In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for gas cooled reactors and pressurised heavy water reactors. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'. COUNT 5
QSN1 What percentage of uranium in nature is uranium-235? ANS1 0.7204% QSN2 What is the term for the amount of uranium-235 needed to sustain a nuclear chain reaction? ANS2 critical mass QSN3 What is the most prevalent natural isotope of uranium? ANS3 uranium-238 QSN4 What percentage of natural uranium is isotope 238? ANS4 99.2742% QSN5 Along with gas cooled reactors, what type of reactor doesn't use uranium-235? ANS5 pressurised heavy water