October 21, 2019

An international team of scientists, led by the Helmholtz Zentrum Dresden-Rossendorf (HZDR), have found a new compound of plutonium with an unexpected, pentavalent oxidation state. This new phase of plutonium is solid and stable, and may be a transient phase in radioactive waste repositories
Plutonium, has been shown to be transported by groundwaters from contaminated sites for kilometres in the form of colloids, which are formed by interaction with clay, iron oxides or natural organic matter. A team of scientists lead by HZDR studies the chemistry of actinides under environmentally relevant conditions, by synthesizing such compounds, and then studying their electronic and structural behaviour both with advanced synchrotron X-ray methods experimentally as well as theoretically.
The latest paper of the international team shows how an experiment seemingly gone wrong leads to a breakthrough: the discovery of a new stable form of plutonium.
It all started when Kristina Kvashnina, physicist from HZDR and based at the ROBL beamline (Rossendorf beamline) at the ESRF, and her team were trying to create plutonium dioxide nanoparticles using different precursors to be studied at ROBL. When they used the Pu (VI) precursor, they realized that a strange reaction took place during the formation of the plutonium dioxide nanoparticles. “Every time we create nanoparticles from the other precursors Pu(III), (IV) or (V) the reaction is very quick, but here we observed a weird phenomenon half way”, explains Kvashnina.
Stable phase of Pu(V)! – no, it is impossible, it doesn’t exist, the synthesis must have gone wrong”, said, at the time, the team of chemists, from the Moscow State University when they all together looked at the data. “Chemists were in complete disbelief, but the results were quite clear”, Kvashnina adds.
Many scientists work on prediction of what happens to the nuclear waste in million years. “It is a difficult task and only theoretical predictions are possible, but the existence of this new Pu(V) solid phase, which is stable, will have to be taken into account from now on. It will change, for sure, the theoretical predictions of plutonium behaviour in the environment over a period of million years”, concludes Kvashnina.
The ESRF (European Synchrotron Radiation Facility) is the world’s most intense X-ray source and a centre of excellence for fundamental and innovation-driven research in condensed and living matter science. Located in Grenoble, France, the ESRF owes its success to the international cooperation of 22 partner nations. The ESRF can produce X-rays 100 billion times brighter than the X-rays used in hospitals. These X-rays, endowed with exceptional properties, are produced by the high energy electrons that race around the storage ring, a circular tunnel measuring 844 metres in circumference.
(Source: ESRF – Image: Landschaft der Forschungsinfrastrukturen)