When talking about the bomb he is making Oppenheimer refers to it has "something unique, something nobody has ever perfected
before. Do you know why? Because it's near impossible." but the device he is making is a fictionalised replica of the Fat Man bomb dropped on Nagasaki.
Nuclear scientists are not given top secret logistical information on the transport of dangerous materials.
Scott has his gun drawn and pointed at Matthius when Kwon pulls up next to him. He would not run for cover rather than just shoot a known terrorist that drove into his line of fire.
Austria has no nuclear weapons program so would not have plutonium cores for Kwon to steal.
The IRA made improvised bombs out of fertilizer and plastic explosives. There is no cross-over between this and the skills and knowledge needed to construct a nuclear weapon.