Multi-Dimensional Determination of Thermal Diffusion Coefficients in Fuel Rod Bundles Based on Thermal Mixing Experiments

MOLINA, T.; MARCEL CHRISTIAN PABLO

Washingon

Conferencia; 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20); 2023

American Nuclear Society

Having a good knowledge of thermal diffusion coefficients (TDCs) is crucial to confidently predict turbulent thermal mixing in nuclear fuel bundles. Such a knowledge, however, is not easy to achieve. In previous works thermal and enthalpy 2D profiles were reconstructed from experimental data obtained in a 37 fuel rod bundle geometry. Such a study allowed identifying complex thermal patterns which could not be explained by symmetry arguments. In this work an algebraic model for determining a large number of TDCs is developed and afterwards used. The model makes use of 21 independent mixing tests in which all 60 subchannel temperatures are measured at the outlet of the test section.A well-established subchannel code is used to solve the momentum balance. Moreover, the energy balance between the subchannels is modeled for the whole test domain treating the TDCs as unknowns. Before solving the equations, a dimensional analysis is performed to identify the system rank. The model applies a dimensional reduction through a linear transformation of the system of equations. As a result, sets of 24 TDCs could be determined for each test run. The developed tool succeeded in obtaining highly accurate estimations of the temperature 2D profiles, compared with other conventional models or correlations, especially in the reconstruction of non-symmetrical complex patterns. Moreover, the Reynolds dependence of each TDC could also be obtained.