The Hanford Nuclear Reservation was established in Washington State in 1943 as part of the Manhattan Project and the Cold War to produce plutonium for nuclear weapons. The Manhattan Project was a research and development undertaking led by the United States to produce the first nuclear weapons.
This production generated millions of gallons of radioactive and other hazardous wastes, which are stored in 177 underground tanks. During WWII the alloying elements needed to make stainless steel were unavailable, so the tanks were made of carbon steel. A number of them have begun to leak radioactive wastes into the ground water.
The U.S. Department of Energy (DOE) is responsible for managing and cleaning up the waste. By removing the radionuclides that contribute most of the radioactivity, the DOE plans to retrieve the waste from the tanks to produce high-level waste (with more than 90% of the radioactivity and less than 10% of the total volume) and low-activity waste.
The high-level waste and at least one-third of the low-activity waste are to be vitrified (immobilized in glass waste forms). The high-level fraction is slated for disposal in a deep geological repository at a site to be determined. The low-activity waste is intended to be disposed in near-surface facilities.
Blending Radioactive Waste with Cement, Slag, and Fly Ash is one Cleanup Solution
To treat the remaining portion of the low-activity waste, DOE plans to build an additional facility for “supplemental treatment.” While many stakeholders have assumed vitrification will be used, DOE is also considering other approaches.
One of these is to mix the radioactive waste with cementitious materials to make a waste-form grout. The Government Accountability Office recommended that “DOE develop updated information on the performance of treating [low-activity waste] with alternate methods, such as grout, before it selects an approach for treating supplemental [low-activity waste].”
These grouts are designed to immobilize not only the radioactive waste, but also any toxic heavy metals and other hazardous materials that may be present. This approach has been used successfully at the Savannah River Site in South Carolina, where low-activity waste is mixed with portland cement, slag cement, and fly ash to make Saltstone. The liquid Saltstone is poured into concrete vaults, where it sets and hardens. When a vault is full, it is covered with a concrete cap and layers of soil.
As yet, the DOE and the State of Washington have not agreed on a mutually acceptable method for treating the supplemental waste. Congress has called for an evaluation of the available technologies.
Beton’s Dr. Rachel Detwiler has been asked to serve on the National Academy of Sciences committee overseeing this evaluation.