzleiter, T., 2009), and of tests HR-43 to HR-45, performed in the THAI+ facility(Freitag et al., 2017a). The reference test for HR-49 is HR-12, which was performed in
identical thermal hydraulic conditions as HR-49 but using the TTV vessel only during the
NEA THAI project (NEA, 2010). Tests of the current series investigated the effect ofcounter-current flow on the NIS PAR (HR-46) and the effect of the chimney height on the
NIS PAR start-up and performance (HR-47). The strength of the counter-current flow wasincreased in HR-48 and HR-49 as compared to test HR-43, whereas for HR-49 steam
content and pressure were also increased. In test HR-50, the AREVA PAR was exposed tonatural convection inside the THAI+ configuration.

OECD/NEA THAI-3 PROJECT FINAL REPORT28  NEA/CSNI/R(2021)8
Table 3.2. Test conditions as specified and as measured for the HR test series
Test #
HR-46

HR-47

HR-48

HR-49

HR-50

specified

P0
[bar]

T0 [°C]

1.5

75

c

Steam

[vol.%]
25

NIS

measure
d

1.5

77.2

27.2

specified

1.5

75

25
NIS

measure
d

1.5

77.8

27.8

specified

1.5

75

25

1.5

77.6

26.9

specified

3.0

117

60

measure
d

119

61.6

1.5

75

25

1.51

100.8

17.1

Flow velocity
at PAR inlet
[m/s]

0.87

0.44

≈ 0.5
(blower)

AREVA

naturalconvection bywall heating/cooling

Effect of countercurrent flow

0.41

0.34

Strength ofcounter-current
flow

≈ 1.0
(blower)
1.45

Objective

Chimney effect incounter-current
flow

≈ 1.0
(blower)
*

AREVA
3.0

Flow velocity invicinity of PAR
[m/s]
≈ 0.5
(blower)

0.85
AREVA

measuredmeasured
specified

PAR unit

0.32-

Pressure and temperature; countercurrent flow
PAR exposed tonatural convection

Note: * vane wheel above PAR failed during the test

The test procedure for the HR test series consisted of a preconditioning phase followed by
the main test phase. The desired thermal hydraulic conditions and the steam contents as
depicted in Table 3.2 were established in the preconditioning phase. The main test phasestarted with the release of hydrogen into the vessel. Time t = 0 s corresponds to the start
time of the first hydrogen injection to reach the target concentration level.

3.3.3. Test results
The comparison of the test results of HR-46 and HR-47 and of the previous HR tests using
the NIS PAR under similar thermodynamic boundary conditions (Kanzleiter, T., 2009),
reveals that the first onset of hydrogen recombination is much faster under conditions ofcounter-current flow in the THAI+-facility. However, the recombination rate issignificantly reduced as long as the hydrogen concentration remains below about
2-3 vol.-% for these two tests due to an initially stable downward flow and later oscillationsof the flow direction inside the recombiner. As soon as the hydrogen concentration at the
PAR inlet exceeds about 3-5 vol.-%, a stable upward gas flow inside the recombiner was
established and the recombination rate of HR-46 matched the test results of HR-14, whereas
the recombination rate of HR-47 remained reduced. Both during the first and second
hydrogen injection phase of test HR-47, flow oscillations were observed for relatively highH2-concentrations.
In Figure 3.10, the hydrogen depletion efficiency of HR-14, HR-15, HR-46 and HR-47 is
depicted as a function of the hydrogen concentration at PAR inlet. For hydrogenconcentrations above a certain value, the hydrogen depletion efficiency of HR-46 matches
the results of HR-14 and HR-15 with values between 50 and 60%. Below a certain
concentration, lower efficiencies are recorded for HR-46 due to the oscillations of flow
direction. For test HR-47 with reduced chimney height, the efficiency is increased by about
10% due to reduced internal gas velocity, which in turn increases the residence time of thehydrogen at the catalytic cartridges. However, the reduced self-induced buoyancy makes

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  29

the PAR in HR-47 more susceptible to the external counter-current flow, which induces
oscillations already at low hydrogen concentrations.
Apart from the delayed PAR start-up behaviour during the second hydrogen injection
sequence in test HR-47, no measurable impact on the catalyst temperature could be
identified by exposing the PAR to counter-current flow conditions.
During tests HR-46 and HR-47, glowing particles were detected inside the PAD and TTV.
Owing to their very low density, these “glow worms” remained airborne for an extended
period of time and were transported within the large convective loop that was driven by theblower. Even though no dedicated measurements were installed to quantify the exact timeof the first appearance of these glowing particles, they could be traced visually as long as
the hydrogen content inside the THAI+ system was above 4 vol.-%. Below thisconcentration their frequency of appearance reduced significantly.
In Figure 3.11 the start-up of the AREVA PAR under counter-current flow conditions (tests
HR-43 and HR-48) is compared to tests HR-7 and HR-8 with quiescent conditions andsimilar thermodynamic initial conditions, Figure 3.11. The onset of recombination during
test HR-43 with reduced blower frequency was detected at a certain (relatively low)H2-concentration and at slightly higher concentration during HR-48 with maximum blower
frequency. Under quiescent flow conditions, in tests HR-7 and HR-8 the first indication of
PAR operation was detected at noticeably higher H2 concentrations.
The impact of the counter-current flow conditions on the depletion efficiency for hydrogenconcentrations above a certain value is also small, Figure 3.12; i.e. tests HR-43 and HR-48
indicate similar efficiencies of 60 – 70% as HR-7 and HR-8. For decreasing hydrogenconcentration, the efficiency of tests HR-7 and HR-8 increases to 80% and 90%,
respectively, while the efficiency for test HR-48 decreases to 50%. This decrease is caused
by PAR internal flow oscillations due to competing downward-directed flow from theblower and self-induced upward directed buoyancy driven flow. Though this reduces theperformance of the recombiner, the overall recombination rate under such low hydrogenconcentration is generally small; hence, the reduced efficiency under these conditions
impacts the overall hydrogen depletion only marginally.

3.4. Tests with aerosol release from a pool (WH-tests)
Tests WH-24 and WH-28 aimed at quantifying the re-entrainment of soluble fission
products (CsI-aerosol) from water pools at elevated temperatures. In test WH-24, demineralised water was used initially, while in test WH-28 a surfactant was added to reduce
the surface tension of water.
The focus of the investigations was on the re-entrainment of aerosols relative to the initialamount dissolved in water and on water pool hydrodynamics (e.g. bubble dynamics) underrealistic containment conditions. These investigations shall contribute to the validation andfurther development of dedicated empirical or semi-mechanistic models of advanced LP
and CFD codes used for reactor applications by providing experimental data.
Details of the tests are provided in the respective Technical Reports (Freitag et al., 2017b),(Freitag et al., 2018).

3.4.1. Test configuration
The configuration of tests WH-24 and WH-28 consists mainly of the smaller vessel of the
THAI+ facility, namely the parallel attachable drum (PAD), Figure 3.13. The THAI test
vessel (TTV) is used as a reservoir for hot gases released from the PAD vessel. The benefit
of using the PAD as compared to the TTV is a smaller particle dilution inside the gas space
OECD/NEA THAI-3 PROJECT FINAL REPORT30  NEA/CSNI/R(2021)8
above the water pool, which improves detection limits of particle measurements by filters,
impactors and gas scrubbers.

Additional process components
Added to the basic configuration (see section 3.1) were the following components:

Downcomer pipe
A DN 100 steel pipe (105 mm ID, 4.6 mm wall thickness) is installed in the PAD verticalaxis as a downcomer,

Air injection
Air is either injected into the vessel as purging air to allow for superheated conditions inside
the vessel and or into the sump via the downcomer pipe for bubble generation.

Water injection
Cold decalcified water is injected into the PAD sump at bottom centre. Water is injected at
the beginning of the test, and if necessary, later in between phases to maintain the waterlevel in the vessel.

Salt (CsI) dosing
A large vessel for salt injection at the beginning and a smaller vessel of 8 L volume for reinjection during the test are installed. High concentrated salt is injected into the PAD sump
via a pipe. Salt is injected via this dosing vessel if necessary, in between test phases tocompensate for concentration reduction by condensing steam or loss through the spill-overlines.

Gas exhaust line
The gas inside PAD is relieved at its top into the TTV.

Spill-over lines
Two spill-over lines are installed inside the PAD sump compartment, both connected tofilling funnels of 60 mm diameter. The spill-over lines are connected to the two condensate
collectors outside of the PAD vessel to measure the water volume that was removed fromthe PAD sump.

Additional instrumentation
Added to the basic instrumentation (see section 3.1.4) were the following components:

Sump salt concentration
The sump recirculation line is connected to an online electrical conductivity sensor. It is
used to measure the salt concentration inside the pool water during the test using apredetermined calibration.

