Instead, it was approved only by the director of the plant (and even this approval was not consistent with established procedures).Īccording to the test, the thermal output of the reactor should have been no lower than 700 MW at the start of the experiment. No detrimental effect on the safety of the reactor was anticipated, so the test program was not formally coordinated with either the chief designer of the reactor or the scientific manager. The test procedure was to begin with an automatic emergency shutdown. The test focused on the switching sequences of the electrical supplies for the reactor. The test procedure was to be repeated again in 1986, and it was scheduled to take place during the maintenance shutdown of Reactor Four. In 1985, the tests were attempted a third time but also yielded negative results. The system was modified, and the test was repeated in 1984 but again proved unsuccessful. An initial test carried out in 1982 showed that the voltage of the turbine-generator was insufficient. This potential still needed to be confirmed, and previous tests had ended unsuccessfully. Analysis indicated that this residual momentum and steam pressure might be sufficient to run the coolant pumps for 45 seconds, bridging the gap between an external power failure and full power from the emergency generators. To solve this one-minute gap, considered an unacceptable safety risk, it had been theorised that rotational energy from the steam turbine (as it wound down under residual steam pressure) could be used to generate the electrical power required. The Chernobyl reactors used water as a coolant with reactor 4 fitted with 1,600 individual fuel channels each requiring a coolant flow of 28,000 litres per hour.Īs the cooling pumps require electricity to cool the reactor, in the event of a power failure, Chernobyl’s reactors had three backup diesel generators these would start up in 15 seconds, but took 60–75 seconds to attain full speed and reach the 5.5‑megawatt output required to run the main pump. RBMK reactors, like those in use at Chernobyl, following an emergency shutdown will continue to emit 7 % of their thermal output and therefore must continue to be cooled. The testĪn inactive nuclear reactor continues to generate a significant amount of residual heat. The test was incorporated into a scheduled shutdown of reactor 4. The accident occurred during an experiment to test a way of cooling the core of the reactor in an emergency situation.
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