IT-based design with not a word about one reactor element (7)
I believe the answer is:
cadmium
'element' is the definition.
(cadmium is a kind of element)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for cadmium that I've seen before include "Potentially dangerous element" , "A yellow" , "reactor component" , "Soft bluish-white metallic element" , "Metal resembling zinc" .)