Because highly enriched uranium (HEU) is a key ingredient in nuclear weapons, it is important to track how much civil HEU exists and where it is. However, national civil HEU stocks are difficult to estimate, with transparency policies varying by country and few countries providing official declarations of their stocks. As a result, Civil HEU Watch--a project of the Institute for Science and International Security--provides national estimates of civil HEU stocks in countries that do not provide public declarations. This study relies on open source information to derive these estimates. The Nuclear Threat Initiative (NTI) provided funding in order to generate accurate data for the NTI Nuclear Security Index.
In total, ISIS estimates that 132-137 tonnes of HEU were in civil stocks in a total of 29 countries as of the end of 2014, with a central estimate of 134 tonnes. About 16.5 tonnes of HEU exist in the non-nuclear weapon states (NNWS), almost all of which resides in 10 NNWS states. The nuclear weapon states (NWS) possess a combined estimated total of 115-120 tonnes.
The full report from ISIS is available here.
The 2016 NTI Index will be released in January.