Phase transformation and stability studies of the Zr-H system
Författare
Summary, in Swedish
Popular Abstract in English
Zirconium alloys are widely used in nuclear power reactors as cladding material for their fuels due to the high strength, good corrosion resistance and low neutron absorption cross-section, even in extreme environment, that is characteristic for zirconium. The element, however, also has strong affinity for hydrogen, and when both are present they readily react and form a family of compounds called hydrides. It is well known that even small amounts of hydrides in zirconium based materials will cause the material to loose ductility, making it brittle, and susceptible to cracking. In the case of nuclear fuel, these zirconium based alloys are not only the cladding of uranium fuels in the reactors but also the first barrier of defense of nuclear waste and radioactive substance in general, and as such the problem of hydrogen absorption and hydrides formation becomes significant and important to study.
Despite the fact that zirconium hydrides have been extensively studied for about half a century, the basic nature and mechanisms of hydride formation, the transformation between various phases of hydride, and their exact crystal structures are not yet fully understood. In order to find answer to some of these problems, the precipitation and dissolution, that is the formation and removal, of hydrides, in pure zirconium powder were carried out and studied. The processes were monitored in real time using high resolution synchrotron and neutron radiations, whereby whole diffraction patterns of crystal structures where recorded of zirconium and the hydrides. These patterns were used in the analysis of the environments and conditions that are important for the formation of hydrides, as well as to answer questions about the mechanisms and speed with which these events occur.
Based on the observations during these experiments, and the results of the analysis, a better understanding of the behavior of different hydride phases has been achieved. In particular during thermal treatment and in-situ hydrogenation compared to those being reported in literature. Some new findings were also reported. The main ones being: 1. All commonly reported zirconium hydride phases were recorded, for the first time, in a single in-situ experiment. 2. The complete reversible transformation between two different zirconium hydride phases was observed. 3. The phase transformation type between two commonly reported zirconium hydrides, called delta and epsilon, was analyzed and defined. 4. The preparation route of a controversial zirconium hydride, known as gamma zirconium hydride, is introduced and its exact crystal structure and formation mechanisms are also discussed in detail.
Zirconium alloys are widely used in nuclear power reactors as cladding material for their fuels due to the high strength, good corrosion resistance and low neutron absorption cross-section, even in extreme environment, that is characteristic for zirconium. The element, however, also has strong affinity for hydrogen, and when both are present they readily react and form a family of compounds called hydrides. It is well known that even small amounts of hydrides in zirconium based materials will cause the material to loose ductility, making it brittle, and susceptible to cracking. In the case of nuclear fuel, these zirconium based alloys are not only the cladding of uranium fuels in the reactors but also the first barrier of defense of nuclear waste and radioactive substance in general, and as such the problem of hydrogen absorption and hydrides formation becomes significant and important to study.
Despite the fact that zirconium hydrides have been extensively studied for about half a century, the basic nature and mechanisms of hydride formation, the transformation between various phases of hydride, and their exact crystal structures are not yet fully understood. In order to find answer to some of these problems, the precipitation and dissolution, that is the formation and removal, of hydrides, in pure zirconium powder were carried out and studied. The processes were monitored in real time using high resolution synchrotron and neutron radiations, whereby whole diffraction patterns of crystal structures where recorded of zirconium and the hydrides. These patterns were used in the analysis of the environments and conditions that are important for the formation of hydrides, as well as to answer questions about the mechanisms and speed with which these events occur.
Based on the observations during these experiments, and the results of the analysis, a better understanding of the behavior of different hydride phases has been achieved. In particular during thermal treatment and in-situ hydrogenation compared to those being reported in literature. Some new findings were also reported. The main ones being: 1. All commonly reported zirconium hydride phases were recorded, for the first time, in a single in-situ experiment. 2. The complete reversible transformation between two different zirconium hydride phases was observed. 3. The phase transformation type between two commonly reported zirconium hydrides, called delta and epsilon, was analyzed and defined. 4. The preparation route of a controversial zirconium hydride, known as gamma zirconium hydride, is introduced and its exact crystal structure and formation mechanisms are also discussed in detail.
Avdelning/ar
Publiceringsår
2015
Språk
Engelska
Dokumenttyp
Doktorsavhandling
Ämne
- Materials Engineering
Nyckelord
- zirconium hydride
- γ-ZrH
- synchrotron X-ray diffraction
- neutron diffraction
- hydrogen charging
- in situ phase transformation
- hydrogen embrittlement
- hydrogen induced degradation
Status
Published
Handledare
- Christina Bjerkén
- Per Ståhle
ISBN/ISSN/Övrigt
- ISBN: 978-91-7623-553-9
- ISBN: 978-91-7623-552-2
- LUTFD2/TFMT--15/1015--SE(1-65)
Försvarsdatum
3 december 2015
Försvarstid
10:15
Försvarsplats
M:E, M-Building, Ole Römers väg 1, Lund University, Faculty of Engineering, LTH.
Opponent
- Lars Hallstadius