In reading up on the Chernobyl nuclear disaster, I came across an article in the Los Angeles Times from August 1986 which reports that flawed reactor design was a major factor in the catastrophe (a claim which is now known to be true). Relevant excerpt here:
These analysts say that Soviet authorities appear to recognize that operator errors at the Chernobyl plant on the night of April 25-26 were not the sole cause of the accident, and that technical flaws in the reactor's design contributed to the worst accident in the 44-year history of nuclear energy.
In particular, they said, a distinctive feature of the Chernobyl design, which sets it apart from conventional nuclear power plants in most of the world, is its tendency to generate a sudden and uncontrollable burst of power if large steam bubbles, or "voids," are allowed to form in the reactor core, as they did before the accident.
My question is: did the Soviet engineers or the Soviet government know the of the flaws inherent to Chernobyl's reactor design when construction began in 1972? If so, how serious did the engineers or government consider these flaws to be?
The actual designers of the reactor were well aware that the control rods caused power spikes when inserting all control rods at once, as it had been observed at a few existing RBMK power plants. Few others knew, however. Also, according to G Medvedev in Chernobyl Notebook, the safety problems of RBMK reactors was discussed when deciding what type of reactor to site in Ukraine prior to construction beginning at Chernobyl.
Boiling reactors are known to have instabilities in the high power-low flow operating mode. This includes the RBMK reactor.
The difference is how the core responds to these instabilities. For graphite moderated cores, the instabilities can lead to power excursions which cause what we saw at Chernobyl. For something like a water moderated BWR, the worst that can happen is cracking of the fuel cladding and localized heat damage to the fuel/core.
It was understood that the graphite tips can cause a reactivity increase. There is a safety limit for RBMK reactors that a minimum number of control rods must be at least partially inserted at all times. When the tips are pre-inserted into the core, and further insertion just adds more neutron absorber and causes power to go down, if you have too many or all of the rods removed, then during the scram you have a prompt power spike. This was known, and is why a safety limit was established.
Safety limits for nuclear reactors are those things which must never be violated to ensure core damage or catastrophic failure does not occur. The operators violated their licenses by exceeding them intentionally.