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Post-Crash Fuel Reflood


Examination of VVER Fuel Behavior under Severe Accident Conditions. Quench Stage

Tech Area / Field

  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

8 Project completed

Registration date

Completion date

Senior Project Manager
Tocheny L V

Leading Institute
NIIAR (Atomic Reactors), Russia, Ulianovsk reg., Dimitrovgrad

Supporting institutes

  • Nuclear Safety Institute, Russia, Moscow\nElectrostalsky Machine Building Plant (EMZ), Russia, Moscow reg., Elektrostal


  • IRSN - Institut de Radioprotection et de Sûreté Nucléaire, France, Fontenay aux Roses\nForschungszentrum Karlsruhe GmbH, Germany, Karlsruhe\nCEA / Direction de l'Energie Nucleaire (DEN), France, Saclay\nEuropean Commission / Joint Research Center / Institute for Transuranium Elements, Germany, Karlsruhe

Project summary

One of the main aspects of reactor safety validation lies in study of the processes in fuel rods under accident conditions to predict and to control accident process, to improve fuel technology and its operation, to reduce consequences or prevent severe accidents.

Currently VVER reactors are the basis for nuclear energy in Russia, Ukraine, Bulgaria, Hungary, Czech, Slovakia and Finland. These reactors operate rather reliably under steady-state and transient conditions. VVER fuel behavior is currently examined under design-basis accident conditions when the cladding remains intact that allows cooling and unloading the core as well as carrying out fuel transportation. However, for the fuel of this type there is lack of data on its behavior under severe accident conditions.

Great uncertainty of the processes of severe accidents, complexity of the problems to describe design element behavior and, hence, large cost and labor expenditures of experiments make almost impossible to carry out necessary work to validate safety by one separate country. Therefore examinations aimed at development of the codes which allow to assure safety of reactor operation are carried out under international cooperation. Particular attention is paid to VVER reactor while carrying out international projects. However, difference in the core design and materials raises the problem for application of examination results and codes aimed mostly at PWR operation safety to VVER reactors.

The purpose of the Project is to find out any possibilities to apply developed data base to describe the VVER core behavior under severe accident conditions carrying out limited number of the experiments which allow to find out if the difference in VVER and PWR designs and materials is significant.

The primary task of the Project is to obtain data on VVER reactors core behavior under severe accident conditions in order to develop physical models and codes applicable to VVER reactors. This task is assumed to be solved as complementary to the QUENCH project in FZK, Karlsruhe. Realization of the same methodical approach will allow comparison of the behavior of VVER and PWR materials and design elements as well as to provide the possibility of application of the same approach to develop the numerical codes and determine safety criteria of these reactors.

Within the frame of the Project it is assumed to carry out the small-scale tests and an integral experiment under quench conditions with VVER material in order to build up a database for model development and verification of codes. The integral fuel bundle experiment will be carried out using non-irradiated materials. The small-scale experiments with irradiated fuel are assumed to be carried out in order to develop the database for irradiated core materials.

The SFD-VVER project "Examination of VVER Fuel behavior under Severe Accident Conditions. Quench Stage" includes the following stages:

STAGE A. Spent ROD-QUENCH: Study of the spent fuel rod segments behavior under reflood conditions. At this stage the experimental data on spent fuel rod characteristics after reflood will be obtained. Heated up to different temperatures pre-oxidized spent fuel rod simulators will be cooled down by water. Changes in their structure, fragmentation and fission gas release will be examined. Besides, hydrogen generation is planned to be examined.

Project executors: SSC RIAR, Dimitrovgrad. Project co-executors: IBRAE.

STAGE B. Fresh FA-QUENCH: Integral experiment of QUENCH type using model bundle with 31 fuel rod simulators under QUENCH conditions. The result of the work will be the database for VVER bundle behavior under quench conditions, in comparison with available database for PWR bundles.

Project executors: JSC "MSZ", Electrostal (delivery of the elements for model FA); Forschungszentrum Karlsruhe, Germany (fitting and equipment of FA simulators, testing at the test facility, post-test examinations); SSC RIAR, Dimitrovgrad, (post-test examinations of model FA); Project co-executors: IBRAE.

STAGE C. FA Quench Model: Development of models and codes to describe VVER core behavior under severe accident conditions (“quench” stage).

The obtained results will allow to make a conclusion on the behavior of VVER fuel under severe accident conditions during the core reflood and modification and/or adaptation of codes and physical models for PWR fuel behavior to VVER reactor case.

Project executor: IBRAE, Moscow. Project co-executors: SSC RIAR.

Interconnection of the SFD-VVER Project with other projects:


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