Yes this is a known fact about the lack of containment for RBMK's and the positive void coefficient, although after 1986 all existing RBMK's were retrofitted to decrease void coefficient and increase safety systems and make sure workers cannot make such blatant mistakes as before.The main concern of US and EU authorities with respect to RBMKs and VVER-440s was the lack of a containment structure and the inability to contain the consequences of a loss of coolant accident (LOCA) or reactivity insertion accident (RIA), i.e., a core disruptive accident. Vessel embrittlement (somewhat related to LOCA) is another concern.
Another concern with respect to the RBMK is the positive void coefficient, which was a critical factor in the Chernobyl accident. "Reactors cooled by boiling water will contain a certain amount of steam in the core. Because water is both a more efficient coolant and a more effective neutron absorber than steam, a change in the proportion of steam bubbles, or 'voids', in the coolant will result in a change in core reactivity. The ratio of these changes is termed the void coefficient of reactivity. When the void coefficient is negative, an increase in steam will lead to a decrease in reactivity."
That being said then in 2011 Fukushima happened , quite frankly can we even calculate the risk of a well maintained and retrofitted RBMK having a destructive event VS any other Gen 2 reactor in operation even with a containment?
I do realize the RBMK flaws and any way we slice it it's history and no new block will ever be built.