Japan said on 1 April that it will give up more of its highly enriched uranium (HEU) in a bid to tighten control over unused nuclear material. Japanese Prime Minister Shinzo Abe told the Nuclear Security Summit in Washington of a new plan to remove HEU from the Kyoto University Critical Assembly in Osaka Prefecture, in addition to a similar pledge made in the previous meeting of the biennial summit in 2014.

"Japan is working to complete the removal of more than half a ton of highly enriched uranium and plutonium, which is the largest project in history to remove nuclear material from a country," said President Barack Obama who is hosting the summit. A joint USA-Japan statement said Japan will give up HEU, including some weapon-grade material, and transport it from to the USA for final disposal.

Japan has already removed 331kg of plutonium and hundreds of kilograms of HEU from the Fast Critical Assembly (FCA), a research facility in Tokaimura, northeast of Tokyo in line with the 2014 pledge. The amount of HEU to be removed from the Osaka facility is some 45kg, Japanese media reported, quoting people familiar with the project.

Meanwhile, US-bound plutonium recently shipped from Japan will be disposed of at the Waste Isolation Pilot Plant (WIPP in New Mexico after being processed for "inertion" at the Savannah River Site in South Carolina, according to an official of the Department of Energy’s National Nuclear Security Administration (NNSA). "The plutonium will be diluted into a less sensitive form at the SRS and then transported to WIPP for permanent disposal deep underground," said Ross Matzkin-Bridger in charge of the operation at the NNSA .

"The dilution process involves mixing the plutonium with inert materials that reduce the concentration of plutonium and make it practically impossible to ever purify again," he told Kyodo News in a recent phone interview.

It is hoped that the final disposal of the plutonium at WIPP may defuse local concerns in South Carolina. "The Department of Energy has signed a Record of Decision to implement our preferred option to prepare 6 tonnes of surplus plutonium from the SRS for permanent disposal at the WIPP near Carlsbad, New Mexico," Matzkin-Bridger explained. "This includes all foreign plutonium that we bring to the United States under our nonproliferation programmes."

As to the HEU from Japan’s FCA, it will be "down-blended" to low enriched uranium at the Y-12 National Security Complex in Oak Ridge, Tennessee, he explained. In the future, LEU will be used for research purpose at research reactors both in the USA and Japan, possibly including the FCA. "This project was accomplished on an accelerated timeline well ahead of schedule, thanks to the hard work and strong cooperation from both sides," said a US-Japan joint statement released on 1 April on the sidelines of the Nuclear Security Summit.

However, the materials so far transferred from Japan are only a small part of the total. Currently, Japanese utilities possess over 47t of separated plutonium. At the last Nuclear Security Summit two years ago, Abe restated Japan’s international promise not to possess any plutonium that it has no use for. But the stockpile of the nuclear material has since slightly increased.