Bubble measurements
Gas bubble measurements are based on a high-speed camera and image processing
software. The PAD vessel sump was equipped with optical accesses at H = 0.65 m andH = 2.1 m. A high-speed camera (Photron FastCam SA 1.1) that records 1 000 frames per
OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  31

second was alternately placed at these optical accesses. The focusing depth wasapproximately 10 mm. This arrangement makes it possible to track bubble dynamics of theuprising air, steam, or steam/air bubbles.

3.4.2. Test procedure
Tests WH-24 and WH-28 were divided into individual phases (12 for WH-24 and 13 for
WH-28) that are grouped into three phenomenological categories:a)Particle re-entrainment from a heated pool by injection of air and steam/air
mixturesb)Particle re-entrainment from boiling pool by injection of steam and steam/air
mixturesc)

Particle re-entrainment from flashing pool induced by depressurisation

In Table 3.3, the individual test phases are specified. Details of the test procedure discussed
in the following refer to test WH-28; those of test WH-24 are essentially the same. Test
phases a1) to b4) are performed at stationary pressure conditions, i.e. 2.5 bar, using theregulation valve that is installed in the upper connecting pipe between PAD and TTV. To
dry out the salt loaded water droplets that will be released from the water pool, a sufficient
superheating of the vessel atmosphere is required to obtain aerosol particles. This
superheating is ensured by vessel wall heating to approximately 140 °C and by the injectionof pre-heated purge air above the water surface. The water volume inside the sump isregulated by using the spill-over lines before each test phase.
Pool flashing was induced by depressurisation. The depressurisation rates of phases c1) toc3) refer to accident conditions during a filtered containment venting operation of a German
SWR72 type BWR or Japanese BWR, whereas c4) is envisaged at significantly lower
pressure reduction being typical for PWR with a large containment volume. The specified
initial test conditions and the envisaged flow rates during the subcooled pool phases (a1 toa5), the boiling pool phases (b1 to b4) and the depressurisation phases (c1 to c4) are listed
in Table 3.3.
Table 3.3. Specified test conditions for the phases of test WH-28
Test
phase

19
-

Steam injection
flow rate(kg/h)
70
70
70
70
210
350
210
-

c2)

-

-

-

c3)

-

-

-

c4)

-

-

-

a1)
a2)
a3)
a4)
a5)
b1)
b2)
b3)
b4)
c1)

Air injection flow
rate
(kg/h)
80
80
19
19
19

OECD/NEA THAI-3 PROJECT FINAL REPORT

Water
temperature
(°C)
46
60
60
90
120
boilingboilingboilingboiling

Purge air flow
rate
(kg/h)
0
0
145
145
145
145
145
145
145
-

Depressurisation rate

BWR type
1 bar/5 min
BWR type
3 bar/5 min
BWR type
1 bar/ 15 min
PWR type 0.1 bar/30min32  NEA/CSNI/R(2021)8

3.4.3. Test results
WH-24
In the WH-24 test, the sump of the vessel was filled with about 4.6 m3 of water in which
10 g/L caesium iodide (CsI) was dissolved as a representative fission product. The aerosol
re-entrainment was quantified based on the concentrations of CsI particles released fromthe sump.
The bubble measurements performed using decalcified water without additional CsI toprotect the high intensity light sources from high halide content inside the water poolprovided useful insights about the phenomenology of the gas release from the downcomer.
The gas release from the downcomer exhibits two kinds of appearance; a quasihomogenous gas release as shown in test phases a3), a4) and b1) is characterised by low
injection rates of non-condensed gases, and a pulsed gas release as shown in phases a1),a2), a5), b2), b3) and b4) Figure, 3.14 and Figure 3.15. With respect to bubble dynamics,
some differences, such as primary bubble formation frequency and maximum ascendingheight before break-up into globules, and bubble size at water surface are observed between
present results and the literature e.g. EPRI tests (Paul et al., 1991). As an example, acascaded reduction of bubble sizes from initially large structures was not recorded in thepresent study and a complete break-up of the primary bubble occurred within 3- 4 times
the primary bubble diameter. The most significant difference between the actual THAI tests
and the EPRI test (Paul et al., 1991) is the temperature of the water pool and the pressure
above the water surface – EPRI tests being performed at ambient pressure using cold water(20°C).
In all test phases, particle size distribution measurements with cascade impactors were
performed. Generally, very small particles were measured using the impactors, see Figure
3.16. Overall, the particle sizes were very similar, which can be explained by the fact that
all measurements were performed within the deposition-controlled region. Large water
droplets that might have been generated in the transition region under high superficial
velocities did not exceed a height of 2 m above the water surface which was found to be
the transition region between momentum controlled and deposition-controlled region
according to Kataoka and Ishii (1984).
Entrainment rates between 𝐸 = 5 ⋅ 10−6 and 𝐸 = 8 ⋅ 10−5 were determined based on
different measurement techniques during test WH-24. Even though a large scatter wasobserved in the measurements in each of the test phases, two main trends can be identified.
The entrainment increases for increasing superficial velocities as long as the two-phaseflow can be attributed to the bubble flow regime and the entrainment rate is constant, oreven slightly decreasing, within the transition regime and the churn turbulent flow regime
while increasing the superficial velocities further. This finding is supported by Figure 3.17,
which indicates that the average bubble diameter increases for increasing injection Weber
number. Therefore, hence the relative frequency of bursting bubbles reduces for increasing
gas injection rates.
In this context it needs to be mentioned that WH-24 was the only test where gaseous
injection into the pool was carried out by means of a downcomer pipe. Most of the otherinvestigations used a heating coil installed into the sump to generate steam bubbles. The
entrainment rate itself can be influenced by additional parameters apart from the superficial
velocity, e.g. by the atmospheric pressure (von Rohr, 2000).

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  33

WH-28
Direct measurement of the bubble column by high-speed digital imaging was not performedin test WH-28 due to a high opaqueness created by adding the surfactant and antifoaming
liquid. Therefore, a separate lab test series was conducted to evaluate the influence of thesurfactant on the bubble column behaviour. Measurement of the bubble column width wasused to approximate the superficial velocity based on the area through which the gas
bubbles break through the pool surface. Test WH-28 covered a similar range of superficial
velocities as test WH-24, ranging from 0.01 to 0.12 m/s.

Effect of surfactant on entrainment
The droplet entrainment in test WH-28, using pool water with reduced surface tension, wasmeasured in 13 test phases. Compared to WH-24, the pool water was conditioned with athermally stable surfactant, which reduced the surface tension to about 25-30 mN/m ascompared to 70 mN/m for decalcified water at room temperature.
Entrainment rates between E = 3 ⋅ 10−6 and E = 3 ⋅ 10−3 were determined based on
different measurement techniques during test WH-28, with generally very low values
during the flashing phases and very high values during subcooled and boiling phases
located in the bubble flow regime.
By comparing the results of tests WH-24 and WH-28, it can be concluded that theentrainment calculated from the aerosol measurements in tests with a surfactant was about
one order of magnitude higher compared to the de-mineralised water of test WH-24.
Results from different particle measurement techniques that have been used to evaluate theentrainment in tests WH-24 and WH-28 indicate that the absolute entrainment is subject touncertainty by a factor of 2 – 5.

Effect of surfactant on size of released particles
The addition of the surfactant favoured the release of larger droplets, which in turn might
explain the larger entrainment rates, under the assumption that a similar droplet entrainment
frequency is given.
The mass median particle diameters during the flashing phases exhibited a similar increase
as for the subcooled and boiling phases of tests WH-28 and WH-24. Assuming the absolute
entrained mass to scale with 𝑀𝑀𝐷3 , an increase of the entrainment by 10 to 30 could be
expected. Therefore, it must be concluded that the number of droplets generated when
flashing a liquid of reduced surface tension is smaller compared to flashing decalcified
water.

