A
novel way to immobilize radioactive forms of iodine using a microwave,
has been discovered by an expert at the University of Sheffield.
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 15.7 million 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.
Professor
Neil Hyatt, from the University´s Department of Materials Science and
Engineering, has now found a way of locking up iodine radioisotopes in a
durable, solid material suitable for ultimate disposal, like lead
iodovanadinite(Pb5(VO4)3I). The research, which was published in the
Journal of Nuclear Materials, demonstrates how his simple, inexpensive
and rapid method can be done at atmospheric pressure.
Professor
Hyatt and his team created a solid material for immobilization of
iodine with the formula Pb5(VO4)3I, by heating a mixture of lead iodide,
lead oxide and vanadium oxide.
Previously,
this has only been achieved using high pressure and a sealed container,
because iodine is volatilized at high temperature. However, using the
knowledge that vanadium is a good absorber of microwaves at 2.45 GHz –
the frequency used in domestic microwave ovens – the team were 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
2.45 GHz microwaves, so once this is formed, the sample cannot absorb
microwaves, so the temperature does not get high enough for the iodine
to volatilize.
Iodine-131
was the harmful gas emitted from the Fukushima power plant in Japan
following the earthquake and tsunami last month, 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 immobilization in a solid material,
which could be rapidly deployed in an accident scenario.
Professor
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.”
