What is the effective multiplication factor k-effective?

What is the effective multiplication factor k-effective?

• A. The ratio of neutrons produced by fission in one generation to neutrons lost (absorbed or leaked) in the previous generation.
• B. The amount of heat produced per fission event.
• C. The rate of fuel burnup per cycle.
• D. The ratio of total neutrons in the core to neutrons emitted from the reactor.

Answer: (A)

The key idea is how many neutrons keep the reactor going from one generation to the next. k-effective is the ratio of neutrons produced by fission in the next generation to the neutrons lost in the current generation (through absorption or leakage). This tells you whether the neutron population is steady, growing, or shrinking. If the ratio is about one, the reactor is critical and operates with a steady neutron population. If it’s greater than one, the population increases and the system is supercritical; if it’s less than one, it decreases and the system is subcritical. This is why the correct description fits: it explicitly compares production by fission to losses, capturing the balance that determines the reactor’s state. The other ideas describe different things—heat per fission, fuel burnup rate, or a comparison between total neutrons present and those emitted—which do not define how the neutron population is balanced from generation to generation.

The key idea is how many neutrons keep the reactor going from one generation to the next. k-effective is the ratio of neutrons produced by fission in the next generation to the neutrons lost in the current generation (through absorption or leakage). This tells you whether the neutron population is steady, growing, or shrinking. If the ratio is about one, the reactor is critical and operates with a steady neutron population. If it’s greater than one, the population increases and the system is supercritical; if it’s less than one, it decreases and the system is subcritical.

This is why the correct description fits: it explicitly compares production by fission to losses, capturing the balance that determines the reactor’s state. The other ideas describe different things—heat per fission, fuel burnup rate, or a comparison between total neutrons present and those emitted—which do not define how the neutron population is balanced from generation to generation.