Actually, nuclear KNOWLEDGE is quite widespread BUT nuclear ENGINEERING is not because it requires a lot of specific (so controllable) physical ressources and t

Actually, nuclear KNOWLEDGE is quite widespread BUT nuclear ENGINEERING is not because it requires a lot of specific (so controllable) physical ressources and technologies (values, tweaks and hacks), that is controlled by a few states monopoly. So engineering is more easily restricted efficiently. A parallel reasoning would be with face recognition: the algorithms are quite widespread (the knowledge) and new algorithms build on shared knowledge of the field, but the tuning of the parameters, of the input datas, the access to top hardware to speed up learning process, evaluate new strategies, and access to big databases are not. The problem for a state to get the face recognition technology is either to obtain the parameters or to invest time and money to build it. So it's not really "bannable" because theses resources are available everywhere (and lots of companies are ready to provide it). A more "bannable" tech would be "quantum computer" because it relies on new engineering tech, not only on knwoledge.