Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1729101 | Annals of Nuclear Energy | 2012 | 8 Pages |
Exposure of nuclear fuel rods to air can lead to accelerated oxidation of the cladding, since the effect of nitrogen degrades the oxide layer which hence becomes a less effective barrier to the transport of oxygen to the metallic surface, resulting faster oxidation kinetics. The oxide layer typically becomes porous and can breakaway, a process known as breakaway oxidation. Exposure to air is most likely after a prior period of oxidation in steam. A new model has been developed which captures the initially protective effect of the oxide layer and transition to breakaway. The first stage of assessment was performed using detailed time-resolved data from separate-effect tests performed under controlled isothermal conditions over a range of temperatures and gas compositions. Following implementation into a new version of RELAP5/SCDAPSIM, a second stage of assessment is carried out, namely simulation of an independent integral air ingress transient experiment. This is the subject of Part 2 of this paper. The modelling approach allows extension to alternative cladding alloys such as those recently being deployed in reactor cores.
► A new oxidation model for steam and air with N2 as a catalyst has been developed at PSI. ► The model captures the initially protective effect of the oxide layer and transition to breakaway. ► The first stage of assessment was performed using detailed time-resolved data from separate-effect tests. ► The tests were performed under controlled isothermal conditions over a range of temperatures and gas compositions. ► The modelling approach allows extension to alternative cladding alloys.