Important Note: This website contains historical data from the INSP project. As of 2004 the site is no longer maintained and certain sections do not work correctly.

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Important Note: This website contains historical data from the INSP project. As of 2004 the site is no longer maintained and certain sections do not work correctly.

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Historical Issues

The safety problems at Soviet-designed reactors have several underlying causes. The most significant is the historical isolation of the plants' operators, designers, and regulators. In the closed society of the Soviet Union, these personnel could not exchange information or technology with the international nuclear community and had limited interaction even with their counterparts in Soviet countries.

Another significant cause was a lack of emphasis on safety. Goals for low-cost production of electricity often outweighed safety goals. Regulatory bodies responsible for enforcing safety standards were ineffective, especially when their safety directives ran counter to production goals.

The new governments of countries with Soviet-designed reactors have invested millions of dollars toward improving the safety of their nuclear power plants. However, their economic and technical resources are insufficient to address many of the risks. For more information on historial issues, see the timeline.

Reactor Types

Two basic designs, called RBMK and VVER, were used to build 59 of the 65 operating reactors addressed in cooperative safety efforts.

Four reactors at Chornobyl nuclear power plant
The four reactors at Chornobyl nuclear power plant are examples of the RBMK boiling-water graphite moderated design. Chornobyl's four reactors include Unit 4 where the 1986 accident occurred and Unit 3, which continues to operate. Units 1 and 2 are shut down.
An RBMK reactor uses graphite to moderate neutrons--or slow down the nuclear chain reaction. The nuclear fuel is contained in about 1,700 pressure tubes. Cooling water passes through the tubes, where it is boiled by the nuclear heat to produce steam. The steam is routed to a turbine generator, which produces electricity.

A number of problems are inherent in RBMKs. If several pressure tubes rupture simultaneously, the force can raise the reactor lid, releasing radioactive fission products. An RBMK reactor is susceptible to power instabilities. Increased boiling can boost power levels, creating an uncontrolled nuclear reaction. The RBMKs lack a containment system to prevent release of radioactive materials to the environment. The RBMK's emergency core cooling system, fire-protection system, and electronic control-and-protection system do not meet international standards. Fourteen RBMK reactors are in operation. Chornobyl Unit 4, which exploded in 1986, was an RBMK. The thermal-hydraulic instabilities inherent in an RBMK contributed to the accident at Chornobyl (more on the Chornobyl accident).

VVER reactors use pressurized light water for core cooling and to moderate the nuclear chain reaction. Forty-five VVER reactors are in operation. There are three principal models.

Four reactors at Kola nuclear power plant
The four reactors at Kola nuclear power plant are examples of the VVER pressurized light-water moderated reactor, similar to Western pressurized water reactors. Most of the 65 operating Soviet-designed reactors at 21 nuclear power plants are VVER or RBMK designs.
The earliest, the VVER-440/230, has a limited containment system and virtually no emergency core cooling system. Its backup safety systems, fire-protection systems, and electronic control-and-protection systems are inadequate.

The VVER-440/213 reactor is an enhanced version of the 230 model. It has an emergency core cooling system and a "bubbler condenser tower" that provides some containment. Fire-protection and electronic control-and-protection systems are inadequate.

The VVER-1000, the largest and newest model, meets most modern safety standards. It has an emergency core cooling system and a containment building. However, its fire-protection and electronic control-and-protection systems have shortcomings.

In 1996, two Russian plants with uniquely designed reactors requested U.S. collaboration in safety improvements. The Bilibino plant has four LWGR-12 light-water-cooled, graphite-moderated reactors. The Beloyarsk plant operates a BN-600 breeder reactor, cooled by liquid sodium.

In 1997, the Asian nation of Kazakhstan requested U.S. collaboration in improving safety at its Soviet-designed BN-350 breeder reactor at Aktau.


SummaryKey Accomplishments
IntroductionPerformace Measurement
and Future Directions
Historical Issues and Reactor TypesTimeline
Reducing RisksContacts

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