Idaho’s IWTU resumes heat-up following repairs

February 2, 2023, 7:01AMRadwaste Solutions

The Department of Energy’s Office of Environmental Management (EM) said that heat-up of Idaho’s Integrated Waste Treatment Unit (IWTU) resumed in January. Crews began heating the IWTU in December in preparation of radiological operations, but the facility was shut down 10 days later after operators noticed a small leak of nonradioactive material inside one of the unit’s processing cells.

Located at the DOE’s Idaho National Laboratory Site, the IWTU is intended to treat Idaho’s 900,000 gallons of sodium-bearing liquid waste, converting it to a solid using a steam-reforming process.

After repairs were made to the IWTU equipment responsible for the leak, crews removed a partial obstruction that was in a line into the carbon reduction reformer, a key treatment vessel in the steam-reforming process, EM said.

Before and after photos show modifications made to the affected valve body in a cell of the IWTU at the INL Site. (Photo: DOE)

The leak: According to EM, the leak occurred during a normal purging process, which directs bursts of nitrogen through stainless-steel lines to prepare for the transfer of treated waste simulant.

Following the shutdown and cooldown of the IWTU, an investigation of the leak revealed a damaged valve body inside one of the facility’s two cells where dried, treated material will be transferred to long, stainless-steel canisters. Inspections of the damage indicated erosion of the valve body due to the interaction of alumina and nitrogen purges.

Alumina, a commonly used material in sandpaper, is introduced into the IWTU’s steam-reforming process to improve the movement, or fluidization, of dried waste material inside the facility’s primary reaction vessel. Inspections extended to other parts of the facility that have similar valves, but no other wear was noted.

To perform the repairs, welders installed a thick, stainless-steel plate over a hole that had formed in the valve body.

Next steps: EM said that moving forward, the canister-fill cell lines will be purged for a shorter duration to reduce the likelihood of wear to the valves.

EM also noted that the leak of nonradiological material allowed engineers to consider how they would respond in case of a similar event during radiological operations. Radiation exposure would be primarily managed by shielding and increasing the distance between the worker and the source of radiation. Contamination levels would be controlled though use of containment tents, ventilation, and cleanup.

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