Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Nuclear > Zirconium > Flashcards

Zirconium Flashcards

1
Q

Why is Zirconium used in nuclear fuel?

A

Cladding must be of good neutron economy, high neutron flux, generate heat, minimal creep
Zirconium - low thermal neutron absorption cross section, good mechanical properties, corrosion resistance, radiation tolerance, machinability

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

What are the problems associated with Zirconium?

A

Production of H, burning int high temperature steam
Long term corrosion resistance, H pick up, hydride embrittlement
Anisotropic properties HCP structure at low T

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

How is Zirconium extracted?

A

Kroll - zirconium silicate/oxide
2Mg (l) + ZrCl4 -> Zr (s) + 2MgCl2 (s)
Vacuum arc melting to alloy

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

Why is HF removed from Zr?

A

Hf has much higher neutron cross section - can be used in control rods

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

How are Zr tubes formed?

A

Extrusion, drawing or pilgering

Pilgering most commonly used - cold + mandrill

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

What are the crystallographic structures of Zr?

A

HCP - ABABA, 6 fold symmetry

BCC - no close packed

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

What are the crystallographic planes in HCP?

A

Basal - (0002)
Prismatic - {1 -1 00}
Pyramidal (1st) - {1 -1 0 1}

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

What is the burgers orientation relationship?

A

During phase transformation of high T beta BCC to low T alpha HCP - close packed planes and directions overlap
Shared planes {0001}A//{110}B

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

What are the two deformation modes of HCP metals?

A

Dislocations - line defects on discrete directions and planes
Twins -

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

What are the different types of dislocations?

A

Screw
Edge
Mixed

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

How can yield occur by dislocations?

A

Existing dislocations become mobile - Schmid

New dislocations emitted - Frank Read sources

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

What is a double arm Frank-Read source?

A

Applied shear stress moves dislocation
Sessile at either end, mobile middle portion
Dislocation glides and opens up (two screw sources)
Continues till bows so far to pinch itself
Terminates on existing dislocation loop
New loop forms

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

Which crystal orientations are associated with soft and hard grains?

A

Hard - load parallel/perpendicular to basal/prismatic -> pyramidal only active slip system of much higher CRSS
Soft - basal or prismatic active

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

What is crystal twinning?

A

At low temp and high stress rates, especially in hard grains, significant lattice shear due to rotation of the lattice occurs

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

What are the two twinning modes in Zr and their consequences?

A

Contraction twin - C1 - under tension -> rotation 85 of c axis
Extension twin - T1 - under compression -> rotation 65 of c axis

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

How can crystallographic texture be analysed?

A

EDX - pole figures
Stereographic projection
EBSD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the effects of texture?

A 
Mechanical properties
Irradiation creep
Thermal expansion, conductivity
Radiation transport
Elastic properties
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How can texture be described?

A

Kearn’s factor

volume fraction of axis along each of the three major poles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is texture formed?

A

Due to crystal rotation as crystal deforms by dislocations, twinning
Soft grains deform first and reorientate
Texture changes with heat treatment - recovery, recrystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the strain paths for pilgering?

A

Radial strain - reduce radius
Hoop strain - reduce thickness
Biaxial - both simultaneously

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Why alloy Zr?

A

To change mechanical and corrosion properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the effect of oxygen?

A

Alpha stabiliser - raises beta -> alpha transus

potent interstitial solution strengthener

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the effect of tin?

A

Alpha stabiliser
Dilute solution, improves waterside corrosion resistance
Creep strengthener

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the effect of niobium?

