A significant amount of zirconium is formed by the fission process; some of this consists of short-lived radionuclides (Zr and Zr which decay to molybdenum), while almost 10% of the fission products mixture after years of decay consists of five stable or nearly stable isotopes of zirconium plus Zr with a halflife of 1.53 million years which is one of the 7 major long-lived fission products. Zirconium is commonly used in cladding of fuel rods due to its low neutron cross section. However, a small share of this zirconium does capture neutrons and contributes to the overall inventory of radioactive zirconium isotopes. Zircalloy cladding is not commonly reused and neither is fission product zirconium, which could be used in cladding as its relatively weak radioactivity would be of no major concern inside a nuclear reactor. Despite its high yield and long live, Zr-93 is generally not deemed to be of major concern as it is not chemically mobile and emits little radiation.