NSUF 18-671: Radiation-Induced Changes to the Nanometer-Sized Pores in Fine-Grained Nuclear Graphite
Graphite is a critical material for the deployment of multiple Generation-IV nuclear reactor concepts. The usable lifetime of graphite in these Gen-IV reactors is determined by the irradiation-induced changes to the volume and material properties. Numerous research programs have studied the changes that occur to the physical properties of graphite when it is exposed to temperatures and neutron fluences that would be experienced during a reactor operation. These programs resulted in the measured property changes, but none included a comprehensive study into the microstructural changes. Therefore speculations have been made as to which microstructure features change during irradiation and if they control any of the physical property changes, but there has never been any supporting evidence. Additionally, a thorough investigation into the irradiation-induced microstructure changes has always been difficult since many metallography techniques are not applicable to graphite. Instead most of the microstructure investigations have relied on optical microscopy techniques, which are limited by the optical resolution. This research proposes to use nitrogen adsorption/desorption isotherms at 77 K to investigate the neutron irradiation-induced changes that occur to the nanometer-sized pores in nuclear graphite. These pores are too small to be observed in optical microscopy, and the number that could be investigated with SEM or TEM would be too low to give a good understanding of global material’s properties. Gas adsorption is well suited for characterization of porous materials (catalysts, adsorbents, plastic materials) and has a large potential for characterization of nanometer range accessible pores in nuclear graphite. The thought has long been held that these fine pores are what are filled in and subsequently created during volume changes observed at the macroscale after irradiation, but that has never been proven. This research proposes to investigate whether the changes to the size and number of nanometer-sized pores is related to the observed volume changes. Three irradiated fine-grained graphite specimens will be characterized by adsorption/desorption of nitrogen at liquid nitrogen temperature (77 K). The specimens were irradiated in the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) for the strategic planning partnership with Tokai Carbon Co., Ltd. Three specimens from the lowest irradiation temperature (300°C) with three different irradiation-induced volume changes (maximum contraction, returned to original volume, and swelled) will be used for this work. These specimens were selected to investigate how the volume change is related to the BET surface area, total pore volume and pore size distribution of accessible fine pores in the nanometer range. This research will result in a preliminary understanding of the microstructural changes of nanoporosity in graphite irradiated graphite and on their relationship with total volumetric changes at the macroscale or with some other properties affected by neutron irradiation. This work is expected to require 3-9 hours of total setup time for the runs, and require up to 10 days of total time for all the measurement to complete.
Additional Info
| Field | Value |
|---|---|
| Abstract | Graphite is a critical material for the deployment of multiple Generation-IV nuclear reactor concepts. The usable lifetime of graphite in these Gen-IV reactors is determined by the irradiation-induced changes to the volume and material properties. Numerous research programs have studied the changes that occur to the physical properties of graphite when it is exposed to temperatures and neutron fluences that would be experienced during a reactor operation. These programs resulted in the measured property changes, but none included a comprehensive study into the microstructural changes. Therefore speculations have been made as to which microstructure features change during irradiation and if they control any of the physical property changes, but there has never been any supporting evidence. Additionally, a thorough investigation into the irradiation-induced microstructure changes has always been difficult since many metallography techniques are not applicable to graphite. Instead most of the microstructure investigations have relied on optical microscopy techniques, which are limited by the optical resolution. This research proposes to use nitrogen adsorption/desorption isotherms at 77 K to investigate the neutron irradiation-induced changes that occur to the nanometer-sized pores in nuclear graphite. These pores are too small to be observed in optical microscopy, and the number that could be investigated with SEM or TEM would be too low to give a good understanding of global material’s properties. Gas adsorption is well suited for characterization of porous materials (catalysts, adsorbents, plastic materials) and has a large potential for characterization of nanometer range accessible pores in nuclear graphite. The thought has long been held that these fine pores are what are filled in and subsequently created during volume changes observed at the macroscale after irradiation, but that has never been proven. This research proposes to investigate whether the changes to the size and number of nanometer-sized pores is related to the observed volume changes. Three irradiated fine-grained graphite specimens will be characterized by adsorption/desorption of nitrogen at liquid nitrogen temperature (77 K). The specimens were irradiated in the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) for the strategic planning partnership with Tokai Carbon Co., Ltd. Three specimens from the lowest irradiation temperature (300°C) with three different irradiation-induced volume changes (maximum contraction, returned to original volume, and swelled) will be used for this work. These specimens were selected to investigate how the volume change is related to the BET surface area, total pore volume and pore size distribution of accessible fine pores in the nanometer range. This research will result in a preliminary understanding of the microstructural changes of nanoporosity in graphite irradiated graphite and on their relationship with total volumetric changes at the macroscale or with some other properties affected by neutron irradiation. This work is expected to require 3-9 hours of total setup time for the runs, and require up to 10 days of total time for all the measurement to complete. |
| Award Announced Date | 2016-08-16T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | Anne Campbell |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 671 |