After the recent earthquake and tsunami that struck Japan, and the resulting chaos that surrounded the Fukushima power plant, nuclear energy is once again causing a stir. Countries around the world are re-examining their nuclear plants, and Germany and Switzerland have even gone so far as to pledge the closure of all of their nuclear plants.

Of the numerous radioactive waste materials produced during fission, one of the most long-lived is I. As the human thyroid gland requires iodine, it is therefore possible that long term exposure to I will result in the radioisotope accumulating to dangerous levels.

At present I is largely disposed of in the sea, under the expectation that mixing with harmless I will dilute the radioisotope to safe levels. However, methods of storing I have been proposed. One such method involves locking the iodine up as solid lead iodovanadate, Pb(VO)I. Unfortunately the production of Pb(VO)I can take several hours, requiring high temperatures and pressures. In addition, because iodine is volatized at high temperatures the reaction must be performed in a sealed container.

With this is mind a team of researchers from the University of Sheffield set out to design a quick and easy method of producing Pb(VO)I [Stennett et al., J Nucl Mater (2011) doi:10.1016/j.jnucmat.2011.04.041]. After realizing that VO strongly absorbs microwave radiation at a frequency of 2.45 GHz, the team hypothesized that lead iodovanadate could be produced by mixing PbO, VO, and PbI in a domestic microwave oven.

After mixing the reactants, and placing them in the microwave oven, the team managed to produce a material composed 90 % Pb(VO)I and 10 % Pb(VO) in just 180 seconds.

How can the materials be produced so quickly, without a sealed container or high pressures? High pressures and a sealed container are usually required, because when heated in a conventional oven, the iodine at the surface volatizes, as the surface is much hotter than the core. In a microwave, as the penetration depth of the radiation is much larger than the sample, the core temperature is much higher. The reaction can then proceed without the iodine volatizing. Furthermore, as Pb(VO)3 is a poor microwave absorber compared to VO, once the final compound is formed, the temperature does not continue its rapid ascent.

Team leader Prof. Neil Hyatt explained that the team is now hoping to apply the same method to other materials. “Our method is potentially suitable for application to all halides, which are among the most difficult of radionuclides to immobilise due to their volatility at high temperature.  So we will be working to demonstrate the wider applicability of the approach as well as exploring the alteration behaviour of this class of apatites under repository relevant conditions.”

Stewart Bland