Which is not a high-level radioactive waste? contaminated clothing fuel rods reactor coolant control rods

Actually the answer on this question would be:

“reactor coolant”

The reactor coolant mostly used is simply sea water, or water could be. The role of the reactor coolant is simply to cool the reactor. It does not come into contact with any radioactive source since it only cools the reactor from the outside, it acts like a jacket of coolant.