Sale of lots of uranium in operation (7)
I believe the answer is:
auction
'sale of lots' is the definition.
(I've seen this before)
'uranium in operation' is the wordplay.
'uranium' becomes 'u' ('U' can be a synonym of 'uranium').
'in' indicates putting letters inside.
'operation' becomes 'action'.
'u' going inside 'action' is 'AUCTION'.
'of' is the link.
(Other definitions for auction that I've seen before include "Competitive sale" , "Where things are sold to the highest bidder" , "Public sale by bid" , "Public sale - type of bridge" , "Offer to bidders" .)