Katherine McFadden

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.

Modeling of a Z-IFE Hydrogen Plant Using MELCOR-H2.

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.

SecPop Version 4: Sector Population Land Fraction and Economic Estimation Program: Users? Guide Model Manual and Verification Report.

Abstract A hypothetical Z-Inertial Fusion Energy (IFE) plant was coupled to a sulfur iodine (SI) thermochemical cycle using a new version of MELCOR called MELCOR-H2. MELCOR-H2 was designed to model nuclear reactors that are coupled to thermochemical plants for the production of electricity and hydrogen. The Z-IFE input model consisted of three major system components - a fusion heat source control volume with several types of boundary conditions, an SI loop, and a Brayton secondary system. The components were coupled in order to investigate system feedback and hydrogen production. The input model was modified so that various parametric studies could be conducted. Particular emphasis was placed on plant operating temperature and maximizing hydrogen production. This paper summarizes the results of the SI system model as it was driven by temperature changes in the primary circuit that simulated those that would occur in a Z-IFE driven reactor.

Software regression quality assurance for MACCS2 : version 2.5.0.0 through version 2.5.0.9.

................................................................................................................. iii TABLE OF CONTENTS .................................................................................................. v LIST OF FIGURES ........................................................................................................ vii LIST OF TABLES .......................................................................................................... ix ABBREVIATIONS AND ACRONYMS ........................................................................... xi

MELCOR-H2 : A modular, generalized tool for the dynamic simulation and design of fully-coupled nuclear reactor/hydrogen production plants

The “State-of-the-Art Consequence Analyses (SOARCA) Project: Uncertainty Analysis” has used a newer version of the MELCOR Accident Consequence Code Systems Version 2 (MACCS2) than what was previously used in the “SOARCA Project Volume 1: Peach Bottom Integrated Analysis,” NUREG/CR-7110 Volume 1. A software regression quality assurance program has been implemented for MACCS2. The documentation for the quality assurance from MACCS2 Version 2.5.0.0 through 2.5.0.9 ensures continuity between code versions and provides insight into the changes made within MACCS2.