Compare the activity of a fresh fuel rod $(238$g$,97\%238$U$,3\%235$U$)$ and a spent fuel rod.

Assumption: fresh fuel rod: $238$ g$,100\%238$U

spent fuel rod: $95\%238$U$,2\mathrm{.}5\%137$Cs$,2\mathrm{.}5\%135$Cs

$($proportion in $\%$ of the atoms$)$