Chernobyl Unit 4 reactor effects

By approximately 11 00 pm Friday evening, the local electricity demand had subsided, and the load dispatcher gave permission for Chernobyl Unit 4 to continue with its power reduction. At this point, another step in a string of unfortunate events occurred when the automatic reactor control unit did not adjust for the new lower power level. The operators had reset the reactor monitoring system to the requested level, but had failed to reset the reactor automatic controller. The reactor s response was a dramatic drop in power, down to 30 MWt, 1 % of the normal operating level (US NRC, 1987). In effect, the automatic controller inserted control rods, which drove the overall core power dramatically lower than was intended. 

Consider the damage in the last few decades due to the use of nuclear reactors, divided by the amount of available energy produced. Two well-known examples of such damage are at Three Mile Island in the United States in 1979, and even more at Chernobyl in the Soviet Union in 1986. Both of these were caused by human error. At Three Mile Island, the economic damage was great, but there was hardly any effect on health. In Chernobyl, the effect on human health was considerable, but still small compared to the publicity it generated. 

Nuclear accidents at Three Mile Island, Pennsylvania, in 1979 and Chernobyl, Ukraine, in 1986 had a devastating effect on public opinion in the United States and, to a smaller degree, elsewhere in the world. At Three Mile Island only about 50 curies of radiation were released to the environment and there were no casualties. The explosion at Chernobyl was a very different story. About 100 million curies were released, leading to at least 31 fatalities. Moreover, 135,000 people were permanently evacuated from the region surrounding the reactor. Since then, all the other reactors at Chernobyl—three, in addition to the one that exploded—have been permanently shut down. 

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