Professor Hojin Ryu and his research team from the Department of Nuclear & Quantum Engineering have successfully developed a new method to immobilize iodine-129 (I-129), a radioactive isotope of iodine, through a cold-sintering process. The results were published in the Journal of Hazardous Materials as “Non-Volatile Immobilization of Iodine by the Cold-Sintering of Iodosodalite” on November 11.

I-129, created mainly from the processing of used fuels (fission reactions of uranium and plutonium in nuclear reactors), is the longest-lived isotope of iodine, with a half-life of 15.7 million years. It is also the major contributor to radioactive doses in repositories and therefore requires more action regarding its storage and management.

Many methods to immobilize I-129 compact the isotopes into matrices. Among these, a ceramic-based matrix called sodalite was the topic of study for Professor Ryu’s research team, as it boasts a high loading capacity, simple processing, thermal stability, and chemical durability.

A cold-sintering process is conducted in low temperatures and uses a transient liquid. During the process, two powder mixtures, a melting point depressant with a low melting point (A) and one with a higher melting point (B), is heated until A melts while B remains solid. Then, while the temperature is kept constant, A diffuses through B and becomes solid again. When performed with appropriate conditions, a uniform structure can be created.

However, other conventional methods either use high temperatures, which has the risk of more than 50% of the volatile radioactive isotope vaporizing into the atmosphere, which would be detrimental to human health, as it can cause thyroid cancer, and the environment, or require additional material such as glass and cement. Furthermore, these methods consume large amounts of energy and require long processing periods.

The cold-sintering method developed by the research team demonstrates immobilization of I-129 under low temperatures into a ceramic matrix without the use of additional material, resulting in no volatile loss of iodine up to 300°C.

Using this result as a basis, Professor Ryu’s research team plans to extend their research into more types of radioisotopes such as cesium.