TNT explosions cannot be blocked using a shield. When blocking while TNT explodes, the shield does not take any durability and does not protect the player from any damage. Creeper explosions, however, can be completely blocked using a shield.
- Get a shield, TNT, and flint and steel
- Set gamemode to survival
- Place the TNT on front of you
- Activate it
- Block with the shield
→ You will still take explosion damage