NSUF 18-1539: Post-irradiation examinations of SiC composites neutron irradiated at 300°C to 30dpa
Silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites continue to undergo development for fission applications worldwide because of the inherent advantages of the material, including low activation, high-temperature capability, relatively low neutron absorption, and radiation resistance. SiC/SiC composites are being considered for use in current light water reactors (LWRs), most Gen IV reactor concepts, and future-generation nuclear power reactors. Recent research highlighted that SiC/SiC composites showed limited mechanical degradation following neutron irradiation at 800°C to 70 dpa. On the other hand, recent research has also found degradation phenomena: irradiation at 320°C to 92 dpa significantly degraded the strength of a specific SiC/SiC composite, a chemical vapor infiltrated (CVI) SiC matrix composite consisting of Hi-Nicalon Type-S (HNS) SiC fibers coated with an SiC/PyC (pyrolytic carbon) multilayer interphase. Such degradation is associated with interphase damage. To improve the irradiation resistance of SiC/SiC composites at an LWR temperature of ~300°C, SiC/SiC composites with a modified interphase have been neutron-irradiated to 12 dpa and tested. The mechanical tests revealed that there was no notable irradiation effect on the strength of the material. The proposed work will extend the post-irradiation examination activities to a higher neutron dose. The focus of this proposal is to test CVI SiC/SiC composites reinforced with single-layer PyC-coated HNS fibers, which are currently being explored for LWR cladding and channel box applications, following neutron irradiation at ~300°C to 30 dpa. Five composite specimens will be evaluated. The irradiation resistance of the composites will be investigated based on the dynamic Young's modulus, and flexural behavior. The dynamic Young's moduli of the SiC composites will be determined using the impulse excitation of vibration method. Four-point flexural tests using a 4-point-1/4-point fixture will be conducted. Analysis of the flexural behavior will provide the proportional limit stress, ultimate flexural strength, and apparent strain of failure. For understanding the radiation effect on the strength, a novel high-speed nanoindentation mapping of the specimens will also be conducted to evaluate hardness and modulus of fiber and matrix. In addition, two SiC passive temperature monitors will be evaluated using a dilatometer to investigate actual irradiation temperatures. The samples are currently in the LAMDA facility at Oak Ridge National Laboratory and ready for testing. The experiments in the LAMDA laboratory will take up to 12 days, without analysis. This work will provide critical experimental data on how high-dose neutron irradiation at LWR-relevant temperatures affects the mechanical properties of recent nuclear-grade SiC composites, a topic that has not been explored previously. Comparisons of irradiation resistance among SiC/SiC composites have used previous studies; this study will show how modification of the interphase affects the irradiation resistance and consequently will guide better design of composites for use in high-dose radiation environments. It is anticipated that the duration of the testing will be up to 4 months.
Additional Info
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| Abstract | Silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composites continue to undergo development for fission applications worldwide because of the inherent advantages of the material, including low activation, high-temperature capability, relatively low neutron absorption, and radiation resistance. SiC/SiC composites are being considered for use in current light water reactors (LWRs), most Gen IV reactor concepts, and future-generation nuclear power reactors. Recent research highlighted that SiC/SiC composites showed limited mechanical degradation following neutron irradiation at 800°C to 70 dpa. On the other hand, recent research has also found degradation phenomena: irradiation at 320°C to 92 dpa significantly degraded the strength of a specific SiC/SiC composite, a chemical vapor infiltrated (CVI) SiC matrix composite consisting of Hi-Nicalon Type-S (HNS) SiC fibers coated with an SiC/PyC (pyrolytic carbon) multilayer interphase. Such degradation is associated with interphase damage. To improve the irradiation resistance of SiC/SiC composites at an LWR temperature of ~300°C, SiC/SiC composites with a modified interphase have been neutron-irradiated to 12 dpa and tested. The mechanical tests revealed that there was no notable irradiation effect on the strength of the material. The proposed work will extend the post-irradiation examination activities to a higher neutron dose. The focus of this proposal is to test CVI SiC/SiC composites reinforced with single-layer PyC-coated HNS fibers, which are currently being explored for LWR cladding and channel box applications, following neutron irradiation at ~300°C to 30 dpa. Five composite specimens will be evaluated. The irradiation resistance of the composites will be investigated based on the dynamic Young's modulus, and flexural behavior. The dynamic Young's moduli of the SiC composites will be determined using the impulse excitation of vibration method. Four-point flexural tests using a 4-point-1/4-point fixture will be conducted. Analysis of the flexural behavior will provide the proportional limit stress, ultimate flexural strength, and apparent strain of failure. For understanding the radiation effect on the strength, a novel high-speed nanoindentation mapping of the specimens will also be conducted to evaluate hardness and modulus of fiber and matrix. In addition, two SiC passive temperature monitors will be evaluated using a dilatometer to investigate actual irradiation temperatures. The samples are currently in the LAMDA facility at Oak Ridge National Laboratory and ready for testing. The experiments in the LAMDA laboratory will take up to 12 days, without analysis. This work will provide critical experimental data on how high-dose neutron irradiation at LWR-relevant temperatures affects the mechanical properties of recent nuclear-grade SiC composites, a topic that has not been explored previously. Comparisons of irradiation resistance among SiC/SiC composites have used previous studies; this study will show how modification of the interphase affects the irradiation resistance and consequently will guide better design of composites for use in high-dose radiation environments. It is anticipated that the duration of the testing will be up to 4 months. |
| Award Announced Date | 2018-09-17T12:02:54.8 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | TAKAAKI KOYANAGI |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1539 |