The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Delayed Hydride Cracking

475 Pages·2012·8.56 MB·English

by  Manfred P. Puls (auth.)

Engineering Materials
For furthervolumes:
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Manfred P. Puls
The Effect of Hydrogen
and Hydrides on the
Integrity of Zirconium
Alloy Components
Delayed Hydride Cracking
123
Manfred P.Puls
MPPConsulting
Oakville, ON
Canada
ISSN 1612-1317 ISSN 1868-1212 (electronic)
ISBN 978-1-4471-4194-5 ISBN 978-1-4471-4195-2 (eBook)
DOI 10.1007/978-1-4471-4195-2
SpringerLondonHeidelbergNewYorkDordrecht
LibraryofCongressControlNumber:2012940465
(cid:2)Springer-VerlagLondon2012
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To my family:
Wife Gloria; children Larissa and Nicholas;
grandchildren Alexander, Jessica,
Pascale, Benjamin and twins Ashton and
Brayden
Preface
Zirconium alloys are widely used in nuclear reactors, their most challenging
applications being as cladding for nuclear fuel in Pressurized and Boiling Water
Reactors (PWR and BWR, respectively) and as pressure tubes in CANDUTM and
Pressurized Heavy Water (PHW) reactors. The possible failure of these compo-
nentshasconsequencestothesafeandeconomicoperationofthesereactors.Data
andunderstandingtopreventanysuchfailuresis,therefore,ofgreatimportanceto
the nuclear industry. It was recognized early on in the development of the design
of nuclear reactors that these alloys have an affinity for absorbing hydrogen both
during their manufacture and operation. When the hydrogen solubility limit in
thesealloysisexceeded,theirexcessamountresultsintheformationofzirconium
hydrideprecipitates.Theseprecipitateshavebeenshowntobelessductilethanthe
surrounding zirconium alloy matrix. In the 1960s when the first commercial
nuclear reactors were being designed and built, the initial concern regarding the
presence of these precipitates was their potential for decreasing the fracture
toughnessofzirconiumalloycomponents.Thisledtoaninitialintensive studyof
the physical and mechanical properties of zirconium hydride in its bulk form and
as precipitates uniformly distributed in the alloys. Somewhat later, in the early
1970s, as a result of leaks found in some over-rolled pressure tubes in two of the
earliest commercial CANDU reactors, a time-dependent failure mechanism
associated with hydrogen and hydrides in the pressure tube alloy was discovered
andsubsequentlyextensivelystudied.Thistime-dependentfailuremechanismwas
initially referred to by a variety of different names but is now universally called
Delayed Hydride Cracking (DHC). A vast body of knowledge has since appeared
in the open literature and in internal reports on this topic including some review
articles. To acquaint oneself with this knowledge, however, a thorough review of
the literature can be an arduous and sometimes confusing task since models,
measurement methods, and data have changed over the years, been revised or
updated, taking on different forms over time.
This book, then, is an attempt to provide the reader with a more coherent
account of this topic than is obtainable through a reading of the extant literature.
EmphasisinthisbookisplacedonshowinghowthefundamentalaspectsofDHC
vii
viii Preface
have informed the methods—and provided the underpinning—for its practical
applications. In so doing, the book provides more detailed descriptions of the
currenttheoreticalandexperimentalfoundationsofthepropertiesandbehaviorof
hydrogen, hydrides,and DHC inzirconium and its alloys than is usuallyfound in
individual papers inthe literature. Although emphasisis on zirconium alloys, this
book has been presented in such a way that it could also serve as a basis for the
treatment of other hydride forming metals. In fact, it is noted that the reverse has
frequently been the case with the knowledge produced concerning the properties
and behavior of hydrogen and hydrides in other hydride forming material pro-
vidingstartingpointsforquantifyingandunderstandingtheseinzirconiumalloys.
The book is not meant to be an exhaustive source of the documented work
involving DHC. Nevertheless, the author has attempted to give as complete an
account of the present state of knowledge of this field as possible. To make the
derivationsofthetheoreticalmodelsreproducedinthisbookmoreunderstandable,
backgroundinformationisprovidedtoshowhowthesederivationsfollowfromthe
general theories of the diffusion of atoms in crystalline solids, the macroscopic
theory of irreversible thermodynamics, thermodynamics of coherent misfitting
