Background

This project was a follow-up of a previous project (UK/TS/TR1) which consisted in the transfer of neutronic codes to the Scientific Technical Center of Ukraine (STC, the Ukrainian Technical Support Organisation).

The overall objective of this project was to improve the STC technical capability on VVER 440/213 reloading scheme analysis, to take into consideration the specific Ukrainian regulation in order to modernise the transferred codes and to complement the technical capabilities of the STC in the field of neutronic evaluation by the transfer of additional codes.

The specific objectives were:

• Task 1: Transfer by the contractor of methodology to develop a library of constants for VVER 440/213 reloading schemes.
• Task 2: Preparation by the STC of VVER 440/213 library of contents
• Task 3: Preparation by the contractor of VVER 440/213 library of contents
• Task 4: Comparison and checking results of tasks 2 and 3 in order to finalise the library
• Task 5: Definition by the STC of the requirements for codes modernisation, as far as the already transferred codes are concerned (codes PYTHIA, DERAB, PREPAR and RETINA-MADAM).
• Task 6: Adaptation by the contractor of the above mentioned codes
• Task 7: Verification by the STC of the achievement of task 6.
• Task 8: Transfer of codes used for the fuel transport, the spent fuel storage, the fuel behaviour during LOCA and the fluence on the Reactor Pressure Vessel wall. This transfer had to be completed by the transfer of the corresponding documentation, by training and by the study of practical cases.

Project Results

• Task 1: On the basis of the contractor’s experience in the preparation of group of constants for the core calculation of the VVER-440 in Greifswald, the methodology to prepare a library of constants for a VVER 440/213 was transferred.
• Task 2: The STC was supported to compare the technical data between the Rovno NPP and the Greifswald NPP and to check the technical input parameters. Afterwards, the STC created its library of content with the code NESSEL-4.
• Task 3: On the basis of the above mentioned input parameters, the contractor performed independent calculations with the code NESSEL-4 to create a library which would be compared with the STC’s library.
• Task 4: Both libraries were compared and were found in almost complete agreement. There were some differences which had a negligible effect on the calculated safety relevant parameters.
• Task 5: Codes were modified to satisfy the STC’s requirements, for example to take into account the new operation regimes (new fuel assembly types, the transition cycles).
• Task 6: The content of this task was changed to the training of STC experts in statistical data evaluation, in order to assess experimental data and the corresponding uncertainties in the codes.
• Task 7: The accuracy of the modified codes was verified on the basis of operational data from Ukrainian NPPs.
• Task 8: The codes OMEGA (Monte-Carlo code) and FEM (2D Stationary Neutron Diffusion code) were transferred and the STC experts were trained in the use of those codes for the fuel transport and the spent fuel storage.