what isotopes are used as nuclear reactor fuel? (select all answers that apply)
Most commonly used fuel is U235, a naturally occurring radioactive isotope of uranium. Occurs naturally at 0.7% of uranium ore, but must be enriched to 3%. Formed in cylindrical pellets (1.5cm long) and stacked in hollow metal rods (4 m long). About 100 rods are bundled together to make a fuel assembly.