The Reactors at Juaragua

Juragua 1 and 2 are VVER-440 reactors, a type still in use in eastern Europe, Finland, and the former Soviet Union (table) Further information on the VVER-440 reactors can be found on the International Nuclear Safety Center Web Site.
Operable VVER-440 Reactors 
ARMENIA Medzamor 2 V270* April 1983
BULGARIA Kozloduy 1
Kozloduy 2
Kozloduy 3
Kozloduy 4
July 1974
Oct. 1975
Dec. 1980
May 1982
Dukovany 2
Dukovany 3
Dukovany 4
Feb. 1985
Jan. 1986
Nov. 1986
June 1987
FINLAND Loviisa 1
Loviisa 2
Feb. 1977
Nov. 1980
Paks 2
Paks 3
Paks 4
Dec. 1982
Sep. 1984
Sep. 1986
Aug. 1987
Kola 2
Kola 3
Kola 4
Dec. 1973
Feb. 1975
Dec. 1982
Dec. 1984
Bohunice 2
Bohunice 3
Bohunice 4
June 1981
Jan. 1981
Feb. 1985
Dec. 1985
Rovno 2
Dec. 1980
Dec. 1981
*Many sources list Medzamor 2 and its inactive twin, Medzamor 1, as Model V230 reactors. The NEI Sourcebook refers to both as Model V270, a variation of V230. For more information, see Nuclear Energy Information Center, Source Book on Soviet-Designed Nuclear Power Plants 1996.

East European Countries with VVER-440 Reactors in Service

"VVER" is the Soviet designation for a pressurized light water moderated reactors, which is designated PWR in western designs. This type of unit is generally regarded as less vulnerable to fire than the RBMK graphite-moderated reactors (LGR) employed at Chernobyl. The number that follows VVER, in this case 440, represents the gross capacity. In the United States, all operable reactors are either of the PWR type or Boiling Water Reactors (BWR). In addition to the PWR type and LGR type in use in Russia and the Ukraine, Russia has one Fast Breeder Reactor. 

Juragua units 1 and 2 belong to the “second generation” of the VVER family. Reactors in this generation reflect the “first uniform safety requirements” incorporated by Soviet designers.(1) The “second generation” includes Model V318, a version not generally regarded as meeting western standards but clearly superior to the V230 and to the RBMK type. The VVER-440 Model V318 reactors at Juragua are based on V213. Model V318 added a number of safety features, including a steel-lined concrete dome-shaped structure to inhibit the release of radioactive particles.(2) Excellent diagrams of both the RBMK type reactor and the Model V230 reactor can be viewed in the Nuclear Energy Institute Sourcebook. 

In 1989, the U.S. Nuclear Regulatory Commission completed a limited special study that compared the Cuban VVER 440/318s and a somewhat similar U.S. pressurized light water reactor. NRC concluded that both reactors are designed to accommodate similar types of accidents, but it is difficult to determine the relative capability of the different designs to deal with more severe accidents. “An assessment of the actual relative risk of the Cuban plants may well be different, depending on specifics that have not been evaluated and on information we do not have.” 

Unlike Chernobyl 4, the VVER-440 incorporates a containment structure to inhibit the release of radioactive materials during a nuclear accident. Lacking such a structure, Chernobyl 4 spewed contaminants into the atmosphere, soil, and groundwater. Juragua’s containment structure is divided into two zones, and this leads to one of the criticisms of the design. If there is a nuclear accident, the top of the structure is weaker than the bottom. “The result of the two-zone system is that while the lower zone is designed to accommodate a maximum over pressure of 1.5 atmospheres, the upper zone can only accommodate a maximum over pressure of 0.5 atmospheres.”(3) By comparison, the VVER-1000, (a newer) Soviet model comparable to western designs, can accommodate 4 atmospheres over pressure throughout. 

The Helms Burton Act lists a number of concerns about the Juragua reactors’ design. In Section 111, entitled, “Withholding of Foreign Assistance from Countries Supporting Juragua Nuclear Plant in Cuba,” the Act states:

(4) In a September 1992 report to the Congress, the General Accounting Office outlined concerns among nuclear energy experts about deficiencies in the nuclear plant project in Juragua, near Cienfuegos, Cuba, including– In the list that follows, the Act refers to the possible structural flaw: (F) the possible inadequacy of the upper portion of the reactors’ dome retention capability to withstand only 7 pounds of pressure per square inch, given that normal atmospheric pressure is 32 pounds per square inch and United States reactors are designed to accommodate pressures of 50 pounds per square inch. In attempting to reduce a complex technical argument to terms easily comprehensible to the layman, however, errors resulted. Normal air pressure at sea level (the level at which the plant is being constructed) is 14.7 pounds per square inch. Since 14.7 pounds per square inch is still greater than 7 pounds per square inch, the statement still implies that the dome cannot survive when exposed to the atmosphere.

