Systematic Technology Evaluation Program for SiC/SiC Composite-based Accident-Tolerant LWR Fuel Cladding and Core Structures (M2FT-14OR0202244). PDF Download

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Languages : en
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Fuels and core structures in the current light water reactors (LWR's) are vulnerable to catastrophic consequences in the event of loss of coolant or active cooling, as unfortunately evidenced by the March 2011 Fukushima Dai-ichi Nuclear Power Plant Accident [1-3]. This vulnerability is attributed primarily to the rapid oxidation kinetics of zirconium alloys in a water vapor environment at very high temperatures [1, 4]. Current LWR's use Zr alloys nearly exclusively as the materials for fuel cladding and core structures. Among the candidate alternative materials for the LWR fuel clads and core structures to enable so-called accident-tolerant fuels (ATF) and accident-tolerant cores (ATC), silicon carbide (SiC) - based materials, in particular continuous SiC fiber-reinforced SiC matrix ceramic composites (SiC/SiC composites or SiC composites), are considered to provide outstanding passive safety features in beyond-design basis severe accident scenarios [3, 5, 6]. The SiC/SiC composites are anticipated to provide additional benefits over the zirconium alloys, including the smaller neutron cross sections, general chemical inertness, ability to withstand higher fuel burn-ups and higher temperatures, exceptional inherent radiation resistance, lack of progressive irradiation growth, and low induced-activation / low decay heat [7]. SiC/SiC composites are finding specialty applications as industrial materials as they mature and their application technologies grow [8]. Moreover, SiC and SiC/SiC composites are among the materials that have most extensively been studied for the effects of irradiation for nuclear applications.

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Languages : en
Pages : 18

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Advanced fuel claddings made entirely or mainly of silicon carbide (SiC) ceramics and/or composites are considered very attractive elements of the accident-tolerant fuels for the light water reactors. In order to translate the promise of SiC composite materials into a reliable fuel cladding, a coordinated program of component level design and materials development must be carried out with many key feasibility issues addressed a-priori to inform the process. With the primary objective of developing a draft blueprint of a technical program that addresses the critical feasibility issues; assesses design and performance issues related with manufacturing, operating, and off-normal events; and advances the technological readiness levels in essential technology elements, a draft plan for the Systematic Technology Evaluation Program for SiC/SiC Composite Accident-Tolerant LWR Fuel Cladding and Core Structures was developed in the FY-14 Advanced Fuels Campaign of the U.S. Department of Energy's Fuel Cycles Research and Development Program. This document summarizes the status of execution of the technical plan within the activities at the Oak Ridge National Laboratory.

Author: Gregory Welch Daines
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Languages : en
Pages : 164

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Silicon carbide (SiC) has been proposed as an alternative to zirconium alloys used in current light water reactor (LWR) fuel cladding because it exhibits superior corrosion characteristics, high-temperature strength, and a 1000°C higher melting temperature, all of which are important during a loss of coolant accident (LOCA). To improve the performance of SiC cladding, a multilayered architecture consisting of layers of monolithic SiC (mSiC) and SiC/SiC ceramic matrix composite (CMC) has been proposed. In this work, the mechanical performance of both the tubing and the endplug joint of two-layer SiC cladding is investigated under conditions associated with the LOCA. Specifically, SiC cladding mechanical performance is investigated after exposure to 1,400°C steam and after quenching from 1,200°C into either 100°C or 90°C atmospheric-pressure water. The samples consist of two-layer SiC, with an inner SiC/SiC CMC layer and an outer monolith SiC layer. The relationship between mechanical performance and sample architecture is investigated through ceramography and internal void characterization. The two-layered SiC cladding design offered an as-received failure hoop stress of about 600 MPa, with little strength reduction due to thermal shock, and the tube failure hoop stress remained above 200 MPa after 48 hour high-temperature steam oxidation. The cladding showed pseudo-ductile behavior and failed in a non-frangible manner. The designs investigated for joint strength offered as-received burst strength above 30 MPa, although the impact of thermal shock and oxidation showed possible dependence on architecture. Overall, the cladding showed promising accident-tolerant performance. Because the implementation of SiC is complicated by the need for an open gap and low plenum pressure, thorium-based mixed oxides (MOX) are a promising fuel for SiC cladding because they have higher thermal conductivity and lower fission gas release (FGR). Previous efforts at MIT have modified the FRAPCON code to include thorium MOX fuel. In this work, the fission gas release and thermal conductivity models of FRAPCON-3.4-MIT are validated against published data. The results of this validation indicate a need to update the FGR model, which was accomplished in this work.

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Languages : en
Pages : 38

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SiC-based ceramic matrix composites (CMCs) [5-8] are being developed and evaluated internationally as potential LWR cladding options. These development activities include interests within both the DOE-NE LWR Sustainability (LWRS) Program and the DOE-NE Advanced Fuels Campaign. The LWRS Program considers SiC ceramic matrix composites (CMCs) as offering potentially revolutionary gains as a cladding material, with possible benefits including more efficient normal operating conditions and higher safety margins under accident conditions [9]. Within the Advanced Fuels Campaign, SiC-based composites are a candidate ATF cladding material that could achieve several goals, such as reducing the rates of heat and hydrogen generation due to lower cladding oxidation rates in HT steam [10]. This work focuses on the application of SiC cladding as an ATF cladding material in PWRs, but these work efforts also support the general development and assessment of SiC as an LWR cladding material in a much broader sense.

Author: Pierre Guenoun (S.M.)
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Languages : en
Pages : 68

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Limited data has been published (especially on experimental work) on integrated multilayer SiC/SiC prototypical fuel cladding. In this work the mechanical performance of three unique architectures of three-layer silicon carbide (SiC) composite cladding is experimentally investigated under conditions associated with the loss of coolant accident (LOCA), and analytically under various conditions. Specifically, this work investigates SiC cladding mechanical performance after exposure to 1,400°C steam for 48 hours and after thermal shock induced by quenching from 1,200°C into either 100°C or 90°C water. Mechanical performance characteristics are thereafter correlated with sample architecture through void characterization and ceramography. The series with a reduced thickness did not have a pseudo-ductile regime due to overloading of the composite layer. The presence of the axial tow did not yield significant difference in the mechanical behavior most likely because samples were tested in the hoop direction. While as-received and quenched samples behaved similarly (pseudo ductile failure except for one series), non-frangible brittle failure (single-crack failure with no release of debris) was systematically observed after oxidation due to silica buildup in the inner voids of the ceramic matrix composite (CMC) layer. Overall, thermal shock had limited influence on sample mechanical characteristics and oxidation resulted in the formation of silica on the inner wall of the CMC voids leading to the weakening of the monolith matrix and brittle fracture. Stress field in the cladding design is simulated by finite element analysis under service and shutdown conditions at both the core's middle height and at the end of the fuel rod. Stresses in the fuel region are driven by the thermal gradient that creates stresses predominantly from irradiation induced swelling. At the endplug, constraints are mainly mechanical. Stress calculations show high sensitivity to the data scatter and especially swelling and thermal conductivity. No cladding with the design studied here can survive either service or shutdown conditions because of the high irradiation-induced tensile stresses that develop in the hot inner monolith layer. It is shown that this peak tensile stress can be alleviated by adjusting the swelling level of the different layers. The addition of an under-swelling material such as PyC or Si can reduce the monolith tensile stress by 10%. With a composite that swells 10% less than the monolith, the stress is reduced by 20%.