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Extension of the OFFBEAT fuel performance code to finite strains and validation against LOCA experiments

Edoardo Luciano Brunetto, Carlo Fiorina, Andreas Pautz, Alessandro Scolaro

The mechanical analysis of nuclear fuel behavior under base-irradiation conditions has traditionally been performed adopting the small-strain approximation. However, many cases of interest for fuel behavior involve the occurrence of large rod deformations that overcome the validity limits of the small-strain approach such as the cladding ballooning during Loss Of Coolant Accidents, the Pellet-Cladding Mechanical Interaction in case of a Missing Pellet Surface or bending experiments on spent fuel rods. For this reason, the mechanical framework of the open-source fuel performance code OFFBEAT is extended to finite strains. To allow for validation against cladding burst experiments, high-temperature models tailored for LOCA regime including creep, Zircaloy phase-transition and cladding burst criteria are also implemented in the code and described in the present work. The paper presents the implementation and the verification of the large-strain mechanical solver implemented in OFFBEAT, together with the results of the validation performed against the PUZRY and the IFA-650.2 LOCA experiments.

ELSEVIER SCIENCE SA2023

Investigation and Validation of Unstructured Mesh Methodologies for Modeling Experimental Reactors

Carlo Fiorina, Mathieu Hursin, Tom Mager, Andreas Pautz

This paper summarizes a methodology developed at Ecole Polytechnique Federale de Lausanne for the neutronic modeling of the CROCUS experimental reactor and proposes solutions to the challenges one may face while modeling a research reactor with a complex geometry. Indeed, the double-lattice configuration of CROCUS makes it difficult to use codes for neutron diffusion and transport relying on a structured mesh description. For this reason, and based on the available in-house competences, we decided to make use of the neutronic capabilities of the GeN-Foam multiphysics solver, which takes advantage of general finite volume methodologies on unstructured meshes to provide sufficient flexibility for the study of unconventional reactor designs. In this work, GeN-Foam is used to build a first SP3 model of CROCUS based on an unstructured mesh to have an explicit modeling of the double lattice and the water gap between the two lattices. Form functions are then used to reconstruct the intra-pin fission rates for validation against measured distributions. We also discuss the limitations of the SP3 approximation of neutron transport in regions with steep neutron flux gradients and the planned future developments.

MDPI2022

On the development of multi-physics tools for nuclear reactor analysis based on OpenFOAM (R): state of the art, lessons learned and perspectives

Carlo Fiorina

In the last two decades, the use of OpenFOAM as a multi-physics library for nuclear applications has grown from a sporadic use for exploratory studies to a widespread application for the analysis of innovative reactor concepts and highly complex problems. This review paper provides an overview of the past and current development efforts in the field and summarizes some of the lessons learned during 10 years of R&D activities participated by the authors. The objective is to provide readers with an understanding of the benefits and challenges of this approach, thus facilitating an informed decision about its potential adoption for future studies.

ELSEVIER SCIENCE SA2022