Researchers turn liquid nuclear waste into stable solids using engineered minerals

Researchers in Manchester, England, have developed two promising methods to capture 99% of dissolved technetium-99, a radioactive byproduct of nuclear fuel production.

In the first experiment, scientists locked the isotope directly into the structure of an engineered mineral, offering a way to convert radioactive liquid waste into a stable solid for long-term disposal.

In a separate study, the team used a mineral found in human bone alongside a nuclear medicine compound to trap 99% of the contaminant. This technique could help stop radioactive pollution from spreading through groundwater at legacy nuclear sites.

The experiments at the National Nuclear User Facility’s RADER laboratories targeted a long-lived byproduct of nuclear fuel production and reprocessing. Technetium-99 can move easily through water and soil, making it difficult to contain at legacy nuclear sites such as Sellafield in the UK and Hanford in the US.

Trapping technetium as a mineral forms

In the first study, the researchers used an engineered mineral known as a layered double hydroxide. They found that technetium-99 could become part of the mineral’s structure as it formed.

The study provides the first evidence that this type of mineral, already used in other areas of environmental remediation, can directly incorporate the isotope.

The approach could be used to treat liquid effluents generated during nuclear power plant operations.

It could also help turn radioactive liquids into stable inorganic solids during decommissioning, when operators need to prepare waste for long-term disposal.

Samuel Shaw, a professor of environmental mineralogy at the University of Manchester, said, “We’re not simply removing technetium from the effluent; we’re locking it up directly into a mineral structure to provide much greater long-term stability.”

“Understanding and optimizing these processes could open up new routes for treating radioactive wastes, and we are working with Sellafield through the Game Changers program to determine whether this new tool can help with the decommissioning of this legacy nuclear site,” he added.

A compound borrowed from nuclear medicine

In groundwater, the aim is to keep the isotope from spreading beyond contaminated areas. For that study, the Manchester team worked with Pacific Northwest National Laboratory and the Christie NHS Foundation Trust.

They tested methylene diphosphonic acid, or MDP, a compound used in nuclear medicine to bind the short-lived isotope technetium-99m to hydroxyapatite, a calcium phosphate mineral found in bone.

The researchers chemically reduced technetium-99 and combined it with MDP to form a soluble complex. They then introduced hydroxyapatite, which captured 99% of the complex from solution under conditions similar to those at legacy nuclear sites.

Testing the approach in flowing water

Further experiments suggested the phosphate-based method could also work in flowing groundwater. The researchers propose combining it with remediation techniques that form phosphate minerals at contaminated sites.

That combination could help hold the isotope in place over the long term and limit its spread through groundwater and soil.

“This study demonstrates new ways of capturing and immobilizing technetium in stable minerals, helping to build the toolkit needed for the safe cleanup of nuclear legacy sites,” said Callum Robinson, a radionuclide research associate at the University of Manchester.

Both 99% results came from tests in solution. The collaboration with Sellafield will examine whether the engineered mineral could help treat waste during decommissioning at the site.

Source: https://interestingengineering.com/energy/new-method-locks-technetium-99