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Iodine-135 is an isotope of iodine with a half-life of 6.6 hours. It is an important isotope from the viewpoint of nuclear reactor physics . It is produced in relatively large amounts as a fission product , and decays to xenon-135 , which is a nuclear poison with the largest known thermal neutron cross section , which is a cause of multiple ...
The iodine pit, also called the iodine hole or xenon pit, is a temporary disabling of a nuclear reactor due to buildup of short-lived nuclear poisons in the reactor core. The main isotope responsible is 135 Xe, mainly produced by natural decay of 135 I. 135 I is a weak neutron absorber, while 135 Xe is the strongest
Iodine-135 is a fission product of uranium with a yield of about 6% (counting also the 135 I produced almost immediately from decay of fission-produced tellurium-135). [6] This 135 I decays with a 6.57 hour half-life to 135 Xe. Thus, in an operating nuclear reactor, 135 Xe is being continuously produced.
Neutron capture inside the reactor transmutes much of the xenon-135 that would otherwise decay to Cs-135. Caesium-137, with a half-life of 30 years, is the main medium-lived fission product, along with Sr-90. Cs-137 is the primary source of penetrating gamma radiation from spent fuel from 10 years to about 300 years after discharge.
Neutron capture (29 barns) slowly converts stable 133 Cs to 134 Cs, which itself is low-yield because beta decay stops at 134 Xe; can be further converted (140 barns) to 135 Cs. 6.3333%: Iodine, xenon: 135 I → 135 Xe: 6.57 h: Most important neutron poison; neutron capture converts 10–50% of 135 Xe to 136 Xe; remainder decays (9.14h) to 135 ...
This page lists radioactive nuclides by their half-life.
Because 95% of the xenon-135 production is from iodine-135 decay, which has a 6- to 7-hour half-life, the production of xenon-135 remains constant; at this point, the xenon-135 concentration reaches a minimum. The concentration then increases to the equilibrium for the new power level in the same time, roughly 40 to 50 hours.
The overall yield of xenon-135 from fission is 6.3%, though most of this results from the radioactive decay of fission-produced tellurium-135 and iodine-135. Xe-135 exerts a significant effect on nuclear reactor operation . It is discharged to the atmosphere in small quantities by some nuclear power plants. [20]