Nuclear Fuel Behavior During Chernobyl Accident
Development of the Models for Nuclear Fuel Behavior During Active Phase of Chernobyl Accident
Tech Area / Field
- ENV-SPC/Solid Waste Pollution and Control/Environment
- FIR-MAT/Materials/Fission Reactors
- FIR-MOD/Modelling/Fission Reactors
8 Project completed
Senior Project Manager
Tocheny L V
Kurchatov Research Center, Russia, Moscow
- Institute of Safe Atomic Power Engineering Development, Russia, Moscow
- CEA Commissariat a l'Energia Atomique, Cadarache, France, Saint-Paul-lez-Durance\nEuropean Commission / Joint Research Center / Institute for Transuranium Elements, Germany, Karlsruhe\nGRS mbH, Germany, Berlin\nAtomic Energy Canada Limited, Canada, ON, Chalk River\nCEA / Institut de Radioprotection et de Surete Nucleaire, France, Saint-Paul-lez-Durance\nForschungszentrum Karlsruhe GmbH, Germany, Karlsruhe
Project summaryThe "Chernobyl lessons" are very costly for the world society. That is why it is very important to understand and use them completely including, first and foremost, the results of the giant and practically unrepeatable "experiment" on nuclear fuel contained in the reactor core.
Understanding of processes, which underwent this fuel during the active phase of the accident, is of much importance from the viewpoint of general nuclear industry safety-related issues. Such understanding is equally important as regards specific practical issues to be solved in the future during removal of fuel containing masses (FCM) from the "Object Shelter".
Unfortunately, so far attempts to develop a valuable nuclear fuel behavior model at the active accidental stage have not met with success.
There are papers based on wrong assumptions, which were rejected during subsequent investigations at Object "Shelter". There are also papers, which only outlined solutions of inpidual problems important for such a model development.
There are also a number of speculations pursuing, as a rule, not technical objectives and contradicting experimental data.
However to date one is able to develop a realistic and comprehensive model based on both the analysis & investigation results of systematic 16-year investigations of the post accidental status of the Chernobyl reactor, on the one hand, and on the up-to-date computer codes dealing with the dynamic of corium behavior, on the other hand.
The main benchmark materials for the development of such a model should be:
– Investigations on determining radionuclide composition, activity and heat generation of fuel at the 4th Chernobyl Nuclear Power Plant (NPP) Unit immediately before the accident carried out by the RRC "Kurchatov Institute" in 1986-2001;
– Studies of the releases from the Unit 4 damaged reactor performed at the RRC "Kurchatov Institute", and IBRAE RAS in 1986-2001;
– Work on the dynamic behavior model for corium formed during the Chernobyl accident performed at IBRAE RAS in 1986-2001;
– Database on FCM of Object "Shelter" developed in 1998–2002 at the RRC "Kurchatov Institute" in the frames of the French-German initiative which contains more than 6000 records and analyses of FCM samples;
– The whole complex of activities performed in 1986–2003 at the Chernobyl NPP site by specialists of Russian and Ukrainian research institutions.
Principal tasks to be solved in the frames of the given project can be subpided into the following two categories:
Tasks on the development and verification of the nuclear fuel behavior model during the active phase of the Chernobyl Accident:
Task 1. To develop the model and describe the subsequent processes, such as: dispersion, melting and spreading of FCM, comprehensive information on the location, burn up, nuclide composition, decay heat generation, etc. of the Chernobyl NPP 4th Unit fuel before the accident is required. Such information can be obtained through verification of computational efforts and a large body of data on FCM sample analyses. (Computational & analytical work which results will be summarized in the form of a report).
Task 2. Based on analysis of verified data on composition and quantity of radionuclides released from the core during the active accident phase, on nuclear, chemical and mineralogical composition of lave-like FCM, on the geometry of intrareactor compartments the key parameters (and their range) will be determined, which later will be described by the developed model (Computational & analytical work which results will be summarized in the form of a report).
Task 3. Work on direct analysis of uranium and zirconium concentrations in metallic melts will be performed for further comparison with the results of model computations. All investigations will be performed using certified measurement methods and up-to-date controlling & measuring instrumentation (Experimental work, which results will be summarized in the form of a report).
Task 4. Models of corium formation after the reactor core degradation will be developed and corium behavior dynamics will be calculated. The relevant computer codes will be developed. Based on the results obtained in Tasks 1 through Task 3 a most reasonable model describing transformation of the 4th Unit reactor fuel to the post-accidental FCM state will be chosen. (Computational & analytical work, development of computer codes; the results will be summarized in the form of a report).
Tasks related to the use of the developed model to solve application problems:
Task 5. FCM generation model will be used for assessments of composition and physical state of materials located in the depth of their large amounts, from which one has failed to get necessary samples. (Computational & analytical work, which results will be summarized in the form of a report).
Task 6. Thermal model of interactions of fuel with serpentine and concrete will help to get an answer to what extend strength properties of concrete constructions on the way of melt spreading have changed (Computational & analytical work, which results will be summarized in the form of a report).
Task 7. The model to be developed will help to clarify the issue of the presence of uranium and zirconium in the molten metals being housed in appreciable amounts within Object "Shelter". (Computational & analytical work, which results will be summarized in the form of a report).
Task 8. The newly created model will be used to predict long-term corium behavior in the melt localization systems (core-catchers), which are being developed for some NPP concepts with PWR (EPR, VVER-1000). (Computational & analytical work, which results will be summarized in the form of a report).
An important peculiarity of the present project consists in the greatest possible use of huge experimental data obtained in investigations at Object "Shelter" (after its analysis and verification) in combination with the most modern computer codes describing corium behavior. To date only collaboration between RRC "Kurchatov Institute" and IBRAE will allow to perform this work and to solve the whole range of tasks (from radiological to material studies) related to the Object "Shelter" safety (the dismantlement strategy) and to the general problems of nuclear industry safety as well.
The project executors have collected a wide experience of work on the subject under consideration.
The proposed project fully complies with the ISTC goals & objectives, namely:
– Provides a support for applied researches in the environment protection & nuclear safety areas;
– Ensures additional employment for 19 highly skilled specialists involved into other nuclear program implementation.
As foreign collaborators, leading German and French institutes will be involved performing investigations in the safety area and possessing a rich experience of work at the Chernobyl NPP site (Gesellschaft fur Anlagen- und Reaktorsicherheit (GRS) mbH and l'Institut de Radioprotection et de Surete Nucleaire). To ensure information exchange during the Project implementation, the Project Task deliverables are to be submitted to the foreign collaborators, and joint working meetings - to discuss the Project implementation results - are to be held.
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