DYN3D/ATHLET and ANSYS CFX calculations of the OECD VVER-1000 coolant transient benchmark


DYN3D/ATHLET and ANSYS CFX calculations of the OECD VVER-1000 coolant transient benchmark

Kliem, S.; Höhne, T.; Rohde, U.; Kozmenkov, Y.

Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/ATHLET coupled code system. Phase 1 of the benchmark (V1000CT-1) refers to the main coolant pump (MCP) switching-on experiment conducted in the frame of the plant-commissioning activities at the NPP Kozloduy-6 in Bulgaria.
The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. A DYN3D/ATHLET model of the primary and secondary circuit of the plant including MCP characteristics, boundary conditions and benchmark-specified nuclear data library was created. For an adequate modeling of the redistribution of the coolant flow in the reactor pressure vessel (RPV) during the transient a simplified mixing model for the DYN3D/ATHLET code was developed and validated against a computational fluid dynamics (CFD) calculation with the code ANSYS CFX. The results of the coupled code calculation are in good agreement with the available experimental data. The discrepancies between experimental data and the results of the calculation do not exceed the accuracy of the measurement data. This concerns the initial steady state data as well as the time histories during the transient.
The above mentioned CFD model was used also in the second phase of the benchmark (V1000CT-2). In this part of the benchmark, post-test calculations of coolant mixing experiments at the same NPP are carried out. The comparison is made with assembly-wise mixing coefficients being the results of the experiments. The numerical grid model contains 4.7*106 tetrahedral elements. Different advanced turbulence models were used in the numerical simulations. The best agreement with the experimental data at the core inlet shows the Detached-Eddy-Simulation. Strong fluctuations occur in the downcomer of the RPV. The results show a clear sector formation of the affected loop in the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%.

  • Contribution to proceedings
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia
    Proceedings of the 5th International conference on safety assurance of NPP with WWER
  • Lecture (Conference)
    5th International conference on safety assurance of NPP with WWER, 29.05.-01.06.2007, Podolsk, Russia

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Publ.-Id: 9555