Twenty-five years ago, the explosion at Chernobyl cast a radioactive cloud over Europe and a shadow around the world. Today, the tragedy at Japan's Fukushima Daiichi nuclear power plant continues to unfold, raising popular fears and difficult questions.

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Visiting Chernobyl a few days ago, I saw the reactor, still deadly but encased in concrete. The town itself was dead and silent - houses empty and falling into ruin, mute evidence of lives left behind, an entire world abandoned and lost to those who loved it.

More than 300,000 people were displaced in the Chernobyl disaster; roughly 6 million were affected. A swathe of geography half the size of Italy or my own country, the Republic of Korea, was contaminated.

It is one thing to read about Chernobyl from afar. It is another to see for it. For me, the experience was profoundly moving, and the images will stay with me for many years. I was reminded of a Ukrainian proverb: "There is no such thing as someone else's sorrow." The same is true of nuclear disasters. There is no such thing as some other country's catastrophe.

As we are painfully learning once again, nuclear accidents respect no borders. They pose a direct threat to human health and the environment. They cause economic disruptions affecting everything from agricultural production to trade and global services.

This is a moment for deep reflection, a time for a real global debate. To many, nuclear energy looks to be a clean and logical choice in an era of increasing resource scarcity. Yet the record requires us to ask: Have we correctly calculated its risks and costs? Are we doing all we can to keep the world's people safe?

Because the consequences are catastrophic, safety must be paramount. Because the impact is transnational, these issues must be debated globally.