What does k_eff = 1 signify in reactor operation?

What does k_eff = 1 signify in reactor operation?

• A. Critical state with a steady neutron population.
• B. Subcritical state.
• C. Supercritical state.
• D. Neutron population is unstable.

Answer: (A)

k_eff is the effective multiplication factor that tells you how the chain reaction behaves from one generation to the next. When k_eff equals 1, the number of neutrons in each generation is the same as in the previous one, so the neutron population stays steady over time. This is a critical state—the reactor is self-sustaining without the neutron population growing or shrinking, because production equals losses from absorption and leakage. If k_eff were greater than 1, the population would grow (supercritical); if it were less than 1, it would decline (subcritical). The idea of instability isn’t present at k_eff = 1, since the population doesn’t change, though real systems can drift with changes in reactivity.

k_eff is the effective multiplication factor that tells you how the chain reaction behaves from one generation to the next. When k_eff equals 1, the number of neutrons in each generation is the same as in the previous one, so the neutron population stays steady over time. This is a critical state—the reactor is self-sustaining without the neutron population growing or shrinking, because production equals losses from absorption and leakage. If k_eff were greater than 1, the population would grow (supercritical); if it were less than 1, it would decline (subcritical). The idea of instability isn’t present at k_eff = 1, since the population doesn’t change, though real systems can drift with changes in reactivity.