Matt Richards

H2-MHR PRE-CONCEPTUAL DESIGN SUMMARY FOR HYDROGEN PRODUCTION

Hydrogen and electricity are expected to dominate the world energy system in the long term. The world currently consumes about 50 million metric tons of hydrogen per year, with the bulk of it being consumed by the chemical and refining industries. The demand for hydrogen is expected to increase, especially if the U.S. and other countries shift their energy usage towards a hydrogen economy, with hydrogen consumed as an energy commodity by the transportation, residential and commercial sectors. However, there is strong motivation to not use fossil fuels in the future as a feedstock for hydrogen production, because the greenhouse gas carbon dioxide is a byproduct and fossil fuel prices are expected to increase significantly. An advanced reactor technology receiving considerable international interest for both electricity and hydrogen production, is the modular helium reactor (MHR), which is a passively safe concept that has evolved from earlier high-temperature gas-cooled reactor (HTGR) designs. For hydrogen production, this concept is referred to as the H2-MHR. Two different hydrogen production technologies are being investigated for the H2-MHR; an advanced sulfur-iodine (SI) thermochemical water splitting process and high-temperature electrolysis (HTE). This paper describes pre-conceptual design descriptions and economic evaluations of full-scale, nth-of-a-kind SI-Based and HTE-Based H2-MHR plants. Hydrogen production costs for both types of plants are estimated to be approximately

H2-MHR conceptual designs based on the sulphur–iodine process and high-temperature electrolysis

2 per kilogram.

Conceptual Design of the NGNP Reactor System

For electricity and hydrogen production, the advanced reactor technology receiving the most international interest is a modular, passively safe version of the high-temperature, helium-cooled reactor referred to in the USA as the Modular Helium Reactor (MHR). Because of its ability to produce high-temperature helium, the MHR is well suited for a number of process-heat applications, including hydrogen production. Two hydrogen-production technologies have emerged as leading candidates for coupling to the MHR: (1) thermochemical water splitting using the Sulphur–Iodine (SI) process and (2) High-Temperature Electrolysis (HTE). In this paper, we provide an update on conceptual designs being developed for coupling the MHR to the SI process and HTE. These concepts are referred to as the SI-based H2-MHR and the HTE-based H2-MHR, respectively.

Hydrogen Generation Using the Modular Helium Reactor

In May 2010, General Atomics (GA) was awarded a contract by the U.S. Department of Energy (DOE) under the Next Generation Nuclear Plant (NGNP) project to develop the conceptual design for a steam-cycle modular helium reactor (SC-MHR) demonstration plant. The SC-MHR is a graphite-moderated, helium-cooled reactor that is designed to produce steam for industrial applications and/or electricity production using a Rankine cycle. The SC-MHR operates with a thermal power level of 350 MW and a coolant outlet temperature of 725°C. This paper provides an overview of the conceptual design of the SC-MHR reactor system (RS), including assessments of core performance in the areas of reactor physics and power distributions, temperature/flow distributions, fuel integrity, and fission product release.Copyright

Parametric Assessments of High-Pressure and Low-Pressure Conduction Cooldown Events for the VHTR

Process heat from a high-temperature nuclear reactor can be used to drive a set of chemical reactions, with the net result of splitting water into hydrogen and oxygen. For example, process heat at temperatures in the range 850°C to 950°C can drive the sulfur-iodine (SI) thermochemical process to produce hydrogen with high efficiency. Electricity can also be used to split water, using conventional, low-temperature electrolysis (LTE). An example of a hybrid process is high-temperature electrolysis (HTE), in which process heat is used to generate steam, which is then supplied to an electrolyzer to generate hydrogen. In this paper we investigate the coupling of the Modular Helium Reactor (MHR) to the SI process and HTE. These concepts are referred to as the H2-MHR. Optimization of the MHR core design to produce higher coolant outlet temperatures is also discussed.Copyright

Evaluation of a Vessel Cooling System for the VHTR

The Very High Temperature Reactor (VHTR) has been selected by the U.S. as the Generation IV technology for the Next Generation Nuclear Plant (NGNP), and both the U.S. and Japan have been developing VHTR concepts based on a prismatic, block-type core design. For these VHTR concepts, the primary coolant (helium) inlet temperature is expected to be in the range 490°C to 590°C and the outlet temperature is expected to be in the range 850°C to 950°C. Passive safety is one of the fundamental requirements for the VHTR, and the VHTR is designed to be passively safe even during Loss of Coolant Accidents (LOCAs) and Loss of Flow Accidents (LOFAs). For the VHTR, these two transient events are referred to as a Low-Pressure Conduction Cooldown (LPCC) and High-Pressure Conduction Cooldown (HPCC), respectively. During both events, the decay heat is conducted through the graphite to the vessel. The heat is transferred from the vessel by thermal radiation and natural convection to a passive Reactor Cavity Cooling System (RCCS). In this paper, we describe parametric studies of LPCC and HPCC events using a 30-degree sector, 3-dimensional ANSYS model of the VHTR, which includes a detailed radiation exchange model between the RPV and RCCS.© 2008 ASME

MHR design, technology and applications

The Very High Temperature Reactor (VHTR) has been selected by the U.S. as the Generation IV technology for the Next Generation Nuclear Plant (NGNP), and also by the Republic of Korea for the Nuclear Hydrogen Development and Demonstration (NHDD) project. One of the key long-lead items for the VHTR is the Reactor Pressure Vessel (RPV). In the absence of active vessel cooling, the RPV temperature during normal operation is determined by the design point selected for the primary coolant inlet temperature and the design of the reactor internal components, including the physical location of riser channels that route the coolant flow to the plenum above the reactor core. For the VHTR, the primary coolant (helium) inlet temperature is expected to be in the range 490°C to 590°C and the outlet temperature is expected to be in the range 850°C to 950°C. For the RPV, both SA-508/533 steel and higher alloy steels with higher temperature capability (e.g., 9Cr-1Mo-V steel) are being considered. Because of its extensive experience base as an ASME Section III code-approved material for Light Water Reactor (LWR) pressure vessels, SA-508/533 steel is emerging as a strong candidate for the VHTR RPV. However, in order to use this material, the RPV temperature must be maintained below ASME code limits, which are 371°C during normal operation and 538°C for up to 1000 h during accident conditions.Copyright