How is nuclear waste transformed into glass logs?

[Mariko]

I was watching this news program about nuclear waste treatment plants in which the nuclear waste is somehow turned into glass logs. Would someone mind explaining this process-how would you turn nuclear waste to glass logs?

 

[Astronuc]

The process is known as vitrication.

In commercial nuclear fuel, the uranium bearing fuel is in the form of ceraminc UO₂, a metal oxide. Most of the fission products are entrained as metal oxides, although metal inclusions are found, and there are other elements like I, Br (halides) and Xe, Kr (noble gases) present. The fuel and fission products are encased/enclosed (or otherwise hermetically sealed) in a tube (cladding) of Zirconium alloy (usually, but it could also be a stainless steel) which is seal-welded at both ends (hopefully) with barstock of the same alloy comprising the cladding.

In vitrification, the fuel is oxidized, and then mixed with glass materials so as to form a type of glass which entrains any fuel (if it is not recovered, as in recycle or reprocess) and fission products. The vitrified was is then encapsulated in a corrosion resistant material (e.g. stainless steel or nickel-based alloy), which can then be placed in a repository.

A related process is Synroc, in which a composition representing thermodynamically stable synthetic igneous rock is used instead of glass. The theory is that Synroc is less likely to allow fission products and transactinides to leach into the envirnoment if there is a subsequent breach of the repository and waste containers.

 

[selfAdjoint]

Astro, I have read that using IFR technology the "high-rad' actinides in waste could be converted to "low-rad" and then vitrified to form a block that would be safe and stable and whose remaining radiation would decay to background in some reasonable span of time.

Is this so? Can you give any evaluations or details?

 

[Morbius]

Astro, I have read that using IFR technology the "high-rad' actinides in waste could be converted to "low-rad" and then vitrified to form a block that would be safe and stable and whose remaining radiation would decay to background in some reasonable span of time.

Is this so? Can you give any evaluations or details?

selfAdjoint,

If you want the radiation to decay in a relatively short period of time - then you want
to leave that part of the waste as "high-rad". The half-life is inversely proportional
to the activity.

Ideally, all the actinides should be recycled back to a reactor to be used as fuel.

The only thing that should find its way to the waste stream should be the fission
products. The longest lived fission product of any consequence is Cesium-137
which has a half-life of 30 years. So in 20 half-lives; about 600 years; the activity
of the waste will be less than the material that was originally dug out of the ground.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Astro, I have read that using IFR technology the "high-rad' actinides in waste could be converted to "low-rad" and then vitrified to form a block that would be safe and stable and whose remaining radiation would decay to background in some reasonable span of time.

Is this so? Can you give any evaluations or details?

What comes to mind immediately is 'actinide burning'.

The objective of the IFR was to 'burn up' or utilize the longer lived transuranics, e.g. isotopes of Pu, Cm, Am so that they would not be around for 1000's, 10 000's or 100 thousands of years. Instead they would be fissioned to shorter lived radionuclides as is the case with U-235 and Pu-239, and the fission products decay rapidly to inert (stable, non-radioactive) nuclides in a vitrified form in a protected repository.

At the same time, the energy produced is converted to electricity.

Let me dig up the details.

 

[Mariko]

Thanks for the info- Appreciated and wonderful as always!