Evaluation of sodium boiling models using KNS-37 LOF experiments

Abstract

The computational codes used in the evaluation of the ESFR-SMART reactor performance and specifically their sodium boiling models are assessed using two KNS-37 LOF experiments, i.e. L22 and L29 tests, where boiling onset and two-phase flow regime up to dry-out occurred. The well-equipped KNS-37 experimental facility provided very valuable information for understanding the physical phenomena occurring in a 37-pin subassembly under LOF conditions, as well as experimental data to be used for computational tools validation. NATOF-2D, SAS-SFR, TRACE, ASTEC-Na, CATHARE-2 & CATHARE-3 and NEPTUNE_CFD codes have been used in this exercise in order to compare the various boiling models and conclude on the advantages and limitations of them based on the comparison against the experimental data. Beyond boiling onset, the various sodium two-phase flow approaches determine the ability of the code to correctly represent the rewetting and voiding phases as well as cladding dry-out onset. A simulation performed by a CFD approach (NEPTUNE_CFD code) considering liquid-vapor interfaces by an interface-tracking method is also shown and compared with the others approaches. Conclusions on each code performance are presented where the improvements needed to solve the issues encountered are included. This paper provides a first step in the process to investigate the required evaluation of the sodium two-phase flow models able to assess the safety of new SFR core designs (e.g. low void cores) under accidental conditions such as ULOF transients.

Review of Euratom projects on design, safety assessment, R&D and licensing for ESNII/Gen-IV reactor systems

“…Reactor based on open publications [6,7]. -A computational exercise on sodium boiling modelling was conducted based on a KNS-37 sodium loop experiment featuring sodium boiling in pin-bundle geometries [8].…”

Analysis of sodium boiling initiated by unprotected loss of flow in European sodium fast reactor core with different subassembly designs

“…A validation has been performed in (Chenu, 2011) on incorporated sodium boiling model in TRACE considering annular flow as the dominant regime up to dryout and a smooth breakdown of the liquid film after dryout onset. Recently, validation of the models was performed using the KNS-37 sodium boiling experiment, which has been reported in (Perez-Martin et al, 2022).…”

“…In this study, the specific sodium boiling modeling aspects included in TRACE by PSI have not been evaluated but rather emphasis was given to analyze the specific behavior of the ESFR-SMART core design. This is because such study has been performed in (Perez-Martin et al, 2022), based on the validation exercise of TRACE with a ULOF sodium boiling experiment.…”

Experiment and Codes to Support Safety Assessments for Sodium Fast Reactors (KASOLA, SOLTEC and KARIFA)

“…A review of the history of experiments for sodium fast reactors revealed that most of them were dedicated to one topic to answer special question of investigation of phenomenology or deliver data for system codes, especially for thermal hydraulics [1]. At KIT, a huge amount of data has been gathered and have been made partially available for the European projects JASMIN [2] and ESFR-SMART [6]. Today, the ongoing evolution of computer and codes, especially CFD codes, require more data with higher local and temporal resolution.…”