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

They provide the extra reactivity needed to sustain fission

Answer

They increase the average neutron energy above the fission threshold

Answer

They are absorbed by control rods to reduce reactor power

Question 2

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

Accepted Answer

Eta (η)

Answer

k-effective (k-eff)

Answer

Epsilon (ε)

Answer

Resonance escape probability (p)

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

To reflect fast neutrons back into the core

Answer

To absorb excess neutrons and prevent supercriticality

Answer

To shield operators from neutron radiation

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

Reactor power rises as temperature increases, requiring operator action

Answer

Control rods must be inserted whenever coolant temperature rises

Answer

The reactor will scram automatically if temperature drops below setpoint

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

Fraction of thermal neutrons that cause fission rather than capture in U-238

Answer

Fraction of fast neutrons that escape resonance capture while slowing down

Answer

Average number of neutrons produced per thermal neutron absorbed in the moderator

Question 6

A reactor is described as 'prompt critical.' What does this mean?

Accepted Answer

The reactor is exactly critical using only prompt neutrons, without needing delayed neutrons

Answer

The reactor has reached its maximum licensed power level

Answer

All delayed neutron precursors have decayed to their equilibrium concentrations

Answer

The reactor control rods are fully withdrawn and at their minimum worth position

Question 7

What is 'reactor period' and how is it used operationally?

Accepted Answer

The time in seconds for reactor power to change by a factor of e (~2.718); operators use it to judge rate of power change

Answer

The calendar interval between required reactor shutdowns for refueling

Answer

The time required for a full control rod insertion during a scram

Answer

The half-life of the most abundant fission product in the core