The causes of the accident and investigation
A state commission formed in the Soviet Union to investigate the causes of the disaster, the primary responsibility for the catastrophe on the operational staff and management of disaster. To investigate the causes of the accident the IAEA has established an advisory group known as the Advisory Committee on Nuclear Safety (INSAG), which is based on material provided by the Soviet side, and oral statements of specialists (a delegation of Soviet specialists headed Legasov VA, which was not " reaktorschikom "), in its report in 1986 also generally supported this view. It was alleged that the accident was the result of the unlikely coincidence of a number of violations of rules and regulations of operating personnel, catastrophic accident acquired due to the fact that the reactor was brought into nereglamentnoe state.
In 1993 INSAG published an additional report, updated the portion of the report INSAG-1, which focuses on the causes of the accident. Looking for new sources of information, INSAG pointed out that many of them are contradictory, noting that "the most important are the reports of two Soviet commissions, headed by N. Steinberg, and AA Abagyanom, which included the above-mentioned report in the form applications. The first commission was composed mainly of former employees of the Chernobyl nuclear power plant, the second - from the professional design organizations, as well as the organizations authorized to provide operational support for the RBMK. This report reviewed "some details of the scenario presented in INSAG-1", as well as change some of the "significant findings".
Including INSAG-7 the effect of increased reactivity in case of emergency shutdown of the reactor, for which information was confirmed by the Soviet side in 1987. Evaluating his views, INSAG-7 said the combination of two serious design defects: the failed designs of rods and positive feedback from the reactivity, while noting that "are unlikely to actually have some value, was whether positive overshooting reactivity in the crash last event that caused damaged reactor. What is important is that such a deficiency existed and it could be the cause of the accident. Also in INSAG-7, it was noted that some accusations against the staff who carried out the experiment, as reflected in INSAG-1 does not correspond to reality, however, noting "a fairly carefree attitude to the blocking of the protection of the reactor as the technological requirements for safety and operators alike."
As in the previously issued report INSAG-1, emphasis in the report INSAG paid insufficient (at the time of the accident) "safety culture" at all levels, including design, maintenance, operational support and oversight for safe operation.
Finally, INSAG-7 formed a tentative conclusions about the causes of the accident, including pointing out that:
"We can say that the accident was the result of low safety culture not only at the Chernobyl nuclear power plant, but in all of Soviet design, operating and regulatory organizations, nuclear power, which existed at that time,
"As indicated in INSAG-1, the human factor should still be considered a key element among the causes of the accident"
"The biggest reprehensible that unapproved changes in the testing program were once deliberately made on the spot, although it was known that the unit is not in the condition in which it was supposed to be in the tests.
INSAG identified a number of problems that contributed to the occurrence of the accident:
Installation actually did not meet safety standards in effect during the design and even had unsafe design features;
Insufficient analysis of security
Insufficient attention to the independent review of security;
Regulations on the operation are not adequately justified in the safety analysis;
Insufficient and ineffective exchange of vital information on safety as between operators and between operators and designers;
Lack of understanding of HR aspects of their station security-related;
Lack of respect for staff with formal requirements of regulations for operation and testing program;
Not an effective regulatory regime, were unable to resist the demands of industrial necessity;
General lack of safety culture in nuclear matters at both the national and local level
Thus, the basis of the accident was considered "low culture of safety not only at the Chernobyl nuclear power plant, but in all of Soviet design, operating and regulatory organizations, nuclear power, which existed at that time." Under the criticism of the IAEA were all the organizations involved in while in atomic energy, and were part of the Ministry of Energy of the USSR, the USSR and the Middle engineering GAN USSR, etc.
The following are the technical aspects of the accident, caused mainly inadequacies RBMK reactors, as well as violations and errors made by staff of the station during the last for the 4-th block of Chornobyl experiment.