Poison in my reactor

40 protons and 48 neutrons is all it takes to have the second greatest neutron killer in a nuclear reactor. 88Zr has an enormous neutron capture cross section, reaching 6 orders of magnitudes higher than neighboring nuclei, even its somewaht heavier cousins. Read the commentary on the research work by Jennifer Shustermann and collaborators in Nature by Stephen Heinitz and Ulli Köster in this link

(both images come from the original works listed above)