What is the purpose of soluble poisons in a reactor system?

Soluble poisons serve a critical role in a reactor system by achieving reactivity control. In nuclear reactors, maintaining the right balance of reactivity is essential for safe and efficient operation. Soluble poisons, such as boron and lithium compounds, are materials that can absorb neutrons when dissolved in the reactor coolant. This neutron absorption effectively reduces the number of available neutrons that can contribute to the fission process, thus controlling the reactor's power output.

By adjusting the concentration of soluble poisons in the coolant, reactor operators can fine-tune the reactivity levels of the core. This versatility is especially important during various operational scenarios, including startup, shutdown, and during changes in power output. The ability to add or remove these soluble poisons provides a fast response mechanism for controlling the reactor's reactivity, ensuring it stays within safe operational limits.

While other options may relate to different aspects of nuclear reactor operation, they do not accurately reflect the primary function of soluble poisons. For example, increasing neutron speed is not a purpose of soluble poisons; rather, it is about neutron moderation. Enhancing heat transfer and improving fuel burnup are processes influenced by other factors, such as coolant properties and fuel design, but do not directly pertain