Hi this is probably a bit of a silly question but I've been thinking a lot about the use of zirconium in nuclear plants. I know that zirconium has a very low neutron absorption cross section and that's why it is used for constructing things like pressure tubes. If this is the case, why do the pressure tubes still need to be stored in waste containers when they are removed from the plant, is the zirconium becoming radioactive through neutron absorption? If this is the case what forms of radiation can the zirconium give off even when it is removed from the reactors?
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Zirconium is composed of several isotopes, it generally has a low (but not zero) effective cross section for thermal neutrons, but it is activated by fast neutrons.
In addition, it is not used pure, but in the form of an alloy. For example, zircaloy4 used as fuel rod cladding material for PWR reactors contains tin, iron, chromium and hafnium.
All these components become radioactive at different levels, especially with very long irradiation times (3 to 5 years), in significant thermal , épithermal and fast neutron fluxes since they constitute the core of the reactor.
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$\begingroup$ In theory, say the material was pure zirconium and that is undergoing neutron capture due to the high neutron flux would the only radioactive isotope you'd find be Zirconium 93, 95 etc? I was reading somewhere that the naturally occuring stable isotopes are 90, 91, 92 and 94. Would this mean it would just give off beta and gamma radiation? Basically I'm trying to work out if there would be a neutron flux outside of the waste container but can't work out where those neutrons would come from $\endgroup$ Commented Jun 11 at 10:34
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$\begingroup$ Sorry, I don't understand your question which mixes nuclear waste, pure zirconium and now, neutron emitters. What type of nuclear waste are you talking about? “Pure” zirconium (what degree of purity?) is not used in the large-scale nuclear industry. There are neutron emitters in spent nuclear fuel because there is formation of fissile products undergoing spontaneous fission, these products are inside the storage container and some neutrons can pass through the protection within admissible limits. $\endgroup$ Commented Jun 12 at 4:45
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Zirconium has a very low cross section, but it will be slightly activated. However, compared to the fuel, the activation is trivial.
The reason the zirconium is still included in the waste container is that the cladding has bonded to the fuel and there is no easy way to remove it. In addition, if the zirconium is removed, something else would have to be added to give the fuel structural integrity. It is easier to just leave it on.
