Table Of ContentShengyao Jiang · Jiyuan Tu ·
Xingtuan Yang · Nan Gui
Multiphase Flow
and Heat Transfer
in Pebble Bed
Reactor Core
Multiphase Flow and Heat Transfer in Pebble Bed
Reactor Core
Shengyao Jiang Jiyuan Tu
(cid:129) (cid:129)
Xingtuan Yang Nan Gui
(cid:129)
Multiphase Flow and Heat
Transfer in Pebble Bed
Reactor Core
123
Shengyao Jiang Jiyuan Tu
TsinghuaUniversity RMIT University
Beijing,China Melbourne, VIC,Australia
XingtuanYang Nan Gui
TsinghuaUniversity TsinghuaUniversity
Beijing,China Beijing,China
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Foreword by Goodarz Ahmadi and Takashi
Hibiki
Since the Three Mile Island accident in 1979 and the Chernobyl accident in 1986,
designing an inherently safe nuclear reactor has attracted worldwide attention. In
thiscontext,“thegenerationIVadvancednuclearpowersystem”,wasproposed.In
an effort to optimize the High-Temperature Gas-cooled Reactor (HTGR), consid-
ered as a safe and efficient reactor, Institute of Nuclear and New Energy
Technology (INET) at Tsinghua University has developed a demonstration reactor
and conducted extensive research in the past decades. This book provides a com-
prehensive collection of the research methods and achievements of the authors’
team on HTGR over the years.
This book starts with an introduction to HTGR and the critical issues such as
pebble flows, gas-phase hydrodynamics, and inter-phase heat transfer
(thermal-hydraulics) inside the reactor core. It provides a detailed understating
of the granular flow, which is quite interesting and meaningful. Granular flow is
common,butitsdynamicsisquitecomplicated,especiallyforthequasi-staticflow
regime inside the HTGR core. To provide a deep understanding of the flow
mechanisms, the authors have carried out both experimental, phenomenological
analysis, and numerical studies using the discrete element method and the contin-
uumapproach.Flowcharacteristicssuchasvelocity,mixing,intermittency,aswell
as the subdivision offlow regimes are explained thoroughly in this book.
The inherent safety of HTGR at high power requires a thorough knowledge
of the two-phase heat-transfer processes. In this regard, a full-radius-scale
heat-transfer testing facility has been built, and an overview of the experimental
process for measuring the thermal properties of a pebble bed under different con-
ditions is presented. The authors have also developed several numerical models,
including thermal radiation and conduction, which have been shown to be appro-
priate for the heat-transfer study of the pebble bed. Each model and its application
areexplainedindetail.Theseinnovativeresearchworksareofgreatsignificanceto
ensure the balance between safety and economic competitiveness.
v
vi ForewordbyGoodarzAhmadiandTakashiHibiki
Lastbutnotleast,thediscussionsrelatingtotheoptimizationofthepebblebed,
including the two-region pebble bed, wall structure, and friction optimization, are
allpromisingtechniques,whichcanpromotefutureimpactfulideasinthedesignof
pebble beds.
This book is full of profound, innovative, and instructive insights. It introduces
state-of-the-art research progresses on pebble flow and heat transfer, with inter-
estingunderlyingphysicsrevealingthecomplicatedinteractionsandmechanismsin
theHTGRcore.Werecommendthisbooktothosewhoareinterestedinmultiphase
flows and heat transfer. The research methods introduced in this book can also be
applied to many other fields such as chemical industries, mineral processing,
geophysical applications, agricultural industries, pharmaceutical industries, energy
production, powder technology, and so on. For professionals, researchers, and
engineeringdesignersworkingwithpebblebeds,thisbookisanexcellentreference
and source of inspiration, especially for the future development of HTGR.
July 2020 Goodarz Ahmadi
Distiguished Professor
Clarkson University
Potsdam, USA
Takashi Hibiki
Professor Emeritus
Purdue University
West Lafayette, USA
Foreword by Hongguang Jin
High-Temperature Gas-cooled Reactor (HTGR) is considered one of the most
promising solutions for Generation IV advanced reactors by researchers in the
nuclear energy field. Extensive studies have been carried out in China, the USA,
Germany,andSouthAfrica,whichhavepromotedthedevelopmentofpebble-type
HTGR significantly. Among suchefforts, Prof. Jiang and his team from Institution
of Nuclear and New Energy Technology (INET) of Tsinghua University in China
have had extraordinary contribution.
Approved as one of the “Major Project”s of National Science and Technology
andbasedontheforwardstudiesof10MWhigh-temperaturereactor(HTR-10),the
pebble flow and the heat transfer in the pebble-type HTGR are investigated pro-
foundly. The high-temperature reactor-pebble-bed module (HTR-PM) is under
constructioninShandongProvinceinChina.Agreatnumberoffindingsfromprior
studieshavebeenvalidatedinthisproject,whichprovidedinstructiveknowledgeto
scientists and personnel in the nuclear power industry.
High uniformity and the minimum stagnation of the pebble flow are highly
desiredwithgraphite-coatedfuelpebblesinthefuelcycletopreventoverheatingat
specific areas when the reactor is in operation. By conducting experimental com-
parisonsofdifferentbedconfigurations,Prof.Jiangandhisgrouphaveinvestigated
thestateoftheartoftheschemeofpebble-bedconfigurationandidentifiedthebulk
dynamicsandphenomenaofpebbleflows.Basedonthework,theyhaveproposed
relevant parameters to analyze the flow pattern and uniformity, and optimized the
Particle Tracking Velocimetry (PTV) method, which has proven to be very effec-
tive.Accordingtotheexperimentsandvelocitycharacteristicsofthepebblebed,a
correlationtimeandanewintermittencyindexareproposedfrombothmacroscopic
and microscopic perspectives to analyze the flow pattern, which has significant
value to future optimization of the pebble flow.
