On: Chinese Tokamak reaches over 100M degrees

[red75prime]

It is low-backgroud steel([0]), not no-backbround steel. Potassium-40, for example, is a naturally occurring radioisotope. See Banana equivalent dose ([1]).

[0]: https://en.wikipedia.org/wiki/Low-background_steel

[1]: https://en.wikipedia.org/wiki/Banana_equivalent_dose

[consp → red75prime]

To add: C-14, Al-26, Cl-36, Ca-41, Ca-48, V-50 and more in trace quantities can be present.

Try pointing a Geiger counter at a brick or ever better plaster wall and be surprised about the amount of radiation you get during the day.