IDAHO FALLS, Idaho - A scaled model of the Integrated Waste Treatment Unit (IWTU) performed exceptionally well during a recent month-long demonstration, continuing EM and cleanup contractor Fluor Idaho’s progress in confirmatory testing and preparations to start up the facility.
Engineers frequently adjusted the operating parameters of the pilot plant at the Hazen Research facility in Colorado, including the simulant feed rate, temperature, and product particle size to assess the process under varying conditions. Despite the intentional changes, the pilot plant produced the desired dried granular waste product. It treated the same simulant waste used in prior demonstrations at the IWTU.
“We operated over a wide range of operating conditions to assess performance and the pilot plant handled all conditions as designed," said IWTU Technical Issues Resolution Project Manager Leo Thompson. “This testing confirms that the process of converting simulated waste into a carbonate form works over a wide range of conditions. We learned a tremendous amount about the behavior of the process at different conditions, which we can apply to the IWTU for its next demonstration run."
Thompson said the pilot plant continued to produce wall-scale on the interior of its reaction vessel, just like the IWTU did in its six demonstrations. But the varying conditions revealed trends that help the team understand the formation mechanisms. Under some conditions, minimal scale formed. The scale, resembling bark, has the potential to produce fluidization challenges in the IWTU, but the Hazen testing is giving engineers a better understanding why it forms, if and how it can be minimized, and its effect on the waste treatment process.
“We have a better idea of the factors that control wall-scale formation," said Thompson. “Importantly, the wall-scale had no effect on the fluidization inside the Hazen reaction vessel."
The IWTU will use a fluidized bed steam-reforming process to treat the remaining 900,000 gallons of liquid radioactive waste from the Idaho Site’s underground tank farm. The facility’s primary reaction vessel, the Denitration Mineralization Reformer (DMR), contains billions of tiny beads kept in a fluidized state with the help of superheated gases. Liquid waste enters the fluidized bed, coating the beads like the formation of pearls. The waste product is transferred to stainless steel canisters and ultimately concrete vaults.
Engineers are modifying IWTU. They completed work to install a new ring header with an improved design in the DMR using an 18-inch manway. The ring header injects gases and steam into the reaction vessel to fluidize the beads that form during waste treatment. The ring was damaged in a prior demonstration. The engineers are developing the improved design using computer simulations, pilot testing, and input from industry experts.
Engineers will reconfigure the bottom of the DMR to a conical shape to prevent a prior problem from repeating: the creation of “sand castles" that greatly affect the fluidization of the waste product during demonstrations. The DMR’s present shape results in the creation of “dead zones," which allow treated product to settle and accumulate at the vessel’s bottom. The new design will be tested in the pilot plant and installed in the IWTU this fall, with another demonstration to follow.
Source: U.S. Dept. of Energy, Office of Environmental Management
