Chemistry Flashcards
1
Q
Definition of pH
A
-Log[H+].
Units in Moles/Liter
2
Q
Acidic, Neutral or Basic?
A
0-7= Acidic
7= Neutral
7-14= Basic
3
Q
Definition of General Corrosion
A
Uniform dissolution or attack on metal from all surfaces in contact with water.
2 conditions:
1: Metal and water in contact
2: Chemical reaction between them to form an oxide.
4
Q
Conditions to form Magnetite
A
> 400F and NO Dissolved O2
5
Q
Benefit of general corrosion
A
Film of magnetite slows down corrosion.
Provides passive barrier to Iron ions passing through into the water
6
Q
Factors that affect corrosion rate
A
Temperature: high temp raises rate.
pH: extreme high/low pH raises rate (>12 causes caustic embrittlement).
Dissolved O2: more O2=more corrosion.
High Water Velocity (FAC).
7
Q
3 undesirable characteristics of CRUD
A
1: Fouls heat transfer surfaces.
2: Clogs flow passages/ fouls demins.
3: Increase radiation levels.
8
Q
How CRUD Bursts happen
A
Significantly changed pH.
Dissolved O2 changes.
Large temperature change.
Mechanical shock to the system.
9
Q
Chemical used and reason for intentional CRUD Burst.
A
Hydrogen Peroxide (H2O2).
Send CRUD to CVCS Demins to decon the RCS during cooldown for REFOUT.
Lowers radiation levels.
10
Q
1: 2 dissimilar metals in contact with electrolyte
2: Difference in potential between them creates current flow.
A
Galvanic Corrosion
11
Q
Ways to minimize Galvanic Corrosion.
A
1: Use metals that are corrosion resistant.
2: Use metals close to each other in electronegativity.
3: Maintain high water purity.
12
Q
1: localized attack at/in a mechanical crevice.
2: The crevice becomes a concentration cell.
3: Type of Pitting Corrosion.
A
CREVICE CORROSION
13
Q
Ways to minimize Crevice corrosion
A
1: Eliminate Crevice.
2: Perform crevice cleaning.
3: Reduce contaminants.
14
Q
1: A deep attack in/on a small area of the metal.
2: The metal at the bottom of the pit acts as an anode and loses electrons forming corrosion products and deepens the pit.
A
PITTING CORROSION
15
Q
How to minimize Pitting Corrosion
A
Minimize/eliminate dissolved O2.
16
Q
Intergranular corrosion which occurs at Hi temp water, stainless steel and the presence of O2 and chlorides.
A
CHLORIDE STRESS CORROSION
17
Q
Conditions for Chloride Stress Corrosion along grain boundaries.
A
Presence of Chlorides and Dissolved O2 with metal under tensile stress.
18
Q
Difference between Chloride Stress and Fluoride Stress Corrosion.
A
The presence of Fluorine contamination vs Chloride contamination. The mechanics are the same.
19
Q
Corrosion caused by:
1: High caustic levels and the subsequent metal attack.
2: High pH.
A
Caustic Stress Corrosion.
20
Q
How to minimize Caustic Stress Corrosion.
A
Maintain system pH below high caustic levels (corrosion rate of iron between pH of 4-10 is relatively low due to pH).
21
Q
Definition of Boric Acid Corrosion Wastage
A
Localized attack of ferrous steel (carbon steel) due to high concentrations of boric acid resulting in metal wastage.
22
Q
Ways to minimize Boric Acid Corrosion Wastage.
A
1: Minimize RCS (boric acid) leaks.
2: Cladding carbon steel or substituting stainless steel.
3: Keep boric acid covered metal dry.
23
Q
TRM 8.4.1 Steady State and Transient limits for Dissolved O2
A
1: <= 0.1 ppm SS.
2: <=1 ppm Transient
24
Q
TRM 8.4.1 Steady State and Transient limits for Chloride
A
1: <=.15 ppm SS.
2: <=1.5 ppm Transient.
25
TRM 8.4.1 Steady State and Transient limits for Fluoride
1: <=.15 ppm SS.
2: <=1.5 ppm Transient.
26
What is Hydrogen Blistering
Surface bulges from subsurface voids produced in a metal by hydrogen absorption in low strength alloys.
