I don't think that peaceful nuclear explosives (PNEs) were merely a public relations exercise or an excuse for nuclear testing. The USSR pursued them too and it

I don't think that peaceful nuclear explosives (PNEs) were merely a public relations exercise or an excuse for nuclear testing. The USSR pursued them too and it was hardly beholden to public opinion. The US started testing applications for PNEs before there was any limitation on nuclear explosive testing. The USSR started PNE tests in the mid 1960s, after atmospheric testing was banned but before there were any treaty limitations on underground explosions. These are the respective projects for the two countries: https://en.wikipedia.org/wiki/Project_Plowshare https://en.wikipedia.org/wiki/Project_Plowshare (US) https://en.wikipedia.org/wiki/Nuclear_Explosions_for_the_National_Economy https://en.wikipedia.org/wiki/Nuclear_Explosions_for_the_Nat... (USSR) The engineering allure was basically the same as that of early atomic energy projects: nuclear fuel is much less expensive than chemical fuel, joule-for-joule. In 1969 the International Atomic Energy Agency published an article "Possibilities for Peaceful Nuclear Explosives" that gives the flavor of this argument. The nuclear explosion differs in equivalent size from chemical high explosives by several orders of magnitude. A 25 kiloton nuclear explosive (TNT equivalent - 25,000 tons) may be emplaced in a cylindrical bore hole less than a metre in diameter; even a 1 megaton explosive charge (TNT equivalent - 1,000,000 tons) would not take up more space than that. On the other hand, 25,000 tons of TNT would require a spherical cavity, 30 metres in diameter. Even if that much TNT could be assembled in one place, its emplacement costs would be enormous. Nuclear explosives are also relatively inexpensive. The US AEC has projected a charge of $350,000 for a 10 kiloton and $600,000 for a 2 megaton explosive. Equivalent TNT costs are, respectively, $4,000,000 and $800,000,000. Thus, even for "small" shots, potential economies are considerable, while for large ones, chemical explosives simply are not economically feasible. https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull11-3/11303580312.pdf https://www.iaea.org/sites/default/files/publications/magazi... PNE programs never delivered on the early promise for a variety of reasons (including "there are few attractive civil uses for even a 10 kiloton blast") but those numbers certainly were alluring at first glance. IIRC, India also had some early interest in nuclear explosives stoked by comparisons with TNT like that given above. One thing not highlighted by the AEC's numbers is that the costs were so low only because the US had already invested enormous resources into developing nuclear explosives for military purposes. A country starting a civil-only nuclear explosives program, with the aim of blasting harbors or whatnot with atomic bombs, would find that the conventional TNT route was much less expensive.