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Xenon-135 (135 Xe) is an unstable isotope of xenon with a half-life of about 9.2 hours. 135 Xe is a fission product of uranium and it is the most powerful known neutron-absorbing nuclear poison (2 million barns; [1] up to 3 million barns [1] under reactor conditions [2]), with a significant effect on nuclear reactor operation.
135 I undergoes beta decay with half-life of 6.57 hours to 135 Xe. The yield of 135 Xe for uranium fission is 6.3%; about 95% of 135 Xe originates from decay of 135 I. 135 Xe is the most powerful known neutron absorber , with a cross section for thermal neutrons of 2.6×10 6 barns , [ 1 ] so it acts as a " poison " that can slow or stop the ...
It has a half-life of about 9.2 hours and is the most powerful known neutron-absorbing nuclear poison (having a neutron absorption cross-section of 2 million barns [21]). 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.
The period of time in which the reactor is unable to override the effects of xenon-135 is called the xenon dead time or poison outage. During periods of steady state operation, at a constant neutron flux level, the xenon-135 concentration builds up to its equilibrium value for that reactor power in about 40 to 50 hours. When the reactor power ...
Cs-134 has a half-life of 2 years and may be a major source of gamma radiation in the first 20 years after discharge. Caesium-135 is a long-lived fission product with much weaker radioactivity. Neutron capture inside the reactor transmutes much of the xenon-135 that would otherwise decay to Cs-135.
The remainder and the unlisted 54.4478% decay with half-lives less than one year into nonradioactive nuclei. This is before accounting for the effects of any subsequent neutron capture; e.g.: 135 Xe capturing a neutron and becoming nearly stable 136 Xe, rather than decaying to 135 Cs which is radioactive with a half-life of 2.3 million years
When the reactor is shut down, iodine-135 continues to decay to xenon-135, making restarting the reactor more difficult for a day or two, as the xenon-135 decays into cesium-135, which is not nearly as poisonous as xenon-135, with a half-life of 9.2 hours. This temporary state is the "iodine pit."
Xenon-136 is produced when xenon-135 undergoes neutron capture before it can decay. The ratio of xenon-136 to xenon-135 (or its decay products) can give hints as to the power history of a given reactor and the absence of xenon-136 is a "fingerprint" for nuclear explosions, as xenon-135 is not produced directly but as a product of successive ...