Preheat oven to 425 degrees F
Place flour, sugar, baking powder, salt and butter into the bowl of a food processor and pulse until the butter bits are the size of small peas. Pour the mixture into a large mixing bowl and add the heavy cream, orange juice, egg and orange zest. Mix with a fork until loosely incorporated and then add the rhubarb and knead together with your hands.
On a baking sheet, form the dough into a flattened disk, about 12-14 inches in diameter. Cut the disk into wedges and paint them with egg wash. Sprinkle with sugar.
Bake until the scones are browned and firm, about 20-25 minutes.