Results of VVER-440 fuel assembly head benchmark. M. Bykov

A. Shishov, O. Kudryavtsev, D. Posysaev, OKB “GIDROPRESS”, Russia

20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Nuclear applications of three-dimensional thermal hydraulics


In the VVER-440/213 type reactors, the core outlet temperature field is monitored with
in-core thermocouples, which are installed above 210 fuel assemblies. These measured
temperatures are used in determination of the fuel assembly powers and they have important
role in the reactor power limitation. For these reasons, correct interpretation of the
thermocouple signals is an important question. In order to interpret the signals in correct way,
knowledge of the coolant mixing in the assembly heads is necessary. Computational Fluid
Dynamics (CFD) codes and experiments can help to understand better these mixing processes
and they can provide information which can support the more adequate interpretation of the
thermocouple signals.
This benchmark deals with the 3D CFD modeling of the coolant mixing in the heads of
the profiled fuel assemblies with 12,2 mm rod pitch. Two assemblies of the 23rd cycle of the
Paks NPP?s Unit 3 are investigated. One of them has symmetrical pin power profile and
another possesses inclined profile. In this benchmark, the same fuel assemblies are
investigated by the participants thus the results calculated with different codes and models can
be compared with each other. Aims of benchmark was comparison of participants? results
with each other and with in-core measurement data of the Paks NPP in order to test the
different CFD codes and applied CFD models. This paper contains OKB ?GIDROPRESS?’s
results of CFD calculations this benchmark. Results are:
? In-core thermocouple signals above the selected assemblies;
? Deviations between the in-core thermocouple signals and the outlet average coolant
temperatures of the assemblies;
? Axial velocity and temperature profiles along three diameters at the level of the
? Axial velocity and temperature distributions in the cross section at the level of the
? Axial velocity and temperature distributions in the center plane of the assembly head

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