Steve Fetter, formerly the Obama White House's assistant director of the Office of Science and Technology Policy, thinks China's concerns are not purely political.
"I've had private discussions with China in which they ask, 'Why does Japan have all this plutonium that they have no possible use for?' I say they made have made a mistake and are left with a huge stockpile," said Fetter, now a professor at the University of Maryland. "But if you were distrustful, then you see it through a different lens."
For at least four or five years, said Leonard Spector, deputy director of the Center for Non-Proliferation Studies in Monterey, the Japanese plutonium stockpile has been mentioned as a threat in Chinese defense white papers.
(Read more: Going nuclear and small with new type of reactor)
Japan, of course, has its own security concerns with China and North Korea. North Korea's nuclear weapons program is a direct threat to Japan. Some of its Nodong missiles, with a range capability of hitting anywhere in Japan, are believed to be nuclear-armed. "Nodong is a Japan weapon," said Spector.
There have been confrontations between China and Japan over small islands north of Taiwan. The dispute has recently escalated. In October, state-controlled media in China warned "a war looms following Japan's radical provocation," Tokyo's threat to shoot down Chinese drones.
Most experts agree that China is the greater threat, because as one expert said, "If North Korea attacked Japan, the U.S. would flatten it"-- and thus China is the country Japanese officials, particularly the right, want to impress with their minimal deterrence.
But experts also note that another nation in the region seems to have been impressed by the Japanese "bomb in the basement" strategy, not as a threat but as a model.
There are fears that if Japan opens the Rakkosho plant, it will encourage South Korea to go the same route as its neighbor. The U.S. and South Korea have been negotiating a new civilian nuclear cooperation pact. The South wants to reprocess plutonium, but the U.S. is resisting providing cooperation or U.S. nuclear materials.
Jeffrey Lewis believes that the South Koreans want to emulate Japan, and says there is a "bigger bomb constituency in South Korea , about 10 to 20 percent [of the population]," than in Japan.
"The least of my concerns is that Japan would get a nuclear weapon," said Fetter. "But China and South Korea will use this as an excuse, each in their own way."
And, in fact, not everyone believes that Japan COULD go all the way. Jacques Hymans, a professor of international relations at the University of Southern California, believes the process would be thwarted by what he calls "veto players," that is, government officials who would resist a secret program and reveal it before it reached fruition.
He wrote recently that Japan has more levels of nuclear bureaucracy than it once had, as well as more potential "veto players" inside that bureaucracy because of Fukushima. He said that any attempt to make a bomb would be "swamped by the intrusion of other powerful actors with very different motivations."
Still, even without a bomb, Japan has achieved a level of nuclear deterrence without building a bomb and suffering sanctions. That may be a more impressive achievement than actually building a bomb.
--By NBC News