A new serious problem with stainless steel canisters for nuclear wastes

Schematic of a stainless steel nuclear waste canister, with radioactive particles (purple) trapped inside in glass and the acidic spiral that starts when water, steel, and glass are brought together. Guo et al/Nature Materials

Stainless steel may not be the best choice for storing nuclear waste. https://newatlas.com/energy/stainless-steel-storing-nuclear-waste/

By David Szondy January 28, 2020 A new study by researchers at Ohio State University suggests that stainless steel may not be the best choice for containing high-level nuclear waste. By simulating long-term storage conditions, the team found that the storage materials interact with each other more than previously thought, causing them to degrade faster.

The storage of nuclear waste is more than a perennial political football, it is an existential problem. Whatever one’s opinions about nuclear power or weapons, there are thousands of tons of nuclear waste temporarily stored around the world, meaning that a way must be found to store it all

safely in the long term.

The most important type of nuclear waste is the high-level waste left over from reprocessing nuclear fuel or from nuclear weapon production. Such waste is made up of a complex mixture of radioactive isotopes with half-lives ranging from years to millennia. Though reactors have been operating all over the world for over 75 years, only Finland has started to build a permanent storage facility for such very dangerous waste.

That may show a remarkable lack of political will or even courage, but perhaps this reluctance will turn out to be serendipitous. That’s because the favored way of storing high-level waste is to vitrify it. That is, to mix the isotopes with molten glass or ceramics to form a chemically inert mass that can be sealed in stainless steel canisters before being sealed in an underground storage facility.

That plan may now have to change if the Ohio study is correct. Led by Xiaolei Guo, the team took glasses and ceramics and put them in close contact with stainless steel in various wet solutions for 30 days in conditions similar to those that would be found in the proposed US Yucca Mountain nuclear waste repository.

In the real-life scenario, the glass or ceramic waste forms would be in close contact with stainless steel canisters,” says Xiaolei. “Under specific conditions, the corrosion of stainless steel will go crazy. It creates a super-aggressive environment that can corrode surrounding materials.”

They found that the steel interacted with the glass or ceramic to produce severe and localized corrosion that both damaged the steel and corroded and cracked the glass and ceramics. According to the team, this is because the iron in stainless steel has a chemical affinity with the silicon in glass, accelerating corrosion.

This indicates that the current models may not be sufficient to keep this waste safely stored,” says Xiaolei. “And it shows that we need to develop a new model for storing nuclear waste.”

The research was published in Nature Materials. Source: Ohio State University

January 30, 2020 - Posted by Christina Macpherson | Reference, safety, USA, wastes

2 Comments »

Heat released by a spent fuel assembly
A uranium oxide (UOX) fuel assembly weighs approximately 500 kg. Five years after being unloaded from the reactor, it emits heat equivalent to around a dozen 100 watt light bulbs. This heat release steadily tails off, falling to 85 watts after 300 years. Spent fuel assemblies must be cooled prior to disposal, either in a pool or in dry silos.
https://www.radioactivity.eu.com/site/pages/Spent_Fuel_Heat.htm

A dozen 100 watt light bulbs is quite a bit of heat actually in an 8 foot by 5 foot nuclear waste canister.

There is a full spectrum of alpha emitters, beta emitters, and gamma emitters from the many radionuclides present in high level, nuclear waste canisters.
The radioactive material emits radiation that interacts with the canister-case materials and other materirials in the cask, to create gas. Any water present will generate hydrogen gas, from radiation attacking water molecules.

There are the corrosion and embrittling aspects of the radiation interaction, with the steel shells that contain the waste.

Nuclear waste storage, is a fantasy world of convenient omission

Comment by kw | January 30, 2020 | Reply
- kw – the heat present is not an issue for the stainless canister. Hydrogen gas might well be, if it formed in substantial quantities. However, 1) there is little or no water in the new canister when it is sealed, and 2) there is dry air in the canister, and the oxygen from that and from the radiolysis (2.H2O 2.H2 + O2) would recombine with the hydrogen fast enough to prevent it from being available to cause embrittlement. So I don’t see the “convenient omission” you refer to.
  
  Comment by js | February 6, 2020 | Reply