Why Japan Won't Acquire Nuclear Weapons

North Korea's recent nuclear test has spawned many nightmare scenarios, including the possibility that pacifist Japan will go nuclear, triggering a new arms race. Both U.S. Secretary of State Hillary Clinton and Defense Secretary Robert Gates have warned of just that possibility, and on May 31 former secretary of state Henry Kissinger said that unless Beijing reins in Pyongyang, it should expect to "live in an Asia in which South Korea and Japan have nuclear weapons."

It sounds plausible. After all, Japan is one of the only great powers that doesn't already boast its own nuclear deterrent. Though Tokyo has officially vowed never to possess, build or even allow nuclear weapons onto its territory—promises born from Hiroshima and the pacifist constitution imposed on Japan by its U.S. occupiers after the war—some big-name Tokyo politicians have questioned that stance in recent years. In April, Goji Sakamoto, a lawmaker from the ruling Liberal Democratic Party, said that Japan should at least "threaten" to go nuclear. Shinzo Abe, who was prime minister from 2006 to 2007, once reportedly told a room full of college students that possessing nukes wouldn't violate Japan's constitution as long as the arsenal was "small in scale." And after Pyongyang's first nuclear test in 2006, senior LDP member Shoichi Nakagawa and Prime Minister Taro Aso (then foreign minister) called for public debate on the question.

Yet this is all just rhetoric. For one thing, despite North Korea's threats and China's growing military and political power, the Japanese people remain dead set against building nuclear weapons. Polls conducted over the past three years show that less than 20 percent of the public currently says it favors possessing such a deterrent.

For another, Japan—a crowded island nation—lacks the space to test a bomb. Japan has large stockpiles of plutonium for its nuclear-energy industry. But plutonium-type bombs require physical testing to verify their efficacy. (Uranium bombs are considerably simpler and so may not need physical testing, but Japan doesn't have the weapons-grade uranium to make such a device.) While some experts argue that Japan could test a plutonium weapon by detonating it underground, others—including former defense chief Shigeru Ishiba—insist that there is simply nowhere to do so in such a densely populated nation. Simulations would not be sufficient; those only work after at least one actual test.

Japan, moreover, now occupies the nuke-free high ground and would risk losing its innocence if it went nuclear. According to an internal 1995 study by Japan's defense establishment, reversing the country's no-nukes policy would trigger the collapse of the Nuclear Non--Proliferation Treaty regime, as the withdrawal of the world's only nuclear victim could fatally undermine confidence in the system. Such a move would also severely damage relations with Washington—Tokyo's most important ally—and the alarm in Beijing and Seoul could set off a nuclear race across East Asia. Japan would get the blame.

The consequences for Japan's energy supplies and economy could be equally catastrophic. If Japan broke out of the NPT, the countries that now supply it with nuclear fuel, including Canada, Australia and the United States, would surely hold back their shipments, which are currently conditioned on the fuel's peaceful use. That would be a nightmare for Japan, which relies on nuclear energy for nearly a third of its electricity.

There's one other roadblock to consider: Japan's top nuclear hawks have seen their power weaken considerably in recent years. Abe lost most of his clout after abruptly resigning as prime minister two years ago. In February, Nakagawa resigned as finance minister in disgrace after appearing drunk at a news conference. And Aso is practically a lame duck these days, with little room for bold moves.

Of course, the political environment may change if North Korea continues to act belligerently or if China proves to be a real threat, as Japanese hawks fear. But even then, most Japanese experts believe that their country would stop short of building a bomb of its own. At most, it might temporarily allow the United States to base nukes on Japanese territory. Another option would be to develop the means to stage a conventional strike against North Korea's launchpads.

But even the strike plan won't become reality anytime soon, as senior lawmakers and experts say current proposals are "amateurish" and poorly thought out. And any revision of the non-nuke policy would be a much greater stretch, given the weakness of the hawkish wing of the ruling LDP. There are still many good reasons to try to rein in North Korea's nuclear program, and its attempts to build missiles that could deliver those weapons to the U.S. and Japan. But the risk that Japan will go nuclear is not one of them.