The discussion focuses on the types of spent fuel generated by various nuclear power reactors worldwide, highlighting the operational statistics of reactors in the US, France, Russia, and other countries. It explains that spent fuel is produced when the fissile material is depleted and fission products accumulate, making further operation uneconomical. There is a query regarding the potential for bomb-making from spent fuel, noting that while the plutonium content is lower than optimal, it may still be sufficient with effort. The conversation also touches on the geometric characteristics of fuel in different reactor types, which influence the spent fuel's composition and discharge burnup. Overall, the thread provides insights into the complexities of spent nuclear fuel and its implications for safety and security.