300 600 NL, river decision with Kings

[IHaveStrong9]

10 handed, effective stacks 100K

Open UTG with KK to $1800. folded around to the BB who has a very tight image. He reraises to $7000. You decide to flat call.
(Pot-$15,100)
Flop-QJ6 rainbow. the player checks. whats his hand range? bet or check? you decide to check.
(Pot-$15,100)
Turn-8
Board is now Q J 6 8 with 2 diamonds. The tight player now bets out $17,000. Fold, Call, or Raise? You decide to call.
(Pot-$49,100)
River-6
Board is now Q J 6 8 6. Pot is $49,100. The tight player bets out $40,000. Call, fold, or shove?

So I am questioning every street and what is the best play.