3.5. Iodine release from a boiling pool – test Iod-32
The mass transfer of volatile iodine at the gas/water interface is covered in most iodine
behaviour codes by the two-film theory, which describes the exchange of volatile iodine inboth directions. Mass transfer models for non-boiling conditions are established; however,experimental data on a technical scale to develop or to validate mass transfer models inboiling conditions are sparse. Sump boiling increases both the water motion and the surface
area between sump water and gas phase, which will be available for the iodine masstransfer, e.g. by the formation of ascending steam bubbles. Therefore, it was expected thatvolatile iodine is released much faster in boiling conditions than in non-boiling conditions.
The test Iod-32 was aimed at quantifying this effect.
Details of test Iod-32 are provided in the respective Technical Report (Funke et al., 2018)

OECD/NEA THAI-3 PROJECT FINAL REPORT34  NEA/CSNI/R(2021)8

3.5.1. Test configuration
The configuration of test Iod-32 consists mainly of the smaller vessel of the THAI+ facility,
namely the parallel attachable drum (PAD) Figure 3.18. The TTV is used as a reservoir forgases released from the PAD vessel. The benefit of using the PAD compared to the TTV
is a smaller dilution of the iodine release from the pool inside the gas space above the waterpool, which improves the detection limits of iodine measurements by online sensors andgas scrubbers.
Supply systems and instrumentation correspond to those of test WH-24, see section 3.1.4.
Additionally, the following devices were installed:

Iodine injection
The iodine injection consists of a 5 L dosing vessel mounted inside a glove box and apressure accumulator upstream the dosing vessel. Steel tubes (9 mm inner diameter)connect the pressure accumulator, dosing vessel and PAD vessel. The pressure accumulator
is filled with defined amounts of diluted H2SO4 for each iodine injection, to support fastand quantitative emptying of the iodine solution from the dosing vessel into the PAD sump
water. The dosing vessel contains the I-123-labelled aqueous I2 solution for each iodine
injection.

Spray system
The TTV is connected to the PAD via the exhaust line. To increase the reservoir capacityof the TTV, its pressure is reduced to about 0.5 bar before the iodine injection. A spraysystem is installed to cool down the atmosphere and to condense steam that is injected fromthe PAD into the TTV during several test phases. The resulting pressure reduction in the
TTV will increase its reservoir capacity with respect to the PAD.
The spray operates by recirculating water from the cold TTV sump. Spray water also covers
the walls, efficiently transporting all iodine into the TTV sump by iodine wash-out fromatmosphere and by iodine wash-off from surfaces. The iodine inventory in TTV is thus
simply monitored by sampling from the recirculated TTV sump.

Online detectors for deposited iodine and gas-borne iodine
Three lead-shielded NaI scintillation detectors outside the test vessel are focused to monitor
the I-123 radiation from inside the vessel. They indicate the evolution of the iodine activity
either on iodine deposition coupons or in the gas phase. The measurement is quasicontinuous and typically every 30 s the count rate is recorded during transient phases.
During less transient phases, i.e. in later stages of Iod-32, the count rate is recorded every
10 min.

3.5.2. Test procedure
The procedure for test Iod-32 consisted of a preconditioning phase followed by the main
test phases, as listed below:Preconditioning phase to establish initial conditions in the THAI facility

I2 release from non-boiling sump (reference phase, pH 3)

I2 release from boiling sump at low steam injection rate, pH 3

I2 release from boiling sump at high steam injection rate, pH 3

I2 release from boiling sump at high steam injection rate, pH~9
OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  35

The specified initial test conditions are listed in Table 3.4 and Table 3.5 for PAD and TTV,
respectively. The desired thermal hydraulic conditions were achieved by heating of the
PAD walls and controlled air injections. The pool water temperature was increased using
steam injections through the downcomer. The time t = 0 is defined as beginning of the firstiodine injection into the PAD sump.
Table 3.4. Specified test conditions in PAD
Test
phase
Pre.

p (bar)T (°C)

2.5

117 (gas)c(vol.Steam
%)
72

110
(water)(satur.)

PAD sump
Initial filling deionised water 1028 L, H= 0.25 m
inside PAD
Conditioning to pH= 3

1

2.5

up to 90

Injection of ~1 g radio-labelled I2
Activity ~0.5 GBq

2

1.3 bar after
depressurisation

up to 90

Injection of ~1 g radio-labelled I2
Activity ~ 0.5 GBq
Steam inj. mass flow rate 5 g/s, injection duration
10 min3

1.3 bar after
depressurisation

up to 90

Steam inj. mass flow rate 20 g/s, injection
duration 10 min

4

1.3 bar after
depressurisation

up to 90

NaOH injection to reach pH = 9,
Steam inj. mass flow rate 20 g/s, injection
duration 10 min

Table 3.5. Specified test conditions in TTV
Test
phase

P (bar)T (°C)cPre.

0.5 (partial vacuum)

20 (gas)

1–4

Vacuum pump will be switched off and remain off before injection of iodine into PAD, TTV pressure will riseduring each injection phase, spray system running

Steam(vol.-%)0

TTV sump
Initial filling deionised water 500 L, H = 0.43 m inside
TTV
Conditioning to pH ~9

Iodine injection
The measurement of iodine in Iod-32 was essentially based upon the use of I-123
radiotracer (T1/2 = 13.22 h). An activity amount of 1.11E+9 Bq was delivered for test
Iod-32. The I-123 activity was divided into two parts to enable two iodine injections. For
each I2 injection, 4.7 L of I2 solution in diluted H2SO4 (pH 1.4, 0.038 mol/L) was prepared,
obtained from dissolving solid I2 globules. About half of the I-123 activity was added.
Samples were taken to quantify the injected amounts of I-123 and I2.

3.5.3. Test results
The first I2 injection (0.73 g) started the reference phase, phase 1, and a small, constantgaseous I2 level of about 1E−7 g/L was observed after a certain time in the PAD gas space,
due to I2 mass transfer at the gas/water interface in non-boiling conditions (see Figure 3.19),
though the I2 in the sump was completely consumed during phase 1. To run the first boilingphase, phase 2, a second I2 injection (0.73 g) was performed. The sump boiling increased
the gaseous I2 concentration by two orders of magnitude (see Figure 3.19). The online
detectors indicated that the initiation of boiling by depressurisation of the PAD was predominantly increasing the I2 in the PAD atmosphere, and that the quasi-stationary boiling

OECD/NEA THAI-3 PROJECT FINAL REPORT36  NEA/CSNI/R(2021)8
by steam injection into the sump for 10 min produced a further but slower increase of thegaseous inventory. Taking into account that the gas atmosphere is permanently transferredto the TTV during the steam injection and boiling phase, this slow increase indicates
however that still considerable amounts of I2 are released from the sump to the gas phase.
The results of several sump measurements in the PAD provide a consistent view of the I2
evolution in the sump during the test. I2 masses in the PAD sump as obtained from thedifferent chemical analyses agree well with each other, Figure 3.20. The scattering of thedata, especially for the iodide electrode data, was within known bands of data uncertainties.
After both I2 injections the aqueous I2 was depleted at approximately the same rate, whichis equivalent to a half-life of 14 minutes, pre-dominantly by I2 reaction with the immersed
steel walls of the PAD sump. The rate was very similar in both test phases and can beaveraged to 3 / h. This short half-life was limiting the amount of I2 release to the gas phase.
The I2 depletion rate is also similar to a down-scaled GRS/COCOSYS design calculation.
This I2 measurement is important for calibration of models of I2 conversion into iodide at
immersed steel surfaces. As there was no more I2 available in the sump at the end ofphase 2, the planned second boiling phase at an increased steam injection rate was skipped.
The boiling at the beginning of the alkaline test phase 3 did not increase the gas-borne
iodine in the PAD atmosphere. The volatile iodine in the sump had been consumed alreadyduring phase 2 and no release of volatile iodine was expected anyway. Additionally,phase 3 showed that there was no release of non-volatile, droplet-bound iodine.
Compared to the I2 release from the sump in non-boiling conditions during the reference
phase, the I2 release due to boiling was higher by roughly a factor of 10. This I2 releasefactor was limited in Iod-32 by the fast I2 depletion in the sump water due to the I2 / steel
reaction.
In the gas phase, the first boiling increased the I2 concentration by a factor of 100. Thiseffect is obviously influenced also by the adsorption/desorption of I2 onto/from steel walls
exposed to the PAD gas atmosphere. The presence of a gaseous stratification just above thesump is also strongly suspected (for geometric and thermal hydraulics reasons). It might
have led to (1) an inhomogeneous iodine concentration in the gaseous phase and (2) to anunderestimation of the measured iodine gaseous concentration at the equilibrium in nonboiling conditions.
The additional test objective to measure an equivalent I2 release from the sump duringboiling at an increased steam injection rate could not be realised, due to the complete I2
consumption during the previous test phase.
The overall iodine mass balance at the end of the test was essentially closed (91%),
including inventories in the PAD and the TTV.

3.6. Iodine resuspension - test Iod-34
The objective of test Iod-34 was to measure the resuspension of iodine from painted
surfaces by hydrogen deflagration, where the (thermally aged) paint was pre-loaded withgaseous iodine in a representative manner. Iodine measurements in the test vessel were
performed to determine the rate and efficiency of I2 deposition on painted surfaces and steel
surfaces, to determine the speciation of the released iodine (iodine in aerosol form,
molecular iodine, organic iodide), and to monitor the iodine loadings on the surfaces. Thisrequires the use of the I-123 radiotracer technique. Furthermore, paint degradation was tobe characterised.
Details of test Iod-34 are provided in the respective Technical Report (Funke et al., 2019).

