TOKYO — The Japanese government announced Tuesday that it will spend $470 million on a subterranean ice wall and other steps in a desperate bid to stop leaks of radioactive water from the crippled Fukushima nuclear plant after repeated failures by the plant’s operator. The decision is widely seen as an attempt to show that the nuclear accident won’t be a safety concern just days before the International Olympic Committee chooses among Tokyo, Istanbul and Madrid as the host of the 2020 Olympics. The Fukushima Dai-ichi plant has been leaking hundreds of tons of contaminated underground water into the sea since shortly after a massive 2011 earthquake and tsunami damaged the complex. Several…