Inside B Reactor at Hanford. The 586 square mile Hanford site was perhaps the most classified ground of WW II. It's the site of B Reactor, the world's first large-scale nuclear reactor of any kind. The site produced plutonium for the Trinity device, the Nagasaki weapon and Cold War weapons. This year 48 tours with 2000 seats are being offered to the site. Within 15 minutes of online registration, 500 seats were claimed.