There are 13 decommissioned and de-fuelled nuclear powered submarines awaiting disposal that are stored safely afloat—seven at Rosyth and four at Devonport (Plymouth). Two other submarines at Devonport are awaiting de-fuelling prior to being stored afloat pending disposal. The spent fuel is the only high-level radioactive material on these submarines.
On leaving naval service each submarine contains approximately 83 tonnes of intermediate-level waste (ILW) and 81 tonnes of low-level waste (LLW). A proportion of the ILW will decay over time to LLW. For example, after 30 years, the quantity of ILW would have reduced to approximately 19 tonnes and the LLW proportionally increased to 145 tonnes.