Session: 07-01: Thermal-Hydraulics Experimental Studies - I

Paper Number: 64509

Start Time: August 4, 2021, 01:15 PM

64509 - Study of Recent Sodium Pool Fire Model Improvements for Melcor Code 

Sandia National Laboratories (SNL) and Japan Atomic Energy Agency (JAEA) have exchanged sodium fire modeling information and related experimental data under a collaboration established in the area of advanced reactor modeling and simulation within the Civil Nuclear Energy Research and Development Working Group (CNWG) established by the U.S. – Japan Bilateral Commission on Civil Nuclear Cooperation in 2012. As part of this collaboration, benchmark analyses of sodium fire experiments have been conducted to validate sodium fire analysis codes in the U.S. and Japan. Validation of MELCOR sodium fire modeling under the framework of the CNWG collaboration is the subject of this paper.

MELCOR, which is developed by SNL for the U.S. Nuclear Regulatory Commission, is a systems level computer code. It has traditionally been used in safety analysis of Light Water Reactors (LWRs). Over the past nearly 15 years, MELCOR capabilities have been expanded to support application to safety assessment of advanced non-LWRs, such as Sodium-cooled Fast Reactors (SFRs) and High Temperature Gas Reactors (HTGRs). In the event of sodium coolant leakage, significant hazards can arise in containment during an SFR accident due to sodium fires or the interaction of sodium with concrete. The severity of these hazards requires modeling of new sodium chemistry phenomena not encountered in traditional LWR applications. A new package named Sodium Chemistry (NAC) has been added to MELCOR to provide the necessary capabilities to support analysis of the full spectrum of SFR accidents. Sodium fire models in the NAC package are derived from earlier CONTAIN-LMR models, which is a legacy control volume containment safety analysis code applicable to Liquid Metal Reactors (LMRs). Sodium properties and equation of state (EOS) have also been implemented in MELCOR to support SFR analyses. Basic verification of sodium fire models in the NAC package was initially conducted through comparison with CONTAIN-LMR.

This paper describes the validation of an improved set of MELCOR sodium pool fire models proposed for the NAC package. This modeling represents an enhancement relative to the original CONTAIN-LMR modeling that formed the original basis for the NAC package models. A benchmark analysis of the F7-1 pool fire experiment of JAEA is carried out using these improved models. The improved models include pool heat transfer, pool oxide layer, and pool spreading. Analytical results, such as gas, pool and structure temperatures are compared to the experimental data and the results of the SPHINCS code which is a sodium fire analysis code developed at JAEA. The base case analysis, where the original CONTAIN-LMR models are used, exhibits a combustion rate and associated temperature excursions that are smaller relative to the experimental data and SPHINCS results during the initial phase of the sodium fire. However, during the later phase of the sodium fire, relatively higher combustion rates and temperature excursions are noted in the simulation compared to the experimental data and SPHINCS results. These deviations are modest. The improved sodium pool fire model for the NAC package agrees well with the experimental data and SPHINCS results over the entire course of the sodium fire. This study illustrates these enhanced capabilities for MELCOR to reliably simulate sodium pool fire events.

Presenting Author: Mitsuhiro Aoyagi Japan Atomic Energy Agency

Authors:

Mitsuhiro Aoyagi Japan Atomic Energy Agency
David Louie Sandia National Laboratories
Akihiro Uchibori Japan Atomic Energy Agency
Takashi Takata Japan Atomic Energy Agency
David Luxat Sandia National Laboratories