Briefly, the RMBK was a very unusual reactor design, optimized for the demands of the Soviet bureaucracy and production needs. The basic requirements that the RMBK was trying to satisfy were:

• the design had to be a relatively cheap way of producing gobs of electrical energy

• the reactor was designed to be capable of being designed and manufactured locally, as opposed to in a centralized facility (this is related to the cheapness and the labor model)

• the military (who essentially ran the reactor development program) wanted it to be capable of also producing plutonium for military purposes (no RMBKs actually did this, but they wanted the option)

The result was a reactor that looks very different from most Western reactors and looks even different from the other main Soviet design, the VVER, which is basically the Soviet equivalent of the Pressurized Water Reactor (PWR). The PWR/VVER both require very specially produced reactor vessels, and both use expensive containment domes, and both are essentially difficult to use for the production of military plutonium (you can't circulate fuel through them very quickly). The RMBK by comparison does not have a special reactor vessel, lacked a containment dome, and could circulate fuel very quickly. Importantly they could use the existing Soviet industrial workforce very efficiently, without the need to construct new facilities or train workers for radically new skills — this was a high priority in the late 1970s USSR, when the design was approved.

The RBMK had significant safety problems which are obvious in retrospect, though it is of note that with careful operation, the accident rate can still be very low (there have been RMBKs operating continuously since Chernobyl without incident). Similarly one can run VVER/PWRs in ways that produce accidents (Three Mile Island was PWR accident), and the other major design in operation, the Boiling Water Reactor, has its own flaws as well (Fukushima was a BWR accident). Obviously the lack of a containment dome is dangerous no matter what — this was also an artifact of the Soviet bureaucracy and engineering culture, in which to admit the possibility of engineering fault was seen as attacking the Soviet state.

I think it is worth noting that every reactor design has the hallmarks of its original priorities and goals written upon it. The RMBK is not unique in this respect, though the specific priorities and goals are very attuned to the place and period it was created, and, regrettably, said priorities and goals were less focused on safety than they ought to have been, with grave consequences.

As I always emphasize, you can design a reactor for whatever priorities you want (safety, economy, plutonium production, whatever), but some of these priorities can interfere with one another (e.g., if you optimize for economy you can cut into safety, and vice versa). So it is important that you know what your priorities are, and what priorities your production and regulatory systems are set up to honor. In the case of the RBMK, it is clear that safety and transparency were far too under-valued, both in the reactor design, but also in its operation.

If you would like a lot more detail into the development of the RBMK and VVER, Sonja D. Schmid's Producing Power: The Pre-Chernobyl History of the Soviet Nuclear Industry (MIT Press, 2015) is the best technical history of Soviet reactor development prior to Chernobyl, and goes into great detail into how the institutional divisions (between, say, the military and civilian aspects of nuclear power in the USSR) and priorities shaped these technologies.