H2 will not diffuse and causes bulges in fuel cladding.
pH must be >11 (caustic)
27
What is Hydrogen Embrittlement
Loss of ductility and tensile strength (becomes brittle) in a metal from H2 absorption.
pH must be >11.3 (caustic).
28
2 mechanisms of fission product release to RCS
Tramp Uranium and Cladding Defect
29
Define Tramp Uranium
UO2 imbedded in fuel cladding (Zircaloy also contains 0.1-1.0 ppm uranium naturally occurring impurity)
30
Define Cladding Defect
Pinholes, cracks, etc. through which fuel generated fission products can leave the fuel and enter the RCS.
31
2 methods for monitoring fuel cladding integrity during power operations
1: Gross activity (sample for tritium, Total Gas Activity, and Non-gas Activity)
2: Iodine 131/133 ratio (different half lives, I-133 is shorter and a quick buildup indicates fission product release)
32
Define Dose Equivalent I-131
1: Concentration of I-131 equivalent to mixture of all radioiodines present.
2: Concentration that would produce thyroid dose as if all Iodines were I-131
3: Conversion factors of Iodine reflect their half-life and volatility, etc.
4: Dose Equiv <=1.0 microCurie/gm.
33
Define Dose Equivalent Xe-133
Based on acute dose to the whole body and considers the noble gases which are significant in terms of contribution to whole body dose.
34
Define CRUD
Metal oxides deposited or suspended in the RCS.
35
CRUD Cycle
1: Corrosion (outside core).
2: Corrosion products release.
3: Corrosion products deposit in core.
4: Corrosion products activate.
5: Corrosion products release again.
6: Corrosion products deposit outside core.
36
CRUD Burst causes
1: Significant temperature changes. (ie large power changes)
2: Significant pH changes.
3: Mechanical agitation.
4: Chemical introduction (Hydrogen Peroxide).
37
3 Major classifications of activation products
Activation of:
1: Corrosion products.
2: Water/water impurities.
3: Tritium production.
38
Give examples of activated corrosion products
Co-60, Ag-110, Fe-59, Cr-51, Mn-56, Mn-54, Zn-65, Co-58.
39
Give examples of activated water/water impurities.
N-16, Na-24, N-17, O-19, K-40, K-42, Ar-41.
40
Give examples of production of Tritium
1: 3Li6 + 0n1 -> 2a4 + 1H3
2: 5B10 + 0n1 -> 2 2a4 + 1H3
3: 1H2 + 0n1 -> 1H3 + gamma
41
Explain production of N-16
8O16 + 0n1 -> 1p1 + 7N16.
42
Why is N-16 bad mkay?
N-16 is a very high gamma emitter (6.12 MeV).
Most abundant activation product and most limiting include for shielding installation around the RCS.
(7.13 sec half life, not a concern after Rx S/D).
43
Where does majority of Tritium come from?
Neutron absorption of B-10. (~80% of Tritium production)
44
Hazards of Tritium.
1: Not removed by filtration, ion exchange or evaporation.
2: Low level beta emitter which becomes a concern if inhaled, ingested or absorbed in the skin.
3: Can’t be detected by whole body count, only by urinalysis.
4: Biological half-life of 8-14 days.
45
Tech Spec limit for RCS Specific Activity
3.4.16:
1: <=1 microCurie/gm Dose Eq I-131.
2: <=215.1 microCurie/gm Dose Eq Xe-133.
46
Basis for Tech Spec 3.4.16, RCS Specific Activity.
Ensures the 2 hour whole body dose to an individual at the site boundary during SLB or SGTR will be a small fraction of the allowed whole body dose. ( TEDE-25 R, Thyroid -300 R)
47
4 reasons for maintaining primary chemistry control.
1: Maintain material integrity.
2: Minimize Corrosion.
3: Reduce Radioactivity.
4: Assist in Reactivity Control.
48
Method of O2 control in RCS at power.
H2 blanket in VCT. (Gamma flux combines 2 H2 and O2 to form 2 H2O).
49
Primary source of O2 in RCS.
Radiolytic decomposition of water.
2 H2O <-> 2 H2 + O2 (reversible reaction).
50
Reasons for upper limit of [H2] in RCS
1: Excess H2 is wasted.
2: Problems degassing.
3: Explosive concern when >4% and <96%.
