Joining Silicon Carbide for Advanced LWR Fuel Cladding Yutai Katoh 1 , Lance L. Snead 1 , Charles H. Henager, Jr. 2 , Tatsuya Hinoki 3 , Monica Ferraris 4 , Steve T. Gonczy 5 1 Oak Ridge National Laboratory: P.O. Box 2008, Oak Ridge, TN 37831-6138, katohy@ornl.gov 2 Pacific Northwest National Laboratory: Richland, WA 99352, USA 3 Kyoto University: Gokasho, Uji, Kyoto 611-0011, Japan 4 Politecnico di Torino, Torino, Italy 5 Gateway Materials Technology, Inc., Chicago, IL, USA INTRODUCTION The application of silicon carbide composites for light water reactor cladding has received considerable attention over the past decade. If proven successful, this would prove not only the first application of ceramic composites to nuclear systems but potentially achieve a significant enhancement in safety margin for the current light water reactor fleet. There are two generic design types employing SiC composites for light water reactor cladding: fully ceramic SiC clad, and ceramic/metal hybrid cladding. For these clads, some combination of fibrous ceramic composite to achieve fracture toughness is used with layer or multiple layers of mololithic SiC ceramic (fully ceramic) or metallic lining (hybrid) to seal the inherently porous and microcracked composite. There are many technological, reactor operational, economic, materials interaction, and fabrication issues surrounding each generic design. For the fully ceramic system this then requires an end-cap seal, which is one of the critical technologies that must be achieved prior to moving forward with this concept. The purpose of this work is to review the current status of bonding of SiC with particular emphasis on the possibility of application of techniques to nuclear structures. Finally, results will be presented on an international collaboration of test methods, joint development, and neutron irradiation yielding the first irradiation stable SiC joints at relatively low doses. JOINING METHODS The critical need and lack of methodologies to join silicon carbide composite in nuclear applications has been discussed for more than two decades [1]. This is in contrast to the ability to join SiC, or SiC/SiC to itself or other materials, which can be done in a reliable and rugged manner through a number of conventional and advanced techniques. Those methods include diffusion bonding using various active fillers, transient eutectic phase routes such as nano-infiltration and transient eutectic-phase (NITE) process, glass-ceramic joining, brazing, SiC reaction bonding, MAX-phase joining, preceramic polymer routes, transient liquid metal joining, and selected area chemical vapor deposition (CVD). Primary considerations specific to nuclear application include the resistance against neutron irradiation, adequate strength and reliability, compatibility of the processing condition with design requirement, chemical compatibility with the specific operating environment, and the ability to satisfy the hermeticity requirement. In the current work, diffusion bonding using titanium filler [2], NITE joining using slurry or tape approach [3], calcia-alumina (CA) glass-ceramic joining [4], and Ti 3 SiC 2 MAX phase reaction bonding [5] were evaluated. The joint specimens for evaluation were produced using either chemically vapor-deposited (CVD) SiC, NITE-SiC, or Tyranno™-SA3 / NITE SiC-matrix composite as the base material to be bonded together. METHODS FOR STRENGTH DETERMINATION One of the challenging situations faced by the development effort for ceramic composite joints is the lack of adequate standard test methods allowing acquisition of mechanical properties data in a reliable and reproducible manner. This is particularly the case when limitations are imposed by specimen preparation or test article geometry or dimensions. Practically, simple methods such as cantilever shear, double-notched shear, and asymmetric four point flexure are frequently adopted for shear strength determination of ceramic composite joints. However, none of those test methods is capable of producing reasonably pure shear stress state within the joint and the interfacing volumes. Torsion of solid specimens was identified as one of the appropriate test methods that are capable of providing true shear strength of ceramic joints using miniature specimens. Based on this conclusion, development of torsional shear test method using solid cross-section specimens was performed. The objective of this effort was to develop a small specimen test technology (SSTT) for this method so that reproducible and reliable shear strength values are obtained in a true shear stress state with the specimen sizes compatible with the internal volume and dimensions of the small “rabbit” irradiation capsules for High Flux Isotope Reactor (HFIR). Among a variety of specimen geometries and sizes, test specimens specifically with the 6 mm x 6 mm x 3 mm envelope dimensions, 1 mm curvature diameter for the Transactions of the American Nuclear Society, Vol. 107, San Diego, California, November 11–15, 2012 405 Nuclear Fuels and Materials: SiC and TRISO