Japan faces its nuclear taboo amid calls to move on from Hiroshima

Few people are angrier that North Korea has joined the nuclear club than Sunao Tsuboi. As a 20-year-old student, he was burnt from head to toe when the United States dropped the Fat Man atom bomb on Hiroshima in August 1945. He still bears the scars all over his face and body.

"We're furious about this test," he said of Japan's 270,000 atom bomb survivors. "It means that more countries are sure to follow. Our greatest worry is that Japan will now feel it has to have its own nuclear weapon."

Japan's history means any talk of developing its own nuclear option has long been taboo. But in the wake of Pyongyang's apparently successful test, the limits of the debate are being tested. Yasuhiro Nakasone, a former prime minister, is the latest politician to suggest that Japan should "study the nuclear issue". While this week, Japan's largest newspaper, The Daily Yomiuri, said the country should reconsider its aversion to the bomb. Politics not technology hinders the development of Japanese nuclear weapons. The world's second-largest economy also boasts one of the largest nuclear industries. It has 55 reactors and the use of a huge new reprocessing plant that will add to the 45 tons of plutonium stored in the country.

In 2002 a senior opposition figure Ichiro Ozawa spelled out the implications when he told China that it would be "a simple matter" for Japan to build "3,000 to 4,000 nuclear warheads" if its neighbour got "too inflated". Most experts believe a Japanese bomb could be built in six months.

In public at least, the new Prime Minister, Shinzo Abe, resists such calls. In a parliamentary Q&A session this week he stood by Japan's nuclear principles: that it will not "manufacture or possess nuclear weapons or allow their introduction".

But the rhetoric has not always matched the reality. Nuclear-armed US vessels have secretly docked in Japanese ports and in the 1970s a nuclear feasibility plan was commissioned.

In the short term, most experts believe Pyongyang's bomb is likely to push Tokyo closer to the US. Mr Abe has already pledged to speed up the development of a joint missile defence shield and to boost defence ties, a strategy that brings him into conflict with the "pacifist" constitution.

Against a background of growing regional instability, few of the atom bomb survivors are now prepared to bet that the nuclear freeze will last forever.