Transuranic waste is typically waste that is contaminated with man-made radioactive elements which are heavier than uranium (meaning the elements have higher atomic numbers than uranium on the Periodic Table of the Elements). Since they come after uranium on the periodic table, they are referred to as “transuranic”. The concentration of these transuranic elements in the waste determines whether it is transuranic (TRU) waste or low-level waste.
More than 70,000 containers of this waste (sometimes referred to as suspect TRU waste) were stored under a layer of dirt in the in the 1970’s and 1980’s, in the 200 Area Low-Level Burial Grounds of the Hanford Site. The intention was to retrieve the waste (which is why sometimes it is also referred to as retrievably-stored waste) at a later date when a national repository was established to accept transuranic waste.
With the 1999 opening of the Waste Isolation Pilot Plant (WIPP) outside of Carlsbad, New Mexico, TRU waste from Hanford is now being retrieved, packaged to meet WIPP’s acceptance criteria, and shipped to WIPP for permanent disposal.
The waste was stored in boxes and 55-gallon and 85-gallon drums. The waste consists of tools, clothing, and other materials needed during the plutonium production mission at Hanford. As the waste was expected to be dug up when it was originally stored in the 70’s and 80’s, a typical TRU waste trench consists of several levels of drums stacked on asphalt pads, separated with plywood, draped with tarps, and then covered with dirt.
During retrieval, crews unearth the drums and boxes, check for the stability of the container holding the waste, and determine the level of radioactivity within the container. If the container is damaged or corroded, it must be carefully placed into a second container called an overpack, so that the materials don’t spill onto the ground during removal from trenches. The stability of the containers holding the waste varies. In some trenches, most of the containers are in good shape and can be safely removed without the need for an overpack. In other trenches, most containers are damaged or corroded requiring an overpack.
While most transuranic elements emit alpha particles, which are the least penetrating form of radiation where a sheet of paper or the outer layer of skin will protect workers, some TRU waste drums require special handling to protect workers from inhaling the particles. Because of this, crews often work in protective clothing and breathing equipment before they can put the containers into overpacks for safe removal from the trench.
Because the definition of transuranic waste has changed over time, only about half of the retrievably-stored waste is considered transuranic waste. The other half is low-level waste. The TRU waste is shipped to WIPP for disposal. The low-level waste is treated as necessary and disposed at Hanford.
If the container is determined to contain TRU waste, it has to go through a certification process before it can be shipped to WIPP. The process involves x-raying of the container to determine if any prohibited items such as liquids are inside. If the prohibited items are identified they are removed at the appropriate facility at Hanford. The concentration of transuranic elements in the container is measured (assayed) to verify that the waste is TRU waste. Once certified for shipment, the waste can be packaged for safe transportation to New Mexico. It’s estimated that more than 1200 shipments of waste will leave Hanford for the WIPP during the TRU retrieval program. As of 2009, more than 400 shipments of TRU waste have been transported off the Hanford Site, and the equivalent of over 46,000 drums of waste has been removed from the ground.