AsianScientist (Jul. 29, 2016) – Scientists in Japan may have found a way to manage nuclear waste more easily, by converting two major radioactive isotopes found in nuclear waste into more easily managed isotopes. Their research was published in the journal Physical Letters B.
“Treating the nuclear waste generated by nuclear power plants and other facilities is a major problem around the world. There are two types—minor actinides, which can be dealt with using fission reactions, and fission products, for which more scientific research on nuclear reactions is needed,” said RIKEN chief scientist Dr. Hiroyoshi Sakurai, who is the head of the Radioactive Isotope Physics Laboratory at the RIKEN Nishina Center for Accelerator-Based Science in Japan.
A promising way to solve the problem of long-lived fission products is to transmute problematic isotopes into more manageable forms. Isotopes such as cesium 137 and strontium 90, with half-lives of around 30 years, can be transmuted either into stable nuclei that do not emit radioactivity, or into isotopes with short half-lives so that they will rapidly decay. However, as Sakurai noted, there is little data on these reactions.
Because these fission products do not capture thermal neutrons effectively, the group decided to use a process called spallation, where the collision involves high-energy protons or deuterons rather than neutrons. A deuteron is a stable particle that is composed of a neutron and proton.
The group also decided to use a reverse setup, colliding the cesium and strontium atoms into the protons and deuterons—which might be easier since the protons are lighter and easier to accelerate.
In the experiment, the group created a beam of the most common natural isotope of uranium, called uranium 238. In the Superconducting Ring Cyclotron, they accelerated uranium 238 to about 70 percent of the speed of light and smashed it into a beryllium target, causing it to fission into isotopes such as cesium 137 and strontium 90. These beams were then collided with proton and deuteron targets.
From their experiments, the researchers found that the spallation reaction was much more effective than previous methods in transmuting the two isotopes. They also found that the reaction was 20 percent more effective with deuterons than protons.
“We were happy to find that 89 percent of the cesium 137 atoms and 96 percent of the strontium 90 isotopes were transmuted to either stable nuclei or short-lived species with half-lives under one year,” said Dr. Wang He, the first author of the paper.
The article can be found at: Wang et al. (2016) Spallation Reaction Study for Fission Products in Nuclear Waste: Cross Section Measurements for 137Cs and 90Sr on Proton and Deuteron.
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Source: RIKEN; Photo: Pixabay.
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