51
Method of O2 control in RCS while starting up.
Hydrazine (added between 140-180F)
N2H4 + O2 -> 2H2O + N2
52
Upper RCS temperature for Hydrazine addition and why
At >200F hydrazine breaks down.
53
Why are CVCS demins bypassed during hydrazine addition?
Decomposition products of hydrazine will exhaust resin and cause release of chlorides into the RCS.
54
TRM temp values where O2 concentration limits are in effect.
TRM 8.4.1:
O2 limit is applicable when RCS > 250F
55
Method of pH control in RCS
LiOH (enriched Lithium-7)
56
Why enriched Lithium-7 is used for pH control in RCS?
Li-6 will generate Tritium, so Li-7 used instead.
57
How excess Lithium is removed.
Cation Demineralizer (Cat Bed, delithiatiion).
58
Why is Lithium allowed to lower over core life to maintain the same pH? (6.9-7.2)
As Boron concentration lowers, less Lithium is required to offset the acidic effect from the boric acid.
59
How do demineralizers purify water.
Filtration and ion exchange.
60
List decontamination factors indicative of new vs spent resin.
DF = inlet concentration / outlet concentration.
DF >25 = new resin.
DF =1 = completely exhausted resin.
61
Type of resin used in normal (in service) mixed bed demin.
Li7OH
62
Type of resin used in the standby mixed bed demin.
HOH. (If used throughout cycle it can be converted into Li7OH bed for free)
63
Type of resin used for Cation Demin.
H+ resin (used for delithiation).
64
Type of resin used for deborating demin.
OH- resin (can remove up to 50 ppm boron per bed).
65
2 reasons for using Cation Demins.
1: Delithiation.
2: Removal of radioactive impurities (Cs-137).
66
When in core life are the Deborating Demins used and why?
Later on in core life as the amount of water required to dilute Boron increases dramatically and becomes un feasible.
67
Effect of DP on Demineralizers.
HI DP means flow obstruction blockage.
LO DP could indicate Channeling.
Both could indicate resin fouling and resin exhaustion (need chemistry sample to verify).
68
Define Channeling with respect to Demineralizers.
Caused by excessive flow rate, an open path is created through the resin bypassing the resin and lowering effectiveness of the Demin.
69
Effects of channeling in a demineralizer.
1: RCS flow may bypass the resin
2: Contact time with resin is reduced and lowers effectiveness of the demin. (May indicate low DP as well).
70
Gases that would normally be present in the RCS.
O2
N2
Ar
He
Xe
Kr
71
Locations in RCS or subsystems where gases could be removed.
VCT
BA Evap
CVCS HUT
PZR - due to hi temps (spray)
72
Describe Denting in SG U tubes
Plastic deformation occurring at the tube support plates due to corrosion buildup.
73
Describe Wastage corrosion
Localized corrosion caused by acidic attack in low flow areas.
74
Describe Pitting in SG U tubes
Localized attack at sludge sites that may penetrate the SG tube.
75
Describe Stress Corrosion Cracking with respect to SG U tubes
Tube cracking at the SG U bend caused by Chlorides and/or stress.
76
Describe Intergranular Attack on SG U tubes.
Corrosion of SG tube grain boundaries at tube sheet crevice or dry out areas.
77
Describe Fretting of SG U tubes.
Local wear from impact or sliding of tubes against support plate or the other tubes due to flow induced vibration.
78
Describe Erosion-Corrosion with respect to SG U tubes.
Mechanical damage from impingement of SG tubes from suspended corrosion products or reactive chemicals.
79
Describe Fatigue with respect to SG U tubes.
Circumferential tube cracking as a result of cyclic flow or temperature stress.
80
2 functions of Hydrazine in reducing plant corrosion.
1: O2 scavenger
2: Raises pH
81
Why is Cation conductivity better indication of condenser leak than standard conductivity?
When NaCL enters the Cation bed, Na+ exchanges with H+ and the H+ combines with Cl to form HCl which has a strong conductivity signature.
82
State locations sampled for cation conductivity on the Hi Range Conductivity Recorders.
1: Total Hotwell
2: Total Feedwater
3: SG Blowdown
4: Feedwater Cation
5: Total Hotwell Cation
6: Makeup Plant Effluent
83
Chemical Constituent Administrative Specifications 5.2 parameters and req’ts for SG Operation in mode 1 (>50% power)(non-tech spec)
Na, Cl, Sulfate and Cation Conductivity.