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  37

3.6.1. Test facility
The THAI+ configuration for test Iod-34 consists of the TTV and the smaller parallel
attachable drum (PAD) (Figure 3.1). In this configuration, the PAD is only used for storing
the iodine-loaded spray water after spraying in the TTV for iodine sampling. Figure 3.21
shows details of the TTV test configuration as used for Iod-34 test.
For a detailed description of the test configuration with basic process equipment andinstrumentation, see section 3.1. Additional equipment and instrumentation used for test
Iod-34 are described in the following.

3.6.2. Additional process equipment
Painted surfaces
The whole painted surface area of test Iod-34 amounts to 10.65 m², established by painted
coupons inside the TTV. The epoxy-type paint was GEHOPON, representative for German
containments and a THAI standard. All painted surfaces were artificially pre-aged bythermal treatment for 21.1 h at 160 °C in air atmosphere, which is a THAI standard
procedure.
The main part of the painted surface area (93.9%) was provided as 20 square steel sheets,
1.5 mm thick, 500 mm edge length, painted on both sides, and distributed within the TTV.
Two completely painted cylindrical deposition coupons, made of stainless steel were within
the TTV for online monitoring of the iodine deposition on paint.
The post-test surface analyses of some of these smaller coupons ("PTA coupons") include
SEM/EDX and microscopic analyses performed by Framatome at Erlangen. Additionalsurface analyses, especially FTIR spectroscopy on some PTA coupons were also performedby IRSN at Cadarache.

Igniter
A remotely controlled arc igniter was installed in the TTV sump compartment at anelevation of H = 0.5 m. The ignition is initiated by delivering an arc sequence of 1 s
duration. The integral energy delivered during the igniter operation time of 1 s is 10 J.

Iodine injection
Gaseous iodine is injected into the TTV with pre-heated synthetic air as carrier gas from a
10 L gas bottle. The carrier gas is directed onto a baffle plate in the centre axis. The
injection is a THAI standard for I2 puff release injections.
The injected chemical form is gaseous molecular iodine, I2, radio-labelled with I-123. To
promote a quantitative I2 injection, the carrier gas flow is usually maintained for
10 minutes.

Spray system
In the TTV, an upwardly oriented spray nozzle is installed at an elevation of H = 8.4 m at
the centreline. The spray operates by injecting decalcified water stored in intermediate bulk
containers.

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3.6.3. Test procedure
The test procedure for the Iod-34 test consisted of a preconditioning phase followed
originally by the main test phases, as listed below.
Phase 0. Preconditioning phase to establish the specified initial test conditions in TTVPhase 1. I2 injection and deposition of I2 onto the painted surfaces (and steel surfaces)
Phase 2. Fresh water spray for removing the iodine from gas phase and steel surfaces
Phase 3. Spray water removal, superheating of vessel atmosphere and H2 injection
Phase 4. Release of iodine from paint due to deflagration
The specified initial test conditions are listed in Table 3.6.
The desired thermal hydraulic conditions were achieved by heating the TTV walls to about
90 °C and by the controlled injections of air, steam, and hydrogen and the respective
pressure adjustments. The gas concentration measurement system was switched on and off
regularly during the hydrogen injection sequence to reduce sampling losses.
The time t = 0 min was defined as the time of the onset of the I2 injection. Ignition was
triggered at t = 1 200 min.
Table 3.6. Specified test conditions in TTV
Test phase
1
2
4

p
TGas
cSteamCH2
bar abs.
°C
vol.-%
Vol.-%
1.35
90
25
none
Three times spray operation with 1 m³ decalcified
water each
1.5
90° C
25
10

Phase description
I2 injection and depletion
Removal of gaseous I2 and iodine deposits on steel walls
H2 deflagration and iodine resuspension

3.6.4. Test results
Phase 1: I2 deposition
During the first test phase, the initially injected gaseous I2 was removed from the gas phaseby deposition onto painted and steel surfaces. Within 5 hours, the gaseous I2 was decreased
to a level of less than 1% of the initial injection.

Phase 2: Sprayings
Three sprayings were performed during phase 2. After the end of the three sprayings thegas-borne iodine concentrations were further decreased. About 30% (≙ 0.3 g) of theinjected iodine (1 g) not fixed on the painted surfaces was removed, consistently
determined from samplings in the TTV and PAD sumps.
A complete wash-down of the iodine loadings from steel surfaces was not clearly
evidenced. Thus, uncertainty remains over the actual iodine loading on the steel surfacesof the TTV after the spraying and the iodine distribution between paint and steel surfaces
cannot be quantified.
The gas phase iodine concentration just before H2 deflagration was at a very low level ofabout 2E-8 g/l, i.e. the gas phase was practically free of iodine. An increase in iodine
concentration in the gas phase due to deflagration can thus be measured accurately.

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As expected, most of the iodine previously deposited on the painted surfaces remained
there after washing, so the paint represents a sufficient iodine source for a sensitive
measurement of iodine released to the gas phase during the test phase with H2 deflagration.

Phases 3 and 4: H2 deflagration
The H2 deflagration strongly degraded the painted surfaces, showing blistering, cracks andcraters, Figure 3.22.
Consistent with paint degradation, significant aerosol concentration was observed visually.
No direct aerosol sampling had been foreseen, and the measurement of the total organiccarbon from gas scrubbers and gas sampling tubes turned out not to achieve the necessary
sensitivity for aerosol measurement.
Gaseous organic iodide was measured after deflagration at levels representing 50% of thetotal gas-borne iodine. This is by far the highest organic iodide concentration ever produced
in a test with painted surfaces in THAI. The composition of the other 50% of gas-borne
iodine cannot be concluded uniquely based upon measurements. The observation of a gasborne iodine concentration being persistent over 5 hours allows two interpretations of theother 50% iodine fraction, namely (1) iodine in an aerosol form of very small particle
diameters, and (2) iodine as molecular iodine, whose deposition back onto the paint ishampered by paint degradation. The H2 deflagration strongly degraded the painted surfaces,
showing a flaky structure in the paint, including blistering, cracks and craters. Degradation
was approximately similar over the whole THAI vessel, and was increased at the edges ofthe painted coupons.
Since the distribution of the primary iodine loading between paint and steel surfaces is
uncertain, the iodine release fraction from paint can be estimated to be in the range of 4%
to 9% of the primary loading. This assessment is based on the measurement of iodine in
the gas phase of the TTV after deflagration with the Maypacks, and on the results of theonline monitoring of steel and painted deposition coupons.
The release of iodine from paint in aerosol form due to hydrogen deflagration is a new pathfor iodine containment codes. The paint degradation probably also changes the conditions
and the mechanism for thermal release of volatile organic iodide from paint. As the thermal
release of volatile organic iodide from paint is so far modelled in iodine codes using onlya simple fractional release rate with an Arrhenius-type temperature dependency, such amodel is not necessarily suitable for extrapolating to deflagration-relevant temperatures.
Furthermore, surface temperatures instead of gas temperatures probably need to be used
for scaling, at least for iodine releases in fast transients like hydrogen deflagrations.

3.7. Aerosol resuspension by hydrogen deflagration - test HD-46
The objective of test HD-46 was to measure the resuspension of aerosols deposited onvertical, horizontal and containment-typical grating surfaces by a hydrogen deflagration
with ignition at the bottom of the vessel. Furthermore, the test aimed to investigate therelease of gaseous iodine by thermal decomposition of CsI particles due to hydrogendeflagration.
Details of test HD-46 are provided in the respective Technical Report (Freitag et al., 2019).

3.7.1. Test configuration
The test configuration for test HD-46 with the CsI injection position, the grating positions
and some of the aerosol instrumentation are shown in Figure 3.23. Though not shown in
the figure, four gas scrubbers were used as further aerosol instrumentation.
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Six slabs of containment-typical gratings were installed in the vessel at two heights andthree different azimuthal angles. The total surface area of these gratings was 1.95 m². About
25% of the total horizontal cross section was occupied by metal bars. In all, 22 deposition
coupons representing horizontal (11 coupons) and vertical (11 coupons) surfaces of thevessel were installed.
The spark igniter was located at the bottom of the THAI vessel.
For a detailed description of the test configuration with basic process equipment andinstrumentation, see section 3.1.

