Mix butter, minced tarragon, chives, and lemon peel in small bowl.
Melt 2 tablespoons herb butter in large skillet over medium heat. Add leeks and thyme; sauté 5 minutes. Reduce heat to medium-low; sauté until very tender, about 6 minutes longer.
Bring 8 cups water and tarragon sprigs to boil in large saucepan over high heat. Add beans and cook until crisp-tender, about 4 minutes. Using slotted spoon, transfer beans to bowl of ice water. Add peas to boiling water; cook 2 minutes. Using slotted spoon, transfer peas to bowl with beans; drain. Add shrimp to saucepan, reduce heat, and simmer until opaque in center, about 2 minutes. Using slotted spoon, transfer shrimp to small bowl. Add shells to saucepan; boil until liquid is reduced to 1/4 cup, about 40 minutes. Discard shells and tarragon sprigs. Stir lemon juice into cooking liquid. Remove pan from heat; whisk in remaining herb butter. Stir in shrimp. Reheat leeks. Stir in beans and peas. Serve shrimp with sauce alongside vegetables.
