> They built the RBMK reactors (like the one at Chernobyl) specifically because the dual-use design allowed them to generate civilian electricity while simultaneously harvesting plutonium for weapons, creating a fundamentally unstable system.

It was more that the RMBK was more designed around existing Soviet manufacturing capacity, they could and did build more conventional reactor designs as well but they required enormous pressure vessels the USSR only had one factory to produce. The RBMK on the other hand is not a monolithic pressure vessel, it's a collection of hundreds of individual pressurised tubes which were much easier for the Soviet manufacturing base to produce. It was actually a clever idea on the face of it, the problem was more it had inherently dangerous behaviour in certain regimes (the infamous positive void coefficient of reactivity) and the positive scram effect wasn't known until well into their deployment. The operators were also given contradictory operating instructions which failed to highlight the safety-critical nature of certain parameters.