Disposal volume increase kept within 20%; technology transferred to Green Radiation

Son Seong-jun, a senior researcher at the Korea Atomic Energy Research Institute, measures the compressive strength of a cement solidified body containing carbonized spent resin. [Korea Atomic Energy Research Institute]
Son Seong-jun, a senior researcher at the Korea Atomic Energy Research Institute, measures the compressive strength of a cement solidified body containing carbonized spent resin. [Korea Atomic Energy Research Institute]

A path has opened to safely solidify and dispose of radioactive waste that has long been stored temporarily at nuclear power plants due to a lack of viable disposal methods. The technology carbonizes the waste to limit volume expansion while preventing radioactive materials from leaking out, and is expected to be used in handling radioactive waste generated during nuclear power plant decommissioning.

The Korea Atomic Energy Research Institute announced Wednesday that a research team led by Dr. Im Seung-ju of its Nuclear Facility Clean Technology Development Division had developed a solidification technology that carbonizes spent radioactive ion-exchange resin and then hardens it using cement or geopolymer, and transferred the technology to Green Radiation. The transfer was made under terms of a fixed licensing fee of 100 million won ($72,200) and a running royalty of 2 percent of sales.

Spent ion-exchange resin is a filter material used to purify radioactive liquid waste generated during the operation and decommissioning of nuclear power plants. Once the resin has absorbed radioactive materials and can no longer be used, it must be solidified and permanently disposed of.

The challenge is that spent resin expands easily when it absorbs water. Mixing large quantities into cement causes internal cracking, making it difficult to meet the acceptance criteria of the Gyeongju low- and intermediate-level radioactive waste disposal facility. Reducing the resin content, on the other hand, increases the volume of the solidified body and raises disposal costs.

The research team solved the problem using a carbonization technique that thermally decomposes the spent resin by heating it in an oxygen-free environment. By identifying optimal temperature and processing conditions, the team suppressed moisture absorption and swelling in the resin.

In tests, carbonized spent resin was incorporated at up to 40 percent of the total weight of the solidified body and hardened with both cement and geopolymer. The results met all major acceptance criteria at the Gyeongju disposal facility, including compressive strength, thermal cycling, immersion, leaching and free liquid tests.

Spent ion-exchange resin before carbonization (left) and after carbonization (right). [Korea Atomic Energy Research Institute]
Spent ion-exchange resin before carbonization (left) and after carbonization (right). [Korea Atomic Energy Research Institute]

Particularly notable is that even with binder content reaching up to 60 percent of the total weight, the final solidified body's volume increased by no more than 20 percent compared to the carbonized spent resin alone, minimizing the growth in disposal volume during the solidification process.

The technology also passed leaching tests used to assess the risk of radioactive materials escaping into the environment. The cesium leaching index was 9.18 for the cement solidified body and 10.41 for the geopolymer body, while the cobalt leaching index came in at 10.43 and 13.77, respectively — all well above the disposal acceptance threshold of 6.0.

The technology is significant in that it achieves both stable solidification of spent resin and minimization of disposal volume at the same time. It is expected to help reduce disposal costs not only for spent resin currently held in temporary storage at nuclear power plants, but also for radioactive waste produced during plant decommissioning.

Green Radiation, the technology recipient and an affiliate of the Korea Atomic Energy Research Institute, plans to use the development to enter the spent ion-exchange resin solidification processing business.

The research team has completed domestic patent applications and is pursuing patents in the United States, Japan, Europe, China and the UAE.

"The significance lies in being able to carbonize difficult-to-handle radioactive spent resin for stable solidification, reducing both the volume and cost of waste that must be permanently disposed of," Im said.


nbgkoo@heraldcorp.com