Lecture 7: Materials & Fuel Flashcards

1
Q

What are the three aims of understanding for materials used in nuclear reactor?

A

Understand the failure processes due to radiation.
Understand the corrosive nature of water.
Understand the corrosive nature of temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define displacement damage:

A

Damage as a result of nuclear interactions, typically scattering, which can cause lattice defects.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the two potential interactions between radiation and materials?

A

Shielding - properties of material are not degraded.
Damage - changes caused to material properties.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does the intensity of a narrow beam of mono-energetic particles vary through a material?

A

Intensity decreases exponentially.
I=I_0 e^-nsigmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define the linear attenuation coefficient:

A

Describes the fraction of beam that is absorbed or scattered per unit thickness of material.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Define the half-value layer (HVL):

A

Thickness of material required to reduce the intensity of radiation by 50%.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the equation to calculate the half-value layer?

A

HVL = 0.693 / u

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Define the attenuation length:

A

Reciprocal of linear attenuation coefficient.
The average distance travelled by a particle before it is absorbed or scattered.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the units of mass attenuation coefficient?

A

u / rho = cm2 / g

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Which radiation type is most penetrating?

A

Gamma rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What material properties are needed to absorb gamma rays?

A

High atomic numbers and high density.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define radiation damage:

A

Disruption to an initially undamaged structure caused by high-energy radiation passing through it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the effect of radiation damage?

A

Causes degradation and aging.
Restricts performance and defines service lifetime.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the effect on yield stress as a result of irradiation?

A

Increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the effect on elongation as a result of irradiation?

A

Reduces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Do materials become more or less brittle as a result of irradiation?

A

More brittle

17
Q

What happens to the dimensions of a material after radiation?

A

Swelling increases volume.

18
Q

List eight defects induced by radiation damage:

A

Vacancies
Interstitials
Electronic
Voids
Bubbles
Dislocations
Loops
Precipitates

19
Q

Define vacancies:

A

Missing atoms

20
Q

Define interstitials:

A

Atoms at sites in the crystal lattice not usually occupied.

21
Q

Define electronic defect:

A

Missing or trapped electrons

22
Q

Define voids:

A

clusters of missing atoms

23
Q

Define dislocations:

A

Line defects that start and end at surfaces or grain boundaries.

24
Q

Define loops:

A

Line defects that loop back on themselves

25
Define precipitates:
second phase particles
26
Define bubbles:
clusters of gas atoms occupying voids
27
What are the four components of a nuclear fuel assembly?
Fissile substance (e.g. U235) Host matrix (e.g. oxide or metal U238) Metal cladding (to prevent fission gases escaping) Additional fittings (to hold structures together and locate into reactor)
28
Is U238 fertile or fissile?
Fertile
29
How many fuel assemblies per core in a PWR?
193
30
How many pins per fuel assembly in a PWR?
200
31
Why are fuel pellets dished/concave at each end?
To accommodate the increased thermal expansion of the pellet interior relative to the edges.
32
Why are fuel pellet edges chamfered?
To ease the assembly of pellets into pins and prevent damage.
33
How is LLW disposed of?
Placed in metal containers and buried.
34
How is ILW disposed of?
Encapsulated in cement
35
How it HLW disposed of?
Immobilised in glass and stored underground