original_query: What is the role of control rods in controlling x in a nuclear reactor?
query: What is the role of control rods in controlling xenon buildup in a nuclear reactor?
answer: Control rods help manage the xenon-135 buildup in a reactor.  Xenon-135 has a high neutron absorption cross-section, so its buildup can reduce reactor efficiency. Control rods absorb neutrons, compensating for the extra neutron absorption by xenon and helping maintain a safe and controlled neutron flux.