Thermal Hydraulic Models for Neutronic and Thermaly Hydraulic Feedback in CITVAP Code

Abstract

The improvements in the computational systems (increasing the memory and storage capacity and the enhancement of calculation power) allows the development of innovative methods for reactor calculations, including not only more accurate theories and numerical methods, but also adding more prediction capabilities and additional engineering information to perform the numerical analysis of the system. As an example, nowadays it is possible to integrate different tools with interdisciplinary or multi engineering information allowing an integrated approach to the problem to be solved. The INVAP calculation line is used in a wide range of applications (mainly MTR, CAREM and CNA-2), where some of them requires a thermal hydraulic model to evaluate the distribution of the fuel, coolant and moderator temperatures and the coolant and moderator densities. For those cases, such parameters are needed for a proper evaluation of neutronic behavior of the core.
Currently CITVAP has several thermal-hydraulic models depending on the geometry considered; 1D geometry, to calculate each channel of the reactor core, and a 3D geometry to use more complex thermal-hydraulic model of the core. The models are for MTR and NPP. The simulations involve natural convection and forced circulation. In the last upgrade of CITVAP, the possibility to use any external thermal hydraulic model was added.
All these models are used for the thermal hydraulic feedback of the neutronic calculation, but in some cases can be used for further key analysis in reactor design. Accordingly, there is the possibility to evaluate thermal margins to critical phenomena, perform the evaluation of the temperature distribution for the oxide layer growth calculation and perform the calculation of the power feedback coefficient.