They are blaming 'construction vibration' and 'soil subsidence'.
The tunnel was used to store highly radioactive waste.
How much you wanna bet that the collapse is due to the steel in the concrete having been severely corroded by the radiation ?
Radiation is extremely 'corrosive' - and is a constant problem in nuclear plants. Even 'stainless' steel (which is much weaker than low hydrogen, high carbon steel) corrodes when exposed to radiation.
This one will cause a major shutdown of the nuclear industry in this country.