VITRIFICATIONAnd Its Use in Treating Hazardous Waste

HAZARDOUS WASTE

• There are several radioactive/hazardous waste treatment plants across the globe

• The soon-to-be largest facility is the Hanford site in Washington, expected completion 2019

• 50+ million gallons of nuclear waste are stored here in underground tanks• By-product of plutonium production during World War II and the Cold War era

• Fear of tanks leaking launched new thoughts on treatment/containment

Innovative way to treat radioactive waste is by VITRIFICATION

VITRIFICATION

• Turning a substance into glass

• Usually done by rapidly cooling (through the glass transition phase) an amorphous material below the threshold temperature

• Two methods of vitrification as it applies to treating waste• Single step method• Step-wise method

• Most common• AVM (Atelier de Vitrification Marcoule)• Developed in 1978

AVMBASIC METHOD

CALCINER

• Tubular kiln with a slight incline that rotates about 30 rpm1

• Liquid waste is fed into the kiln along with calcinating additives

• The additives main job is to covert the liquid radioactive waste into a granular solid by evaporating the waste in the fluidized bed of the vessel

• Where does the evaporated waste go?

AVMBASIC METHOD

SCRUBBER

• Air pollution control device used to remove the particulates and/or gases from the exhaust stream

• Stream is made of gases from the calciner and melter, which are exhausted through the calciner and treated in the scrubber

• Traps the particles and dissolves them in a continuous flow of boiling nitric acid

• This solution is recycled to the calciner

AVMBASIC METHOD

MELTER

• The granular solid from the calciner is fed directly into the melter

• A melter is a melting furnace, usually metallic or ceramic

• Heated by medium-frequency induction to temperatures of about 1150oC

• Along with the granular waste, fragmented glass is also fed into the melter

• The glass and radioactive waste mixed at a high temperature will bond together

CERAMICMELTER

Heated by induction

Some have a life span of about 5 years, some melters only lastsix months2

AVMBASIC METHOD

STEPS AFTER MELTER

• Product is poured into an capsule-like container with a stainless steel liner.

• When cooled, it solidifies into a glass that is extremely resistant to water.

• The canisters have lids welded onto them, are washed, then double checked for contamination on the outside surface via a swabbing machine before being put into storage.

• The process of vitrification allows for the immobilization of waste for thousands of years. 3

The melted product is poured into an encapsulation container with a stainless steel liner. When cooled, the melt solidifies into the glass. After the glass is formed, it is extremely resistant to water. The canisters with the fission that were made into glass are closed with a swab machine and are transferred to a ventilated storage area for safety. The process of vitrification allows for the immobilization of waste for thousands of years [1].

[1] "Waste Form Release Calculations for the 2005 Integrated Disposal Facility Performance Assessment" (PDF). PNNL-15198. Pacific Northwest National Laboratory. July, 2005. Retrieved 2006-11-08.

SUMMARY

• Vitrification is the process of making glass out of an amorphous material

• This is a relatively simple process, even when treating hazardous waste, but requires a lot of time and money especially considering the life span of some equipment and the safety measurements involved

• Although the glass produced is still hazardous, it is much more stable than liquid radioactive material and will not leak into the soil and nearby water systems

SOURCES

1) Baehr, W. "Industrial Vitrification Processes for high-level liquid waste solutions." IAEA. APRIL 1989: n. page. Print.

2)  Sawai, Masako. "Rokkasho Reprocessing Plant: Vitrification Problems Continue ." Citizens' Nuclear Information Center. n.d. n. page. Web. 14 Apr. 2013.

3) "Waste Form Release Calculations for the 2005 Integrated Disposal Facility Performance Assessment" (PDF). PNNL-15198. Pacific Northwest National Laboratory. July, 2005. Retrieved 2006-11-08.

4) Images: http://www.ntec.ac.uk/nuclear_intro/fuelcycle.html, Baehr, W. "Industrial Vitrification Processes for high-level liquid waste solutions." IAEA. APRIL 1989: n. page. Print., and Sawai, Masako. "Rokkasho Reprocessing Plant: Vitrification Problems Continue ." Citizens' Nuclear Information Center. n.d. n. page. Web. 14 Apr. 2013., respectively.