If we are playing the game of how scary they could be with a stash of uranium, the absolute worst thing I could imagine with 40kg of material would be making uranium rounds for some of their captured anti-tank weaponry.
I'm assuming here that they have purified but non-enriched uranium, not just ore. They could, with extensive expertise and machining capability (both of which are doubtful, but not beyond the realm of imagination), create rough approximations on American or Soviet designed depleted uranium rounds. They certainly have a few weapons (including T60 and 72 tanks) capable of firing a uranium sabot round if they could produce such a tool.
Their deploying DU (or non-depleted uranium; the essential chemical/mechanical workings are near identical) weapons, even in a single verifiable case, would be catastrophic in psychological effect. Not to mention it being a highly effective munition; DU sabots fracture on impact, with each splinter (including the tip of the primary round) remaining sharp even as the dust from the splintering ignites as it expands within the target.
The amount of uranium in question would only provide a very small number of shells, or a more significant but still small number of small arms rounds (harder to verify their use and so get the psychological punch). But it's more feasible approach than pretending they could get an actual nuclear WMD of any sort from such material.