Complex sentence: The BR2 reactor is one of the five main reactors producing molybdenum-99 which decays into technetium-99m, the radioisotope used in more that 80% of diagnostic imaging procedures in nuclear medicine.
Split into simpler sentences: The BR2 reactor is one of the five main reactors producing molybdenum-99. Which decays into technetium-99m, the radioisotope used in more that 80% of diagnostic imaging procedures in nuclear medicine.