3.7.2. Test procedure
The test procedure for the HD-46 test included a preconditioning phase followed by themain test phases as listed below:
Phase 0 Preconditioning phase to establish initial conditions in the THAI vessel
Phase 1 CsI injection and deposition onto surface
Phase 2 Pressure relief and recovering of coupons
Phase 3 Establishing specified conditions for the deflagration in the THAI vessel
Phase 4 Measurement of CsI resuspension and I2 release from CsI due to deflagrationinduced high-temperature conditions.
CsI particles were injected into the THAI vessel using a two-fluid nozzle with compressed
air as carrier gas. The CsI aerosols deposit by stirred settling onto the vertical and horizontal
walls as well as on step gratings, which are commonly used as staircases or raised floors incontainments. Deposition coupons were recovered after four days of settling time toquantify the particle distribution among the surfaces, resulting in 7 wt.-% on vertical walls,
6 wt.-% on six typical step gratings and the remaining mass on the lower dished head andthe sump compartment of the vessel.
The specified initial test conditions are listed in Table 3.7. The desired thermal hydraulicconditions were achieved by heating the TTV walls and controlling the air, steam andhydrogen injections. The time t = 0 min is defined as the time when the CsI injection
started, while time tHD = 0 min is defined as the initiation of the hydrogen deflagration.
Table 3.7. HD-46: Specified test conditions in TTV
Test phase14pbar abs
1.3
1.5

TGas
°C
90
90

c
Steam
vol.-%c
H2
vol.-%

25

10

Phase description
CsI injection and depletion
H2 deflagration, CsI resuspension and decomposition

3.7.3. Test results
Hydrogen deflagration
The peak pressure during the deflagration was below five bar. This pressure is almost
identical to the reference test HD-22. Measured temperatures exceeded 900 °C in thecentreline of the TTV.

Aerosol resuspension
The filter measurements performed during test phase 3, before the deflagration, reveal
loadings on the filter paper that are below the detection limit of the measurement system.
The aerosol concentrations are therefore considered to be below 0.01 g/m3. The particle
OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  41

loadings at all stages of the impactor were below the detection limit as well. This makes it
possible to conclude that the aerosol concentration inside the vessel was negligible before
the hydrogen deflagration. A total of 242 g CsI was injected during phase 1 into the THAI
vessel.
The first two impactor measurements after the hydrogen deflagration, starting at t HD = 5
and tHD = 50 min, exhibit a pronounced bimodal distribution. About 8% of the masscollected on the impaction stages belongs to the very fine particles and about 92% of themass corresponds to the larger MMD. The size of the very fine particles remains similar
for the next impactor measurement, starting at tHD = 50 min, but the larger MMD increases,
indicating particle growth. The particle mass of the fine particles reduced to about 3%
relative to the totally collected mass.
With respect to the thermal decomposition of CsI in test HD-46, the mass ratio of gaseousiodine relative to the gas-borne CsI, cI,gas /cCsI , was about 1% for the first GS measurementand decayed rapidly due to the depletion of gaseous I2. This finding of test HD-46
corresponds roughly to a conversion factor of 2%. The thermal decomposition of CsI by ahydrogen combustion has been investigated by various experimenters (Nelson, et al.,1985), (Kupferschmidt, et al., 1992), (Brown et al., 1990), (Schmitt, al., 1993), (Gupta etal., 2009), (Deschamps and Sabroux, 2003). Conversion factors between 1.4% and 50%
were reported by the experimenters. However, initial test conditions (pressure, temperature,steam content), test facilities (vessels, burners, PAR), and test procedures (particle
generation, particle injection, particle size distribution, gas composition prior todeflagration, standing flames, particle flow through PAR) were so different that a directcomparison is not possible.

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Figure 3.1. THAI+ configuration and dimensions of the system

Source: Becker Technologies, 2020.

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Figure 3.2. Arrangement of the two-vessel facility within the THAI building

Source: Becker Technologies, 2020.

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Figure 3.3. HD-40 to HD-45 test configuration: Position of igniters, supply systems, DN150 connection pipeand 3-bladed fan

Source: Becker Technologies, 2020.

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Figure 3.4. HD-43, HD-22 and HD-36: Pressure transient

Source: Becker Technologies, 2020.

Figure 3.5. HD-43 to HD-45, HD-36, HD-22: Flame front propagation

Source: Becker Technologies, 2020.
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Figure 3.6. HD-36, HD-43 to HD-45: Peak pressures for different initial flows as function of volumetric flow.
(** peak pressures extrapolated to HD-44 with H2 concentration of 10.2 vol.-% using the slope of the AICC)

Source: Becker Technologies, 2020.

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Figure 3.7. PAR unit (example NIS) and blower position. No blower was installed in HR-50.

Source: Becker Technologies, 2020.

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Figure 3.8. NIS PAR 1/8 module used in test HR-46 with 1 m chimney (left) and in test HR-47 with 0.25 m
chimney (right)

Source: Becker Technologies, 2020.

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Figure 3.9. ½ FR-380 size AREVA PAR unit used in HR tests HR-48 to HR-50

Source: Becker Technologies, 2020.

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Figure 3.10. H2 depletion efficiency of NIS PAR tests HR-14, HR-15, HR-46, and HR-47

Source: Becker Technologies, 2020.

Figure 3.11. Recombination rate at the start-up of AREVA PAR tests HR-7, HR-8, HR-43 and HR-48

Source: Becker Technologies, 2020.

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Figure 3.12. Depletion efficiency of AREVA PAR tests HR-7, HR-8, HR-43 and HR-48

Source: Becker Technologies, 2020.

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Figure 3.13. WH-24, WH-28: Gas injections and gas releases

Source: Becker Technologies, 2020.

Figure 3.14. Primary bubbles leaving the downcomer during phases of low non-condensed volumetric gas
flow, a3), a4) and b1)

Phase a3)

Phase a4)

Phase b1)

Source: Becker Technologies, 2020.

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Figure 3.15. Initial bubbles leaving the downcomer exit, phases a1), a2), a5), b2), b3), and b4.

Ellipsoid a1): 𝑟1 = 𝑟2 = 228 px, 𝑟3 = 160 px

Ellipsoid a2): 𝑟1 = 𝑟2 = 209 px, 𝑟3 = 156 px

Ellipsoid a5): 𝑟1 = 𝑟2 = 210 px, 𝑟3 = 181 px

Ellipsoid b2): 𝑟1 = 𝑟2 = 297 px, 𝑟3 = 276 px

Ellipsoid b3): 𝑟1 = 𝑟2 = 360 px, 𝑟3 = 307 px Ellipsoid b4): 𝑟1 = 𝑟2 = 340 px, 𝑟3 = 300 px
Source: Becker Technologies, 2020.

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Figure 3.16. Mass median diameter of particles as function of the superficial velocity, forboiling and subcooled pool conditions

Source: Becker Technologies, 2020.

Figure 3.17. Average bubble diameters at ImgLow (H = 0.675 m) and ImgUpp (H = 2.125 m) in comparison
to THAI tests WH7-WH15 measured 100 mm below the water surface

Source: Becker Technologies, 2020.

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Figure 3.18. Iod-32: Gas injections and gas releases

Source: Becker Technologies, 2020.

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Figure 3.19. Iodine concentrations in PAD atmosphere

Source: Becker Technologies, 2020.

Figure 3.20. I2 masses in PAD sump, measured data, down-scaled COCOSYS pre-test design calculation by
GRS, and exponential fit to measured data

Source: Becker Technologies, 2020.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  57

Figure 3.21. Iod-34: Test configuration: Iodine injection, sump recirculation, online radiation detectors,
large painted surfaces and sampling stations

Source: Becker Technologies, 2020.

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Figure 3.22. Iod-34: Photographs of painted coupons, comparison of surface degradation, before
deflagration (left), after deflagration (right)

Source: Becker Technologies, 2020.

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Figure 3.23. HD-46 test configuration: CsI injection, horizontal gratings, laser extinction measurement,
aerosol sampling filter and impactor station

Source: Becker Technologies, 2020.

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4. Conclusions

Conclusions were drawn from the results of the experiments conducted in the THAI/THAI+
test facility regarding the following topics:Hydrogen deflagration (HD) tests in two-vessel geometry (HD 40-45);

Hydrogen PAR tests (HR 46-50);

Soluble and gaseous fission product (CsI, iodine) release from a boiling pool(WH-24, WH-28, Iod-32);

Resuspension of iodine from paint by hydrogen deflagration (Iod-34);

Resuspension of aerosol deposits from surfaces by hydrogen deflagration (HD-46).

4.1. HD experiments
The hydrogen deflagration test series consisted of six tests (HD40-45) performed in the
two-vessel configuration (THAI+) under uniformly mixed and stratified gas atmosphereconditions. The conclusions drawn from the results of the experiments HD-40 to HD-45
are listed below, and include the conclusions from the results of experiments performed
previously in THAI/THAI+ tests.


During combustion, no pressure difference between the two vessels was observed,
i.e. the two-vessel geometry behaved in this respect like a single vessel.

