In 10+ years of educational efforts aimed to expand knowledge about nuclear electricity generation, one question pops up again and again, with minor variations: how were the RBMK types at #Chernobyl different from today's reactors? I'll answer it here for future reference 🧵
I found 5 technical differences to today's reactors that contributed to the accident. Whereas you might find reactors operating with any single one of these characteristics, I'd be surprised to find any reactor that has 2+ since supervision was globalized e.g. through @WANOComms
1. Lacking instrumentation and control meant that the operating crew rarely ever had an adequate situational awareness since they were busy w/ monotonous jobs. The automation was already low level for 1986, the Soviet Union was sanctioned through CoCom and was behind in all ICT.
2. Positive void coefficient. Neutrons don't care for the phase of the H2O they meet, but they care for the density, meaning that steam absorbs and moderates less of them. In RBMK, the neutrons breezing through steam get moderated but less absorbed in graphite. Heat => more heat.
3. Incorrect construction of the control rods (MCR1 below) gives incorrect and unexpected neutron dynamics. This is also referred to as the tip effect. It was known to Soviet researchers at the time but not shared through training and operating procedures.
4. No full pressure containment. Upon boiling off the water coolant, the biological shield was easily shoved aside by the expanding steam. The building above that was not pressure proof, it's just cheaper without all the concrete and steel.
5.Combustible graphite in the core provided a transport mechanism (=pollution) for the radioactive inventory once decay heat met the air. Once a reactor is open and dry there is going to be pollution, but not as much if it's only concrete or comparatively inert metals.
With these deficiencies and the tragedy of the lives lost, the dangers of nuclear fission have been maxed out. Claims regarding even worse scenarios e.g. @HBO are false and therefore misleading regarding energy policy. Chernobyl was terrible, but not top3 in NRG deaths. end 🧵