Friday's massive earthquake that ravaged Japan's northeast region led to the first-ever state of emergency issued for nuclear plants, including the evacuation of a neighborhood.

The situation is a fresh reminder of the serious latent danger of nuclear power stations and shatters assurances that nuclear power plants are safe because they are carefully designed.

And failures at nuclear plants in the quake raises a fundamental question: How can earthquake-prone Japan coexist with nuclear power plants?

The emergency core cooling system (ECCS), which pours water into the nuclear reactor core to cool it in case of an accident, was deemed a key to the multiple safety system for those reactors.

If an earthquake hits, reactors shut down automatically. But that alone cannot prevent an accident because the nuclear fuel continues emitting heat. If the core is not properly cooled down, it could melt the fuel rods and trigger a disastrous explosion.

In the 1979 Three Mile Island accident in the United States, cooling water poured out of the core to the extent that it almost caused a catastrophe.

The circumstances at Japanese reactors are now moving toward a similar situation.

From the initial development phase of nuclear power generators, the question over their safety has revolved around the reliability of the ECCS.

The ECCS failed to work in Japan, an advanced nation in the field of nuclear power generation, and at more than one reactor.

A power outage caused the failure.

Nuclear power stations generate power. But if the power supply is cut off during an accident, everything in the plants stops. That is why they are equipped with multiple emergency power generators so the ECCS can be kept in operation no matter what happens.

The current turmoil shows the need for a change in the design concept.