Compared to the tests in the two-vessel facility, preceding tests performed in the
single THAI vessel with the same initial conditions showed generally slightly
higher peak pressures. This applies for both the well-mixed and stratified tests andeven for tests with jet ignition-like combustion and has been attributed to anincreased heat transfer due to the different surface/volume ratio (higher for the twovessel facility). HD-42 is exceptional in this context due to noticeable pressure
oscillation occurring inside the PAD, which leads to peak pressures being larger in
the THAI+ configuration compared to the single THAI vessel.



For the tests with a stratified atmosphere and upward burn direction, thecomparison of single (THAI) and two-vessel tests (THAI+) showed nounambiguous trend with respect to peak pressures. With respect to H2 stratification,
peak pressures were highest for the tests with homogeneous H2 distribution (steam
concentration and temperature still stratified). The reason is the higher mean H2concentration and the complete combustion in these tests. Any enhancing effectwith respect to peak pressure, e.g. due to larger scale or interacting flame fronts inthe two-vessel facility, was not determined.

Combustion modes similar to jet ignition could be observed only in the two-vessel
facility. In the tests HD-40, HD-41 and HD-36, it occurred always as a downward,
fast combustion in the upper half of the PAD and was most pronounced for test
HD-36, with average H2 concentrations higher than for tests HD-40 and HD-41. In
addition, test HD-36 exhibited the highest mean H2 concentration (10.3 vol.-%) andthe steam was superheated. It should be emphasised that to achieve a real jet
ignition with a pressure increase higher in the downstream compartment than in the
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ignition compartment, higher H2 concentrations than those used in the present test
series are required, as has been found by many other experiments conducted
elsewhere.
Flame acceleration was observed in the test series, particularly inside the lower andupper connection tube, caused by diameter change ahead of the expanding flame
and increased turbulence in the connecting pipes. The most pronounced flame
acceleration occurred in the lower connecting pipe in test HD-41 (H2 concentration
12 vol.-% in the pipe, quasi no steam, relatively low temperature), with a flame
speed of approximately 50 m/s.

For some of the tests, a flow velocity of up to 7.5 m/s in the interconnecting pipes
and up to 0.3 m/s in the PAD was established prior to ignition. This flow produced
significant initial turbulence in the interconnecting pipes, with an associated highflame speed in the pipes even opposite to the initial flow direction. Peak pressuresincreased slightly with flow velocity. The comparison to a test with the same initialconditions, but without initial flow, revealed a higher flame speed in the upperinterconnecting pipe with downward-directed jet ignition into the upper half of the
PAD, i.e. the influence of an initial flow on combustion behaviour is noticeable.

4.2. HR experiments
Five tests (HR-46 – HR-50) were conducted to investigate the effect of counter-current
flow conditions on PAR performance behaviour. The flow loop with a magnitude of 0.5 m/s
to 1 m/s in the vicinity of the PAR was established with a blower. For tests HR-46 and HR47, an NIS 1/8th module PAR was installed inside the PAD vessel and for tests HR-48 toHR-50 an AREVA FR-380 PAR was installed, which was reduced to half of the numberof catalytic foils of the actual PAR. The main results are summarised below:


Generally, the test results indicate that the AREVA PAR with top cover on thechimney (lateral outlets) provided effective means to protect the PAR from
intrusion of counter-current flow within the range of investigated conditions
whereas the NIS PAR with an open-ended outlet without top cover was prone to
intrusions of counter-current flow in case of low H2 concentrations.



In case of AREVA PAR, counter-current flow had no measurable impact on theperformance behaviour under the investigated conditions.



Large convection loops inside the THAI+ facility were effective measures totransport the hydrogen from its release location towards the recombiners.

Comparing the test results of HR-46 and HR-47 with initially counter-current flow
conditions and of the previous HR tests (initially quiescent) using the NIS PAR
under similar thermodynamic boundary conditions revealed that the first onset ofhydrogen recombination was much faster under conditions of counter-current flow.
However, the recombination rate was significantly reduced as long as the hydrogenconcentration remained below about 2-3 vol.-%, due to an initially stable
downward flow and later oscillations of the flow direction inside the PAR. For
higher hydrogen concentrations, the recombination rate and hydrogen depletion
efficiency of the NIS PAR are in agreement with those determined earlier ininitially quiescent THAI HR-experiments. The shortening of chimney height
resulted in a reduced PAR internal flow, which could be explained by the reduced
buoyancy induced chimney flow. For test HR-47 (NIS PAR), with reduced
chimney height, the efficiency increased by about 10% due to a reduced internal

OECD/NEA THAI-3 PROJECT FINAL REPORT62  NEA/CSNI/R(2021)8
gas velocity, which in turn increased the residence time of the hydrogen at thecatalytic cartridges.

4.3. Soluble and gaseous fission product (CsI, iodine) release from a boiling poolThree tests were conducted to investigate wet resuspension or re-entrainment of aerosols(WH-24 and WH-28) and the release of volatile gaseous iodine (Iod-32) from a water pool
under boiling conditions. The gas superficial velocity was in the range of 0.01 to 0.12 m/s.
In the WH-24 test, aerosol re-entrainment was quantified based on the concentrations of
CsI particles released from the sump within a total of 12 test phases using injection of air,steam and a mixture of steam and air injection through a scaled down DN 100 downcomer
pipe into the vessel sump. The investigated test conditions included aerosol release from apool under subcooled conditions at a broad range of pool temperatures and during flashing
due to depressurisation. The sump of the vessel was filled with about 4.6 m3 of water inwhich 10 g/L caesium iodide was dissolved as a representative fission product. The vessel
walls were heated to 138°C to provide a superheated atmosphere, which was necessary to
dry the aerosol particles released from the sump by entrained water droplets. The aerosol
released from the sump into the gas space has was measured independently by using two
sampling filters, a large integral filter and two gas scrubbers. The size distribution of theaerosol particles was determined using a low-pressure cascade impactor, resulting in small
particles. These particles remain airborne in the long term and will be of relevance for theprediction of a potential radiological source term.
The gas release and the behaviour of the bubble column were measured by high-speed
digital imaging. Digital data processing was applied to evaluate the bubble formation
frequency, the bubble break-up and the terminal velocity of the gas bubbles below thewater’s surface. The bubble diameter below the pool surface was found to increase with
the injection Weber number from about 1.5 mm for low injection gas flows up to 3 mm forhigh steam injection mass flows. The image processing of the bubble column width wasused to approximate the superficial velocity based on the area through which the gas bubble
break-through will occur at the pool surface.
The entrainment calculated from the aerosol measurements was in accordance withprevious experimental findings obtained in the THAI facility and other test facilities.
Entrainment values were between E = 5 ⋅ 10−6 and E = 7 ⋅ 10−5 in test WH-24. The
entrainment in WH-24 initially increased with superficial gas velocities but decreased foreven larger superficial velocities belonging to the transition and churn turbulent flow
regime.
Deviating from test WH-24, for test WH-28 the surface tension of the water was reduced
by adding surfactant and antifoaming emulsion to suppress the foaming tendency of theliquid. The reduction of the surface tension in WH-28 favoured the release of larger
particles compared to WH-24, but on the other hand a high number of tiny particles werealso released, generating bimodal distributions.
The entrainment calculated from the aerosol measurements in tests with surfactant was
about one order of magnitude larger compared to the de-mineralised water of test WH-24.
In test WH-28, entrainment values during different test phases varied between E = 3 ⋅ 10−6
and E = 3 ⋅ 10−3 . The overall highest entrainment rates were obtained in the bubbly flow
regime whereas the entrainment decreases for large superficial velocities corresponding to
the transition and churn turbulent regime.

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Results from different particle measurement techniques that were used to evaluate theentrainment in tests WH-24 and WH-28 indicate that the absolute entrainment is subject touncertainty by a factor of 2 – 5.
Test Iod-32 was performed to study the release of volatile iodine from a boiling sump. The
test was run in the PAD vessel, using the THAI vessel as a pressure relief tank.
At the start of a reference phase in non-boiling conditions, 0.73 g of molecular iodine (I2)radio-labelled with I-123 was injected into the sump water (V = 1.09 m³) of the PAD, anda small amount of I2 was released to the PAD atmosphere within 2.5 hours. The great
majority of the aqueous I2 was converted into non-volatile iodine by reaction with the steel
wall of the sump. This I2 depletion was limiting the I2 releases from the sump.
Before starting the second test phase, another 0.73 g I2 was injected into the PAD sump
(V = 1.09 m3). Boiling was induced by a 5 min depressurisation and maintained by steam
injection into the sump water. The gas atmosphere from the PAD was vented to the TTV
during both the depressurisation and the steam injection phases. This led to a release of I2
from the sump water: the I2 release was ten times higher compared to the non-boilingconditions in the reference phase.
The I2 concentration in the gas was higher by a factor of 100 after boiling, compared to theend of the reference phase. The online detectors indicated a stronger I2 release upondepressurisation compared to the I2 release induced by steam injection into the boiling sump
water.

