MELCOR modification for large-scale hydrogen production using nuclear thermochemical cycles
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abstract
Sandia National Laboratories, together with Purdue University, are in the process of modifying the light water reactor accident analysis code, MELCOR, so that we can model high temperature gas-cooled reactors that are coupled with thermochemical cycles for the large-scale production of hydrogen. Modeling of high temperature gas-cooled reactors requires several code changes so that MELCOR can treat the fuel geometry and reactor materials (e.g. graphite) for conditions not seen in light water reactor applications. Exploratory calculations will be performed using helium as a primary system coolant and a graphite reactor core. In addition, we will add a special module into MELCOR that will model the high-temperature intermediate heat exchanger (IHX), the power cycle (e.g. Brayton), and chemical cycles, such as sulfur-iodine (SI) cycle, the calcium bromide iron oxide cycle, the Westinghouse cycle, as well as others that may be proposed. Because the tool will be modular, additional promising chemical cycles can be easily added and compiled onto MELCOR. The new tool will include a graphical user interface whereby the user will input desired plant properties, including type of chemical model, IHX properties, and power cycle parameters. The output will be key parameters such as the amount of hydrogen production, electrical power output, and overall efficiency. Thus, the tool can be used to quickly evaluate the impact of a given parameter on the overall system performance, economics, and plant safety under normal and abnormal operating conditions. The conceptual design of the tool is shown in Figure 1. Besides being an exploratory design and safety analysis tool, perhaps the most important aspect of this tool will be its unique ability to address the coupled behavior of the integrated facility. By doing so, the tool will greatly facilitate determining conditions that maximize hydrogen production. For example, as shown in Figure 2, hydrogen production is a strong function of reactor outlet temperature. In addition, IHX efficiency is a function of its heat transfer area and other heat exchanger parameters. Furthermore, core geometry, mass flow rates, type of thermochemical cycle, etc, are also crucial for maximization of hydrogen production. The tool will be able to address these and numerous other parameters in an endeavor to produce the maximum amount of hydrogen under the most economically rewarding scenarios while dealing with the safety of the public and environment. In summary, this laboratory-funded research will result in the first fully integrated, fully coupled code that can be used to simulate the entire nuclear and thermochemical plant, maximize hydrogen production, address scalability, and evaluate the potential for safe operation under normal and abnormal conditions. The tool will be ready in less than a year.
