The Chernobyl Disaster occurred on April 28th 1985 at the Chernobyl nuclear power plant in Ukraine. During a reactor shutdown, the neutrons were still releasing energy, so you could not immediately turn off the water to the reactor. Chernobyl had Diesel generators to power the cooling pumps, but these took a minute to come up to speed. The existing energy in the turbines and generators were supposed to provide this energy. Due to electrical demand, the reactor needed to keep operating at a high power level before being shut down for the test. The power-hold mode was not selected when switching over to a different set of flux detectors for low-power operation. This caused the reactor power to drop to 30 MWt, which was returned to 200MWt as the operator by removing some of the control rods. The reactor was stalled, and then brought the reactor back up to a high enough power to operate the steam turbines to run the test. As excessive the cooling water began to boil, this created voids in the neutron-absorbing water that accelerated the reaction. The automatic power controls tried to keep the reactivity stable, but it would take 18 seconds to push the control rods down into the reactor as they didn’t have enough control authority. As the graphite rods were pushed down, they temporarily enhanced the reaction which skyrocketed the power. The maximum power measured 33 GW, but models estimated that it peaked at 330GW. Some people think that it was a small nuclear explosion, that stopped when the fuel was vaporized below the critical point.
[[Xenon-135]] – neutron absorber
[[Chernobyl Reactor]]
[[Negative Void Coefficient]]
[[Positive Void Coefficient]]
[[Neutron Poison]] – caused the reactor to stall in a dangerous condition
Reactor Dead Time – time you need to wait before restarting the reactor
[[Nuclear Power Safety]] – the area around Chernobyl is uninhabitable
Sources
- [1] Scott Manley, Why Chernobyl Exploded – The Real Physics Behind The Reactor, (Jun. 08, 2019). Accessed: Dec. 08, 2022. [Online Video]. Available: https://www.youtube.com/watch?v=q3d3rzFTrLg
- [2] G. Stein, “The practical, physical (and sometimes dangerous) consequences of control must be respected, and the underlying principles must be clearly and well taught.,” IEEE Control Systems Magazine, 2003.
Backlinks
[[Control Surface Rate Limits]]