4.4. Resuspension of iodine from paint by hydrogen deflagration
Test Iod-34 studied the resuspension of iodine from surfaces coated with decontamination
paint by a hydrogen deflagration, where the paint was pre-loaded with iodine in a
representative manner. The reference test for hydrogen deflagration was the THAI test
HD-22 conducted in the framework of the NEA THAI project.
In the first phase of the test, I2 (1 g) was injected into the THAI vessel at a temperature ofabout 90 °C and a steam concentration about 25 vol.-%. Within 5 hours, the gaseous I2 wasdecreased to a level of less than 1% due to deposition onto painted surfaces and steel walls.
In a second test phase, the unwanted but inevitable I2 deposition on steel walls of the THAI
vessel was washed off with three sprayings of fresh, decalcified water and the washediodine was removed from the THAI into the PAD vessel.
Prior to the H2 deflagration, the gas phase iodine concentration was practically free of
iodine. The deflagration produced peak gas temperatures above 900 °C. The iodine releasefrom paint into the vessel atmosphere was measured using gas scrubbers (total gas-borne
iodine), Maypack filters (iodine in aerosol form, molecular iodine, organic iodide) andonline monitoring of the iodine loadings on deposition coupons. SEM/EDX analyses andmicroscopy of used and unused paint coupons were performed to characterise the paintdegradation due to H2 deflagration.
The H2 deflagration induced a significant iodine release from the surfaces to the gas phase.
The iodine release fraction amounts to a range between 4 and 9% of iodine inventory predeposited before H2 deflagration, considering experimental uncertainties of the initialiodine loadings on the painted and steel surfaces. Out of the resuspended amount, 50% of
the iodine released by H2 deflagration was in the form of gaseous organic iodide.
The H2 deflagration strongly degraded the painted surfaces, which showed a flaky structure,including blistering, cracks and craters. Degradation was approximately similar over the

OECD/NEA THAI-3 PROJECT FINAL REPORT64  NEA/CSNI/R(2021)8
whole THAI vessel and increased at the edges of the painted coupons. Consistent with paintdegradation, significant aerosol concentration in the gas atmosphere was observed visually.

4.5. Resuspension of aerosol deposits from surfaces by hydrogen deflagration
The objective of test HD-46 was to study the resuspension of aerosols that were depositedon vertical, horizontal and containment-typical step grating surfaces and the thermal
decomposition of CsI particles by hydrogen deflagration.
In the first phase of the test, CsI particles (242 g) were injected into the THAI vessel andcharacterised by measuring the airborne particle concentration and their size distribution.
Within 29 h after the aerosol release into the vessel, at least 99.5% of the injected CsI mass
was deposited onto the walls. Thereafter, an ignitable gas mixture (1.47 bar, 89.7°C, 23.6
vol.-% steam, 10.1 vol.-% H2) was established in the vessel.
The hydrogen deflagration, with peak pressure of almost five bar and peak gas temperatures
above 900 °C, resuspended about 4% of the previously deposited CsI, which settled much
more slowly.
In addition to particle resuspension, the release of gaseous iodine by thermal decompositionof CsI particles due to the high temperatures during hydrogen deflagration was measured
by using GSs. Aerosol filters were installed upstream of the GS to discriminate iodine ingaseous form from iodine in aerosol form. The mass ratio of gaseous iodine relative to theparticulate CsI was about 1% in the first gas scrubber measurement after the deflagration
event. The I2 concentration decayed rapidly due to the physisorption of gaseous I2 on CsI
particles or the steel walls of the vessel. The corresponding conversion factor that quantifies
the thermal decomposition of CsI by relating the released molar concentration of gaseousiodine to the initial molar concentration of CsI is about 2%.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  65

References
Brown, M.L., E.C. Beahm and W.E. Shockley (1990), The Oxidation of Cesium Iodide in Stationary
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Balewski, B., S. Gupta and K. Fischer (2011), “Water Flow with Bubble Columns - Boiling Water
Reactor Experiments WH-7 to WH-152”, Report 1501361–WH-7-15-FB/TR, Becker Technologies
GmbH, Eschborn, Germany, October 2011.
Deschamps, F. and J.C. Sabroux (2003), “Particulate Iodide to Gaseous Iodine Conversion in a Passive
Autocatalytic Recombiner”, J. Aeros. Sci., Vol. 34, pp 1087-1088, 2003.
Freitag, M., A. Kühnel and G. Langer (2016), “Erweiterung der THAI-Anlage durch einen zweiten
Druckbehälter: THAI+ - Extension of the THAI test facility by a second vessel: THAI+”, Technical
Report 1501455-FB/TR-THAI+, Becker Technologies GmbH, Eschborn, Germany, May 2016.
Freitag, M., E. Schmidt, M. Colombet, von Laufenberg, B., A. Kühnel and S. Gupta (2016),“Rekombinator in Gegenströmung”, HR-43 to HR-45, Technical Report 1501455-TR-HR43-45,
Becker Technologies GmbH, Eschborn, Germany, August 2016.
Freitag, M., B. von Laufenberg and E. Schmidt (2017a), “Hydrogen Deflagration Tests in a Two-Vessel
Test Facility Test series HD-36 – HD-39”, Technical Report 1501455 – TR – HD36-39, Becker
Technologies GmbH, Eschborn, Germany, March 2017.
Freitag, M., B. von Laufenberg and E. Schmidt (2017b), “Re-Entrainment of Fission Products from
Water Pools at Elevated Temperature – Test WH-24”, Technical Report No. 1501516 – TR – WH-24,
Becker Technologies GmbH, Eschborn, Germany, December 2017.
Freitag, M., B. von Laufenberg and E. Schmidt (2017c), “Hydrogen Deflagration Tests in a Two-Vessel
Test Facility Test series HD-36 – HD-39”, Technical Report 1501455 – TR – HD36-39, Becker
Technologies GmbH, Eschborn, Germany, March 2017.
Freitag, M. and E. Schmidt (2017), “Passive Autocatalytic Recombiner Operation under Counter Current
Flow Conditions - Test series HR-46- HR-50”, Technical Report No. 1501516 – TR – HR-46 – HR50, Becker Technologies GmbH, Eschborn Germany, June 2017.
Freitag, M., B. von Laufenberg, E. Schmidt and M. Colombet (2018), “Re-Entrainment of Fission
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Freitag, M. and M. Sonnekalb (2018), “Comparison Report for Blind and Open Simulations of HR-49.
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Freitag, M., E. Schmidt and G. Langer (2019), “Hydrogen Combustion and Flame Propagation in Twocompartment system – Test series HD-40 to HD-45”, Report No. 1501516-TR-HD40-HD45, Becker
Technologies GmbH, Eschborn, Germany, January 2019.
Freitag, M., E. Schmidt, A. Kühnel, M. Colombet and B. von Laufenberg (2019), “Aerosol Resuspension
and Thermal Decomposition by Hydrogen Deflagration - Test HD-46”, Technical Report No.
1501516 – TR – HD-46, Becker Technologies GmbH, Eschborn, Germany, September 2019.

