U.S.-bound plutonium that has recently been shipped out of Japan will be disposed of at a nuclear waste repository in New Mexico after being processed at the Savannah River Site facility in South Carolina, according to an official of the National Nuclear Security Administration.

“The plutonium will be diluted into a less sensitive form at the SRS and then transported to the Waste Isolation Pilot Plant (WIPP) for permanent disposal deep underground,” said Ross Matzkin-Bridger, who is in charge of the operation at the NNSA, a nuclear wing of the Department of Energy.

“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 said in a recent phone interview.

The official made the remarks ahead of the latest Nuclear Security Summit, sponsored by President Barack Obama, which began Thursday in Washington.

On Friday, Prime Minister Shinzo Abe said Japan will give up more highly enriched uranium (HEU) as part of what Obama hailed as an unprecedented bid to tighten control over unused nuclear material.

“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,” Obama said.

Japan already removed 331 kg (730 pounds) of plutonium and hundreds of kilograms of highly enriched uranium from the Fast Critical Assembly, a research facility located in the village of Tokai, Ibaraki Prefecture, in line with the 2014 pledge.

Japan will give up highly enriched uranium, including some at the weapons-usable level, and transport it from the Kyoto University Critical Assembly in Osaka Prefecture to the United States, in a new commitment highlighted in their joint statement released Friday. The amount of highly enriched uranium to be removed from the Osaka facility is some 45 kg (99 pounds).

The government does not disclose the amount of nuclear materials to be transported, citing security reasons.

The fourth such meeting of world leaders is focused on how to secure weapons-usable nuclear materials all over the globe.

At the previous summit in the Netherlands in March 2014, Prime Minister Shinzo Abe agreed to return plutonium and highly enriched uranium upon request from the Obama administration, which is seeking to strengthen control over nuclear materials.

Japan received the plutonium and HEU fuels from the U.S, Britain and France from the late 1960s to early 1970s for research purposes in the name of “Atoms for Peace.” The nuclear fuel delivery, however, has generated controversy in South Carolina since it was reported that it was en route to the U.S. government-run SRS facility in the state.

South Carolina is “at risk of becoming a permanent dumping ground for nuclear materials,” Gov. Nikki Haley said in a recent letter to Energy Secretary Ernest Moniz, calling for the shipment to be stopped or rerouted.

The final disposal at the WIPP, as described by Matzkin-Bridger, may defuse these local concerns in South Carolina.

The WIPP is a repository — about 660 meters underground — for permanently storing nuclear waste created by the U.S. government’s nuclear weapons program.

“The Department of Energy has signed a Record of Decision to implement our preferred option to prepare 6 metric tons 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 programs.”

The HEU from Japan’s FCA will be “down-blended” to low enriched uranium at the Y-12 National Security Complex in Oak Ridge, Tennessee, according to the official. In the future, lightly enriched uranium (LEU) will be used for research purpose at research reactors both in the U.S. 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 U.S.-Japan joint statement released Friday.

“It furthers our mutual goal of minimizing stocks of HEU and separated plutonium,” the document added, emphasizing the importance of the operation in strengthening nuclear security.

In the statement, the Japanese government made a new pledge to remove and transfer HEU fuels from the Kyoto University Critical Assembly (KUCA), another Japanese research institute, to the United States for down-blending and “permanent threat reduction.”

“If the KUCA’s HEU reactor is successfully converted to a LEU unit, it will have a significant meaning for other reactors in the U.S. and European nations, which are pursuing to convert reactors for LEU,” Hironobu Unesaki, a professor at Kyoto University, said. “The KUCA could provide academic outputs for future LEU conversion process worldwide.”

Officials in both nations have praised the bilateral cooperation, which aims to reduce the threat of nuclear terrorism through securing sensitive materials.

However, the materials recently transferred from Japan are only the tip of the iceberg. Currently, Japanese utilities possess over 47 metric tons of separated plutonium, which is equivalent to about 6,000 nuclear bombs.