Complex sentence: The measured core temperature is now below 100 degrees Celsius for all 3 damaged reactors with reactor number 2 finally achieving this status; reactors 1 and 3 had been below 100 degrees since August.
Split into simpler sentences: The measured core temperature is now below 100 degrees Celsius for all 3 damaged reactors. Reactor number 2 finally achieved this status today, while reactors 1 and 3 have been below 100 degrees since August.