In Japan's case, I expect they have strategic reasons for wanting to maintain the domestic expertise and equipment to rapidly develop nuclear weapons, which AFA

In Japan's case, I expect they have strategic reasons for wanting to maintain the domestic expertise and equipment to rapidly develop nuclear weapons, which AFAIK still means they need reactors (unless they want to have an outright disconnected-from-peaceful-use nuclear program, which they currently do not want to do). They've long been regarded as a "technically non-nuclear... but only if on short notice" state, ready to join the Big Boy Club quickly if confidence in their position under America's nuclear umbrella wavers. I doubt they want to lose that, so they're going to want some amount of nuclear power as a plausibly-deniable way to keep up some of the equipment, material, and know-how they'll need to maintain that latent threat, even if it's not the most economical option.