The reactor cavity was sealed by a concrete plug that weighed 22 tons. Big Rock Point went "critical" on September 27, 1962 at 2:35 P. M. Criticality was achieved using seven fuel bundles. By May 1, 1964 the reactor held 84 bundles capable of turning out 75 megawatts, enough power for a city of 100,000, or 65,000 with an industrial-commercial base. During its last years, Big Rock Point generated 67 megawatts, three of which were used to power the plant itself.