The SC-HTGR is a two-loop modular high-temperature steam supply system with inherent safety design allowing co-location with industrial facilities. The 102-column prismatic block annular configuration reactor core geometry provides ideal radial conduction to maximize the benefits of naturally passive decay heat removal.
AREVA's HTGR: Industrial Process Heat, Hydrogen, Electricity
AREVA’s Steam Cycle High-Temperature Gas-Cooled Reactor (SC-HTGR) is a small, modular, graphite-moderated and helium-cooled, high-temperature nuclear reactor with a nominal peak power of 625 MWt.
The SC-HTGR is being developed for a wide variety of applications, including industrial process heat, hydrogen production, and moderate electricity generation.
Building on the experience of past HTGR projects, the SC-HTGR concept relies on established technologies to facilitate near-term deployment with minimum technical risk. At its heart, the SC-HTGR uses a prismatic block-type reactor core based on AREVA’s ANTARES concept. The steam cycle heat transport system is based on HTGR operating experience and development work on early modular HTGR concepts, such as the MHTGR and the HTR-Module.
The SC-HTGR was introduced by AREVA in 2010, as a Generation IV small modular reactor (SMR) design concept. In 2012, the SC-HTGR design was selected by the Next Generation Nuclear Plant (NGNP) Industry Alliance for near-term commercialization of HTGR technology.
Fuel & Core Design
The reactor uses tristructural-isotropic (TRISO) coated particle fuel. At the center of each fuel particle is a kernel of uranium oxycarbide, enriched to less than 20 percent uranium-235. The kernel is surrounded by three alternating layers of pyrolytic carbon and silicon carbide. The particles are embedded in cylindrical compacts of graphite matrix material with a diameter of slightly more than 1 cm, and the compacts are loaded into graphite fuel blocks.
Nominal power distribution is controlled in the core through the use of a combination of particle packing fraction, burnable poison, and enrichment, as appropriate for each specific fuel cycle.
At its heart, the SC-HTGR uses a 102-column prismatic block-type reactor core based on AREVA’s ANTARES concept. The core is sized to take maximum advantage of the passive heat removal capability of modular high-temperature reactors (HTR).
HTGR technology provides improved safety and security through its inherent design, by ensuring no internal or external event could lead to a release of radioactive material, as proven by experimental and demonstration reactors around the world.
No need to evacuate or shelter the public and no threat to food or water supplies under any conditions.
- No harmful release of radioactive material under any conditions is assured by design.
Multiple assured barriers to the release of radioactive material are provided.
- These barriers include multiple layers of ceramic coatings on the nuclear fuel, the carbon encasement, and the graphite core structure. Additional barriers include the reactor vessel and the reactor building. The high temperature and robust structural capabilities eliminate concerns of fuel damage that could lead to significant release of radioactive materials from the nuclear fuel. The ceramic coated nuclear fuel provides the primary containment for radioactive materials rather than depending on a containment building.
Reactor power levels are limited and the nuclear reactor shuts down if reactor temperatures exceed intended operating conditions.
- Inherent to the nuclear reactor design is suppression of the nuclear reaction if the operating temperature increases. Complete shutdown is achieved through automatic insertion of control rods into the reactor core by gravity.
No actions by plant personnel or backup systems are required to either ensure shutdown of the reactor or ensure cooling.
- Conversely, actions of plant personnel cannot achieve conditions that cause the reactor fuel to lose its ability to contain radioactive material.
No power and no water or other cooling fluid is required.
- Heat removal from the reactor occurs naturally and directly to the earth if normal heat transport systems are not available. The low energy density of the reactor core combined with the large heat capacity of the graphite structure results in the reactor taking days to reach maximum temperatures (still well below temperatures that could cause fuel degradation), even if normal cooling systems are not functional.
Reactor materials including the reactor fuel are chemically compatible and in combination will not react or burn to produce heat or explosive gases.
- Helium is inert and the fuel and materials of construction of the reactor core and the nuclear heat supply system preclude such reactions.
Achievable levels of air or water intrusion do not result in substantive degradation of the capability to contain radioactive materials.
- The reactor is maintained shutdown under these conditions.
Spent or used fuel is stored in casks or tanks in underground dry vaults that can be cooled by natural circulation of air and shielded by steel plugs and concrete structure.
- No water is required for either cooling or radiation shielding and no active cooling system is required.
- Co-generation supply of electricity and steam to major industrial processes in petrochemical, ammonia and fertilizer plants, refineries and other industrial plants
- Hydrogen production and supply to industrial plants and to the merchant hydrogen market
- Eleectricity generation for microgrids and load-following
Nuclear reactors are no longer specific to electricity generation. The near term industrial applications that extend the use of nuclear energy for non-electric missions have been shown to be primarily directed toward providing co-generated process heat in the form of steam and electricity.
Markets for the HTGR include a variety of current and future process heat applications. Currently, such applications consume about two-thirds of global energy production, and this energy is almost entirely reliant on fossil fuels, which results in price volatility, supply uncertainty, and unwanted environmental impacts. The HTGR provides an alternative for these markets, with environmental benefits, fuel supply, and price stability. The steam system can be configured to the specific needs of the facility for high- or low-temperature steam and electricity.
The HTGR can also serve small and moderate electrical markets. Using the conventional Rankine cycle with high-temperature steam, a net efficiency of about 43 percent can be achieved in the full electricity-generation mode. This makes the concept an attractive option in markets with limited grids and those requiring incremental capacity addition.
The steam cycle plant also has load-follow capability. Reactor module power level and steam production can be increased or decreased relatively easily. Systems can also shift energy between electricity generation and heat supply dynamically as load conditions vary, all while keeping reactor power constant. This provides the maximum utilization of the nuclear heat source.
Though the HTGR concept was selected to minimize technical risk by relying on existing technology to the maximum extent possible, significant challenges remain on the path to commercial deployment. First of all, remaining technology developments such as fuel and graphite qualifications must be completed. Fortunately, excellent progress in these areas is being made in the U.S. Department of Energy’s Advanced Gas Reactor (AGR) and Advanced Graphite Capsule (AGC) programs. The remaining deployment challenges are largely commercial and regulatory, not technological.
In 2012, the HTGR design was selected by the Next Generation Nuclear Plant (NGNP) Industry Alliance for near-term commercialization of HTGR technology. The program for the NGNP Project is managed by the Idaho National Laboratory with funding through the Department of Energy.
In partnership with the NGNP Alliance, the international organization NC2I is considering AREVA's HTGR concept as a powerful, low-emissions energy source with intrinsic safe operating processes that allow collocation with industrial steam facilities.
Serial production will enhance both production efficiency and quality, with resulting cost benefits. Of course, there is a tradeoff between the benefits of small modular reactors (SMRs) and the economy of scale associated with larger plants. For the HTGR, this tradeoff is balanced by the high thermal efficiency of the system. In addition, the HTGR’s intrinsic safety characteristics eliminate the need for powered cooling systems and other large safety systems. This reduces both plant cost and operating and maintenance costs.
Even for a technology such as the SC-HTGR, which has a large potential market, the deployment time frame must extend over many years. As a result, the lack of large near-term returns makes dedicating the required resources to bring the project to completion a challenge. This is why all existing commercial nuclear reactor technologies have only been successful with large initial governmental support. Sovereign and/or philanthropic investments are expected to be essential during the initial period of HTGR development.