unit 1 is a 439 mw boiling water reactor (bwr3) constructed in july 1967. it started to commercially make electricity on march 26, 1971, and was planned to shutdown in march, 2011. it was damaged during the 2011 sendai earthquake and tsunami. the reactor had high atomic and earthquake safety levels when it was made, but it is now both old and out of date. no one knew such a bad earthquake could happen in japan. unit 1 was designed for a earthquake "peak ground acceleration" shaking motion of 0.18 g (1.74 m/s2) and a seismic "response spectrum" based on the 1952 kern county earthquake. all units were inspected after the 1978 miyagi earthquake when the seismic "ground acceleration" was 0.125 g (1.22 m/s2) for 30 seconds, but no damage to the critical parts of the reactor was discovered.