Type: RBMK
Units: Two operating
Total megawatts (net): 1,850 (925 per operating unit)
Location: Slavutich, Ukraine
Dates of initial operation:
For an overview of the principal strengths and deficiencies of Soviet-designed plants, see Soviet Nuclear Power Plant Designs.
Two of Chernobyl's four units are operational. Unit 4 was destroyed by the 1986 accident, and Unit 2 has not operated since a fire occurred in its turbine building in October 1991. Unit 1 was shut down for maintenance in March 1992; Unit 3 was shut down for maintenance a month later. During shutdown, valve problems similar to those that had plagued the Leningrad (Sosnovyy Bor) plant were detected, extending the outages of the two units while all the fuel-channel control valves were replaced.
After the fire at Unit 2, Ukraine's Parliament voted to move forward the shutdown date for Chernobyl from 1995 to 1993.
Plant Incidents. In January 1993, two small fires occurred at the plant, one in a building housing auxiliary electrical equipment, and the other in a ventilation center in Unit 4's sarcophagus. Both fires were classified as Level 0 on the seven-level International Nuclear Event Scale.
In April 1994, two incidents occurred on successive days. One involved a drop in cooling system water levels after a short circuit in a cable as workers were reconnecting Unit 3 to the grid following planned maintenance; it was classified as Level 1 on the INES. The other incident involved the failure of a controlling arm while nuclear fuel was being moved in Unit 1; it was classified as Level 0.
In October 1994, a through-wall crack in the upper part of a fuel channel tract in Unit 3 was classified as Level 1 on the INES.
In January 1995, Unit 3 was scrammed after an operator closed the wrong valve because of an incorrect inscription on a water level sensor. The event was classified as Level 1 on the INES.
Plant Operations. In 1993, 150 of the plant's highly skilled employees--many of them Russian--left. The loss continued in 1994, with 13 supervisory staff departing in the first three months of the year, including the plant's director. According to Chernobyl's new director, the plant had adequate personnel to fully staff the six shifts needed to operate the two units.
In February 1994, Russia halted the delivery of nuclear fuel to Ukraine because that country had not yet signed the Nuclear Nonproliferation Treaty. At the time of the Russian move, Chernobyl had only about one to two weeks of fuel remaining. The Russians resumed deliveries to Chernobyl in late February 1994
In early April 1994, the Ukrainian government approved the restart of Unit 2. A few weeks later, plant management officially applied to the Ukrainian State Committee for Nuclear and Radiation Safety (GANU) to restart Unit 2. In June 1994, GANU adopted a policy on restart that would require plant management to present an annual report of actions planned to increase plant safety. GANU further said it would make a decision on restart only after the unit had been upgraded to meet current safety standards and a technical safety report had been submitted as a basis for licensing. But in December 1994, GANU was abolished, and its functions were assumed by the newly created Ministry for Environmental Protection and Safety of Nuclear Power Utilization.
In April 1995, plant management ordered repairs to be made to Unit 2. By May, one of the unit's turbogenerators had reportedly been repaired, and plans called for the second one to be replaced with a turbogenerator from the unfinished Chernobyl Unit 5. Before Unit 2 can be restarted--scheduled for late 1996 unless Western funding to close Chernobyl is available--it must complete a safety upgrade program stipulated by the Ministry of Environmental Protection and Nuclear Safety. In October 1995, repair work at the unit had reportedly been suspended because of talks between Ukraine and the G-7 countries about funding Chernobyl's shutdown. In late November, Ukrainian Minister of Environmental Protection and Nuclear Safety Kostenko said that Ukraine had decided not to commission Unit 2 in the first quarter of 1996 as planned.
Chernobyl's two operating units provide roughly 6 percent of the country's electricity.
Plant management has proposed a timetable for fuel channel replacement at Chernobyl if no agreement is reached with the G-7 to close the plant by 2000. According to the timetable, Unit 1--which had 36 fuel channels replaced in 1995--must have all its fuel channels replaced in the 1996-1997 time frame, and Unit 3, in the 1999-2001 time frame. With such replacement, the units could operate until 2010-2015.
