Combine rice and water in a saucepan, and bring to a boil. Reduce heat, cover, and simmer for 20 minutes.
Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
In a large bowl stir together the cooked rice, diced chicken, mayonnaise, yogurt, cream of mushroom soup, and chicken broth. Mix in the lemon juice, onion, water chestnuts, 1 cup of sliced almonds, and celery. Season with white pepper and salt. Transfer the mixture to the prepared baking dish.
In a bowl, toss the remaining 1/2 cup sliced almonds and cornflakes cereal with the melted butter. Spread evenly over the casserole.
Bake 35 to 45 minutes in the preheated oven, until lightly browned.