Assessment of the Combined Effects of Irradiation and Hydrogenation on the Fracture Behavior of Zircaloy Fuel Claddings by Fracture Mechanics

Abstract

In order to study the combined effects of irradiation and hydrogenation on the failure behavior of high burnup light water reactor (LWR) fuel cladding rods during reactivity initiated accidents (RIAs), an analysis based on fracture mechanics has been performed at room temperature for the following two types of claddings: irradiated Zircaloy-2 claddings with precipitated platelet planes of zirconium hydride oriented in the radial direction of the claddings rather than circumferential direction (Type-A), and irradiated Zircaloy-4 claddings with zirconium hydride accumulated locally beneath the outer surface of the claddings (Type-B). A failure assessment diagram (FAD) was constructed using the R6 approach first produced by the former Central Electricity Generating Board (CEGB) in the United Kingdom to estimate the failure stress of the Type-A and Type-B models. It was concluded from the FAD that hydrogenation could be the dominant factor in affecting the strength degradation of the Zircaloy claddings rather than irradiation effect, depending on the distribution and orientation states of the hydride precipitates.

KEYWORDS:

• high burnup
• reactivity initiated accident
• light water reactors
• fuel cladding tube
• Zircaloy
• zir-conium hydride
• hydrogen embrittlement
• radiation effects
• irradiation
• fracture mechanics
• failure assessment diagram
• failure