Summary report on the post-accident review meeting on the Chernobyl accident

After an Executive Summary which gives an overview of the accident at the Chernobyl nuclear reactor, the first section of the main INSAG report presents the understanding of INSAG members of the causes of the accident, concluding that it was the result of a remarkable range of human errors and violation of operating rules, in combination with specific reactor features which compounded and amplified the effects of the errors and led to the reactivity excursion. The second section presents the problem of radionuclide release from the damaged reactor, showing that there was an initial intense release associated with the destructive events in the accident, then the release rates fell over the next few days up to 7x10¹⁶ Bq/d five days after the accident initiation, and at that point the release rates began to increase and reached about 3x10¹⁷ Bq/d nine days after the accident initiation. There was then a drop in the radionuclide release to 4x10¹³ Bq/d and the release rates have continued to decline since that time. The next section describes the accident management at the site, fire-fighting, cleanup of the site and the entombment of the damaged unit. In the fourth section the radiation protection aspects of the accident, the radionuclide transfer through the environment, the exposure of members of the public pointing to the radionuclides iodine-131 and cesium-137 which entered the food-chains, the on-site and off-site emergency response, the decontamination and the health effects including both the early non-stochastic effects and the late stochastic ones are presented. Safety issues to be pursued in order to derive whatever safety lessons can be learned from the Chernobyl accident are considered in Section V. The next two sections present INSAG's observations, conclusions and recommendations based on the lessons learned so far from the accident and ranging from reactor operation to radiation protection and international co-operation in nuclear safety. Finally the report has a technical annex providing information on the operating history of RBMK reactors and background information on the Chernobyl Unit 4 reactor necessary for understanding other parts of the report.