In the 1930s they put about 13,000 tonnes of gold in Fort Knox. (It now has about 4,500 tonnes). Density of gold is about 20g/cm^3, or 20 tonnes per cubic metre. So Fort Knox held up to 650m^3 of gold.
A normal swimming pool is about 25m x 12.5m x 2m which is 625m^3.
https://en.wikipedia.org/wiki/United_States_Bullion_Deposito...
This page indicates Sellafield has 2000m^3 of high level nuclear waste.
https://ukinventory.nda.gov.uk/site/sellafield/
