Even though 2nd generation RBMK reactors do not have a pressure vessel like western nuclear reactors, they have quite interesting systems to handle serious accidents in the coolant loop. Due to a project I’m working on (full dynamic simulation of the power plant) I did some research on how those systems work and painted a new schematic showing those systems.
The schematic was drawn using Inkscape, you can download the svg file here. I usually stick to green for water and red for steam but I used different colors here to make it easier to see where the connections go.
Using the term Emergency Core Cooling System (ECCS) might suggest that this would be a system to cool the core in emergency situations. Such emergency situations include pipe ruptures inside the core and also a rupture of the large distributor or collector headers. Large quantities of heated water will escape in such situations and parts of this feed water will evaporate as it’s no longer under pressure. Condensing and cooling this steam is also something the ECCS systems have to handle.
There are large rooms below the reactor, forming a so called pressure suppression pool. The famous elephant foot is located there. Steam leaked from bursted pipes will either flow directly into that pool or will blow a rupture disc where it can condensate and heat up the water with its evaporation enthalpy. This condensing prevents a pressure built up inside the reactor building. The main safety valves of the main steam also feed their steam into the water inside the pressure suppression pool.
References
Система локализации аварий рбмк-1000. Назначение, состав, принцип работы: Обнинский институт атомной энергетики (studfile.net)
Атомные электрические станции и их оборудование – Системы аварийного охлаждения (leg.co.ua)
The Accident at the Chernobyl’ Nuclear Power Plant And Its Consequences. Information compiled for the IAEA Experts’ Meeting, 25-29. August 1988, Vieanna