With an appropriate preposition:
After about six years inside a reactor, nuclear materials are usually moved to a fuel pool to let their radiation die 1.
  • 1、
【正确答案】 1、out    
【答案解析】 die out意思为“消失”，die away意思为“逐渐减弱，逐渐模糊”。由句意可知，die out正确。