Russian scientists together with European colleagues found that, regardless of the oxidation state of plutonium in the precursor, precipitation with an ammonia solution produced tetravalent plutonium oxide nanoparticles of similar size and crystallinity. Moreover, the crystal structure of nanoparticles did not differ from the structure of large PuO2 crystals. The research results are published in the journal Nanoscience. During the operation of nuclear reactors, radioactive waste is inevitably generated, among which isotopes of plutonium are one of the longest-lived. By the end of 2014, there were about 2,400 tons of plutonium in 33 countries, and over the past ten years, its amount has been growing at a rate of almost 50 tons per year. Many countries dispose of nuclear waste by burying it underground in special containers. However, researchers still do not know for sure what happens to plutonium compounds in nuclear waste and in nature over the years.
Basic environmental studies of the properties of plutonium compounds will help to understand and predict what happens to radioactive isotopes over time. Evgeny Gerber with colleagues from the Moscow State University named after M.V. Lomonosov and institutes of European countries investigated the structure and properties of nanoparticles of plutonium oxide PuO2 - a compound that is often formed as a result of geochemical reactions with this element. Nanoparticles were synthesized by precipitation with an ammonium solution from different precursors: three-, four-, and pentavalent pluton compounds, as well as at pH 8 and strongly alkaline media, in which this value was higher than 10. The samples obtained were examined using a high-resolution transmission electron microscope and a number of X-ray methods using synchrotron radiation
The experimental methods and theoretical calculations used gave similar results. Regardless of the precursor and the acidity of the medium, only nanoparticles of tetravalent plutonium oxide PuO 2 with the same size and crystallinity were obtained. Their diameter ranged from 2.3 to 3.2 nanometers, but, despite their small size, the crystal structure was only slightly different from the structure of bulk PuO2.
The findings are important for understanding the chemistry of plutonium under real-world conditions: according to the authors, the study may prove useful in improving the safety of radioactive waste storage facilities.
In addition to nuclear energy, the law of radioactive decay can be used to determine the age of objects, including the Earth.