Another serious commercial power reactor accident occurred at the Chernobyl nuclear power plant in the Soviet Union. At Chernobyl, on April 26,1986, a nuclear power plant accident released large amounts of radioactive fission products into the environment.

The Chernobyl accident was caused by a combination of errors, deliberate failure to follow procedure, and a poor design. The design of the Chernobyl reactor, which was not a PWR or BWR, resulted in a very rapid increase in power after the water used to cool the core was lost. As a result, the pressure increased to the point that the reactor was blown apart.

Such an accident is impossible at a U.S. PWR or BWR. In PWRs or BWRs, such a loss of water would have shut down the reactor.