Free Range Organic Chicken Salad with Grapes and Walnuts

1 1/2 pounds free range organic  chicken tenders 5 cups water 1 3/4 cups reduced-sodium chicken broth 1/3 cup plain yogurt 1/3 cup mayonnaise 1 tablespoon Dijon mustard 1 cup seedless grapes, halved crosswise 1 cup coarsely chopped walnuts (3 ounces)         3...