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Processes Going on in Nonfailed Rod During Accident Conditions (LOCA and RIA) — Vol. II

Fuel (UO2 and MOX) Performance, Fuel Material

(ZIRAT15/IZNA10 STR)
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.

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Pellet-Cladding Interaction

Fuel Material, Mechanical Properties

(ZIRAT11/IZNA6 STR)
PCI has historically resulted in a large number of fuel failures in BWRs but also to some extent in PWRs. The introduction of various remedies such as power change operation restrictions and liner/barriers in BWRs has reduced the number of PCI failures. However, there are some recent fuel failures in both BWRs and PWRs that has put the PCI failure mode in focus again. The objective of this report is to give a better understanding of the PCI mechanisms, pertinent methods to test PCI performance and PCI remedy technology may improve fuel reliability and reactor safety.

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Mechanical Properties of Zirconium Alloys

Fuel Material, Mechanical Properties

(ZIRAT6/IZNA1 STR)
Adequate mechanical properties are crucial for satisfactory fuel assembly performance: 1) in-pile under normal operation, anticipated operational occurrences and accident conditions as well as, 2) under intermediate storage conditions. The objective of this report is to provide the basic understanding of the mechanical properties of the fuel components that are crucial for the fuel in-pile performance.

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Charged Particle Bombardment of Zirconium Alloys

Dimensional Changes of Fuel Assemblies/Channels and Components, Fuel Material

(ZIRAT19/IZNA14 STR)
The ability of reactor engineers to predict changes in the dimensions of the reactor core components during service is crucial to the safety and efficiency of reactor operation. Successful core design anticipates dimensional changes due to thermal expansion, stress-induced elastic deformation and, to some extent, large stress plastic deformation of core components. Of greater difficulty is predicting dimensional changes due to the effects of the intense irradiation environment, mainly due to high energy neutrons produced by the fission process. Fuel rods, spacers/grids, channels, guide tubes, tie rods, other structural components, etc. – all undergo irradiation-induced dimensional changes due to irradiation growth, irradiation creep, irradiation-altered plastic deformation, and irradiation-influenced corrosion and hydriding of the zirconium alloy components. These topics and process are routinely covered by the ZIRAT Programmes. This Report reviews the effect of ion irradiation (or ion bombardment, used interchangeably in this report) on not only the standard dimensional stability topics but also the full range of properties that can be influenced by ion irradiation. The primary questions addressed are: What properties of zirconium alloys can ion irradiated simulate (emulate or substitute for) neutron irradiation? How, or to what extent, can ion bombardment complement neutron irradiation?

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BWR Fuel Channel Distortion

Dimensional Changes of Fuel Assemblies/Channels and Components, Fuel Material

(ZIRAT16/IZNA11 STR)
In the past ten years approximately half of the 35 BWRs in the United States have reported Control Blade interference due to channel distortion, primarily channel bow. Channels fabricated by all vendors have been affected. This Report is primarily focused on channel distortion; that is, change of shape during in-reactor service: length, bow, bulge and twist. This Report addresses a broad range of channel features which can contribute to normal and problematic performance. In particular, the so-called “shadow corrosioninduced” channel bow phenomena are analyzed.

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In-Reactor Creep of Zirconium Alloys

Dimensional Changes of Fuel Assemblies/Channels and Components, Fuel Material

(ZIRAT14/IZNA9 STR)
In this Report we have attempted to summarize data and mechanisms by addressing the variables that are known to affect irradiation creep. A number of conclusions are reached which give insight into the uses of creep data, mechanisms and models to assess in-service performance of reactor components.

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