3

Front 1

What does NOT afftect K eff?

Back 1

Installed Neutron Sources

Front 2

What if decreased will afftect K eff?

Back 2

fuel enrichment
control rod worth
shutdown margin when the reactor is sibcritical

Front 3

The effective multiplication factor (K eff) describes the ratio of the number of fission neutrons at the end of one generation to the number of fission neutrons at the ____of the ______ generation.

Back 3

end / previous

Front 4

What describes the ratio of the number of fission neutrons at the end of one generation to the number of fission neutrons at the end of the previous generation.

Back 4

The effective multiplication factor (K eff)

Front 5

K eff can be determined by dividing the number of neutrons in the 3rd generation by the number on neutrons in the ______

Back 5

2nd generation

Front 6

6 factor formula?

Back 6

E Lf P Lth F N

Front 7

___ accounts for neutron leakage

Back 7

K eff

Front 8

Lf =

Back 8

Fast non leakage prob

Front 9

Lth

Back 9

Thermal non-leakage prob

Front 10

E=

Back 10

fast fission factor

Front 11

Fast fission factor (E) =

Back 11

fast neutrons produced by ALL fission events / fast neutrons produced by thermal fission

Front 12

• Recall that_____ is the fraction of all neutrons that are born as delayed neutrons.

Back 12

B, the delayed neutron fraction,

Front 13

• The value of ______ depends upon the actual nuclear fuel used.

Back 13

B, the delayed neutron fraction,

Front 14

As previously discussed, the delayed neutron precursors for a given type of fuel are grouped on the basis of _____

Back 14

half-life

Front 15

Delayed neutrons being born at lower energies has two significant impacts.

Back 15

• Fast Fission Factor
• Leakage

Front 16

The power in one portion might be suppressed by over insertion of control rods in that portion of the core, which, for a constant overall power level, results in a relatively higher flux in the remainder of the core.

Back 16

• Power tilt:

Front 17

This situation can lead to xenon oscillations.

Back 17

• Power tilt:

Front 18

_____ is required to exist at all times, even when the reactor is critical. It is important that there be enough negative reactivity capable of being inserted by the control rods to ensure complete shutdown at all times during the core lifetime.

Back 18

• Shutdown margin

Front 19

• A shutdown margin in the range of _____ is typically required

Back 19

one to five percent reactivity

Front 20

____ refers to the fact that the shutdown margin does not take credit for the insertion of the highest worth control rod

Back 20

• The stuck rod criterion

Front 21

• The application of the _____ ensures that the failure of a single control rod will not prevent the control rod system from shutting down the reactor.

Back 21

stuck rod criterion

Front 22

• The term ______ is used to describe the total amount of reactivity added, positive or negative, due to changing a parameter by a given amount.

Back 22

“reactivity defect” (ρx)

Front 23

is the fractional change in neutron population per generation

Back 23

• Reactivity

Front 24

 Poisons are used for:


Back 24

Provide a more uniform power density
 Allow higher enrichment at initial fuel load
 Provide Neutron Flux Shaping

Front 25

Provide a more uniform power density
 Allow higher enrichment at initial fuel load
 Provide Neutron Flux Shaping

Back 25

Poisons

Front 26

 Non-Burnable Poison :_____ in Control Blades

Back 26

Hafnium rods/rodlets

Front 27

____ are used in power shaping, or to prevent excessive flux and power peaking.

Back 27

Non burnable poisons

Front 28

 At the end of cycle (EOC), ______

Back 28

NO burnable poison should remain.

Front 29

The design objective when loading burnable poisons is to increase core reactivity by poison burnout at the same rate of _____due to fuel depletion.

Back 29

reactivity loss

Front 30

____ are built into the core to aid in reactivity control early in core life.
 This allows for more fuel to be loaded into the core.
Gadolinium is a common burnable poison

Back 30

 Burnable Poisons

Front 31

____ Based of Steam Production, Important during normal power operation

Back 31

 Void Coefficient

Front 32

____ Based on Fuel Temperature, Important to stop rapid power rises, as the fuel temperature is first to change, effects outside the cladding in the coolant are secondary and take time to occur.

