The RBMK has a lot of issues that make it really unsuitable for further development: 1. Because of the size of the core, it develops uneven reactivity during o

The RBMK has a lot of issues that make it really unsuitable for further development: 1. Because of the size of the core, it develops uneven reactivity during operation and requires attention to be paid to this. 2. The measures put in place do not entirely eliminate the chance of a power excursion. 3. The cost of a suitable containment building would make RBMK more expensive than an equivalent VVER installation. Also as far as I can tell no such containment building has ever been designed. 4. No international agency or government would allow the construction of a new RBMK. Edit: to be clear, this is not only because of the safety issues, but also because of the nuclear weapon proliferation issues associated with the design. Overall, the cost savings of a RBMK depend on not having a large containment structure and the RBMK was on its way out as a design by time the Chernobyl accident happened. The large number of RBMKs under construction at the time was largely because of initiatives to increase the installed nuclear capacity in the Soviet Union during the mid 80s, existing RBMK sites would receive additional reactors and all but one of the new sites were to receive VVER reactors.