NANTeL Reactor Theory and Fundamentals 2

Question 1

What is the primary role of delayed neutrons in reactor control?

Accepted Answer

They slow the neutron chain reaction enough for mechanical control systems to respond

Answer

Delayed neutrons extend the effective neutron lifetime from microseconds to tens of milliseconds, making the reactor slow enough for control rods and other mechanical systems to regulate power.

Question 2

Which quantity represents the average number of neutrons produced per neutron absorbed in the fuel?

Accepted Answer

Eta (η)

Answer

Eta (η) is the reproduction factor, defined as the average number of fission neutrons emitted per neutron absorbed in the fuel.

Question 3

In a thermal reactor, why is a moderator necessary?

Accepted Answer

To slow fast neutrons to thermal energies where fission cross-sections are much higher

Answer

Fission cross-sections for U-235 and Pu-239 are orders of magnitude larger at thermal energies, so the moderator slows neutrons to maximize the probability of causing fission.

Question 4

What does a negative temperature coefficient of reactivity (TCR) mean for reactor safety?

Accepted Answer

An increase in temperature automatically reduces reactivity, creating inherent self-regulation

Answer

A negative TCR means the reactor is inherently self-regulating: if power rises and temperature increases, reactivity drops, reducing power back toward equilibrium without operator action.

Question 5

The six-factor formula (k∞) for an infinite reactor is expressed as ηεpf. What does the thermal utilization factor (f) represent?

Accepted Answer

Fraction of thermal neutrons absorbed in fuel compared to all thermal absorptions in the core

Answer

Thermal utilization (f) is the fraction of all thermal neutron absorptions in the reactor that occur specifically in the fuel, reflecting competition between fuel and non-fuel absorbers.

(NANTeL) National Academy for Nuclear Training e-Learning Practice Test

(NANTeL) National Academy for Nuclear Training e-Learning Practice Test

NANTeL Reactor Theory and Fundamentals 2