Swedish to English Tech/Engineering Chemistry; Chem Sci/Eng

Hello

I've already seen "bryts ner" (break down) in this text about radon and radioactivity.

But in the sentence:

Blåbetongen kan vara högstrålande eller lågstrålande beroende på var skiffern ***bröts***.

there is no "ner"

So I'm not sure what is meant by "var skiffern bröts"

Surely not the excavation site of the shale so does it mean a fracture line in the material (blue concrete)?

or is "ner" understood tacitly and then it refers to the molecular chains and where they are broken (I'm guessing here as I'm not a scientist)

Thanks in advance

SafeTex