Action levels: (ppb)
1: >5(Na), >10 (Cl, SO4), N/A for CAT
2: >50 (Na, Cl, SO4), >Baseline +1 (CAT)
3: >250 (Na,Cl,SO4), >Baseline +4 (CAT)
84
High SG contaminant requirements
Action level:
1: Corrective action ASAP w/in 21 days
2: Reduce power to 30-50% w/in 24 hrs
3: Reduce power to <5% ASAP, safely
85
Reason for power reduction for SG contamination
1: concentrate contaminants locally at the leak for ease of identification
2: lower Tave to lower corrosion rate
3: Lower SG heat flux causing lower hideout/damage to SGs. Also reduce sludge formation.
86
LCO 3.4.13 requirements
1: No pressure boundary leakage
2: 0.8 gpm unidentified leakage
3: 10 gpm identified leakage
4: 150 gpd primary to secondary leakage through any 1 SG.
87
Describe ionic bond
1 or more electrons wholly transferred from an atom of one element to the atom of another element. (Ex. NaCL)
88
Describe Covalent Bond
Bond formed by shared electrons (Ex. H2O)
89
Describe Metallic Bond
Electrons aren’t shared or exchanged, instead they are free to move throughout the metal as an electron pool. (Ex. Fe)
90
Describe Molecular Bond
Temporary weak charge exists when electrons of neutral atoms spend more time in one region of their orbit than another. The molecule weakly attracts other molecules. (Ex. Water molecules)
91
Describe Hydrogen Bond
Similar to molecular bond. Occurs due to the ease with which hydrogen atoms are willing to give up electron to atoms of O2, Fluorine, or N2. (Ex. Ice crystal structure)
92
Describe Amorphous Solid
No regular arrangement of atoms or molecules. Have properties of solids and have shape/volume, diffuse slowly, lack sharply defined melting points, and resemble liquid that flows slowly at room temp. (Ex. Glass sags over a very long time)
93
Describe Crystalline Solids
Arrays of atoms in regular patterns create crystal structures. Pattern periodically repeats in 3D geometric lattice. Forces with this bonding causes:
Strength, Ductility, Density, Conductivity, and Shape.
94
Describe Grain Structures.
Arrangement of grains in metals. Each grain has crystal or lattice. Grain size determines properties. Smaller grain increases Tensile strength and Ductility. Larger grain improves high temperature creep properties.
95
Describe Body Centered Cubic (BCC) lattice structure
Unit cell has 8 atoms at corners of cube and 1 atom at center of cube.
(Ex. Fe(ferrite), Cr, V- vanadium, Mo- Molybdenum, and W- Tungsten)
High strength and low ductility.
96
Describe Face centered Cubic (FCC) lattice structure
8 atoms at corners of cube and 1 atom at the center of each of the cube faces.
(Ex. Fe(austenite), Al, Cu, Pb, Ag, Au, Ni, Pt- Platinum, Th- Thorium)
Lower strength and higher ductility than BCC metals.
97
Describe Hexagonal Close Packed (HCP) lattice structure.
3 layers of atoms. Top and bottom hexagons have 6 atoms at the corners and 1 in the middle. The middle layer has 3 atoms evenly spaced. Total of 17 atoms. (Ex. Be, Mg, Zn, Cd, Co, Tl- Thallium, Zr)
Not as ductile as FCC metals.
98
What are point imperfections in solids?
Have atomic dimensions. An atom of a different element replaces an atom of the crystal lattice. (Vacancy, Substitutional, Interstitial)
99
Describe Vacancy Point Imperfection
Missing atom in lattice.
Imperfect packing during crystal process.
May be due to increased thermal vibrations of the atom from elevated temps.
100
Describe Substitutional point imperfection.
Impurity at lattice position.
Caused by alloying material added to the metal (intentional), such as carbon.
101
Describe Interstitial Point Imperfection.
Locations between atoms in lattice structure. (ie not in the lattice position)
Impurity in interstitial position (usually unintentional) like in glass.
102
Describe Line Imperfections or Dislocations in metals.
Edge, Screw, Mixed. Cannot end inside a crystal, only at edge or other dislocation or close back on itself. Ease of which dislocations move thru crystals determines their importance.
