atw - International Journal for Nuclear Power | 05.2021

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atw Vol. 66 (2021) | Issue 5 ı September 24 AT A GLANCE Ultra Safe Nuclear Corporation Fully Ceramic Microencapsulated Fuel: Possibilities and Prospect An Historical Perspective on HTGR Fuel High temperature gas-cooled reactors were conceptualized in the 1940s in the U.S. (Daniel’s Pile) and ultimately realized in the 1950s in the UK (Dragon Reactor). The various performance and safety benefits of these systems could only be realized if a fuel system capable of retaining radionuclides at high temperatures (> 1000°C) was possible. In the late 1950s, the Dragon fuel developers abandoned the vented fuel pin designs in favor of small spherical coated fuel particles. Hence was born bi-, and subsequently, tri-structural isotropic (TRISO) fuel particles around which many of today’s advanced reactors are designed. Decades of worldwide research and development have resulted in a well-codified basis of knowledge for manufacturing and performance of the TRISO fuel form that is being leveraged in the design and licensing of these reactors. The high-temperature radionuclide retention capability of TRISO fuel particles, coupled with reactor system designs that allow passive heat removal during off- normal conditions, are the basis of modern, inherently- safe nuclear energy systems. Further improvement in the radionuclide retention capability and environmental stability of the fuel increase safety margins, decreasing the necessary size of the ( Emergency Planning Zone) EPZ. This is particularly important for enabling economical distributed energy generation using micro-reactors that are to be deployed in large numbers (many hundreds or thousands). New Possibilities with FCM® Ultra Safe Nuclear Corporation (USNC) is the leading developer of high temperature gas-cooled micro reactors with its flagship Micro Modular Reactor, MMR. Key to the design of the MMR, is its fully ceramic microencapsulated, FCM®, fuel that comprises TRISO fuel particles embedded inside of a refractory silicon carbide ceramic. FCM fuel was first conceptualized in 2010 by Ultra Safe Nuclear Corporation (USNC) founder, Francesco Venneri, along with scientists at Oak Ridge National Laboratory (ORNL), and has undergone active research and development since. USNC’s reactor technology was built around this revolutionary fuel system and leverages its immense safety and performance benefits to deliver highly economic and inherently safe nuclear energy systems. The FCM fuel architecture is a major change from the historic graphitic-matrix fuel forms and offers significant benefits. The graphitic matrix exhibits complex irradiation behavior (initially shrinks, then expands) and is only able to retain its limited initial strength up to low doses. The silicon carbide matrix, because of its well-known and finite swelling behavior, is able to withstand very high irradiation doses while retaining its configuration and its strength. The graphitic matrix is also readily prone to oxidation, making it susceptible to degradation in the presence of trace amounts of air or moisture leaking into the reactor coolant. The opposite is true for silicon carbide as it exhibits exceptional air and steam oxidation resistance. Finally, and most importantly, the porous, highly inhomogeneous, and amorphous graphitic matrix does not form a hermetic barrier to fission product release. Silicon carbide, on the other hand, is the key constituent in TRISO fuel responsible for the exceptional fission At a Glance Ultra Safe Nuclear Corporation
atw Vol. 66 (2021) | Issue 5 ı September 25 product containment within the fuel particles. When employed as a matrix surrounding the fuel particles, it provides a second highly effective barrier to any trace radionuclide release that may arrive from the particles. These benefits of FCM fuel represent a major evolution in what is now possible in advanced nuclear energy systems such as MMR. FCM as a Flexible Fuel Architecture In the past few years, advances in manufacturing technologies, specifically three-dimensional (3D) printing, have been applied to the production of silicon carbide matrix FCM fuel. The use of 3D printing results in the possibility of geometrically-unconstrained reactor core designs, offering further improvements in performance and safety. FCM fuel, owing to the presence of multiple inherent barriers to radionuclide release, offers a geologically stable repository-ready fuel form. These barriers also increase the difficulty of any attempts at clandestine recovery of actinides, resulting in increased proliferationresistance. In addition to the possibility of once-through disposal of high burnup uranium based FCM fuel, FCM provides an ideal route for disposition of waste from other reactors through transmutation of transuranic elements (TRU). TRU (Np, Pu, Am) from reactor spent fuel may be transformed into TRISO and FCM fuel and optimally destroyed (burned) in MMRs. The FCM compacts act both as a robust fuel form for deep burning and as an ideal waste form for permanent disposition. FCM Manufacturing at Scale AT A GLANCE The highly robust FCM fuel technology, and the associated manufacturing methodology, are wholly agnostic to the overall fuel geometry, type, and configuration of the coated fuel particles. Therefore, FCM fuel, as manufactured today, offers a fully flexible architecture to enable efficient deployment in a range of core designs and reactor systems. Some of these designs benefit from other variants of coated particle fuel, such as uranium nitride TRISO (instead of uranium oxidecarbide) or BISO particles, that lend themselves to highly compact or extraterrestrial-power systems. USNC exclusively owns the intellectual property rights to FCM fuel and associated silicon carbide 3D printing technologies, leveraging them for design and deployment of its various nuclear energy systems that include and expand beyond MMR. Repository Ready Fuel System USNC is actively working on deployment of pilot and commercial-scale manufacturing facilities for production of FCM fuel. Two facilities in the United States (Salt Lake City, UT and Oak Ridge, TN) are currently commissioned and are undertaking pilot production activities. This includes deployment and shakedown testing of production modules for the various serial processing steps to manufacture FCM fuel and full codification and qualification of these modules. USNC’s objective is the widespread deployment of safe, clean, cost-effective, and reliable nuclear energy for the benefit of humanity on earth and beyond. FCM fuel technology is a core component of our value pro position. We are working relentlessly to deploy large-scale manufacturing of this highly robust fuel system and invite partners who share our vision to join us in this endeavor. Kurt Terrani Executive Vice President Ultra Safe Nuclear Corporation USNC shares the vision of dramatically reducing the radiotoxicity, volume, hazard index, and handling cost of spent nuclear fuel originated from advanced reactors and the current fleet of light water reactors. The high radionuclide retention capability of the silicon carbide matrix in FCM fuel, reduces radiological contamination of core materials in advanced reactors. For example, the large hexagonal graphite blocks in prismatic high temperature gas-cooled reactors may only be disposed of as low-level waste when they are fueled with FCM, greatly reducing the waste volume. Contact Ultra Safe Nuclear Corporation info@usnc.com www.usnc.com twitter.com/UltraSafeNuke linkedin.com/company/usnc At a Glance Ultra Safe Nuclear Corporation
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