We have been covering a lot of issues involving disposal of nuclear waste. There is a process called “vitrification” that helps prepare nuclear waste for disposal. The specific meaning of the term is the process of turning something into a glass. For substances that have a glass phase, vitrification would consist of causing the substance to undergo phase transition to its glass state. Chemical processes can also result the creation of a glass. A more general use of the term can apply it to embedding a material in a glassy matrix. This is the sense in which the term is used when referring to the vitrification of nuclear waste.
Nuclear waste is mixed with chemicals/materials that form glass such as sand. Then calcinating chemicals are mixed in to remove the water which would negatively affect the glass. Next, the mixture is continuously fed into a heating furnace and melted along with pieces of glass. The resulting molten glass is then poured into canisters where it solidifies into a hard material resembling obsidian. The glass should be stable for thousands of years and will prevent leaching of waste by ground water. Vitrification can also significantly reduce the volume of the waste which is very important because space is at a premium for temporary or permanent storage.
There is another technique called bulk vitrification in which electrodes are inserted into soil contaminated with nuclear waste. Sufficient electrical energy is fed to the electrodes to heat and melt the soil and the waste it contains. It hardens in a glass which stabilizes the waste. If left in the ground, the glass is less dangerous than the original contaminated soil. If necessary, the glass can be dug out and in much easier to handle that the contaminated soil would have been. This would be very useful in seriously contaminated areas such as the Hanford Nuclear Reservation.
Bechtel National, Inc. is currently designing, constructing, and commissioning the largest radioactive treatment plant in the world at the Hanford Reservation. The United States Department of Energy contracted the creation of the plant, in part, to deal with the enormous amount of waste currently stored at Hanford in leaking underground tanks. The Bechtel plant will be using the vitrification process and heat the vitrification mixture to over two thousand degrees Fahrenheit.
Recently, a memo, written by Gary Brunson to Hanford DOE officials, “listed 34 instances in which Brunson believed Bechtel provided design solutions or technical advice that was factually incorrect, not technically viable, not safe for future vitrification plant operators or otherwise seriously flawed.” The memo called for Bechtel to be immediately replaced as the agency responsible for writing the design requirements for the plant. Bechtel and DOE have managed to agree on the resolution of the issues raised in the memo and the project is going forward.
Although vitrification is a useful treatment for nuclear waste in theory, in practice, as always, the devil is in the details.
