Ocean floor disposal is a method of sequestering radioactive waste in ocean floor sediment where it is unlikely to be disturbed either geologically or by human activity.

Several methods of depositing material in the ocean floor have been proposed, including encasing it in concrete and dropping it (as the United Kingdom has previously done), dropping it in torpedoes designed to increase the depth of penetration into the ocean floor, or depositing containers in shafts drilled with techniques similar to those used in oil exploration.

Ocean floor sediment is saturated with water, but since there is no water table per se and the water does not flow through it the migration of dissolved waste is limited to the rate at which it can diffuse through dense clay. This is slow enough that it could potentially take millions of years for waste to diffuse through several tens of meters of sediment, so that by the time it reaches open ocean it would be highly dilute and decayed. Large regions of the ocean floor are thought to be completely geologically inactive and it is not expected that there will be extensive human activity there in the future. Any future activity or habitation could simply work around the dumping regions in the same way we build around high mountains; water absorbs all radiation in a few meters of distance.

One of the problems associated with this option includes the difficulty of recovering the waste, if necessary, once it is emplaced deep in the ocean. Also, establishing an effective international structure to develop, regulate, and monitor a sub-seabed repository would be extremely difficult.

Beyond technical and political considerations, the London Convention places prohibitions on disposing of radioactive materials at sea and does not make a distinction between waste dumped directly into the water and waste that is buried underneath the ocean's floor. It remains in force until 2018, after which the sub-seabed disposal option can be revisited at 25-year intervals.