To ensure accuracy and impartiality, the following testimony on the Nuclear Regulatory Commission's 1989 study of the Juragua design is quoted in its entirety without comment:

In his testimony before the House, Keith O. Futz, Assistant Comptroller General, U.S. General Accounting Office, summarized the concerns cited in a 1989 study by the U.S. Nuclear Regulatory Commission. According to Mr. Fultz:(4)

Because of Cuba’s proximity to the United States and the risk to which U.S. citizens may be exposed to a radioactive release in case of an accident, NRC performed a limited study to examine the containment design and safety features of the Cuban nuclear power reactors. The study, completed in 1989, discusses similarities and differences in safety characteristics between the Cuban reactors and comparable U.S. reactors.

NRC’s study noted that although the design of the Cuban reactors has many features in common with those of the U.S. PWRs (light water reactors), several differences could lead to significantly different reactions in the event of a serious accident. For example, while the Cuban reactors, like the U.S. PWRs, use water to cool the reactor core, the Cuban reactors use a different system for handling the steam pressure that would be generated by a severe accident. In the Cuban reactors, the steam is condensed so that pressure is reduced in the containment structure. If, in the case of a severe accident, the system for condensing the steam in the Cuban reactors is bypassed and the steam reaches the upper portion of the containment in pressures greater than the upper portion’s designed pressure retention capability of 7 pounds per square inch (other portions of the containment are designed to withstand pressures of about 32 pounds per square inch), the containment could be breached and a radioactive release could occur. In contrast, U.S. PWRs are designed to accommodate pressures of about 50 pounds per square inch throughout the containment structure. The study indicated that the Cuban reactors and the comparable U.S. PWR are designed to accommodate similar types of accidents but concluded that it was difficult to compare the risk posed by the two types of reactors because the information required for such an assessment was not available for the Cuban reactors.

On June 16, 1997, the Cuban Mission responded by a circular letter to the International Atomic Energy Agency to allegations in the Helms Burton Act and subsequent U.S. efforts to discourage third party investment in the Juragua project. The Mission noted that the Section 111 (F) of the Act entitled, “Withholding of foreign assistance from countries supporting Juragua nuclear plant in Cuba” is based on unsubstantiated suppositions and speculations.(5) The letter also insists on Cuba’s right to pursue nuclear power for peaceful purposes. Because the letter does not contain specific technical details, it is not clear which data (if any) are regarded as inaccurate.

The potential problems are not limited to the design. From 1984 to 1991, Pelayo Calante Garcia, a nuclear scientist and engineer, participated in the project. He later left Cuba. According to his subsequent testimony before the U.S. House Western Hemisphere Subcommittee, Mr. Garcia was responsible for inspecting the containment structure. He cautioned that the system to reduce pressure in the structure had never been tested. Also, he cited “defective welds in seals in the containment building and in support structures.” 

Whatever the weaknesses of the Juragua reactors, proponents insist that the design is superior to that of some Soviet-built reactors still in service. The design is less vulnerable to fire than the RBMK reactors that continue to operate in Russia and Ukraine. Critics warn that the weaknesses of the Juragua design, whether or not they can be regarded as critical, have been magnified by poor construction, inferior materials, and insufficient oversight. The efforts of the International Atomic Energy Agency to train Cuban workers and to improve oversight may help reduce problems in the future. 

On June 14 through 18, 1999, the International Conference on Strengthening Nuclear Safety in Eastern Europe discussed the VVER-440 and other Soviet reactors.(6) The Conference was conducted by the International Atomic Energy Agency (IAEA) at its headquarters in Vienna, Austria. IAEA noted several design concerns, including "confinement integrity" (leak tightness) and some of the steps being taken to address the problem.

The results of the Conference are available to be viewed on the IAEA home page. 


1. Nuclear Energy Information Center, Source Book on Soviet-Designed Nuclear Power Plants 1996.

2. The Natural Resources Defense Council, "Backgrounders: The Juragua Nuclear Plant."

3. Fisher-Thompson, Jim, "Recent Film Reveals Flaws of Cuban Nuclear Plant," Daily Washington File, U.S. Information Agency, August 2, 1995. 

4. "Nuclear Safety: Concerns with the Nuclear Power Reactors in Cuba," Statement of Keith O. Fultz, Assistant Comptroller General, Resources, Community, and Economic Development Division, United States General Accounting Office, to the U.S. House of Representatives, Committee on International Relations, Subcommittee on the Western Hemisphere, August 1, 1995, p. 3. 

5. International Atomic Energy Agency Information Circular, INFCIRC/537, July 30, 1997. 

6. International Atomic Energy Agency, "International Conference on Strengthening Nuclear Safety in Eastern Europe."