In a large saucepan, combine the whole celery rib, garlic and peppercorns with 6 cups of water. Using a peeler, remove the zest from 2 of the oranges and add the zest to the pot. Season lightly with salt and bring to a boil. Add the chicken and simmer over low heat for 16 minutes. Remove from the heat and let the chicken stand for exactly 30 minutes. Remove the chicken and pull the meat from the bones, discarding the skin. Shred the chicken and let cool. Reserve the broth for another use.