What else can IFRs use for fuel, besides plutonium?
Their fast spectrum permits IFRs to burn any and all actinides – elements with atomic number 89 (actinium) and greater. This is because, in a fast neutron spectrum, all the actinide isotopes have roughly comparable fission probability (“fission cross section”). The most important actinide elements are uranium (atomic number 92), plutonium (94) and, to a lesser extent, thorium (90). Since currently there is a growing glut of plutonium, continuing to pile up from nuclear weapons and from thermal-reactor operations worldwide, the first IFRs will undoubtedly be fueled primarily with some of that plutonium. How is that different from thermal reactors? In a thermal neutron spectrum, many of the fission products and actinide isotopes absorb neutrons readily without undergoing fission (they have a high “capture cross section”), and the chain reaction is “poisoned” if too much of such material is present. Thus a thermal reactor cannot be a net burner of transuranic actinides. The main starting
