<P> This capability still needed to be confirmed experimentally, and previous tests had ended unsuccessfully . An initial test carried out in 1982 indicated that the excitation voltage of the turbine - generator was insufficient; it did not maintain the desired magnetic field after the turbine trip . The system was modified, and the test was repeated in 1984 but again proved unsuccessful . In 1985, the tests were attempted a third time but also yielded negative results . The test procedure would be repeated in 1986, and it was scheduled to take place during the maintenance shutdown of Reactor Four . </P> <P> The test focused on the switching sequences of the electrical supplies for the reactor . The test procedure was expected to begin with an automatic emergency shutdown . No detrimental effect on the safety of the reactor was anticipated, so the test programme was not formally coordinated with either the chief designer of the reactor (NIKIET) or the scientific manager . Instead, it was approved only by the director of the plant (and even this approval was not consistent with established procedures). </P> <P> According to the test parameters, the thermal output of the reactor should have been no lower than 700 MW at the start of the experiment . If test conditions had been as planned, the procedure would almost certainly have been carried out safely; the eventual disaster resulted from attempts to boost the reactor output once the experiment had been started, which was inconsistent with approved procedure . </P> <P> The Chernobyl power plant had been in operation for two years without the capability to ride through the first 60--75 seconds of a total loss of electric power, and thus lacked an important safety feature . The station managers presumably wished to correct this at the first opportunity, which may explain why they continued the test even when serious problems arose, and why the requisite approval for the test had not been sought from the Soviet nuclear oversight regulator (even though there was a representative at the complex of 4 reactors). </P>

Chernobyl nuclear power plant explosion ukraine april 1986