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Accident Assessment for Chornobyl Reactor Unit 3 from Potential Collapse of Adjacent Building Structures

Overview and Preliminary Conclusions

February 6, 1997


Summary

In a study sponsored by the U.S. Department of Energy, a team of Ukrainian experts reviewed the risk of a serious accident at the operating Chornobyl Unit 3 reactor resulting from the collapse of the damaged structures of the adjacent Unit 4 reactor.

Preliminary conclusions of the assessment are as follows:

  • The risk of such an accident occurring is very small.

  • U.S. experts, who conducted a preliminary review of the assessment, also agree that the risk of such an accident is small and that this issue does not warrant special consideration beyond other safety concerns at the Chornobyl plant.

  • Because of the unlikely occurrence of such an accident, U.S. participants believe that no special preventive measures are needed at this time, and no further detailed evaluation is necessary.

The final report will be available for distribution following a thorough technical review, which also will be used to confirm the preliminary conclusions.

The assessment marks the first project completed by the Chornobyl Center for Nuclear Safety, Radioactive Waste and Radioecology in Slavutych, Ukraine. The United States supported Ukraine in establishing the Center in 1996. The Center serves as an international focal point for developing Ukrainian expertise in nuclear safety and environmental remediation.


Background, Purpose, and Participants

The Department commissioned this assessment a year ago, after British press reports speculated on the potential consequences if the shelter surrounding the destroyed Chornobyl reactor Unit 4 were to collapse. The shelter, which was erected hurriedly in 1986 after the catastrophic accident at that reactor, now is deteriorating. The concern was that the reactor Unit 4 shelter or associated structures could become unstable enough to collapse, creating a serious accident at adjacent operating Unit 3.

The purposes of the study were to assess the possibility of such an accident in Unit 3 and to identify potential consequences.

The Chornobyl Center for Nuclear Safety, Radioactive Waste and Radioecology worked with the following organizations to prepare and review this assessment:

  • Scientific and Technical Center of the Ministry of Environmental Protection and Nuclear Safety of Ukraine

  • Interbranch Agency of the Ukrainian Scientific and Technical Center

  • Chornobyl nuclear power plant

  • Ukrainian Nuclear Regulatory Administration.

U.S. technical experts briefly reviewed the assessment=s methods, application, and conclusions.

Conclusions

  • The study evaluated potential serious accidents in Unit 3 that could result from collapse of the adjacent Unit 4 structures. The area requiring the most careful evaluation was potential damage to safety-related equipment such as control rods or pressure tubes.

  • The possibility that such accidents could occur in Unit 3 was determined to be very small.

  • U.S. experts, in evaluating the assessment, concluded that the approach used was sound and adequately supports the conclusions.

  • Based on the assessment=s findings, the U.S. participants believe that no special preventive measures are needed at this time to protect Unit 3 from structural collapse of the Unit 4 shelter. In addition, no further detailed evaluation is necessary.

Benefits of the Assessment

In addition to the technical results of the assessment, this work generated several additional benefits:

  • Ukrainian scientific and regulatory organizations gained experience in in-depth risk analysis.

  • A broad spectrum of organizations in Ukraine and the United States worked successfully together to conduct the assessment. This cooperation lends credibility to the effort and builds the foundation for future technical collaborations.

  • The assessment marks the first project completed by the Chornobyl Center for Nuclear Safety, Radioactive Waste and Radioecology in Slavutych, Ukraine. The United States supported Ukraine in establishing the Center in 1996. The Center serves as an international focal point for developing Ukrainian expertise in nuclear safety and environmental remediation.

Next Steps

The draft report documenting the assessment contains minor technical errors and inconsistencies. In addition, additional explanation and justification are needed for technical assumptions used in the assessment. U.S and Ukrainian experts are working together on these improvements. However, the assessment=s conclusions are not expected to change.

The assessment is planned for completion in the next two months.

The following individuals from the Scientific and Technical Center of the Ministry of Environmental Protection and Nuclear Safety of Ukraine participated in performing the assessment:

  • Project leader, Scientific Director: I.M. Simonov
  • Head of Department No. 130, Strength and Structures Reliability: V.B. Kritsky
  • Head of Laboratory for Seismic Stability and Nuclear Power Plant Probabilistic Safety Assessment Based on Strength Reliability: A.B. Kritsky
  • Head of Laboratory: A.A. Maliushitsky
  • Head of Laboratory: O.A. Mazurkov
  • Senior Researcher: L.M. Nikolayeva
  • Head of Department: S.N. Kondratyev
  • Engineers: Yu.V. Vigovsky, A.A. Karnaukhov, D.I. Ryzhov, O.V. Gorbenko, M.I. Ulanovsky, A.P. Shugailo
  • Technician: V.A. Levutska

The following individuals reviewed the assessment:

Interbranch Agency of the Ukrainian Scientific and Technical Center

  • V. N. Geras=ko

Industrial Association of the Chornobyl Nuclear Power Plant

  • A.V. Nossovsky
  • V.V. Fomin
  • A.L. Knyshevich
  • E.L. Belousov

Nuclear Regulatory Administration of Ukraine

  • L.S. Bogdan

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