Reactor control sensing: what is measured? In the automatic control system of nuclear reactors, the sensing element is intended to measure the level (intensity) of neutron flux to infer reactor power. Which option correctly reflects this purpose?

Introduction / Context:
Reactor power in fission systems is directly proportional to neutron population and thus to neutron flux. Control and protection systems rely on detectors that respond to neutron flux to regulate reactivity and maintain safe power levels. Recognizing what the sensors measure clarifies how the control loop is structured.

Given Data / Assumptions:

• Standard power reactors using ion chambers, fission chambers, or boron-lined detectors.
• Flux is commonly expressed in neutrons per square centimetre per second (n/cm^2·s).
• Goal is real-time indication of reactor power and rate-of-change (period).

Concept / Approach:

Neutron detectors do not measure temperature, volume, or “density” of flux; they measure flux intensity (or its proportional current) and sometimes its time derivative. Reactor period meters, source range, intermediate range, and power range channels are all based on neutron count or ionization current linked to flux level. Therefore “none of these” is the best choice because the listed options do not state “neutron flux” or “flux intensity.”

Step-by-Step Solution:

Verification / Alternative check:

Plant instrumentation schematics show neutron detectors feeding the reactor protection system and regulating rods via power/period signals, not via temperature or volume. Thermal sensors exist but for coolant monitoring, not primary reactivity control.

Why Other Options Are Wrong:

Temperature and pressure are thermohydraulic variables; volume is irrelevant; “density” does not apply to flux.

Common Pitfalls:

Confusing coolant temperature control with neutron power control; they are coupled but sensed by different instruments.

Final Answer:

none of these