There is a reason the Onagawa Nuclear Power Station was not damaged. The power station itself was not flooded, which was the major factor with Fukushima; but the reasons for the integrity of the power station itself is far more interesting.

The Onagawa Nuclear Power Station is on land without subduction zones or major faults. In Figure 2 (click here) on page 224 clearly illustrates there are no geological features of quake potential.

The primary reason the Onagawa Nuclear Power Station was sound without any signs of damage is because there was no earth movement in the area. The reason the plant didn't malfunction is because there was no flooding and the plant could be shutdown safely. The back-up systems were intact. Let there be no doubt the circumstances at Fukushima was very different than at Onagawa. To assume nuclear plants are safe on or near seimic faults based on the experience of Onagawa is incorrect. If anything it proves having nuclear power stations in zones without seimic activity or the danger of same have the best outcomes. 

Aug 10, 2012

An International (click title to entry - thank you) Atomic Energy Agency (IAEA)-led team of international experts on August 10 delivered an initial report at the end of a two-week mission to gather information about the impacts of the Great East Japan Earthquake on the three-unit Onagawa Nuclear Power Station, and concluded the plant was "remarkably undamaged."

The Government of Japan and the IAEA agreed to deploy a team of 19 members from six countries, including IAEA staff, to the Onagawa plant. The team held discussions with the operators of the plant and reviewed logbooks and repair reports documented after the earthquake.

The Onagawa plant, facing the Pacific Ocean on Japan's north-east coast, was the nuclear power plant closest to the epicenter of the March 11, 2011 magnitude 9.0 earthquake that struck Japan and resulted in a tsunami, the IAEA said.

The agency also said the plant experienced very high levels of ground shaking - among the strongest of any plant affected by the earthquake - and some flooding from the tsunami that followed, but was able to shut down safely.

In its draft report, the IAEA team said "the structural elements of the NPS were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake".
The mission's objective was to observe how structures, systems and components with significance to the safety of the plant responded to the earthquake and heavy shaking.

The IAEA said the findings from the visual investigation will be added to an IAEA data base being compiled by its International Seismic Safety Centre (ISSC) to provide knowledge for Member States about the impact of external hazards on nuclear power plants.

Recommendations have been made that follow-up missions be conducted at Onagawa and reviews be conducted at other nuclear power plants in Japan that have experienced varying magnitudes of earthquakes.

"This is an initial step in a much longer process. The level of cooperation and frank sharing of information that we received from the staff at Onagawa NPS and its owners, the Tohoku Electric Power Company, sets a very good example," said Sujit Samaddar, mission leader and Head of the IAEA's ISSC said.