Photo/IllutrationThe Asahi Shimbun

Japan's nuclear cooperation agreement with the United States was automatically extended July 16 despite growing concerns overseas about Tokyo's huge stockpile of plutonium.

The agreement, now in its 30th year, underpins Japan's problem-plagued efforts at continuing with its nuclear fuel recycling policy.

Japan is the only non-nuclear-weapons state permitted to use plutonium for peaceful purposes.

Its stockpile of this weapons-grade material, both in Japan as well as Britain and France, now stands at around 47 tons, enough to manufacture 6,000 atomic bombs.

Renewal of the agreement brought renewed criticism from other countries about Japan's intentions, especially in light of its recent decision to decommission the prototype Monju fast-breeder reactor that used reprocessed plutonium.

Because of that, Japan now is confronted by the diplomatic challenge of convincing the rest of the world that it is serious about making good use of its plutonium stockpile.

Moves by Japan to use plutonium-uranium mixed oxide fuel in conventional nuclear reactors have not spread beyond a few facilities in the aftermath of the earthquake and tsunami disaster in 2011 that triggered a triple meltdown at the Fukushima No. 1 nuclear power plant.

Against that background, there is growing international criticism at the exception given to Japan to reprocess spent nuclear fuel.

When South Korea was negotiating with the United States in 2015 for its own nuclear energy agreement, it pointed to Japan's arrangement and asked Washington for a similar dispensation to reprocess spent nuclear fuel.

Saudi Arabia has also sought uranium enrichment technology.

At a U.S. Senate hearing in February, Sen. Edward Markey, a Democrat from Massachusetts, said, "I think what's happening in Japan is potentially contributing to an increased risk for nuclear proliferation in that region."

William Newcomb, who once served on a U.N. panel of experts handling economic sanctions against North Korea, weighed in on the issue by citing the historic June summit in Singapore between U.S. President Donald Trump and North Korean leader Kim Jong Un.

Newcomb suggested there could be enormous ramifications if the main result of that summit meeting was not denuclearization of the Korean Peninsula, but only a reduction of nuclear arms.

He said that could lead to other nations also producing nuclear weapons.

"I mean who comes to mind quickly: Japan, Taiwan, Saudi Arabia, even Brazil," he said. "They all have the potential to do something very fast."

The present nuclear energy cooperation agreement with the United States went into effect in 1988. At that time, Japan held only a minimal amount of plutonium.

As construction proceeded with the Monju reactor, the Japanese government's plan to use reprocessed plutonium met little opposition because the technology seemed to offer such tremendous benefits.

At that time, Toichi Sakata was a councilor at the Japanese Embassy in Washington in charge of negotiating the nuclear energy cooperation agreement with the United States. Sakata, 69, would later serve as administrative vice minister of the Ministry of Education, Culture, Sports, Science and Technology.

Recalling that period, Sakata said: "Japan not only had an advanced nuclear energy program, but it had also produced solid results. It was also a state that could be trusted."

But in the 21 years between 1995, when a sodium leak at the Monju reactor forced a shutdown of operations, and 2016, when the government formally decided to scrap the facility, Japan's plutonium stockpile increased threefold.

"If the government is to continue its nuclear fuel recycling program, it will be insufficient to only revise its plutonium usage plan," Sakata said. "The only option available will be to show the world through specific results that it is serious about not holding surplus plutonium."

(This article was written by Keisuke Katori in Washington and Toshihide Ueda, a senior staff writer in Tokyo.)