OECD/NEA THAI-3 PROJECT FINAL REPORT66  NEA/CSNI/R(2021)8
Freitag, M and M. Sonnenkalb (2019), “Comparison Report for Blind and Open Simulations of HD-44.
Hydrogen combustion and flame propagation in two-compartment system with initial convectiveflow”, Report No. 1501516-CR-HD44, Becker Technologies GmbH, Eschborn, Germany, September
2019.
Funke, F., M. Freitag, E. Schmidt, A. Kühnel, G. Langrock and B. von Laufenberg (2018), “Volatile
Iodine Release from Boiling Water Pool at Elevated Temperature – Test Iod-32”, Technical Report
No. 1501516 – TR – Iod-32, Becker Technologies GmbH, Eschborn, Germany, June 2018.
Funke, F., M. Freitag, E. Schmidt, A. Kühnel, G. Langrock and B. von Laufenberg (2019), “Iodine
Resuspension from Painted Surfaces by Hydrogen Deflagration - (Test Iod-34)”, Technical Report No.
1501516 – TR – Iod-34, Becker Technologies GmbH, Eschborn, Germany, October 2019.
Gupta, S., G. Langer, G. Langrock and F. Funke (2009), “Hydrogen Recombiner Test HR-31 CsI-PAR
Interaction”, Technical Report 1501326–HR-QLR-5, Becker Technologies GmbH, Eschborn,
Germany, September 2009.
Gupta, S., M. Freitag, E. Schmidt, M. Colombet, B. von Laufenberg, A. Kühnel, G. Langer, F. Funke, G.
Langrock, et al. (2017), “Ein- und Mehrraumversuche zum Spaltprodukt- und Wasserstoff-Verhalten
im Sicherheitsbehälter – THAI-V. Single- and Multi-Compartment Tests on Fission Product andHydrogen Behaviour in the Containment – THAI-V”, Final Report 1501455-FR, Becker Technologies
GmbH, Eschborn, Germany, April 2017.
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Kanzleiter, T. (2009), “Recombiner Tests HR-14 to HR-16. (Tests using a NIS PAR) Areva, AECL andNIS PAR Comparison”, Quick Look Report, Hydrogen Reactor Safety Research Project 150 1326
OECD-NEA, THAI Project Report No. 1501326-HR-QLR-4, Becker Technologies GmbH, Eschborn,
Germany, October 2009.
Kataoka, I. and M. Ishii (1984), “Mechanistic Modelling of Pool Entrainment Phenomenon”,
International Journal of Heat and Mass Transfer, Vol. 27 (11), pp. 1999–2014, 1984, Elsevier,
Amsterdam.
Kupferschmidt, W.C.H., J.B. Buttazoni, G.J. Evans, D.R. Harris, D.R. Greig, G.W. Koroll and G.G.
Sanipelli, (1992), “The effects of Steam on the Oxidation of Cesium Iodide Aerosol during Hydrogen
Combustion, Advanced containment experiments report”, ACE-TR-B8, 1992.
NEA (2016a), Aerosol and Iodine Issues, and Hydrogen Mitigation under Accidental Conditions in
Water Cooled Reactors: Thermal-hydraulics, Hydrogen, Aerosols and Iodine (THAI-2) Project,
OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_19708.
NEA (2016b), Benchmark Study of the Accident at the Fukushima-Daiichi Nuclear Power Plant (BSAF
Project): Phase I Summary Report, OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_19680/.
NEA (2010), Hydrogen and Fission Product Issues Relevant for Containment Safety Assessment under
Severe Accident Conditions, OECD Publishing, Paris, www.oecd-nea.org/jcms/pl_18928/.
Nelson, L.S., W.B. Benedick, W. Einfeld, K.P. Guay, G.D. Valdez, J.H. Lee, R. Knystautas, M. Fresko
and M. Gaug (1985), “The Behavior of Reactor Core-simulant Aerosols during Hydrogen/Air
Combustion”, Report SAND85-1817C Sandia National Laboratories, Albuquerque, 1985.
Paul, D.D., D.C. Newman and R.A. Cudnik (1991), “Radionuclide Scrubbing in Water Pools. Volume 2:
Gas-liquid Hydrodynamics with Full-scale Downcomers and Horizontal vents”, Report EPRI NP4154-L, Vol. 2, October 1991.

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von Rohr, R. (2000), “Einfluss der Naturkonvektion im Sicherheitsbehälter nach einem schweren
Kernschmelzunfall auf die kontrollierte Druckentlastung”, REVENT II, Teil 3. ETH Zürich,Abschlußbericht für das Bundesamt für Energie, Dez 2000.
Schmitt, R. E., M. Fiedler, V. Friehmelt and L Wandzilak (1993), “Experimentelle Untersuchung überdas Verhalten von CsI bei H2-Verbrennung”, Final Report BF - R 67.818, Battelle-Institut, Frankfurt,
Germany, September 1993.

OECD/NEA THAI-3 PROJECT FINAL REPORT68  NEA/CSNI/R(2021)8

Annex A. List of project reports

The reports listed below are restricted to the project signatories. However, the Management
Board of the THAI Project has agreed that these Quick Look Reports (QLRs) and Technical
Reports (TRs) be disclosed for non-signatory NEA countries after 31 June 2023. They may
be obtained after this date upon request to the NEA Secretariat.

Project deliveries
Quick Look Reports (QLR)
Freitag, M. and E. Schmidt (2018), “Hydrogen Combustion and Flame Propagation in Twocompartment System”, Test series HD-40 – HD-45, Report No QLR- HD-40 – HD-45,
Becker Technologies GmbH, Eschborn, Germany, September 2018.
Schmidt, E. and M. Freitag (2016), “Passive Autocatalytic Recombiner Operation underCounter Current Flow Conditions”, Test series HR-46 – HR-50, Report No. QLR –HR46-50, Becker Technologies GmbH, Eschborn, Germany, August 2016.
Freitag, M. and E. Schmidt (2017), “Re-Entrainment of Fission Products from Water Pools
at Elevated Temperature”, Test WH-24, Report No. QLR – WH24, Becker Technologies
GmbH, Eschborn, Germany, July 2017.
Freitag, M. and E. Schmidt (2018), “Re-Entrainment of Fission Products from Water Pools
at Elevated Temperature with Reduced Surface Tension”, Test WH-28, Report No. QLR –WH28, Becker Technologies GmbH, Eschborn, Germany, September 2018.
Freitag, M., E. Schmidt, F. Funke and G. Langrock, (2018), “Volatile Iodine Release from
Boiling Water Pool at Elevated Temperature”, Test Iod-32, Report No. QLR – Iod32,
Becker Technologies GmbH, Eschborn, Germany, Framatome GmbH, Erlangen, Germany,
March 2018.
Funke, F., M. Freitag, E. Schmidt, A. Kühnel, G. Langrock and B. von Laufenberg (2019),“Iodine Resuspension from Painted Surfaces by Hydrogen Deflagration”, Test Iod-34,
Report No.1501516 QLR–Iod-34, Framatome Work Report D02-ARV-01-145-495,
Framatome GmbH, Erlangen, Germany, Becker Technologies GmbH, Eschborn, Germany,
April 2019.
Freitag, M. et al. (2019), “Aerosol Resuspension and Thermal Decomposition by Hydrogen
Deflagration”, Test HD-46, Quick Look Report No. 1501516 – QLR – HD-46, Becker
Technologies GmbH, Eschborn, Germany, May 2019.

OECD/NEA THAI-3 PROJECT FINAL REPORTNEA/CSNI/R(2021)8  69

Technical Reports (TR)Freitag, M., E. Schmidt and G. Langer (2017), “Hydrogen Combustion and Flame
Propagation in Two-compartment system”, Test series HD-40 to HD-45, Report No.
1501516-TR-HD40-HD45, Becker Technologies GmbH, Eschborn, Germany, January
2019.
Freitag, M. and E. Schmidt (2017), “PAR Operation under Counter Current Flow
Conditions”, Test series HR-46- HR-50, Technical Report No. 1501516 – TR – HR-46 –HR-50, Becker Technologies GmbH, Eschborn, Germany, June 2017.
Freitag, M., B. von Laufenberg and E. Schmidt (2017), “Re-Entrainment of Fission
Products from Water Pools at Elevated Temperature”, Test WH-24, Technical Report No.
1501516 – TR – WH-24, Becker Technologies GmbH, Eschborn, Germany, December
2017.
Freitag, M., B. von Laufenberg, E. Schmidt and M. Colombet (2018), ‘Re-Entrainment of
Fission Products from Water Pools at Elevated Temperature with Reduced Surface
Tension”, Test WH-28, Technical Report 1501516 – TR – WH-28, Becker Technologies
GmbH, Eschborn, Germany, December 2018.
Funke, F. et al (2018), “Volatile Iodine Release from Boiling Water Pool at ElevatedTemperature”, Test Iod-32, Technical Report No. 1501516 – TR – Iod-32, Becker
Technologies GmbH, Eschborn Germany, June 2018.
Funke, F. et al (2019), “Iodine Resuspension from Painted Surfaces by Hydrogen
Deflagration”, Test Iod-34, Technical Report No. 1501516 – TR – Iod-34, Becker
Technologies GmbH, Eschborn, Germany, October 2019.
Freitag, M. et al (2019), “Aerosol Resuspension and Thermal Decomposition by Hydrogen
Deflagration”, Test HD-46, Technical Report No. 1501516 – TR – HD-46, Becker
Technologies GmbH, Eschborn, Germany, September 2019.

Final project report
Gupta, S., G. Poss, M. Freitag, E. Schmidt, M. Colombet, B. von Laufenberg, A. Kühnel,
G. Langer, F. Funke and G. Langrock, (2020), “Fission product behaviour, hydrogen
mitigation, and hydrogen combustion in water cooled reactors under severe accident
conditions”, OECD/NEA THAI-3 Project Final Report No. 1501516–FR-1 (Restricted
Version), Becker Technologies GmbH, Eschborn, Germany, March 2020.

OECD/NEA THAI-3 PROJECT FINAL REPORT