An engineer at Sheffield University has developed a novel way to immobilise radioactive forms of iodine using microwave radiation.
Iodine radioisotopes are produced by fission of uranium fuel in a nuclear reactor. Radioactive iodine is of concern because it is highly mobile in the environment and selective uptake by the thyroid gland can pose a significant cancer risk following long-term exposure.
Furthermore, iodine-129, which is a type of radioactive iodine, has an extremely long half life of 15.7m years, so is one of the most significant long-term hazards faced by the population due to its emission during the geological disposal of nuclear waste.
Prof Neil Hyatt, from the university’s Department of Materials Science and Engineering, has now developed a way of locking up iodine radioisotopes in a solid material suitable for ultimate disposal, such as lead iodovanadinite (Pb5(VO4)3I).
To do so, Prof Hyatt and his team created a solid material for immobilisation of iodine with the formula Pb5(VO4)3I, by heating a mixture of lead iodide, lead oxide and vanadium oxide.
Previously, this had only been achieved using high pressure and a sealed container, because iodine is volatilised at high temperature. However, using the knowledge that vanadium is a good absorber of microwaves at 2.45GHz, the team was able to heat the mixture of chemicals in a microwave oven to produce Pb5(VO4)3I in about three minutes.
The key to the method’s success is that Pb5(VO4)3I is a poor absorber of 2.45GHz microwaves, so once this is formed, the sample cannot absorb microwaves, so the temperature does not get high enough for the iodine to volatilise.
Iodine-131 was the harmful gas emitted from the Fukushima power plant in Japan following the recent earthquake and tsunami, and was a significant contributor to the health effects from open-air atomic bomb testing in the 1950s, and was also emitted during the Chernobyl disaster.
It is hoped the new research will reduce the public health impact associated with the release of radioactive iodine to the environment by providing a simple and inexpensive method of immobilisation in a solid material, which could be rapidly deployed in an accident scenario.
Prof Neil Hyatt, said: ’In spent nuclear fuel, the iodine is not immobilised, so once the containment is breached it simply gets dispersed. At present, iodine-129 released by nuclear fuel reprocessing is discharged direct to the Irish Sea off the coast of Sellafield. Substantial quantities of this radioisotope were also released into the sea off the coast of Japan in the Fukushima incident. Our new method offers a way of safely and rapidly containing this radionuclide, reducing the potential long-term impact on human health from discharge to the environment.’