The accident at Chernobyl Unit 4 resulted from a combination of design and technical deficiencies and operator error.
In January 1993, the IAEA issued a revised analysis of the Chernobyl accident, attributing the main root cause to the reactor's design and not to operator error. The IAEA's 1986 analysis had cited the operators' actions as the principal cause of the accident.
In response to the accident, the Soviet government initiated a major backfitting program to upgrade existing RBMK nuclear units, increasing control rod scram speed from 24 seconds to 10-12 seconds, improving core physics and increasing the uranium fuel enrichment from 2 percent to 2.4 percent.
Because of the 1991 Ukrainian parliament vote to close Chernobyl by the end of 1993, however, Ukraine has not carried out many of the upgrading activities undertaken at RBMK plants in Russia and Lithuania. However, in March 1995 Ukrainian President Kuchma reportedly said that the country has allocated more than $300 million for Chernobyl safety improvements. He also said that replacing major components--mainly pressure tubes--could extend the lives of units 1 and 3 by 10 years, and would cost roughly the same as closing the plant.
U.S. Assistance. The U.S. firm S3 Technologies is assisting the Ukrainians in building a control room simulator for Chernobyl. In addition, under the Department of Energy's International Nuclear Safety Program, Unit 3 will receive fire safety upgrades, and U.S. experts are working with plant staff to upgrade operational safety at Chernobyl (see the section on DOE Programs for details).
Canadian Aid. Ontario Hydro International will use some of the money in Canada's nuclear safety assistance package to Ukraine to adapt Ontario Hydro's dry storage canisters to accommodate RBMK spent fuel bundles from the Chernobyl plant. The canisters will be manufactured in Ukraine.
WANO Exchange Visits. The World Association of Nuclear Operators has sponsored several exchange visits involving the Chernobyl plant. The plant has hosted personnel from the following plant:
Japan's Hamaoka plant (August 1993).
In addition, personnel from Chernobyl have visited the following plants:
Plant Twinning. The Chernobyl plant is twinned with Germany's Grohnde plant.
IAEA Training Seminar. An International Atomic Energy Agency seminar was held at Chernobyl in November 1994. The aim of the seminar--which was attended by IAEA experts, specialists from Ukrainian nuclear plants, and officials from the organizations that manage and regulate those nuclear plants--was to share other countries' plant operating experience and develop a program for improving the safety culture at Chernobyl. A second seminar was held at Chernobyl Oct. 3-5, 1995. The purpose of the seminar was to familiarize plant personnel with the detailed ASSET analysis procedures for plant self-assessment of safety performance in advance of the ASSET peer review mission scheduled for August 1996.
ASSET Mission. The IAEA conducted an Assessment of Safety Significant Events Team (ASSET) mission to Chernobyl in June 1992 to investigate root causes of the Unit 2 fire of October 1991. The fire rendered the reactor's emergency feedwater system inoperable. IAEA's goal was to issue generic recommendations and distribute those to other plants.
The team's generic recommendations:
Check all equipment used for disconnection and isolation of the generator from the grid for proper operation and for acceptance criteria and preventive maintenance.
Check the capacity of the fire-suppression systems in the turbine hall.
Check the vulnerability of emergency feedwater systems to common mode failures.
Check that personnel are aware of the importance of seemingly small deviations, and that operational experience feedback programs pay attention to such small deviations.
The team also made four specific recommendations to Chernobyl management, strongly advising it to implement a "structured management programme" that targets quality control, preventive maintenance, surveillance and the implementation of corrective actions.
In general, the IAEA team reported that it did not receive a clear picture of the Chernobyl organizational structure and accountability for safe operations of the plant. It concluded that the general situation at the plant did not seem to be favorable to Chernobyl's safe operation.
