Causes of the accident at the fourth block of the Chernobyl Nuclear Power Plant

   Determining the causes of the accident at the fourth block of the Chernobyl Nuclear Power Plant is one of the most debatable questions today. There are two camps of professionals who have opposing views on the causes of the destruction of the power plant in April 1986. The first are designers who argue that the principal cause of the accident is unprofessional work by the unit's operating personnel. The second is the direct operational staff, who argue about the existence of significant defects in the design of RBMK reactors and shift the responsibility for what happened to the designers. More than 20 years have passed since the accident and the debate about the original causes has not stopped. Every year that separates us from the events of April 1986 adds new versions and hypotheses.
   Despite the existence of ongoing discussions between designers and maintenance personnel regarding the true causes of the accident, there is an officially adopted list of causes of the Chernobyl reactor explosion. The list of reasons has been defined by a detailed and comprehensive analysis of events leading to the accident at the nuclear facility. It should be noted that in order to ascertain the causes of the accident, the State Commission Gosatomnadzora of the former USSR was created on February 27, 1990.
   The Commission recognized that the design of the reactor allowed for the presence of a positive factor of steam reactivity and a positive factor of reactive power. Thanks to this, as a consequence of mistakes by the reactor designers in the calculation of physical design parameters in the active zone, the reactor was a dynamically unstable system.
   The Commission reviewed 13 versions of the causes of the accident. The most likely version is linked to the presence of the reactivity of the control system and protection of the reactor.
   These are technical reasons. At the same time, experts observed deeper causes of the disaster - a culture of low level nuclear safety in the former USSR. What was behind this? The absence of a developed system of nuclear legislation and the failure to comply with the principle of full responsibility for the safety of nuclear installations by the maintaining organizations. Inadequate attention to human factors and the possible influence on the safety of nuclear power plants. Insufficient attention to the experience of other states and the analysis methodology behind the safety of nuclear power plants in the USSR. As a consequence, for the operation of power units with essential deficiencies of safety (positive stopping of reactivity when inserting rods into the active zone system for protection and management, etc.) which together with inadequate personnel actions were the immediate causes of the accident.



   An analysis of the causes of the accident shows that certain safety systems must operate solely on the basis of signals from technical monitoring of parameters of the power plant control systems, rather than the teams of operators. An example of this approach is the system which was subsequently installed at RBMK reactors - a computerized system for calculating the operating reserve reactivity with an emergency stop signal to the reactor under the condition of reducing the stock below a certain given reactivity level.
   Proceeding from that basis, an exhaustive search for answers about the root causes of the Chernobyl accident continues. Ongoing discussions by experts and the media also continue. Below are materials from publications in the Global Network, which in the opinion of the author of the website "Chernobyl Exclusion Zone" most adequately consider the subject of causes of the destruction of the nuclear unit at the Chernobyl NPP.