It didn't say explicitly, but my guess is that they want to disassemble the first sarcophagus and the original plant in an orderly manner before they eventually

It didn't say explicitly, but my guess is that they want to disassemble the first sarcophagus and the original plant in an orderly manner before they eventually just collapse. Even the new sarcophagus won't last forever, so there also needs to be a plan to eventually deal with the most radioactive material as is done with other highly radioactive waste. (It's entirely likely I expect that the less radioactive stuff will be left on-site, just not as part of crumbling buildings that could eventually collapse, blowing out radioactive dust.)