Metals do form oxide layers, and in many cases, e.g., with stainless steels, the layer is protective. However, some metals form friable oxides, which do not offer much protection, and instead, the oxidation process is unstable. In some cases, in the presence of water or steam, the underlying metal absorbs hydrogen and that enhances the oxidation. Uranium metal was usually clad in aluminum or zirconium alloys.As are most (all?) metals, forming a surface coat of oxide. I doubt some surface oxygen has much effect on reactivity.
Update: Looking in my 1964 text, there is a sentence containing "uranium oxide (U3O8)", so it would appear that oxide refers to the higher oxide rather than UO2. I was at a seminar recently, and some of the discussion was about a particular calciner, which produced uranium oxide (U3O8), which I found surprising. In order to produce UO2, one needs to maintain a reducing environment in the reaction system/calciner.