David Louie

Transient Analysis of Sulfur-Iodine Cycle Experiments and Very High Temperature Reactor Simulations Using MELCOR-H2

Abstract MELCOR is a thermal-hydraulic code used by the United States and the international nuclear community for the modeling of both light water and gas-cooled reactors. MELCOR was extended in order to model nuclear reactors that are coupled to the sulfur-iodine (SI) cycle for cogeneration of hydrogen. This version of the code is known as MELCOR-H2, and it includes modular secondary system components (e.g., turbines, compressors, heat exchangers, and generators), a point-kinetics model, and a graphical user interface. MELCOR-H2 allows for the fully coupled, transient analysis and design of the nuclear thermochemical SI cycle for the purpose of maximizing the production of hydrogen and electricity. Recent work has demonstrated that the hydrogen generation rate calculated by MELCOR-H2 for the SI cycle was within the expected theoretical yield. In order to benchmark MELCOR-H2, we simulated a set of sulfuric acid decomposition experiments that were conducted at Sandia National Laboratories during 2006. We also used MELCOR-H2 to simulate a 2004 Japan Atomic Energy Research Institute SI experiment. The simulations compared favorably with both experiments; most measured and calculated outputs were within 10%. The simulations adequately calculated O2, SO2, and H2 production rate, acid conversion efficiency, the relationship between solution mole percent and conversion efficiency, and the relationship between molar flow rate and efficiency. We also simulated a 6-stage turbine and a 20-stage compressor. Our results were mostly within 1 or 2% of the literature. Then, we simulated a pebble bed very high temperature reactor (VHTR) and compared key MELCOR-H2 results with the literature. The comparison showed that the results were typically within 1 or 2%. Finally, we compared the MELCOR-H2 point-kinetics model with the exact Inhour reactivity solution for various cases, including a 1.0

Development of design and simulation model and safety study of large-scale hydrogen production using nuclear power.

step reactivity insertion. We were able to employ a large time step while successfully matching the theoretical power level. These comparisons demonstrate MELCOR-H2’s unique ability to simulate fully coupled VHTRs for the production of hydrogen.

MELCOR/CONTAIN LMR Implementation Report - FY16 Progress.

Before this LDRD research, no single tool could simulate a very high temperature reactor (VHTR) that is coupled to a secondary system and the sulfur iodine (SI) thermochemistry. Furthermore, the SI chemistry could only be modeled in steady state, typically via flow sheets. Additionally, the MELCOR nuclear reactor analysis code was suitable only for the modeling of light water reactors, not gas-cooled reactors. We extended MELCOR in order to address the above deficiencies. In particular, we developed three VHTR input models, added generalized, modular secondary system components, developed reactor point kinetics, included transient thermochemistry for the most important cycles [SI and the Westinghouse hybrid sulfur], and developed an interactive graphical user interface for full plant visualization. The new tool is called MELCOR-H2, and it allows users to maximize hydrogen and electrical production, as well as enhance overall plant safety. We conducted validation and verification studies on the key models, and showed that the MELCOR-H2 results typically compared to within less than 5% from experimental data, code-to-code comparisons, and/or analytical solutions.

