Understanding the corrosion processes of fuel cladding in pressurized water reactors

Effects of Hydrogenation on the Corrosion Behavior of Zircaloy-4

“…However, variations in Fe and Cr content suggest diffusion processes involving these elements. Zircaloy-4 exclusively presents a unique type of second phase known as Zr(Fe,Cr) 2 [ 34 ]; thus, prior to oxidation, these phases SPP1 and SPP2 corresponded to Zr(Fe,Cr) 2 . Microcracks were observed around the SPP1 and SPP2 because the second phases near the cracks are more easily oxidized and on the contrary, the second phases subsequently promote crack formation [ 35 ].…”

Long-Term Oxidation of Zirconium Alloy in Simulated Nuclear Reactor Primary Coolant—Experiments and Modeling

“…A typical pressurized water reactor (PWR) contains around 200 fuel assemblies, with each fuel assembly featuring hundreds of fuel rods. A fuel rod is composed of fuel pellets stacked inside a cladding tube [ 1 , 2 ], The mechanical integrity of the cladding is essential to nuclear safety because it provides the first barrier for fission products. The technical specifications used to choose PWR cladding material have long been: (1) high neutron transparency, i.e., low thermal neutron cross sections, (2) good thermal conductivity, (3) low creep rate, (4) good ultimate elongation, (5) sound mechanical properties, and (6) good corrosion resistance [ 1 ].…”

“…The trend towards more severe operating conditions for this type of structural material, induced by the need to extend the lifetime and increase fuel burnup, leads to a need for a detailed characterization of correlations between composition, microstructure, and morphology of such alloys, growth kinetics of oxide layers on them, and their susceptibility to localized corrosion [ 1 ]. Even if the qualitative picture of the oxidation process of Zr alloys in nuclear power plant coolants is well established, the intimate mechanism of the transfer of matter and charge through the oxide remains largely unclear.…”

“…According to that mechanism, transport of oxygen by a vacancy mechanism along grain boundaries of the already formed zirconium oxide is the rate-determining step of the overall reaction. It is assumed that water reduction at the oxide/coolant interface consumes electrons generated by metal oxidation, electronic conduction in the oxide proceeding along preferred pathways associated with secondary phase particles incorporated into the zirconium oxide matrix [ 1 , 4 , 5 ]. The extent of the coupling of the electron and ion fluxes is not quantitatively assessed.…”