To optimize the efficiency of the pebble flow with substantially more cases,
numerical models and schemes must be established and adopted. In this work, the
Discrete Element Method (DEM), a widely utilized approach, is employed.
The DEM successfully simulates a real-scale three-dimensional pebble-bed reactor
HTR-PM, and it is reasonable to consider that the pebble flow is a mass flow
vii
viii ForewordbyHongguangJin
problem within the main body of the bed while a funnel flow problem within the
conical base.
Further optimization of the established model is carried out. In addition to the
investigation of the preferable wall structure, Prof. Jiang’s team has performed an
optimizationstudyonflow-correctiveinsert,conicalbase,anddischargingsilofrom
the reactor’s geometric perspective. The authors also contributed to the optimiza-
tion of friction and flow dynamics from the mechanical perspective. The opti-
mizations are very helpful for practical implementations and further developments
of HTGR in the nuclear industry, particularly the 600MW-HTR-PM project.
Quasi-static pebble flow in HTGR has provided numerous ideas to the solution
of non-uniformity and stagnation in the fuel cycle. In addition, heat transfer in a
pebble bed is of vital importance for the safety of the reactor.
Therefore, experiments in the full-radius-scale heat test facility measure the
effective thermal diffusivity and conductivity in four independent tests. Compared
with SANA (Secure Decay Heat Removal in German) and HTTU
(High-Temperature Test Unit in South Africa), this work expands the temperature
range of the effective thermal conductivity in the reactor and the methodology can
be applied to the measurement for temperatures up to 1600 °C, significantly con-
tributing to the improvement of the inherent safety for HTGRs.
Numerical models of heat transfer in pebble beds of HTGRs present a com-
prehensive view on obtaining effective thermal conductivity. Continuum and dis-
crete methods are adopted, and varying scales of radiation are discussed. Among
convective, conductive, and radiative heat transfers, radiation is particularly
importantastheoperatingtemperatureinthereactorisabout800°Candcanreach
1600 °C in transient or severe accidents. In addition, radiation accounts for most
of the transferred heat. The Short-range Radiation Model (SRM), the improved
Short-Range Model (SRM+), the Long-range Radiation Model (LRM), the
Microscopic Scale Model (MSM), the Semi-Empirical Model (SEM), and the
Sub-Cell radiation Model (SCM) perform well under specific circumstances and
inspirethesubsequentresearches.BasedonSRM,furtherimprovementincoupled
CFD-DEMsimulationsbytakingthecoolantintoconsiderationispioneeringinthe
new smoothed void fraction method, which provides a brand-new view and chal-
lenge to investigate it profoundly.
I highly recommend this technical book to those who are interested in the
nuclear power industry, and also to professionals in the development of nuclear
energy, multiphase flow and heat transfer. Although Prof. Jiang’s team focused on
the complex system of helium and pebbles coupled with neutron-physics which
exists in the nuclear reactor core, the common solutions and schemes provided in
this book are indeed also applicable for the gas–particle multiphase flow and
high-temperatureheattransfersystemsinotherresearchfields,e.g.,thepackedbeds
or the spouted/fluidized beds in Engineering Thermophysics. This work not only
ForewordbyHongguangJin ix
demonstrates the latest developments in HTGRs technology, but also proposed
numerous ideas about pebble flow and heat transfer in pebble beds. The radiative
heat transfer particularly deserves close and careful reading if you are carrying out
projects in a similar field.
July 2020 Prof. Hongguang Jin
AcademicianofCAS,Presidentofthe
Chinese Society of Engineering
Thermophysics, Institute of
Engineering Thermophysics, Chinese
Academy of Sciences
Beijing, Peoples’ Republic of China
University of Chinese Academy of Sciences
Beijing, Peoples’ Republic of China
Acknowledgments
Firstly, I would like to thank my research group (Collaborative Innovation Center of
Advanced Nuclear Energy Technology, Institute of Nuclear and New Energy
Technology(INET)atTsinghuaUniversity),Prof.ZuoyiZhang(DeanofINET),Prof.
Yujie Dong (Deputy Dean of INET), and all colleagues of Key Laboratory of
AdvancedReactorEngineeringandSafety,whohaveparticipatedinthecompilationof
this book. It is because of your unremitting support that this book is completed.
It is of great pleasure to work with such an excellent research team, with regular
discussion and exchange of ideas, sharing of the project progress, and helping each
other unsparingly. This book is the result of our team effort. Thanks for your contri-
bution in revising the first draft, sharing your opinions, and putting forward so many
valuable suggestions.
Secondly, I would like to thank all the people and organizations who have
supported this book and our research, in particular, the support from the national
major science and technology project (2011ZX06901-003), National High
TechnologyResearchandDevelopmentProgramofChina(863)(2014AA052701),
as well as Tsinghua University Press and Springer Nature. The publication of this
book is inseparable from your contribution.
Thanks to all prior works cited in this book, from which we obtained countless
inspiration. These inspirational works have laid the foundation and are of great
value to our research.
Finally,Iwouldliketothankalltheresearchers,designers,andregulatorsinvolved
in the research project of the high-temperature gas-cooled reactors. We are looking
forwardtothecontinuedjointeffortstocontributetothefuturedevelopmentofHTGR.
July 2020 Shengyao Jiang
Tsinghua University
Beijing, Peoples’ Republic of China
xi
