In a large saucepan, combine the rice, 3cups (24fl oz/750ml) water, and ½teaspoon salt. Bring to a boil over medium-high heat. Reduce the heat to medium-low, cover, and simmer until the rice is just tender, about 40 minutes. Drain and place in a bowl.
Assemble the salad
Add the celery, cranberries, walnuts, chopped oranges, and orange juice to the rice. Add the oil and stir with a fork to combine. Season to taste with salt and pepper. Spoon the salad into a serving bowl. Sprinkle with the pomegranate seeds, if using, and serve.