The “Right Stuff” for Nuclear Waste Disposal Canisters

Blog by Joe Payer, Corrosion and Reliability Engineer

The “Right Stuff” for Nuclear Waste Disposal Canisters

The metal canisters that will hold the spent fuel or other high-level nuclear waste are part of Deep Isolation’s engineered barrier system; the canisters directly protect the waste from mechani­cal impact, exposure to the chemical environment, and contact with fluids. One of the key decisions then, to ensure the canister’s usefulness as a barrier, is the choice of material used. Our material selection process began with an extensive analysis of the peer-reviewed literature, over the course of months, which of course included examining test results and recorded observations and measurements. I was the lead as a senior corrosion engineer, but the entire technical team helped vet the choice of best material. Our decision is to use highly corrosion-resistant nickel-chromium-molybdenum (Ni-Cr-Mo) alloys which are very stable in the deep underground environment. These alloys also have high strength and are readily fabricable by conventional methods. My paper, “Corrosion-Resistant Alloy Canisters for Nuclear Waste Disposal in Horizontal Drillholes,” summarizes the technical basis for our selection of these alloys and gives both the experimental analysis and real-world experience on performance in a wide range of highly corrosive applications.

Deep Isolation Canister Cross-Section
Cross-section of the canister containing a fuel assembly.

How can we be sure that Ni-Cr-Mo alloys are the best choice for the long time periods needed? The answer lies in the fact that these alloys are passive, that is, they are protected by a self-forming and self-healing film if damaged either chemically or mechanically. This passive film is an extremely thin layer of a chromium-rich oxide, essentially a ceramic material. The general corrosion rates of the passive Ni-Cr-Mo alloy are extremely low; it would take 17,500 years for this type of corrosion to penetrate to the thickness of a quarter, and the canister’s thickness is equivalent to 5-6 quarters.

Corrosion of canister equal to 1 quarter after 17,500 years.
Canister thickness equivalent to 5-6 quarters.

The Ni-Cr-Mo alloys also have high resistance to the localized corrosion processes of pitting, crevice corrosion and stress-corrosion cracking. Alloy 22, one of the Ni-Cr-Mo alloys, is among the most resistant to microbially-induced corrosion; its MIC resistance has been examined under a range of conditions with no evidence of surface damage. Galvanic corrosion also needs to be taken into account and will be addressed when considering the effects of the Ni-Cr-Mo alloy upon the other metals incorporated in the repository, the relative surface areas and the conductivity of filler materials, and the pore waters present in the rock.

A number of beneficial attributes of disposal in deep horizontal drillholes reduce the complexity of corrosion analysis and contribute to our conclusions regarding the high performance of Ni-Cr-Mo alloy canisters.

Read more in my technical paper that has been recently accepted by Energies, a peer-reviewed journal.

Subscribe to Receive Our Newsletter


For more information about our solution, please contact us. 415 915 6506

Deep Isolation, Inc.
2120 University Avenue, Ste. 623
Berkeley, CA 94704