The United Kingdom's Nuclear Decommissioning Authority (NDA) has successfully converted "a can of plutonium residue" into a stable waste form suitable for disposition. This step is part of the program that aims to process "around 400 cans of plutonium residue" stored at the NDA group's Sellafield site. According to the Sellafield CEO, this particular step means that the UK is able to "deal with some of the more problematic plutonium."

The United Kingdom has the largest stock of civilian plutonium, 116.8 tonnes as of the end of 2023 (in addition, there is 21.7 tonnes of Japan's plutonium stored in the UK). In January 2025, the UK government made a decision to immobilize UK-owned plutonium. In August 2025, the government allocated £154 million toward this program.

The United Kingdom is reportedly exploring two immobilization options - Disposal MOX and Hot Isostatic Pressing. Both processes create ceramic material suitable for disposal.

For a discussion of the storage MOX option, see this article:

J. Kang, F. N. von Hippel, A. Macfarlane, R. Nelson, "Storage MOX: A Third Way for Plutonium Disposal?," Science & Global Security, 10, no. 2, (2002): 85-101.