Question

Which of the following is correctly matched with respect to reactors?

• A. Critical – Reactivity is zero; Supercritical – Reactivity is positive; Subcritical – Reactivity is negative
• B. Critical – Reactivity is zero; Supercritical – Reactivity is negative; Subcritical – Reactivity is positive
• C. Critical – Reactivity is non-zero; Supercritical – Reactivity is positive; Subcritical – Reactivity is negative
• D. Critical – Reactivity is non-zero; Supercritical – Reactivity is negative; Subcritical – Reactivity is positive

Answer 1

The correct option is A

Critical – Reactivity is zero; Supercritical – Reactivity is positive; Subcritical – Reactivity is negative

If a reactor is critical, that is, the neutron production is exactly equal to the neutron destruction, the reactivity is zero. If the reactor is supercritical (neutron production > neutron destruction) then the reactivity is positive, i.e., unsafe. If the reactor is subcritical (neutron production < neutron destruction) then the reactivity is negative i.e., safe.