The welding of Zirconium Alloy components is one of the most critical manufacturing processes of Nuclear Reactor fuel. Small amounts of contamination resulting from inadequate cleanliness or from poor atmospheric control during welding may lead to diminished corrosion resistance of the weld and in severe cases to weld failure. Other weld defects such as piping, pore formation or insufficient weld penetration may also result in costly fuel failures. This Report describes the different welding processes used for the various fuel assembly components. A comprehensive discussion of welding Quality Management is included.
The purpose of the report is to describe the fundamentals in crud formation, transport, and deposition, in order to provide a solid basis for evaluating and analysing any fuel operational problem due to crud deposits. The ultimate purpose is to provide knowledge and insight for staff involved in the operation and materials selection in nuclear power plants, in order to prevent the occurrence of any crud-related fuel problems.
This report reviews the experience of the impact of Zn-injection (in PWRs and BWRs) and Nobel Metal Chemical Addition (NMCA) in BWRs on fuel integrity. The report also discusses fundamentals in crud formation related to Zn-injection and NMCA.
The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Hydride Reorientation
Hydride orientation has an important effect on fracture toughness of hydride-containing zirconium alloys because hydrides form as approximately linear arrays of platelet-shaped microscopic precipitates with habits on or near the basal planes of the α–Zr matrix in which they form.
This Stand Alone Report (SAR) addresses a key aspect of the issues raised in the foregoing by providing a comprehensive, self-contained and up-to-date review and analyses of the results of studies carried out on the conditions governing hydride orientation in zirconium alloy pressure and fuel cladding tubes used in nuclear reactors. The report combines a detailed theoretical and experimental overview of this subject with the author’s own analyses of these results. These analyses make use of theoretical advances documented in the author’s 2012 book dealing with the effects of hydrogen and hydrides on the integrity of zirconium alloy components. In the author’s 2012 book, emphasis is placed on delayed hydride cracking, which is a localised failure mechanism.
The objective of this Report is to provide a better understanding of the mechanisms behind the dimensional changes of structural materials in LWRs and CANDUs. Such improved understanding may improve both fuel reliability and reactor safety.
The Report discusses the different parameters impacting PWR fuel corrosion and provides a computer code which allows an equivalent comparison of new alloys irradiated in different reactors at different conditions. The computer code may also assist in identifying the mechanism why the corrosion rate starts to accelerate under certain conditions.
With increased burnup, processes going on inside a nonfailed fuel rod decrease pellet density, lower the fuel melting temperature and thermal conductivity, increase the fission gas release. Also, a high burnup structure is formed at pellet average burnups in excess of about 50 MWd/kgU This volume I of the report describes the processes going on inside a nonfailed fuel rod during normal operation. The associated volume II of the report describes the corresponding information during accident conditions (RIA and LOCA).
Processes going on inside a nonfailed fuel rod may have dramatic impact on fuel performance during normal operation and during accident conditions such as Loss Of Coolant Accident (LOCA) and Reactivity Initiated Accident (RIA) This volume II of the report describes the above information during accident conditions (RIA and LOCA). The associated volume I of the report describes the processes going on inside a nonfailed fuel rod during normal operation.
To meet the current situation with more aggressive reactor environments, a large number of zirconium alloys have been and are being developed. The objective of this Report is to ensure that the new Zirconium Alloys performs satisfactory during normal operation, Anticipated Operational Occurrences (AOOs), postulated accidents and intermediate dry storage.
To meet the current situation with more aggressive reactor environments (higher burnups, changing water chemistries and loading patterns), and resolving fuel performance issues such as BWR channel bowing and PWR assembly bowing, a large number of zirconium alloys have been and are being developed. The main driver for the initial material development in Pressurised Water Reactors (PWRs) has been to reduce corrosion rates and Hydrogen Pick-Up Fractions (HPUFs), which have occasionally limited the maximum discharged burnup.