Wednesday, November 30, 2016

Towards a safer, better nuclear energy future

Compared to most industries, nuclear power looks like (and often is) one of the slowest to innovate. Advances in batteries, solar cells, and biotech hit the news every day, while the phrase “nuclear innovation” rarely makes headlines. Look a little closer though, and you’ll see that researchers are making exciting, innovative, and rapid progress toward a better and safer nuclear energy future.

Nuclear power plants play a big role in energy production. Last year, nearly 20% of the total electrical output of the United States came from nuclear plants. Nuclear power is efficient, cost effective, doesn’t rely on the weather, and is environmentally friendly. At least when everything goes as planned. Disasters like Three Mile Island, Chernobyl, and Fukushima are devastating reminders of what can go wrong.

After a long, rocky, and expensive history, this October saw a nuclear reactor at the Watts Bar Nuclear Generating Station in Tennessee become the first new reactor to provide service in the US in 20 years. This image shows the cooling towers and containment buildings.
Image Credit: Tennessee Valley Authority (CC BY 2.0).

In order to build next-generation nuclear energy systems that are both safer and less expensive, you need materials that can survive extreme amounts of radiation. You also need to know exactly how the materials will respond to different amounts of radiation, and at what point they will fail. When the materials fail, the system fails. Currently, measuring the impact of radiation on a material is a time-consuming and expensive process. A team at MIT hopes to change that.

In an open-source work that will soon be published in the journal Physical Review B, MIT researchers and their colleagues in Mexico and South Africa lay the foundation for a new way to measure a material’s response to radiation. This technique could help scientists more quickly and easily determine which materials are best for nuclear power systems, both old and new.

Imagine that you are walking down the street and see a puddle of unknown liquid. If you cannot touch, taste, or smell it, one way to learn about the liquid is to throw a rock in it. The splash from the rock will make waves appear. Waves travel differently through materials with different properties, such as water, oil, and honey.

This is the idea behind a technique called transient grating spectroscopy, which studies how materials respond to radiation, among other things. It works as follows. Using a laser-based system, researchers create acoustic waves on the surface of a material and observe at what speed they travel. From this, they extract information about the mechanical properties of the material.

Previous research suggests that even low-level exposure to radiation affects the mechanical properties of a material. This means that by monitoring acoustic waves while a material is exposed to radiation, you can theoretically measure how different levels of exposure affect the material.

The first step in determining whether this is a good technique for understanding the effect of radiation is exploring its sensitivity. Researchers need to be able to detect very small changes in the properties of the material caused by radiation.

The researchers explored the sensitivity limits of this technique by using it to measure the acoustic properties of single crystals of aluminum and copper. The acoustic response of a single crystal depends on how it is oriented during your measurement. In some cases, the difference is very small between one orientation and another. Their results show that the technique is indeed sensitive enough to show small differences in properties resulting from radiation exposure.

As a next step, the team created a framework that can be used to simulate this technique and make predictions about how a material will respond to radiation exposure. This work lays the foundation for a number of follow-up studies further exploring the acoustic properties of irradiated materials. If it is as promising as it looks, nuclear engineers and scientists may be able to speed up the pace of progress from decades to days.

There is no denying that we use a lot of energy. Wind and solar energy are becoming more efficient and popular, but they still represent just a small amount of our energy production in the United States (less than 6% combined). As we consider our future needs, it’s important to take a close look at the possibilities, risks, and innovations in every area of energy production.

Kendra Redmond

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