Ōarai (大洗町, Ōarai-machi) is a town located in Ibaraki Prefecture, Japan. As of 1 July 2020, the town had an estimated population of 15,867 in 6,881 households and a population density of 664 inhabitants per square kilometre (1,720/sq mi). The percentage of the population aged over 65 was 34.0%. The total area of the town is 23.89 square kilometres (9.22 sq mi). The Japan Atomic Energy Agency operates a research center in Ōarai with a number of nuclear research reactors, including the Jōyō and High-temperature engineering test reactor facilities.