Numerical implementation and validation of a porous approach for fluid–structure interaction applied to pressurized water reactors fuel assemblies under axial water flow and dynamic excitation

Abstract

The proposed contribution is dedicated to numerical methods for solving strongly coupled fluid–structure dynamic problems where the complexity of the structures and the reduced remaining fluid volume do not allow to handle their exact geometry. Porous approaches are preferred instead but it is mandatory to go beyond classical techniques to account for inertial and convective components of the flow, as explicitly required by the application of the methods to the dynamics of a set of pressurized water reactors fuel assemblies under axial flow and seismic‐like loading. A new computational framework is thus introduced with special care given to stability, robustness, and computational efficiency of the coupled solver. Comparisons with well‐chosen experimental results provide some valuable validation of the numerical methods and demonstrate the ability of the model to reproduce the hydraulic coupling between several fuel assemblies.

A new reduced order model to represent the creep induced fuel assembly bow in PWR cores

“…Although not intended for this purpose, this type of lightweight thermomechanical model could also potentially provide the basis regarding non-linear dynamics. The main difficulty would then lie in the accurate prediction of the fluid-structure interaction between the different assemblies within the PWR core, which remains a very open subject (Divaret et al, 2014;Faucher et al, 2021;Ricciardi, 2022).…”

Adaptive time multiscale algorithms for fluid–structure interaction with impacts - Application to a row of PWR fuel assemblies under seismic loading

“…The key to ensure the best performance for the coupled resolution is thus to benefit from the more favorable stability condition applying to the fluid problem to reduce the number of required solutions of the pressure problem in the fluid, representing most of the computational cost of a simulation. This time multiscale topic has again already been positively addressed in (Faucher et al (2021)), but only in the case without contact. Contacts and impacts deeply change the way the various time scales for fluid and structure interact, taking them into account is a complete new and crucial problem to solve for the proposed numerical framework to completely achieve its goals.…”

“…In many plant designs and concepts, this fluid is a liquid, strongly interacting with the structure dynamics in the case of external solicitations such as earthquakes. For the case of Pressurize Water Reactors (PWR), where the fluid is highly turbulent water, a model dedicated to the accurate representation of this kind of fluid-structure interaction at the assembly and core level has been proposed in (Faucher et al (2021)) and validated against experiments for the case of advanced hydraulic couplings between structures and no structure-to-structure interactions such as contact and impacts. This work must be complemented with the management of the latter interactions to cover all the relevant phenomena occurring in a PWR core during a representative dynamic transient.…”

“…The latter is related to the chosen explicit time integration for structural motion, well suited to robustly handle the strong nonlinearity of the dynamic problem, both material for the equivalent beam representing a full assembly with internal rod-to-grid friction, and kinematic with numerous contacts and impacts occurring during simulations. Complete discussion and justification of the modelling and algorithmic choices can be found in (Faucher et al (2021)). The key to ensure the best performance for the coupled resolution is thus to benefit from the more favorable stability condition applying to the fluid problem to reduce the number of required solutions of the pressure problem in the fluid, representing most of the computational cost of a simulation.…”

“…It is the result of a long range work described in (Ricciardi et al (2009a), Ricciardi et al (2009b), Ricciardi (2016)). It has been concretized into an research software application named FS-Core presented in (Faucher et al (2021)), to which the reader is referred for full details. For the sake of conciseness and to put the focus on the new contributions of the current paper, only the main concepts building the model are provided in next sections.…”