RBMK-1500 belongs the category of "boiling water" reactors. Fundamental reactor parameters are presented at the end of this page. The reactor cooling water, as it passes through the core, is subjected to boiling and is partially evaporated. The steam-water mixture then continues to the large separator drums (3), the elevation of which is greater than that of the reactor. Here the water settles, while the steam proceeds to the turbines (4). The remaining steam beyond the turbines is condensed in the condenser (6), and the condensate is returned via the deaerator (8) by the feed pump (9) to the water of the same separator drum (3). The coolant mixture is returned by the main circulation pumps (10) to the core, where part of it is again converted to steam.
This fundamental heat cycle is identical to the Boiling Water Reactor (BWR) cycle extensively used throughout the world, and is analogous to the cycle of thermal generating stations. However, compared to BWRs used in Western power plants,the RBMK-type reactors have a number of unique features. Each nuclear fuel assembly bank is located in a separately cooled fuel channel (pressure tube). There are a total of 1661 of such channels and the cooling water must be equally divided among that number of feeder pipes. Past the core, these pipes are brought together to feed the steam-water mixture to the above-mentioned separator drums.
The RBMK reactors belong to the thermal neutron reactor category. Due to the large number of metal piping in the core of this type of a reactor, the neutronic characteristics of the reactor are degraded. To improve this situation, the reactors use graphite to moderate (slow down) the fast fission neutrons. This requires a large amount of graphite, so that the graphite stack of the reactor becomes its dominant component, at least by volume.
The fuel assemblies are changed without shutting down the reactor, which is possible only with channelized reactors. Since there are many channels, it is possible to disconnect one of them at a time from the reactor cooling system, change the fuel assembly, and then reconnect the channel.
See further similarities and differences in comparison with other types of generating stations.
Fundamental parameters of the RBMK-1500 reactor Coolant water (steam-water mixture) Heat cycle configuration single circuit Power, MW: thermal (design) 4800 thermal (actual) 4200 electrical (design) 1500 Core dimensions. m: height 7 diameter 11.8 Lattice pitch, m 0.25 x 0.25 Thickness of reactor's graphite reflector, m: end 0.5 side 0.88 Number of channels: fuel 1661 control and shutdown system 235 reflector-cooling 156 Fuel uranium dioxide Initial fuel enrichment for U-235, % 2.0 Nuclear fuel burnup, MWday/kg 21.6 Temperatures, C: maximum temperature at center of fuel pellet 2100 maximum graphite stack temperature 750 maximum fuel channel temperature 360 coolant temperature at fuel channel inlet 260-266 coolant temperature at fuel channel outlet 284 feedwater temperature 190 Pressures, MPa: steam pressure at separators 7.0 heat transport pressure at pressurizers 8.6 Flow rate through reactor (nominal power) kg/s 11667-13333 Steam produced in reactor at nominal power, kg/s 2056-2125 Void fraction at reactor outlet, % 23-29 Maximum fuel channel parameters: fuel channel power, kW 4250 coolant flow rate through fuel channel, kg/s 11 void fraction at fuel. channel outlet, % 36.1 Number of main circulation pumps 8 Capacity of main circulation pumps, kg/s 1944-3056