Efforts to increase the power to the level originally planned for the test were frustrated by a combination of xenon poisoning c, reduced coolant void and graphite cooldown. It was not until about 23:00 on 25 April that the grid controller agreed to a further reduction in power.įor this test, the reactor should have been stabilised at about 700-1000 MWt prior to shutdown, but possibly due to operational error the power fell to about 30 MWt b at 00:28 on 26 April. In accordance with the planned test programme, about an hour later the ECCS was switched off while the reactor continued to operate at half power. Although subsequent events were not greatly affected by this, the exclusion of this system for the whole duration of the test reflected a lax attitude towards the implementation of safety procedures.Īs the shutdown proceeded, the reactor was operating at about half power when the electrical load dispatcher refused to allow further shutdown, as the power was needed for the grid. The planned programme called for shutting off the reactor's emergency core cooling system (ECCS), which provides water for cooling the core in an emergency. Therefore, inadequate safety precautions were included in the test programme and the operating personnel were not alerted to the nuclear safety implications of the electrical test and its potential danger. Unfortunately, this test, which was considered essentially to concern the non-nuclear part of the power plant, was carried out without a proper exchange of information and coordination between the team in charge of the test and the personnel in charge of the safety of the nuclear reactor. This type of test had been run the previous year, but the power delivered from the running down turbine fell off too rapidly, so it was decided to repeat the test using the new voltage regulators that had been developed. (Adequate coolant circulation following completion of the test was ensured by arranging power supplies to four of the eight pumps from station service power the other four pumps were supplied by unit service power.) The aim of this test was to determine whether cooling of the core could continue to be ensured in the event of a loss of power. It was decided to take advantage of this shutdown to determine whether, in the event of a loss of station power, the slowing turbine could provide enough electrical power to operate the main core cooling water circulating pumps, until the diesel emergency power supply became operative. The unit 4 reactor was to be shut down for routine maintenance on 25 April 1986. The combination of these factors provoked a nuclear accident of maximum severity in which the reactor was totally destroyed within a few seconds.Ī full description of the accident, its environmental and health effects, as well as lessons learned, can be found in the information paper on the Chernobyl Accident. In addition, they did not comply with operational procedures a. The operators were not informed of this and were not aware that the test performed could have brought the reactor into an explosive condition. The RBMK reactor design was poor from the point of view of safety and unforgiving for the operators, both of which provoked a dangerous operating state. The accident at Chernobyl was the product of a lack of safety culture. Sequence of Events – Chernobyl Accident Appendix 1ĭuring the course of a safety system test being carried out just before a routine maintenance outage, Chernobyl 4 was destroyed as a result of a power transient on 26 April 1986.
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