UST and KAERI develop integrated process covering radioactive decontamination through waste liquid treatment; operating costs fall 13%, toxic environmental impact down 21% — technology expected to aid Wolsong Unit 1 decommissioning

From left: Miguta Faustin Ngulimi, a UST doctoral graduate; Kim Si-on, a UST integrated-course student; UST Professor Noh Chang-hyun; and Yoon Seok-min, a UST integrated-course student. [Provided by UST]
From left: Miguta Faustin Ngulimi, a UST doctoral graduate; Kim Si-on, a UST integrated-course student; UST Professor Noh Chang-hyun; and Yoon Seok-min, a UST integrated-course student. [Provided by UST]

South Korean researchers have developed a technology that sharply reduces the toxic chemicals used during nuclear power plant decommissioning while actually improving the removal of radioactive contaminants. By handling everything from radioactive decontamination to waste liquid treatment in a single integrated process, the technology is expected to lower both the cost and environmental burden of dismantling nuclear facilities.

The University of Science and Technology (UST) announced Wednesday that a research team led by Professor Noh Chang-hyun of its Korea Atomic Energy Research Institute (KAERI) School had developed an eco-friendly integrated decontamination technology that reduces toxic chemical use and treats radioactive waste liquid in one process.

Decontamination — the removal of radioactive contaminants that accumulate inside pipes — is an essential step in nuclear power plant decommissioning. Conventional decontamination methods, however, have long relied on large quantities of highly toxic chemicals and generate hazardous radioactive waste liquid even after the work is complete.

In heavy-water reactor coolant pipes in particular, an oxide layer containing radioactive cobalt (Co-60) builds up over time. That layer is considered a primary cause of radiation exposure for workers involved in nuclear plant maintenance and decommissioning.

Existing methods used hydrazine, a toxic substance, to dissolve the oxide layer, but fell short when it came to efficiently treating the waste liquid and solid waste generated after decontamination.

To address this, the research team developed an integrated process linking oxide layer removal, metal separation from waste liquid, and decomposition of residual toxic substances into a single continuous workflow.

To replicate conditions similar to actual nuclear plant piping, the team oxidized carbon steel pipes at 300 degrees Celsius for three weeks to form a cobalt-containing oxide layer, then verified the performance of the new decontaminant.

As a result, even after removing the copper component from the conventional decontaminant and reducing the hydrazine concentration to one-fifth of its original level, decontamination performance actually improved.

The new decontaminant dissolved roughly three times more iron in one hour than conventional agents, and its ability to remove cobalt — the source of radioactive contamination — also improved. Sludge generated during the decontamination process was reduced to less than half of previous levels.

The research team then adjusted the acidity of the remaining waste liquid to precipitate iron and cobalt into solid form for separation. They also developed a technique using hydrogen peroxide together with ultraviolet LED light to decompose the hydrazine remaining in the waste liquid.

The team confirmed that using hydrogen peroxide and ultraviolet LEDs simultaneously generates hydroxyl radicals with powerful oxidizing properties, significantly boosting the efficiency of toxic substance decomposition.

A schematic diagram of the eco-friendly integrated decontamination technology. [Provided by UST]
A schematic diagram of the eco-friendly integrated decontamination technology. [Provided by UST]

The technology also showed strong results in economic and environmental assessments. Total hydrazine use across the entire process fell by about 32 percent compared with conventional methods, operating costs dropped by roughly 13 percent, and toxicity-related environmental impact was reduced by approximately 11 to 21 percent.

The technology is expected to be applicable to the decommissioning of heavy-water reactors, including the permanently shut-down Wolsong Unit 1, as well as maintenance work at operating nuclear plants. Researchers said it can simultaneously reduce workers' radiation exposure risk and the burden of waste disposal by improving radioactive contaminant removal efficiency while cutting secondary waste generation.

Miguta Faustin Ngulimi, the UST doctoral graduate who led the research, said the team "improved decontamination performance without using a copper catalyst and while reducing the amount of toxic chemicals used," adding that the work "demonstrated that connecting decontamination and waste liquid treatment into a single process can simultaneously reduce waste generation and operating costs."

Professor Noh said the technology "can be applied not only to heavy-water reactor decommissioning such as Wolsong Unit 1, but also to other reactor types and operating nuclear plants," and pledged to "expand the technology into various industrial sectors requiring hazardous substance remediation, contributing to strengthening competitiveness in nuclear decommissioning."


nbgkoo@heraldcorp.com