Savannah River Nuclear Solutions (SRNS), the management and operating contractor of the US DoE Savannah River Site (SRS), announced the completion of downblending of Swiss plutonium that was brought to (SRS) in 2016. According to SRNS, the program of managing the Swiss material began in 2022.

What SRNS calls "downblending" is, in fact, a process of mixing plutonium with adulterating material to complicate chemical separation of plutonium. This process does not change the isotopic composition of plutonium the way the downblending of highly-enriched uranium does. (This method was developed as part of the "dilute and dispose" program of eliminating surplus plutonium, which was cancelled by an executive order is May 2025.)

The Swiss government reported in 2016 that the shipment included about 20 kg of plutonium.

The Swiss plutonium is designated in the United States as "gap material," as it is not covered by the programs that repatriate US or Russia-origin fissile material. According to SRNS, the Savannah River Site "has received gap material from six countries" so far. The material is stored in the K Area Complex and is "planned to be downblended over the next couple of years."

In addition to Switzerland, the five countries that have sent their plutonium to SRS as part of the gap material program are Sweden (2009-2012), Belgium (2014), Italy (2014), Germany (2016), and Japan (2016).