What is a criticality search?

• A. A procedure to adjust reactivity control devices to bring the system to criticality (k_eff = 1) under specified conditions.
• B. A method to measure core temperature under startup conditions.
• C. A test to determine moderator density coefficients.
• D. A procedure to test fuel rod alignment during operation.

Answer: (A)

The key idea being tested is what a criticality search means in reactor startup. A criticality search is a procedure used to bring the reactor from shutdown to the point where it is exactly critical, with k_eff equal to 1, under predefined conditions. It involves adjusting reactivity—through control rod positions, moderator density, and boron concentration (or other means as allowed by the design)—to locate the precise state where the reactor becomes self-sustaining. This step is done at a low, controlled power level and with careful monitoring of neutron flux and other parameters to ensure the core is at the intended critical condition before proceeding to higher power operation.

The other options describe different startup or test activities that do not aim to bring the core to criticality. Measuring core temperature, testing moderator density coefficients, and checking fuel rod alignment each serve separate purposes unrelated to establishing the exact critical state.