Pasta, Fruit and Walnut Salad

1/2 package shell macaroni
1 - 8 ounce container plain yogurt
1/4 cup frozen orange juice concentrate, thawed
1 - 15 ounce can mandarin oranges, drained
1 cup seedless red grapes, halved
1 cup seedless green grapes, halved
1 apple, cored and chopped
1/2 cup sliced celery
1/2 cup walnut halves

Cook macaroni, according to package directions. Drain. In a small bowl, mix together the yogurt and orange juice. In large bowl, combine macaroni and remaining ingredients. Add yogurt mixture. Toss to coat. Cover and refrigerate.