MATERIAL FOCUS
STAINLESS STEEL: WHEN SUPPLY CHAIN CHALLENGES GO NUCLEAR
S
tainless steel makes for long- lasting equipment in the nuclear industry because of its high
strength and corrosion resistance. But the industry’s special requirements mean that a fabricator who wins a contract for a new nuclear power plant might face a long wait for material. Welding World talks to Andy Backhouse, Lead Technical Manager at Outokumpu, about what’s causing these supply chain challenges.
Q: Why is it a challenge to procure stainless steel for the nuclear industry? AB: In a word, cobalt is the underlying reason. Cobalt is a trace metal in stainless
steel that transmutes into a radioactive isotope following exposure to radioactivity. As a result, when exposed to radiation at the heart of a nuclear power station, the stainless steel pipework, tanks and pool liners will become more radioactive over time. That creates a big health and safety problem that increases steadily. Nuclear authorities around the world
ensure a long service life and minimise risk by defining which grades of stainless steel may be used to contain the primary coolant. For example, the US ASME system allows only stainless steel types 304 and 316 and their close variants to be used. The challenge for fabricators
is that although these are widely available, the authorities often set tight limits on cobalt content to protect workers – and these low-cobalt variations can be hard to source.
Q: Why does stainless steel usually contain cobalt? AB: The austenitic stainless steels used in the nuclear industry typically contain eight to 10 per cent nickel to give the steel the correct microstructure
18 / WELDING WORLD MAGAZINE - ISSUE 03 - MAY 2024
and mechanical properties. But here’s the drawback: nickel and
cobalt often occur together in nature, so nickel ores normally also contain traces of cobalt. This cannot easily be separated, meaning the traces of cobalt remain in the nickel and so, subsequently, in the stainless steel. The low-cobalt requirement
doesn’t have any noticeable effect in most engineering applications, so it’s an unusual requirement.
Q: Where does nuclear stainless steel come from? AB: When working on a nuclear project, contractors should only source material
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