MECHANICAL CHARACTERISTICS OF FUEL RODS IN TRANSPORT CONDITIONS

A synthesis on the mechanical characteristics of unirradiated and irradiated fuel rod claddings was performed by IRSN in order to have reference data for the assessment of the safety demonstrations in normal and accident conditions of transport required by the procedure of package licensing. Indeed, the transport conditions correspond to a range of cladding temperatures (200°C to 550°C) which is only partly covered by the data acquired within the framework of the safety demonstration relative to the reactor normal operating conditions, especially beyond 400°C. This work mainly concerned Zircaloy-4 cladding material (Zy-4). Data about mechanical properties (elastic and ductile properties, creep behaviour), oxidation (in reactor and under air during transport), hydrides, fracture toughness and fatigue behaviour have been collected and synthesized. The laws presented in the document can be used to obtain orders of magnitude of the oxide thickness, the hydrogen contents and the creep deformation rate. The following phenomena which could influence the mechanical behaviour of the cladding were more particularly studied: - oxidation which could become very important during transport in case of cladding temperatures of about 500°C, - creep for which only a few data around 500°C are available and which depends in particular on the internal pressure of the rods, the cladding oxidation and the presence of the hydrides, - recrystallization of Zy-4 at about 500°C, which could have consequences on the mechanical properties of the cladding after cooling during the storage. For other topics of interest for the study of the mechanical behaviour of the cladding, such as the fracture toughness for example, it was identified that the data available is scarce. This paper presents the main results obtained for Zy-4 and for M5TM.