AA vs Nittyish player 400NL

[dtan05]

Full Tilt Poker - No Limit Hold'em Cash Game - $2/$4 Blinds - 6 Players - (LegoPoker HH Converter)

SB: $396.00
BB: $419.90
UTG: $400.00
MP: $1,138.70
CO: $597.20
Hero (BTN): $835.40

Preflop: Hero is dealt A[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/club.gif[/img] (6 Players)
<font color="red">UTG raises to $16.00</font>, 2 folds, Hero calls $16.00, 2 folds

Flop: ($38) K[img]/images/graemlins/spade.gif[/img] 2[img]/images/graemlins/diamond.gif[/img] 8[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">UTG bets $29.00</font>, Hero calls $29.00

Turn: ($96) 6[img]/images/graemlins/diamond.gif[/img] (2 Players)
<font color="red">UTG bets $69.00</font>, Hero calls $69.00

River: ($234) 2[img]/images/graemlins/heart.gif[/img] (2 Players)
<font color="red">UTG bets $185.00</font>,Hero....

does he really 3 barrel AK like this? No indication on his double barreling frequencies...

Villain is 18/12....

I repop here like 99% of the time, but yeah, give that, how do you play riv?