103
Describe Interfacial Imperfections in metals.
Larger than line defects. Occur over a 2 dimensional area.
104
Common characteristics of alloys.
Stronger than pure metals.
Lower electrical conductivity.
Lower thermal conductivity.
(Ex. Steel)
105
Desirable properties of type 304 stainless steel.
Extremely tough.
Resists most types of corrosion.
18-20% Cr, 8-10.5% Ni.
106
Describe Strength in regards to metals.
Ability to resist deformation.
Max load before failure occurs.
107
Describe Ultimate Tensile strength (UTS) of metal.
Max resistance to fracture.
Max load of 1 sq inch cross sectional area with load applied as tension.
108
Describe Yield Strength of metal.
Stress where plastic (permanent) deformation starts.
109
Describe Ductility in metals.
Ability to deform easily on the application of tensile stress, or the ability to withstand plastic deformation without failure.
Bendability and crushbiluty as well.
110
Describe Malleability of metals.
Ability to exhibit large deformation when subjected to compressive stress. Opposite stress of Ductility.
111
Describe Toughness in metals.
The way metal reacts under sudden impacts.
Work required to deform 1 cu. Inch until failure.
112
Describe Hardness in metals.
Ability to resist plastic deformation, penetration, indentation, and scratching.
Good for resistance to wear from friction or erosion (from stm, oil, water flow).
113
Describe Heat Treatment of metal.
Heated metal gains certain properties.
Toughness and Ductility lower while Hardness and Tensile Strength rise.
Unsuitable for type 304 because of its crystal structure.
114
Describe Cooling (Quenching) in metals.
Varying rates of cooling allows control of grain size.
Faster cooling- smaller grain size and harder metal.
115
Describe Annealing in metals.
Slow heating and held for long time and cooled.
Refines metal grain structure to relieve internal stresses, soften the steel and improve ductility.
116
Describe Cold Working in metals.
Plastic deformation at temp (relatively lower) such that work hardening is not relieved. (Not annealed). Decreases Ductility by slipping crystal structure until no more slip.
117
Describe Hot Working in metals.
Higher temp (above re crystallization temp) work to prevent strain hardening (no crystal slip).
Ductility rises and resistance to plastic deformation lowers.
118
Corrosion resistant materials
Stainless steel
Nickel
Chromium
Molybdenum
119
What is the Rx vessel lined with to help mitigate corrosion and why
Carbon steel vessel lined with stainless steel clad to provide a barrier to the carbon steel (high strength, low corrosion resistance) from corroding.
120
How to control Galvanic Corrosion
Use metals with similar electronegetivity.
Use water free of contaminants.
Use corrosion resistant materials.
Use DC current or sacrificial anode.
121
Describe Stress Corrosion Cracking.
Intergranular attack at grain boundary under tensile stress.
122
Methods to control Stress Corrosion Cracking.
Design proper systems/components.
Lower stress.
Remove Hydroxides, Cl, O2.
Avoid stagnate areas for baddies to concentrate.
Lower alloy steel is less susceptible, but more in water with Cl.
Ni based alloys (Inconel) are NOT affected by Cl or hydroxides.
123
Methods to control Chloride Stress Corrosion
Low Cl and O2.
Use low carbon steel.
124
What type of steel is susceptible to Caustic Stress corrosion?
Carbon steel.
Can also occur in Inconel tubing.
Heat treating Inconel at 620-705C improves its resistance to Caustic Stress Corrosion Cracking.
125
Describe H2 Embrittlement.
Steel loses ductility and strength due to tiny cracks from internal pressure of H2 or Methane (CH4) that form at the grain boundaries.
126
Describe Fatigue Failure of metal.
Tendency to fracture by means of progressive brittle cracking under repeated alternating or cyclic stresses at levels considerably below the normal strength.
127
Describe Work Hardening in metals.
Straining metal beyond the yield point in the ductile region. Produces additional plastic deformation and causes the metal to become stronger and more difficult to deform. (Lattice structure slips until no more slip)
128
Describe creep in metal.
At higher temps (typically>1000F) metal deforms at slow rate with constant stress.
Creep rate constant for a long period at constant stress and temp.
Creep rate increases after time and certain amount of deformation until fracture.
