We aim to utilize the heat generated from the High-Temperature Engineering Test Reactor (HTTR) to demonstrate hydrogen production via steam methane reforming in HTTR heat application test. Previously, as a part of a mock-up model test for the HTTR hydrogen production system, the Japan Atomic Energy Agency successfully achieved hydrogen production using a steam reformer heated by helium that was heated to 900 ℃ using an electric heater (Fig. 1). Data on the dynamic characteristics of the steam reformer were collected. Understanding the behavior of the steam reformer under rated operating conditions and replicating this behavior through numerical analysis are essential for comprehending the dynamic characteristics of the plant, including its startup, shutdown, and disturbances, which are key to scaling up the system.
 In this research, a heat and material balance evaluation model for the helium-heated steam reformer was established. This model was used to analyze gas composition and temperature distribution in the reformer during hydrogen production and startup. Its validity was verified by comparing results obtained from the model with experimental results obtained from mock-up model tests.
 The model results pertaining to internal temperature distribution in the steam reformer during hydrogen production and outlet gas composition showed high similarity with the experimental results (Fig. 2). Additionally, the model successfully reproduced temperature changes within the reformer at the start of hydrogen production and the hydrogen yield observed in experiments.
 These results provide valuable insights into the behavior of the steam reformer during hydrogen production, aiding in the selection of operating conditions for the heat utilization tests of the HTTR and supporting the scaling up of the steam reformer. Future improvements to the evaluation model will include the consideration of the time lag of control system and heat transfer effects at the steam reformer’s inlet and outlet structural parts.