Determining Structure Evolution in Isomolded Nuclear Graphite Under Stress
Principal Investigator
- Name:
- Lance Snead
- Email:
- [email protected]
- Phone:
- (208) 526-6918
Team Members:
| Name: | Institution: | Expertise: | Status: |
|---|---|---|---|
| Boris Khaykorich | M.I.T. Massachusetts Institute of Technology | X-ray characterization | Faculty |
Experiment Details:
- Experiment Title:
- Determining Structure Evolution in Isomolded Nuclear Graphite Under Stress)
- Work Description:
- The isomolded nuclear graphite, IG-110, was neutron irradiated with and without a compressive load of 5 MPa at an irradiation temperature of ~400°C over a range of neutron dose up to 9.3x1025 n/m2 (E>0.1 MeV) in HFIR. The table below provides a schematic of the rabbit vehicle used in the experiment (irradiated in 2011) and specifics of the irradiation including measured irradiation temperature. Cap ID E25Dose DPA Irr Temp Stress MPa R11-A1 2.4 1.75 371 4.9 R11-A2 2.4 1.75 375 0 R11-A3 4.6 3.36 401 5.4 R11-A4 4.6 3.36 384 0 R11-A5 7.1 5.12 375 Un-measurable R11-A6 7.1 5.12 371 0 R11-A7 9.3 6.79 421 Un-measurable R11-A8 9.3 6.79 - 0 * Conversion of 1dpa = 0.73 x1025 E>0.1 MeV Following irradiation a range of physical properties were studied to compare the effect of graphite irradiation on microstructure developed under compression and in stress-free condition. Properties studied included: dimensional change parallel and orthogonal to the stress-axis, thermal conductivity, sonic modulus, and the coefficient of thermal expansion. As expected, the IG-110 graphite experienced irradiation-induced creep that is differentiated from irradiation-induced swelling. As part of this Rapid Turnaround Experiment a subset of samples from this experiment, currently in possession of the MIT Nuclear Reactor Laboratory, will undergo microstructural characterization. Funding is sought for the preparation of samples for metallographic and optical examination using equipment at the Nuclear Reactor Laboratory. Specifically, graphite samples will be sectioned and mounted for polishing, optical and x-ray analysis including microtomography. Samples that were irradiated under stress and free of stress will be annealed and the effect of annealing above the irradiation temperature on the pore structure and macroscopic dimensional change determined. Following completion of work samples are to be permanently disposed of. The team members for this project have expertise in fundamental of graphite and x-ray and optical techniques to elucidate microstructure. Dr. Snead has published widely on the effects of irradiation on graphite and is intimately aware of the conditions of this particular irradiation and the supporting property information. Dr. Khayakovich is an expert in the area of X-ray characterization. This work will support the thermophysical property results of this irradiation study now being submitted to the Journal of Nuclear materials. Moreover, when successfully completed, the work will provide insight into the fundamental of irradiation damage in graphite and demonstrate how x-ray microtomography can be applied to map the pore structure in graphite.
Project Summary
Graphite is an important material for a number of reactor systems and particularly for high temperature gas cooled reactors for which it comprises the bulk of the core material. Under neutron irradiation the graphite microstructure undergoes gross microstructural evolution resulting in similarly large property changes. [1] One area of historic and continuing research is that of irradiation creep of nuclear graphite. This irradiation creep, defined as the difference between the irradiation-induced growth of graphite in a stress-free condition and the irradiation-growth under a stressed condition, is of great technical importance to reactor design. As pointed out by Tsang and Marsden [2] , without the stress relief provided by irradiation creep, failure due to the elastic strain caused by irradiation-induced swelling of graphite would preclude its use. Irradiation creep (an inelastic strain) occurs over essentially all temperature and independently of thermal creep and has been modeled extensively with varying degrees of success. [3] While the classically understood model for dimensional change discusses the competition between inter-plane defect formation and annihilation of internal porosity. As irradiation progresses these internal interfaces and porosity become saturated and the graphite moves from densification into swelling. To date the porosity, or range of porosity of relevance to this mechanism has not been identified. The purpose of this work is to use already irradiated nuclear graphite that has been irradiated with and without an applied stress to map the change in internal porosity in the 0.01 to 10 micron pore range. The period of performance is less than 10 months.
Relevance
Nuclear graphite has been and is currently a material of interest the the DOE-NE. Specific examples included core graphite for the HTGR and certain molten salt reactors as well as constituent layers of the TRISO fuel. This work seeks to address a long-standing issue with regards to the anisotropic swelling of graphite. Specifically, we will use graphite that was previously irradiated with and without an applied stress to determine which porosity size is most impacted by irradiation. With such information, in principal, it will be possible to engineer graphites with porosity maximized in specific ranges to extend lifetime. This could have a significant cost impact.
Conference Publications
"Topological and atomic investigation of nuclear graphite using multi-scale x-ray scattering" David Sprouster, Lance Snead, Boris Khaykovich, Yutai Katoh, Anne Campbell, 45th International Conference and Expo on Advanced Ceramics and Composites (ICACC2021) February 8-11, (2021) Link
About Us
The Nuclear Science User Facilities (NSUF) is the U.S. Department of Energy Office of Nuclear Energy's only designated nuclear energy user facility. Through peer-reviewed proposal processes, the NSUF provides researchers access to neutron, ion, and gamma irradiations, post-irradiation examination and beamline capabilities at Idaho National Laboratory and a diverse mix of university, national laboratory and industry partner institutions.
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