If k-effective > 1, the reactor is supercritical and power rises.

If k-effective > 1, the reactor is supercritical and power rises.

• A. The reactor is critical and power steady.
• B. The reactor is supercritical and power rises.
• C. The reactor is subcritical and power falls.
• D. The reactor operates in a transient state.

Answer: (B)

Understanding k-effective is the first thing to grasp: it tells us whether the nuclear chain reaction is increasing, steady, or decreasing. When k-effective is greater than one, each generation of neutrons produces more neutrons than the previous one on average, so the neutron population grows over time. Since reactor power is governed by the rate of fission events, a growing neutron population means the power rises. This state is called supercritical, hence power increases. Critical means k-effective equals one, giving a steady neutron population and constant power. Subcritical means k-effective is less than one, causing the neutron population and power to fall. A transient state describes something changing with time and does not by itself define the sign of power change unless tied to a specific k-effective value.

Understanding k-effective is the first thing to grasp: it tells us whether the nuclear chain reaction is increasing, steady, or decreasing. When k-effective is greater than one, each generation of neutrons produces more neutrons than the previous one on average, so the neutron population grows over time. Since reactor power is governed by the rate of fission events, a growing neutron population means the power rises. This state is called supercritical, hence power increases. Critical means k-effective equals one, giving a steady neutron population and constant power. Subcritical means k-effective is less than one, causing the neutron population and power to fall. A transient state describes something changing with time and does not by itself define the sign of power change unless tied to a specific k-effective value.