Kr-85

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Kr-85 refers to isotope of Krypton $\rm ^{85}_{36}Kr$.

Isotope mass: 84.91252

Contents

Production

Kr-85 is generated in nuclear reactors

Relative yield of Kr-85 in the nuclear waste (among other products of fission) is of order of 0.3% . Yield refers to the fraction of a fission product produced per fission (see https://en.wikipedia.org/wiki/Fission_product_yield ).

For comparison: Yield of Sr-90 is estimatef to be 4.505%, and that of Cs-137 is estimated to be 6.337%.

At the conventional schemes of reprocessing, most of Kr-85 is released into the atmosphere.

The most of fission products are either short–living isotopes (say, less than one day) or long–lining isotopes (that are not so dangerous for human). Kr-85, as Sr-90 and Cs-137, has some intermediate half-time; the last two seem to dominate in the contamination at the scale of 10 years since the nuclear accident.

Use

THe decay channel of Kr-85 can be written as follows:

$\rm ^{85}_{36}Kr \xrightarrow[10.76~y]{\beta,~ 687 \, keV}{}^{85}_{37}Rb$

Average energy of the $\beta$ particle is about 251 keV, the rest is carried with antineutrino.

The abilities of use of Kr-85 for heating may be for one or two orders of magnitude smaller than that due to Sr-90 or Cs-137. As for contamination of soil by Kr-85, it is negligible; the noble gas just flies away with wind.

Heat production

In[90]:= Wkr85 = (0.251 MeV)/(84.91252 amu) Log[2]/(10.76 Year)

Out[90]= (582.2 Joule)/(Kilogram Second)

id est, roughly, one kg of Kr-85 produces of order of 582 Watt due to hot electrons. However, even higher amount of power is carried out by antineutrinos, but is it almost impossible to use that part of power.

References

https://nl.wikipedia.org/wiki/Krypton-85

Keywords

Nuclear waste, Relaxation heat, Tartaria