NSUF 15-584: Proton beam irradiation study of UHTC zirconium diboride (ZrB2)
This work aims to study the microstructural evolution of zirconium diboride (ZrB2) under proton beam irradiation. ZrB2 belongs to the refractory ceramics known to as ultrahigh temperature ceramics (UHTCs). UHTCs possess high melting temperatures >3000 ºC and exhibit inherent thermal stability in extreme environments. Westinghouse currently uses ZrB2 as a coating of about 10 µm on top of the fuel elements. The 10B acts as a burnable absorber producing Li and He, species with much lower neutron absorption cross-sections, allowing for control over the burnup. UHTCs, such as ZrB2, are suitable candidates for the very high temperature and molten salt reactors where operating temperatures are up to ~1000°C with target cumulative displacement damage levels of ~20 dpa and ~200 dpa, respectively, for core internal structures. Moreover, ZrB2 can be manufactured with tailored 10B to 11B ratios that could lead to revolutionary performance improvements in a range of applications including fuel cladding with improved accident tolerance, and plasma facing in fusion designs. For nuclear power applications, the significant challenge facing the development of these materials is a lack of knowledge of the effects of irradiation on the microstructure and properties of ZrB2. The limited resources on this topic report that neutron irradiation of borides results in high internal stresses leading to considerable swelling with micro- and macrofracturing. These observed effects are due to the accumulation of radiation defects in the crystal structure and the transmutation reaction of 10B into Li and He. However, the reported results corresponded to materials with large grain size > 20 µm and with > 3 % porosity, which increase the tendency to fail by cracking. ZrB2 has been extensively studied during the last 10 years and fully dense structures of ZrB2 have been achieved by hot pressing leading to microstructures containing ZrB2 grains of ~6 µm leading to a flexural strength of 565 MPa, a modulus of ~ 490 GPa, a hardness of ~ 22 GPa, and a fracture toughness of ~ 3.5 MPa•m1/2. Like most ceramics, the flexure strength of ZrB2 is inversely proportional to the square root of grain size. This evidences a need for a detailed study of radiation effects of UHTCs manufactured using modern approaches to control their microstructure, and therefore their mechanical properties. In this work, high purity, dense, fine grained ZrB2 will be produced by reactive hot pressing and irradiated with 2.6 MeV protons to damage levels of 0.2, 0.5, 1, and 2 dpa at temperatures of 400ºC and 1000 ºC. The evolution of the microstructure of the irradiated ZrB2 will be characterized. In addition, the effects of irradiation on the mechanical and thermal properties will be measured experimentally. This project will generate new insight into the irradiation response of ultra-high purity ZrB2. In addition, the results will serve as a preliminary test for future neutron irradiation studies. This work is planned to be accomplished within a 6 month period.
Additional Info
| Field | Value |
|---|---|
| Abstract | This work aims to study the microstructural evolution of zirconium diboride (ZrB2) under proton beam irradiation. ZrB2 belongs to the refractory ceramics known to as ultrahigh temperature ceramics (UHTCs). UHTCs possess high melting temperatures >3000 ºC and exhibit inherent thermal stability in extreme environments. Westinghouse currently uses ZrB2 as a coating of about 10 µm on top of the fuel elements. The 10B acts as a burnable absorber producing Li and He, species with much lower neutron absorption cross-sections, allowing for control over the burnup. UHTCs, such as ZrB2, are suitable candidates for the very high temperature and molten salt reactors where operating temperatures are up to ~1000°C with target cumulative displacement damage levels of ~20 dpa and ~200 dpa, respectively, for core internal structures. Moreover, ZrB2 can be manufactured with tailored 10B to 11B ratios that could lead to revolutionary performance improvements in a range of applications including fuel cladding with improved accident tolerance, and plasma facing in fusion designs. For nuclear power applications, the significant challenge facing the development of these materials is a lack of knowledge of the effects of irradiation on the microstructure and properties of ZrB2. The limited resources on this topic report that neutron irradiation of borides results in high internal stresses leading to considerable swelling with micro- and macrofracturing. These observed effects are due to the accumulation of radiation defects in the crystal structure and the transmutation reaction of 10B into Li and He. However, the reported results corresponded to materials with large grain size > 20 µm and with > 3 % porosity, which increase the tendency to fail by cracking. ZrB2 has been extensively studied during the last 10 years and fully dense structures of ZrB2 have been achieved by hot pressing leading to microstructures containing ZrB2 grains of ~6 µm leading to a flexural strength of 565 MPa, a modulus of ~ 490 GPa, a hardness of ~ 22 GPa, and a fracture toughness of ~ 3.5 MPa•m1/2. Like most ceramics, the flexure strength of ZrB2 is inversely proportional to the square root of grain size. This evidences a need for a detailed study of radiation effects of UHTCs manufactured using modern approaches to control their microstructure, and therefore their mechanical properties. In this work, high purity, dense, fine grained ZrB2 will be produced by reactive hot pressing and irradiated with 2.6 MeV protons to damage levels of 0.2, 0.5, 1, and 2 dpa at temperatures of 400ºC and 1000 ºC. The evolution of the microstructure of the irradiated ZrB2 will be characterized. In addition, the effects of irradiation on the mechanical and thermal properties will be measured experimentally. This project will generate new insight into the irradiation response of ultra-high purity ZrB2. In addition, the results will serve as a preliminary test for future neutron irradiation studies. This work is planned to be accomplished within a 6 month period. |
| Award Announced Date | 2015-08-10T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kumar Sridharan |
| Irradiation Facility | None |
| PI | Jessika Rojas Marin |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 584 |