Back 32

 Fuel Temperature (Doppler) Coefficient –

Front 33

_____ Based on Coolant Temperature, Important during low power startups, before getting to saturation pressure

Back 33

 Moderator Coefficient –

Front 34

Void fraction =

Back 34

volume of steam / volume of steam and water

Front 35

 Negative coefficients : As power rises, so raises the temperature of the core and adds negative reactivity, which slows down, or turns, the power rise.

Back 35

 Negative coefficients : As power rises, so raises the temperature of the core and adds negative reactivity, which slows down, or turns, the power rise.

Front 36

____ Desirable because of its self regulating effect.

Back 36

 Negative coefficients:

Front 37

___In this case, the production of prompt neutrons alone is enough to balance neutron losses and increase the neutron population.

Back 37

• Prompt criticality :

Front 38

• A reactor whose reactivity even approaches ____ is likely to suffer damage due to the rapid rise in power to a very high level.

Back 38

prompt critical

Front 39

• If the reactivity of the core is one dollar, the reactor is ____

Back 39

prompt critical.

Front 40

___ is a specific type of core power distribution problem. It is a non symmetrical variation of core power in one quadrant of the core relative to the others.

Back 40

• A power tilt, or flux tilt,

Front 41

# of neutrons produced by fission in one generation / # of neutrons produced by fission in one generation

Back 41

• Infinite multiplication factor ( K infinity)

Front 42

• The condition where the reactor is critical on prompt neutrons, and the neutron population increases as rapidly as the prompt neutron generation lifetime allows is known as____

Back 42

prompt critical.

Front 43

• Sometimes neutron population gets low enough that it cannot be detected by the nuclear instrumentation.
• _____ are frequently used to provide a safe, easily monitored reactor startup.

Back 43

Installed neutron sources

Front 44

The reason that some reactors are designed to be under moderated is if the reactor were over moderated, an increase in temperature would decrease the _____ due to the expansion of the water as its density became lower.

Back 44

Moderator to Fuel ratio

Front 45

Optimum Point
» (_____ increasing the moderator to fuel ratio decreases keff due to the dominance of the decreasing thermal utilization factor.
» _____, decrease in the moderator-to-fuel ratio decreases keff due to the dominance of the increased resonance absorption in the fuel.
If the ratio is above this point, the core is said to be over moderated, and if the ratio is below this point, the core is said to be under moderated)

Back 45

Above / Below

Front 46

Moderator to Fuel Ratio : As the reactor designer increases the amount of moderator in the core (that is, Nm/Nu increases), neutron leakage decreases.
• Neutron absorption in the moderator (Σ) increases and causes a decrease in the thermal utilization factor.
• Having insufficient moderator in the core (that is, Nm/Nu decreases) causes an increase in slowing down time and results in a greater loss of neutrons by resonance absorption.

Back 46

Moderator to Fuel Ratio : As the reactor designer increases the amount of moderator in the core (that is, Nm/Nu increases), neutron leakage decreases.
• Neutron absorption in the moderator (Σ) increases and causes a decrease in the thermal utilization factor.
• Having insufficient moderator in the core (that is, Nm/Nu decreases) causes an increase in slowing down time and results in a greater loss of neutrons by resonance absorption.

Front 47

About 7 percent of the 200 MeV produced by an average fission is released at some time after the instant of fission. This energy comes from the____of the fission products.

Back 47

decay

Front 48

• When a reactor is started up with unirradiated fuel, or on those occasions when the reactor is restarted following a long shutdown period, the _____ will be very low.. .

Back 48

source neutron population

Front 49

• Because the effective delayed neutron fraction is dependent upon the nuclides used as fuel, the ____ is also dependent on the nuclides used as fuel.

Back 49

value of the dollar

Front 50

• When positive reactivity is added to the core there will be a ____ in reactor power.

Back 50

prompt jump

Front 51

The effective delayed neutron fraction is the product of the ______

Back 51

average delayed neutron fraction and the importance factor

Front 52

• The ____ is defined as the fraction of neutrons at thermal energies which were born delayed.

Back 52

effective delayed neutron fraction Beta bar eff

Front 53

• The value of beta bar is the weighted average of the______ of the individual types of fuel.

Back 53

total delayed neutron fractions