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Radioactive Inventory for Decommissioning Reactors

#0841


Evaluation of Radioactive Inventory for Fission Reactor Decommissioning

Tech Area / Field

  • FIR-DEC/Decommissioning/Fission Reactors

Status
8 Project completed

Registration date
30.12.1996

Completion date
02.07.2004

Senior Project Manager
Tocheny L V

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Project summary

The development of decommissioning methodology for the nuclear power reactors is at present a very actual problem of nuclear safety and radioactive waste treatment. The knowledge of radioactive inventory within the out-of-core area plays the crucial role in the decommissioning planning. The main source of construction material activity is the activation under the influence of neutron flux (mainly thermal part) from the reactor core. The known experimental data of radioactive inventory are very scarce and may be used only for the decommissioning planning of the given facility due to difference in the material composition, irradiation condition and so on. Such a situation leads to the strong necessity of radioactive inventory evaluation on the base of reliable computer codes.

One of the oldest type of nuclear power reactor which is common used both in Russia and the Eastern Europe countries is water-water reactor WWER. The planned shut down of the number of these reactors makes the problem of its proper decommission planning including the definition of radionuclide distribution within the out-of-core area and the evaluation of the integral activity and doze as a one of the most important now. In the given project the development of reliable computer code for radioactive inventory evaluation is proposed. The proposed code is based on the program package COROUT developed earlier in the Radium Institute under the technical assistance of International Atomic Energy Agency. In distinction of the existing approaches the code has been originally destined for the decommissioning planning. The code is consistent program package, which includes modules for the calculation of neutron flux distributions, distributions of activity and nuclide concentrations and data library module. During 1995 the code has been tested in the framework of benchmark exercise initiated by IAEA. Calculation results will be as follows:


- detailed neutron flux distribution in out-of-core area;
- distribution of activity and nuclide concentrations in the same points vs. reactor operational history;
- integral activity and dozes.

In order to study the real situation on the Kola Nuclear Power Plant where the WWER-440 reactors are under operation the following experimental investigations are planned:


- measurements of sample activation inside reactor construction components:
- measurements of neutron penetration through the WWER cassette imitator using the facility of nuclear fuel control SCAT in the reactor-like neutron spectra;
- measurements of profile and depth of fuel burning-up at FAMOS facility (together with NUKEM, Germany) that allows to evaluate the distribution of neutron flux inside the reactor core during the reactor operational history.

In addition to the service data (reactor history and power dynamics, geometry model, composition of structural materials and so on) these data give us possibility to work out the data libraries for such kind of reactor and to carry out testing calculations for comparison of calculated results with the available results of measurements for Kola NPP reactor. It is proposed also to work out the computer chart of radionuclide distribution as well as their activity within the reactor constructions during the time of its operation and to perform the radioactive waste classification of construction materials. The performance of given project allows not only to find out the main approaches to the WWER decommissioning methodology but to establish also the fruitful contacts with foreign specialists who are rather interested in this kind of information.

Potential role of foreign collaborators

The problem of fission reactor decommissioning is the international problem where the more and more specialists take part now. A unification of efforts let us possibility to find out the more adequate approach and work out the methodology of solution of this actual problem.


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