After the accident the first two Power Units remained in normal operable state and were shutdown on April 27, 1986. The third Power Unit, technically connected with the fourth one, was shutdown an hour and a half later after the accident.
The issues on re-operation of three Chornobyl NPP Units and carrying out of the required for it activities were among the most important within a plan for the accident consequence elimination. They were settled simultaneously with the activities on preserving the fourth Power Unit.
The recovery work was started with decontamination of the main and auxiliary buildings and structures of Power Units and equipment and personnel workplaces, located in them, as well as adjacent territories. The most contaminated were specific horizontal sections of surfaces of the Turbine Hall [up to 106 β-part./(cm2 min)], as it was contaminated through the destroyed roof of the 4th Power Unit. As of May 20, 1986, dose rate of γ-radiation within the contaminated premises of the first and second Power Units was 10-100 mR/h, the Turbine Hall – 20-600 mR/h.
At first two Power Units the decontamination activities were completed at the beginning of third quarter of 1986. The decontamination activities at the third Power Unit resulted in further improvement of radiation situation at the acting Power Units. As a result of performing a part of the planned activities by the end of July 1987 the dose rate at 3rd Power Unit’s Turbine Hall was drastically reduced and amounted to 7-50 mR/h. Following the completion of Shelter Object construction and a set of works on decontamination of Plant territory the radiation situation at the 1st and 2nd Power Units was finally stabilized and was brought to the fixed standards.
Technical and organizational measures on improving safety of operation of acting NPPs with RBMK reactors were developed based on the analysis of reasons of occurrence and development of the accident at the ChNPP 4th Power Unit. The objective of the safety improvement measures was first of all the reduction of steam void reactivity effect and enhancement of emergency protection response speed.
At the 3rd Power Unit, in contrast to the 1st and 2nd Power Units, a great scope of recovery work was performed. The equipment, pipelines, ventilation ducts and cable paths within the premises of 3rd Power Unit with high levels of γ-background were dismantled to reduce the radiation background. A protection and separation wall within Unit 3 and Unit 4 was concreted and clad in lead to reduce the radiation background. Additional protection walls were erected at other Unit's sections.
The Power Units were ready for resumption of operation:
October 1, 1986 — post-accident commissioning of 1st Power Unit.
November 5, 1986 — post-accident commissioning of 2nd Power Unit.
December 4, 1987 — post-accident commissioning of 3rd Power Unit.
In early 1988, after construction of protective barriers, personnel of the Chornobyl NPP were transferred to a non-rotation based work.
The main objectives of work performance of the 2nd stage at Chornobyl NPP were:
1. Prevention of radionuclide spreading from radioactive contamination area, re-disposal of solid RAW.
2. Creation of conditions within contamination area for radiation-safe vital activity of population.
3. Preparation of the Exclusion Zone and resettled territories of strict control zone to the return to national economy.
4. Preparation for the Chornobyl NPP decommissioning.
Chornobyl NPP officially stopped generation of electricity on 15th of December, 2000. At 13:17, by the order of the President of Ukraine Leonid Kuchma, Power Unit No.3 reactor was shut down forever with a turn of the key.
The decision on the pre-schedule shutdown of Unit 1 was made on November 30, 1996, Unit 2 – on March 15, 1999. The decision on the pre-schedule shutdown of Unit 3 and final shutdown of ChNPP was made by the Cabinet of Ministers of Ukraine on March 29, 2000.
Such actions were caused by the commitments of Ukraine to the world community stipulated in the Memorandum of Understanding between the Government of Ukraine and Governments of the G7 countries and the Commission of the European Community on the Chornobyl NPP Closure. The Memorandum was signed on December 25, 1995.
“...To take all appropriate measures for the ChNPP decommissioning as soon as reasonably practicable”, — the Memorandum said.
After the accident, from 1986 till 2000, the Chornobyl NPP generated 158.6 billion kW- hours of electric energy. Before the accident, from 1977 till 1986, the Plant generated 150.2 billion kW- hours.
At the time when the ChNPP was shutdown the ChNPP had 9000 employees. At the present time the quantity of employees is less than 2400 persons.
