New technique paves way for better nuclear waste treatment facilities

Nuclear power is seen as one way to reduce reliance on fossil fuels, but one of the questions surrounding it is how to deal with nuclear waste. Radioactive waste can be transformed into more stable elements, but this process is not yet viable on a large scale.

New research by physicists at the University of Tokyo reveals a method to more accurately measure, predict and model a key part of the process of making nuclear waste more stable. This could lead to better nuclear waste treatment facilities and also new theories about how some of the heavier elements in the universe came to be.

The word “nuclear” itself can be a trigger for some people, which is understandable in Japan, where the atomic bomb and the Fukushima disaster are among the pivotal moments in its modern history. Yet given the relative scarcity of suitable space in Japan for renewable forms of energy like solar or wind, nuclear power is seen as an essential part of efforts to decarbonize the energy sector.

For this reason, researchers are working hard to try to improve the safety, efficiency, and other issues related to nuclear energy. Associate Professor Nobuaki Imai of the University of Tokyo’s Center for Nuclear Studies and his colleagues believe they can help improve a key aspect of nuclear power, waste treatment.

“Generally speaking, nuclear power works by boiling water using self-sustaining nuclear decay reactions. Unstable elements break down and disintegrate, releasing heat that causes the water to boil and drives turbines. But this process ends up leaving behind unusable waste that is still radioactive,” Imaï said.

“This waste can remain radioactive for hundreds of thousands of years, which is why it is usually buried deep underground. But there is a growing desire to explore another route, one by which unstable radioactive waste can be made more stable, avoiding their radioactive decay and making it much safer to manage. This is called transmutation.

Transmutation is the opposite of nuclear decay; instead of an element breaking apart and releasing radiation, a neutron can be added to an unstable element, transforming it into a slightly heavier version of itself. Depending on the initial substance, this new form may be stable enough to be considered safe.

The problem is that, although this process has been widely known for some time, it has been impossible to quantify it with enough precision to take the next step and ideally produce prototypes of next-generation waste management facilities. .

“The idea actually came from a surprising source: colliding stars, particularly neutron stars,” Imai said. “Following recent observations of gravitational waves emanating from neutron star mergers, researchers have been able to better understand how neutrons interact and their ability to modify other elements.”

“Based on this, we used a range of instruments to better understand how the element selenium, a common nuclear waste product, behaves when bombarded by neutrons. Our technique allows us to predict how materials absorb neutrons and undergo transmutation. This knowledge can contribute to the design of nuclear waste transmutation facilities.

It is difficult for researchers to make these kinds of observations; in fact, they are not capable of directly observing the acts of transmutation. Instead, the team can observe how much of a sample is not transmuted, and by taking measurements to know that transmutation has occurred, they can estimate, albeit very precisely, how much the sample was transmuted.

“We are confident that our measurements accurately reflect the actual rate of transmutation of unstable selenium into a more stable form,” Imai said. “We now plan to measure this for other nuclear wastes. Hopefully this knowledge will combine with other areas needed to realize nuclear waste treatment facilities, and we could see them in the decades to come.”

“While our goals are to improve nuclear security, I find it interesting that there is a two-way relationship between this research and astrophysics. We were inspired by neutron star collisions, and our research can have an impact about how astrophysicists look for signs of nuclear synthesis, the creation of elements in stars, to better understand how elements heavier than iron, including those essential to life, were made.

The work is published in the journal Physics letters B.