As shown in the figure below, the capture cross sections for the fission products change dramatically with time, i.e. with the age of each fission product in the flux. This is due to the fact that some FPs have a very large cross section and so are quickly burnt, whereas others have a small cross section and, as a result, remain much longer.
The figure below shows the evolution with time of the plutonium isotopes. Notice the increasing amount of 241Pu with time, until stabilization is reached at about 14 years.
The shape of the flux in the core evolves over time. The main reason for this is the increasing amount of 240Pu which has a very large cross section at 1 eV. This tends to harden the flux, leading to a change in the mean cross sections. The curve below shows the evolution of the capture cross sections for the main plutonium isotopes.
The curve below shows the evolution of the mean fission cross section for the two fissile plutonium isotopes.
If we compare what has been put inside the ADS to what has been taken out, we get a measure of its incineration capability.
The figure blow shows the number of moles of each nucleus that were put in the reactor during the 15 year evolution, compared to the number of moles extracted during the same period, plus the number of moles present in the core at the end of these 15 years.
The 239Pu is extremely well incinerated. The incineration of other plutonium isotopes is also very good, even if the amount of 242Pu is only divided by a little more than 2. The amounts of 242Am and 243Am are decreased as well. On the contrary, this incineration leads to the creation of curium (the amount of 245Cm remains constant), mainly 244Cm and 246Cm. A relatively small amount of 242Am is produced, as well as all minor actinides above curium (not visible on the linear scale). Uranium isotopes are also produced in small amounts but 237Np is well incinerated.
In the next figure, the proportion of each nucleus in the input salt is compared to its proportion in the output salt, on a log scale. There is proportionally much more 242Pu in the output mixture than in the input one. The fraction of 239Pu is well decreased, as well as the fraction of 241Am and 241Pu even if less so. The 237Np fraction is approximately constant. All other nuclei have a greater fraction in the output mixture. This is of course expected, because their production results from the normal operation of the reactor.