This simulates Chernobyl Unit 4, an RBMK-1000: a graphite-moderated, water-cooled, boiling channel reactor (3200 MWt, two 500 MWe turbines). The model includes point kinetics, xenon, decay heat, boiling channels and drum separators, eight main circulation pumps and the AZ-5 emergency protection. It runs entirely in your browser.
What makes the RBMK dangerous
- Positive void coefficient. Steam absorbs fewer neutrons than water, so more boiling means more power. It is worst at low power with few rods in the core.
- Operating reactivity margin (ORM). The equivalent number of rods kept in the core. Rules required at least 15 (30 normally). Below that, the reactor is hard to control.
- The positive scram. Withdrawn rods carry a graphite "displacer" below the absorber. In the first seconds of an AZ-5 scram, the displacers push water out of the bottom of the core and add reactivity before the absorbers take effect. Full insertion takes about 18 seconds.
- Xenon poisoning. After a power reduction, xenon builds up for hours and pushes power down. Operators then pull rods to keep the reactor going, which eats into the ORM.
Recreating 26 April 1986
- Choose File → 26 Apr 1986 01:23:04. The reactor is at 200 MWt with xenon poisoning, about 6 rods of ORM, all 8 pumps running and the ECCS disabled.
- Press Begin TG-8 rundown test. Pumps 5-8 slow down with the turbine, flow falls and boiling increases.
- About 36 seconds later, lift the cover and press АЗ-5, as the operators did at 01:23:40.
Normal operation
At nominal power, the automatic regulator (AR) holds power at the setpoint and the turbines follow drum pressure. Keep the ORM above 15, keep at least 3 pumps per loop running, and change power slowly. From Shut down, hot you can practise a startup: withdraw RR rods slowly, watch the period, and then hand over to AR.
Numbers are representative, not exact plant data. This is a simplified model for fun and learning, not an engineering tool.