TNT does no damage to player/s. any form or igniting TNT blows it up, destroys surrounding blocks, but does not do damage, possibly even to mobs.
Linked issues
is duplicated by 22
MC-278449
End Crystal giving no damage in Peaceful Mode
Resolved
MC-195753
end crystal explosions dealing no damage to players
Resolved
MC-17215
TNT doesn't kill you in Survival mode when dispensed from a dispenser.
Resolved
MC-8714
Tnt don't do damage when they explode
Resolved
MC-14423
Immune to Explosions While on Horses
Resolved
17 more links
That is the intended property of TNT while in peaceful.