Safety Review Mission. An IAEA mission visited Chernobyl March 7-17, 1994, to review the scope and status of the safety modifications implemented and proposed and to review safety aspects related to operation. The team found "serious safety deficiencies" at the plant, identifying safety shortcomings in four areas: design; inspection; fire protection; and radiological protection.
In the design area, the team found a number of deficiencies in the first-generation Unit 1 and the now-closed Unit 2:
There is poor separation between control and protection systems.
Main steam lines are located directly above control rooms in units 1,2.
Units 1 and 2 lack emergency control rooms.
The control rooms have no filtered ventilation.
The emergency core cooling system (ECCS) of units 1 and 2 cannot cope with breaks in pipes whose diameter is greater than 300 millimeters, and there are no dedicated ECCS pumps.
Pressure relief capability from the reactor cavity is limited to a break in no more than four pressure tubes out of a total of 1,660.
Units 1 and 2 have no check valves in the group distribution headers to protect against a break in a header or in the pressure header of the main circulation pumps.
Units 1 and 2 do not have an accident localization system, so radioactive steam is released directly to the atmosphere in case of overpressure in the reactor building.
Leak rates from hermetic compartments are as high as 40 percent per hour at 40 percent overpressure.
Lack of redundancy and separation in various parts of the service water system makes the entire system sensitive to possible common mode failures.
The team found the plant's equipment for non-destructive examination of metal components to be out of date. According to the team, defect detection is crucial at units 1 and 2 because the ECCS cannot cope with large pipe breaks.
The team also found "serious deficiencies" in fire protection, especially at Unit 1. Plastic floor coverings in the turbine and reactor buildings can generate toxic smoke or fumes, which could add to the severity of a fire. Also, no systematic analysis has been carried out to determine needed fire prevention and mitigation measures.
The team said "a major and urgent reinforcement of radiation protection measures is necessary." It found serious deficiencies in: training and safety culture of radiation protection personnel, calibration of instruments, individual dosimetry and exposure control, adequacy of procedures, and contamination control.
The team said it was also concerned about the plant's ability to obtain modern equipment and spare parts.
Finally, the team cited the deteriorating condition of the sarcophagus surrounding the destroyed Unit 4, which--if it collapses--would have "serious consequences."
As a result of the mission, the IAEA considered the conditions at Chernobyl so grave that it convened a meeting of international experts and Ukrainian representatives to review the plant's safety situation.
ASSET Mission. An ASSET mission visited Chernobyl April 11-22, 1994. The mission looked at the plant's management policy on safety operation and assessed the plant's performance in preventing incidents.
The team reviewed 243 events reported between January 1989 and December 1993. Of these, 110 were considered to be of safety relevance, with 12 events classified as Level 1 on the International Nuclear Event Scale and two classified as Level 2. The remaining 96 were classified as Level 0.
The team identified nine groups of events:
The team said that fuel handling was an area of particular concern, because the fuel route is operated manually and relies on the high proficiency of operators. The team also noted that the frequency of diesel generator failures during the 1992-1993 period was a matter of concern.
The team made a number of recommendations to improve the prevention of events. Among them:
Improve the maintenance and testing of fast-acting emergency core cooling system gate valves.
Consider ways to improve cooperation and teamwork between operations and maintenance personnel.
Ensure that all new or revised criteria for testing equipment be included during the revision of testing procedures.
As part of a preventive maintenance program, schedule corrective actions as soon as possible after the detection of latent weaknesses.
Plant management should consider giving further training in root cause analysis and operational feedback.
The team also suggested that plant management consider inviting an ASSET follow-up mission to the plant in two years.
In addition, the team briefly discussed with plant management the implementation of the recommendations made by the 1992 ASSET mission to the plant. Because of a lack of time, only one recommendation--upgrading generator switch control circuits--was reviewed in detail, with plant management providing information on the specific actions taken to upgrade the circuits.
Planned ASSET Missions. An ASSET peer review of the plant's analysis of events reflecting safety-culture issues is scheduled for Aug. 19-23, 1996, and a second peer review mission is scheduled for July 7-11, 1997.
December 1995
