Low Cost Silicon Carbide Fibers, Tapes, and Architecture for Accident Tolerant Nuclear Fuel Cladding and Components

Since the Fukushima accident, the DOE, nuclear fuel suppliers, and EPRI, have begun to focus R & amp;D efforts on advanced LWR fuel and components that are more accident tolerant than current zirconium alloys. One area of interest are fuels and components fabricated from ceramic composites that do not balloon during LOCA accidents, do not react exothermically with water during post LOCA quench, and do not release explosive gases such as hydrogen. One such material is the Silicon Carbide (SiC) triplex clad developed by Ceramic Tubular Products (CTP) under previous NERI and SBIR grants. SiC composites are also being evaluated by EPRI and CTP for core structural components such as BWR channel boxes. The triplex clad and channel boxes are made from stoichiometric beta phase SiC filaments, twisted into tows of about 1000 fibers, and then braided or wound into either a channel box configuration, or CTPs triplex cladding. Although this filament based composites are resistant to radiation damage, the filaments are prohibitively expensive, and are only available from two foreign suppliers. Estimated cost for a 14 foot SiC composite channel box made from these commercial filaments is about $250,000 compared to a Zircaloy channel box costing about $10,000. At these costs use of SiC composites in commercial nuclear fuel is unlikely. Recently, Free Form Fibers (FFF), a US small business, has begun development (under SBIR grants from NSF and the Army) of a new process for fabricating SiC filaments which promises much lower costs (after scale-up), perhaps leading to a factor of five reduction in costs. One question which has yet to be addressed is how to combine these filaments into a tow or ribbon that is capable of being wound or braided into a pre-form and then infiltrated using CVI to form the composite layer in triplex cladding, or the walls of a BWR channel box. This proposed SBIR project will investigate that question. In Phase 1, we (CTP and FFF) will investigate the feasibility of combining the Free Form filaments onto a flat tape, about 40 to 360 fibers wide, that can be layered and applied to either the fuel rod shape, or the channel box shape, and then infiltrated. A key challenge will be to investigate an appropriate chemical form for the tape that would allow its use during pre-form fabrication, but would burn off without harmful residue during CVI infiltration. We will also investigate the mechanical properties of composites using these new filament and tape precursors. If feasibility is demonstrated during Phase 1, a Phase 2 project will be proposed to expand the filament and tape processing capability at FFF to make wider tapes (400 to 1000 filaments in width), and for CTP to apply these tapes to fabricate and test various pre-form architectures. The goal is to demonstrate a lower cost production process for use in SiC triplex cladding and channel boxes, that would facilitate commercial introduction and thus lead to a vast improvement in the resistance of future LWR fuels and core components to severe accidents. Commercial Applications and Other Benefits: This proposed research can be applied directly in the manufacture and operation of commercial Light Water Reactor fuel for the existing 104 U.S. plants and future Generation 3+ plants and Small Modular Reactors now being planned.