[kodfodrasz]

This is not true in this form. There were unsafe soviet designs, but also there were unsafe western designs. Soviet designs were not all categorically unsafe. The design used at Chernobyl was a problematic design, but still many layers of human error had to be involved to create the accident.

Military reactor designs are generally less safe. Civilian designs were usually OK in the USSR.

[slackingoff2017]

Soviet era designs generally didn't use containment buildings. The RMBK (Chernobyl) in addition used graphite moderator with a positive void coefficient.

In combination this made such reactors intrinsically unsafe compared to their western counterparts, especially the positive void coefficient which can't be found in any western reactors as far as I'm aware.

Not all Soviet designs were as unsafe as RMBK but most were less safe than the average western reactor.

The meltdowns at Fukushima would have been as bad as Chernobyl if the design was similar. And the Fukushima reactors used an old western design dating from roughly the Chernobyl era. The cause of the meltdowns(loss of power) was similar.

The major difference was that Fukushima had containment buildings, no graphite in the core to burn, and a reactor designed to become less critical as the water boils (void coefficient less than 1.0).

[rb1]

It's not just the design(s), it is the implementation too.

At Chernobyl the powers at be (accountants?) got involved and decided to use flammable bitumen coverings on the roof of reactor 3, one would assume to save money. Unsurprisingly, the roof of reactor 3 caught fire.

[fusiongyro]

This is a good example of one of the failings at Chernobyl, but it took many of them coinciding to make the disaster as bad as it was.

They were required to use another material to build the roof, but they were also required to be finished with construction by a certain time. Soviet central planning led to a shortage of the proper roofing material. I'm sure the decision to use bitumen was either made in ignorance or with the assumption that it wouldn't matter for other reasons. Lots of mistakes were made with the assumption that the rest of the system was safe so it wouldn't matter.