Nuclear power and hydrogen production systems have distinct dynamic characteristics and their interaction can produce results hard to predict intuitively. Therefore, it is necessary to use mathematical models describing the transient behavior of these systems. Dynamic models have assisted engineers for several decades in the assessment of safety of nuclear power plants [3, 9]. On the other hand, hydrogen production alternatives utilizing heat and/or electricity from nuclear power plants have been mostly studied within the steady-state regime to make design decisions. Some efforts have been made to understand the dynamics of this system [5, 10]. The hydrogen production plant adds extra complexity to the system because it includes chemical reactions with nonlinear dynamics. The simulation environment used should be able to capture these physical and chemical phenomena. The long term goal of this research is to develop a suite of mathematical models that enable dynamic simulation, sensitivity analysis and optimization studies of the interaction of a nuclear reactor and a hydrogen generation plant.
This paper focuses on dynamic simulation of a coupled system comprising a nuclear reactor and a heat transfer loop. The nuclear reactor generates 600MWth and part of this heat is used to generate high-temperature steam to feed the hydrogen plant. High-temperature electrolysis is considered as the electrochemical process to produce hydrogen. The system has two loops and its components are a nuclear reactor, two heat exchangers, piping and two compressors. The nuclear reactor is a Pebble Bed Modular Reactor (PBMR) and the heat exchanger removing the heat from the nuclear reactor coolant is a compact heat exchanger. The heat exchanger heating the steam is of the tube-in-shell kind [1] and each compressor regulates the gas flowrate in each loop. Helium is considered as the heat transfer fluid for both loops.
The system model encompasses models for each one of the units mentioned previously. The dynamics of the helium in the heat transfer loop were represented with a simplification of the inviscid Navier-Stokes equations [7]. The system of equations was discretized in the axial coordinate in order to calculate detailed state variable profiles around the loop. The nuclear reactor was represented with a model developed by Chunyun Wang at MIT [11], with coupled point-kinetics models, reactivity models and thermal-hydraulic models. The heat exchangers were represented by discretized energy balances. This system model was implemented and solved using JACOBIAN®, a state-of-the-art dynamic simulation software. JACOBIAN® uses an implicit integrator and it can handle differential-algebraic equations and discrete/continuous models.
A simple start-up scenario was used to study the behavior of the system. The start-up schedule had four stages, and the first one was to stabilize the system at a low power level. This was achieved by running the compressors and nuclear reactor at 1% of the designed power level and waiting until the system reached a steady state. Second, the power in both compressors was increased to boost the heat removal capacity of the system, and the flow of steam on the process heat exchanger (PHX) was also increased. Third, the heat generated in the nuclear reactor was boosted until it reached the design point. Finally, the temperature in the cold side of the PHX was raised, representing the start-up of the chemical plant.
1. C. B. Davis, R. B. Barner, S. R. Sherman, D. F. Wilson. Thermal-Hydraulic Analyses of Heat Transfer Fluid Requirements and Characteristics for Coupling a Hydrogen Product Plant to a High-Temperature Nuclear Reactor. Technical Report INL/EXT-05-00453, Idaho National Laboratory, 2005.
2. Y. H. Jeong, K. Hohnholt, M. S. Kazimi and B. Yildiz. Optimization of the hybrid sulfur cycle for hydrogen generation. Technical Report MIT-NES-TR-004, Center for Advanced Nuclear Energy Systems, Massachusetts Institute of Technology, 2005.
3. Michitsugu Mori. Simulation of a BWR-5 plant: Verification and validation of RETRAN-03. Nuclear Technology, 121:245-259, 1998.
4. C. H. Oh, R. Barner, C. B. Davis and S. R. Sherman. Evaluation of working fluids in an indirect combined cycle in a very high temperature gas-cooled reactor. Nuclear Technology, 156:1-10, 2006.
5. S. Oh, N. Brown and S. T. Revankar. Transient Model for the Chemical Chamber in Sulfur Iodine Thermo-Chemical Process, Technical Report PU/NE-06-010, School of Nuclear Engineering, Purdue University.
6. S. B. Rodríguez Jr., R. O. Gauntt, S. T. Revankar and K. Vierow. Development of design and simulation model and safety study of large-scale hydrogen production using nuclear power. 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings, 2005, 8018-8023.
7. Todreas N. E. and Kazimi M.S. Elements of thermal hydraulic design. Hemisphere Publishing Corporation, New York, 1990.
8. B. Yildiz, K. Hohnholdt, and M. S. Kazimi. Hydrogen production using high temperature steam electrolysis supported by advanced gas reactors with supercritical CO2 cycles. Technical Report MIT-NES-TR-002, Center for Advanced Nuclear Energy Systems, Massachusetts Institute of Technology, 2004.
9. B. Yildiz and M. S. Kazimi. Efficiency of hydrogen production systems using alternative nuclear energy technologies. International Journal of Hydrogen Energy, 31:77-92, 2006.
10. K. Vierow, Y. Liao, J. Johnson, M. Kenton, and R. Gauntt. Severe accident analysis of a PWR station blackout with the MELCOR, MAAP4 and SCDAP/RELAP5 codes. Nuclear Engineering and Design, 234:129-145, 2004.
11. R. B. Vilim. Dynamic Modeling Efforts for System Interface Studies for Nuclear Hydrogen Production. Argonne National Laboratory, ANL-07/16, 2007.
12. C. Wang. Design, Analysis and Optimization of the Power Conversion System for the Modular Pebble Bed Reactor System. PhD thesis, Massachusetts Institute of Technology, 2003.