Integration of CONTAIN Liquid Metal Models Into the MELCOR Code

This report describes the progress of the CONTAIN-LMR sodium physics and chemistry models to be implemented in MELCOR 2.1. In the past three years, the implementation included the addition of sodium equations of state and sodium properties from two different sources. The first source is based on the previous work done by Idaho National Laboratory by modifying MELCOR to include liquid lithium equation of state as a working fluid to model the nuclear fusion safety research. The second source uses properties generated for the SIMMER code. The implemented modeling has been tested and results are reported in this document. In addition, the CONTAIN-LMR code was derived from an early version of the CONTAIN code and many physical models that were developed since this early version of CONTAIN are not available in this early code version. Therefore, CONTAIN 2 has been updated with the sodium models in CONTAIN-LMR as CONTAIN2-LMR, which may be used to provide code-to-code comparison with CONTAIN-LMR and MELCOR when the sodium chemistry models from CONTAIN-LMR have been completed. Both the spray fire and pool fire chemistry routines from CONTAIN-LMR have been integrated into MELCOR 2.1 and debugging and testing are in progress. Because MELCOR only models the equation of state for liquid and gas phases of the coolant, a modeling gap still exists when dealing with experiments or accident conditions that take place when the ambient temperature is below the freezing point of sodium. An alternative method is under investigation to overcome this gap. We are no longer working on the separate branch from the main branch of MELCOR 2.1 since the major modeling of MELCOR 2.1 has been completed. At the current stage, the newly implemented sodium chemistry models will be a part of the main MELCOR release version (MELCOR 2.2). This report will discuss the accomplishments and issues relating to the implementation. Also, we will report on the planned completion of all remaining tasks in the upcoming FY2017, including the atmospheric chemistry model and sodium-concrete interaction model implementation.

Predicted Liquid Atomization from a Spent Nuclear Fuel Reprocessing Pressurization Event.

A sodium coolant accident analysis code is necessary to provide regulators with a means of performing confirmatory analyses for future sodium reactor licensing submissions. MELCOR and CONTAIN, which are currently employed by the U.S. Nuclear Regulatory Commission (NRC) for light water reactor (LWR) licensing, have been traditionally used for level 2 and level 3 probabilistic analyses as well as containment design basis accident analysis. To meet future regulatory needs, new models will be added to the MELCOR code for simulation of Liquid Metal Reactor (LMR) designs. Existing models developed for separate effects codes will be integrated into the MELCOR architecture. This work integrates those CONTAIN code capabilities that feasibly fit within the MELCOR code architecture.Implementation of such models for sodium reactor simulation into an actively maintained, full-featured, integrated severe accident code fills a significant gap in capability for providing the necessary analysis tools for regulatory licensing. Current work scope will focus on the following implementation goals:• Phase 1: Implement sodium Equations of State (EOS) as a working fluid for a MELCOR calculation from:○ The fusion safety database○ The SIMMER-III Code○ The SAS4a Code• Phase 2: Examine and test changes to the CONTAIN-LMR Implemented by Japan Atomic Energy Agency, specifically:○ Aerosol Condensation○ Implementation of the capability for simultaneous sodium and water condensation modeling• Phase 3: Implementation and Validation of CONTAIN physics models:○ Sodium Spray Fires (including new test data)○ Sodium Pool Modeling○ Sodium Pool Fires• Phase 4: Implementation and Validation of CONTAIN chemistry models:○ Debris Bed/Concrete Cavity Interactions○ Sodium Pool Chemistry○ Atmospheric ChemistryAn option for changing the EOS for the MELCOR working fluid from water to liquid metal and the heat transfer from water/steam to liquid metal has been implemented into MELCOR. The property models implemented include an analytic EOS model developed for the SIMMER-III code and the fusion safety works done at Idaho National Laboratory (INL). This paper provides a summary of the status of the code development work. A description of the current models implemented together with user requirements and test calculations will be presented.© 2014 ASME

Contaminant Entrainment in a Liquid Fuel Fire.

Spent nuclear fuel reprocessing may involve some hazardous liquids that may explode under accident conditions. Explosive accidents may result in energetic dispersion of the liquid. The atomized liquid represents a major hazard of this class of event. The magnitude of the aerosol source term is difficult to predict, and historically has been estimated from correlations based on marginally relevant data. A technique employing a coupled finite element structural dynamics and control volume computational fluid dynamics has been demonstrated previously for a similar class of problems. The technique was subsequently evaluated for detonation events. Key to the calculations is the use of a Taylor Analogy Break-up (TAB) based model for predicting the aerodynamic break-up of the liquid drops in the air environment, and a dimensionless parameter for defining the chronology of the mass and momentum coupling. This paper presents results of liquid aerosolization from an explosive event.