A

BCC - beta stabiliser

enables microstructures similar to Ti to form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is the effect of Fe/Cr?
Beta stabiliser Forms small secondary phase particles Fe - improves corrosion resistance due to ion transport through oxide layer
26
What is the effect of nickel?
Forms secondary phase particles | Improves hydrogen pick up - corrosion resistance by changing the occupancy of Zr4+ hence changes ion transport
27
From the melt how is Zr4 processed to obtain desired texture?
Hot ingot Quench - little pinning of beta grains Extrusion - high temperature so soft to reduce high ratio - 5% stored dislocation - hardening so must recover Annealing - recovery - anihilates dislocations of opposite signs 80% reduction pilgering - cold Aneal - cant push too far since might crack 70% pilger - colder - engineering decission to go hot to cold Anneal 56% pilger - cooler (reducing % and T each time) Final anneal - globular structure, fine grains texture orientation towards (0002) sample normal
28
What affects the performance of Zr alloys?
Alpha grain size Texture Heat treatments/Welding Alloy chemistry
29
What is the evolution of Zr texture?
Big beta grains -> alpha grains (BOR) Beta grain refinement through processing - annealing Texture switches to (0002) towards sample normal Control re-crystallisaton/growth new grains
30
What is the evolution of Zr microstructure?
Prior beta grains with alpha laths
31
What are secondary phase particles?
Small spherical particles of different crystallographic structure decorating Zr matrix, distributed within alpha matrix eg Fe/Ni/Cr Important for corrosion resistance due to hydrogen pick up
32
How does H affect Zr?
When H is introduced to the system - by low quality alloys or wet fuel H beta stabiliser Forms solid hydrides - brittle - delta FCC hydrides - ZrH2 with CaF2, Zr on corners, H on (1/4 1/4 1/4) gamma - FCT - c/a ratio >1, metastable
33
What is the effect of the morphology of hydrides?
Hydrides grow as a needle-like precipitate (lenticular) - do not fit in Zr structure strain 5%, strain 7% - incoherent interface grow outwards - local hardening, loss in ductility eruption of dislocation loops to balance out misfit strain
35
How do hydrides effect the mechanical properties?
Increasing H conc step drop in modulus Yield stress similar but more complex - reduces by 1/3 Increasing H reduces K1C
36
How does the location of hydrides effect cracking?
Hollow rod shape hence to prevent cracking from hoop stress must align hydrides perpendicular to stress to prevent 'unzipping'
37
How can the location of hydrides be controlled?
Texture
38
How can hydrides be removed?
Niobium picks up hydrogen before hydrides can form - lowers reduction of water Reduces K1c decrease massively with increasing T H remains locked in beta phase so K1c doesn't change much when Nb is present
39
What is delayed hydride cracking?
Hydrides orientated badly for crack propagation Heat -> hydrides at crack tip reorientate Crack progress, stress alleviates Repeat
40
How does temperature cycling effect hydrides?
Reduction in toughness due to dissolution of hydrides at high T then precipitate at low T H diffuses to regions of cold, forms preferentially at areas of high tensile stress
41
What does the concentration of Hydrides at cracks depend on?
Concentration of hydrogen volume of hydrides hydrostatic stress Temperature
42
What are the different stages of crack growth?
Stage 1 - no growth - manageable Stage 2 - stable growth - manageable, not good Stage 3 - unstable crack growth - fast unmanageable
43
What is the process zone model?
Crack processes based upon 'strip yield' delayed hydride cracking occurs when critical displacement vc achieved hydride is thin region of constant cohesive strength process zone -> external stress + cohesive stress = 0 stress reduces as PZ moves through hydride
44
What are the main steps in fuel rod fabrication?
``` Cladding tube, inspection Insert lower end plug - optional weld Pellet stack make up and length check load pellets and weigh Measure length Decon tube open end Insert plentum spring Insert tube with open end into weld chamber Solid/hollow end plug ```
45
When is welding required?
During the solid end plug or hollow end plug stage Grid/guide tube, spacer water rods Fuel channel
46
What are the different welding techniques?
``` Tungsten inert gas Resistance Laser beam Electron beam Spot welding ```
47
What are the principles of tungsten inert gas welding?
TIG - tungsten electrode, arc of electrons, contained with inert shielding gas (argon/helium) Cheap but requires very skilled welder
48
What are the principles of upset welding?
Friction, two parts of similar size pushed together, heat+displacement = fusion
49
What are the principles of laser beam welding?
High power laser, local melting (small spot size, reduces HAZ, dissipated heat small -> reduced HAZ) Clean, automatic
50
What are the principles of electron beam fusion?
Sample in vacuum, part welded with high flux of electrons, locally heats+fuses Clean but expensive
51
What are the principles of spot welding?
Geometry important | Cheap, repeatable
52
How does welding effect the metallurgy and mechanical properties?
Large thermal sink -> large columnar grain in fusion zone HAZ - globular grains High residual stress due to thermal expansion
53
How can residual stress be measured?
Hole drilling Contour drilling Diffraction method
54
How do the conditions in the reactor affect the fuel cladding?
High T and P Steam High neutron flux -> Waterside corrosion and irradiation creep
55
What are the mechanisms of corrosion in Zr?
High T, steam H forms at cathode in half cell - proton released from water, recombines with electrode forming hydrogen H diffuses towards tensile stress, lower chemical potential of hydrogen oxide layer grows during transport
56
What is irradiation growth?
Neutron bombardment generates lots of point defects - vacancies and interstitials Accumulation of defects at traps/sinks - dislocations -> climb -> irradiation growth Occurs in absence of applied stress Crystallographically anisotropic - grows contracts
58
What is irradiation creep?
Elevated temperature deformation - enhanced by defects | Occurs due to pellet clad interactions - causes tubes to collapse and rupture
59
What are the stages of creep?
Primary - transient Secondary - steady state Tertiary - unstable
60
What does creep depend on?
``` Neutron flux applied stress time activation energy texture grain size dislocation density alloy type ```
61
How can creep be mitigated?
Solute strengthening - Sn/Nb/O - inhibits dislocation movement, sinks for vacancies and self interstitials Grain size and substructure - cold worked creep faster than recrystallised Texture - creep and growth anisotropy

Nuclear (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions