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.

The Japanese government has taken positive steps to strengthen quake-resistance standards for nuclear power plants since the Great Hanshin Earthquake struck Kobe and its vicinity in 1995. Steps to enhance their quake-resistance have also been taken, but they apparently were insufficient.

A plant's structure itself is sturdy, but its power generation process involves a complicated facility using multiple combinations of a huge quantity of parts and components.

It is difficult to predict damage to annexed structures, such as the electric power system. And it is impossible to forecast when and where a huge tremor will hit.

Because of its scarce natural resources, Japan has held nuclear power generation as a pillar of its energy policy. It has stuck to that policy even after the Three Mile Island accident led the United States to suspend new plant construction and the 1986 Chernobyl accident in the former Soviet Union prompted many European nations to rethink their nuclear power policies.

Japan in the meantime has been slow in increasing its use of renewable natural energy sources.

Revisions to the country's Framework for Nuclear Energy Policy are currently under study, but Japan will likely adhere largely to the current policies.

Friday's earthquake halted operations at many nuclear power plants. It will take time to resume them. We should be aware that the reliance on nuclear power has ironically created risks in energy supply.

We must be modest in preparing for the danger of earthquakes. We must go back to square one in our discussions and delve into such fundamental questions as how far we should count on nuclear energy in this quake-prone country and whether safety can ever be secured for nuclear power plants.

Otherwise, many people will not be convinced of the need for nuclear energy after going through the fear of radiation leaks in addition to the devastation caused by the killer jolt.

The author is a senior staff writer for Asahi Shimbun. /Asahi Shimbun.