- A new system based on transient grating spectroscopy detects radiation-induced changes to materials in real-time.
- Compared to existing techniques that take half a year to completely characterize a given material, it only takes a day.
High radiation environments, like those found in the cores of nuclear power plants, require extremely high-quality materials. The microstructure, and thus performance, of these materials in nuclear power facilities change drastically over the years of operation.
Most of the materials fail due to enhanced precipitation, volumetric swelling, ballistic inclusion dissolution, irradiation-assisted stress corrosion cracking, and enhanced segregation.
Existing methods for testing material’s ability to withstand such harsh environments are not very effective. They rely on ‘cook and look’ approach, in which materials are subject to high radiation environments and then removed for close inspection. The process, however, is so time-consuming it delays the development of advanced materials for new reactors.
To solve this problem, a research team at MIT and Sandia National Laboratories has built a new system that can effectively trace radiation-induced changes in real-time, and provide more insights than conventional techniques.
Since numerous nuclear facilities are heading towards the end of their operation lifetimes, the technology could help decide which nuclear plants can be safely extended by how much.
The New Way Of Testing Materials
The new laser-based system relies on transient grating spectroscopy (TGS) – an optical technique for measuring quasiparticle propagation. It can detect physical changes in the material, including thermal diffusivity and elasticity, without damaging or changing its properties.
The team has been testing this method for about two years. Now, the system is ready to provide accurate data that can help engineers understand how materials inside reactor vessels degrade over time.
Reference: ScienceDirect | doi:10.1016/j.nimb.2018.10.025 | MIT
This the first time someone has used TGS to closely observe damage caused by radiation. It could detect whether material’s properties have changed during operational years, such as its ability to respond to stresses or conduct heat.
To replicate radiation environments, researchers simulated the effects of neutron bombardment using ion beams, which damage the material in a similar way as actual reactors but are safer to work with and much easier to control. They used ion accelerator of 6 megavolts to simulate years of neutron exposure in hours.
The new system installed and tested at Sandia National Labs | Image credit: Cody Dennett
The measurements are by made by simulating material vibrations using a laser beam and then observing those vibrations at the surface using another laser. This measurement can also be used to determine other related properties, such as damage accumulation and defect in a given material.
Since the system monitors materials in real-time, it is possible to stop the experiment at any critical moment and study the damage(s) in detail. This also allows engineers to pinpoint the mechanistic reasons behind those failures.
The traditional methods take months to find the initial factor that triggered degradation. The new system, on the other hand, could do the same in a few hours. As per the report, the complete characterization of a given material takes only one day, whereas, existing techniques take nearly half a year.
What Next?
So far, the researchers have tested their system on two pure metals: tungsten and nickel. In the coming months, they will use it to test other metals and various kinds of alloys.
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The team is also working to further improve the system’s capabilities and add more diagnostic tools for investigating more properties of materials exposed to radiation.