phases in crystalline solids containing mobile interstitial atoms, self and interac-
tionenergiesofpointandlinedefectsincrystallinesolids,andcontinuumfracture
and solid mechanics. This book could also be useful as a teaching tool in that it
provides an illustration of a specific application of these general theories to a
practical engineering problem. Although the primary emphasis in this book is on
zirconium alloys used in pressure tubes of CANDU and other PHW reactors, the
treatment is sufficiently general for applications to other zirconium alloys and
components used in nuclear reactors, particularly those for nuclear fuel cladding.
Acknowledgments
The author is indebted tohis former colleagues inAtomic Energy of Canada Ltd.
(AECL), Ontario Power Generation, and Kinectrics Inc. (previously named, suc-
cessively,OntarioHydroResearchDivisionandOntarioHydroTechnologies)for
sharing their thoughts, insights, and data with him and for collaboration on joint
publications. Particular acknowledgments go to the following: (1) Roger Dutton
for introducing the author to the theory of subcritical crack growth by diffusion
creep mechanisms (which formed the precursor of the DHC growth rate model)
and his collaboration and support associated with the development of the various
versionsoftheDHCcrackgrowthmodels;(2)LeonardSimpsonforhispioneering
experimental work on DHC growth rate and the determination of embedded
hydride fracture strengths; (3) Brian Leitch for the support provided through his
theoretical calculations of the accommodation energies and stress states in and
around misfitting hydride precipitates to solvus and hydride fracture models; (4)
San-Qiang Shi for his seminal work on the theory of K ; (5) Ian Ritchie and
IH
Zheng-Liang Pan for their outstanding experimental work in the development of
techniquesusingvariousinternalfrictionmethodsforsolvusandhydrideproperty
determinations;(6)StefanSagat,MaxRestaLeviandGordon(GK)Shekfortheir
mastery and inventiveness in the selection and execution of all aspects of DHC
experimentation, (7) Richard Sauvé and Don Metzger for their outstanding mod-
eling of DHC behavior based on their own versatile finite element program.
TheauthorwouldalsoliketoacknowledgetheimportantcontributionsofMarc
Léger to the DHC research community overall through his insights, the generous
sharing of his own work, and his technical leadership.
Also acknowledged is the ongoing leadershipprovidedby Doug Scarth for the
development of flaw assessment methodologies for pressure tubes, both through
his own individual contributions and through his expert guidance as chair of
various technical committees connected with this effort.
The author thanks AECL and the CANDU Owners Group (COG) for permis-
sion to use, where indicated in the text, hitherto externally unpublished data.
ix
x Acknowledgments
Reviews of parts of draft versions of Chap. 3 by Vuko Perovic, of Chap. 9 by
AxelSteuwerandMarkDaymondandChap.11byDougScartharealsogratefully
acknowledged.
Contents
1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Delayed Hydride Cracking. . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Objectives and Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Properties of Bulk Zirconium Hydrides. . . . . . . . . . . . . . . . . . . . 7
2.1 Hydride Phase Compositions, Lattice Structure
and Parameter Determinations . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Crystallographic Properties of the
c-Hydride Phase. . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.2 Phase Relationships, Phase Stability, and
Hydrogen Compositions in the d- and c-Hydride
Phases at the (a + d)/d Phase Boundary. . . . . . . . . . 10
2.1.3 Crystallography of the d-Hydride Phase. . . . . . . . . . 19
2.2 Mechanical Properties of Bulk Zirconium Hydrides . . . . . . . . 22
2.2.1 Yield Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.2 Fracture Toughness. . . . . . . . . . . . . . . . . . . . . . . . 37
2.2.3 Microhardness, Elastic Moduli, Internal Friction. . . . 40
2.2.4 Summary of Mechanical Strength Results . . . . . . . . 49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3 Hydride Phases, Orientation Relationships, Habit Planes,
and Morphologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.2 Hydride Precipitation in a-Zr Alloys: Early Analyses
Derived from Observations of c-hydride Precipitates. . . . . . . . 54
3.3 Hydride Precipitation in a–Zr Alloys: Determinations
of Lattice Transformation Relationships
of c-Hydride Precipitates. . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
xi