The collection of a tiny sample of the debris inside the Unit 2 reactor's primary containment vessel would start the fuel debris removal phase, the most challenging part of the decades-long decommissioning of the plant where three reactors were destroyed in the March 11, 2011, magnitude 9.0 earthquake and tsunami disaster.
https://apnews.com/article/japan-fukushima-nuclear-fuel-debris-cbaaeb5a501af755108393e416456f77