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RO32 ILT GFE Foundational Topics > Corrosion > Flashcards

Corrosion Flashcards

1
Q

What conditions must exist to cause fluoride stress corrosion

A
  • High temperature water
  • Presence of Oxygen and fluorides
  • Tensile stress
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2
Q

Define GENERAL CORROSION

A

A uniform dissolution or attack of a metal from all surfaces in contact with water

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3
Q

State whether a solution is acidic, neutral or basic, given the solution pH value at 25 degrees Celsius

A

Basic: pH > 7

Neutral: pH = 7

Acidic: pH < 7

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4
Q

What controls can be used to prevent or minimize chloride stress corrosion

A
  • Lower chloride content
  • Lower disolved oxygen
  • Use low carbon steels
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5
Q

What are the TRO limits for steady state RCS chemistry

A

TRM 8.4.1

Dissolved O2 <= 0.1 ppm

Chloride <= 0.15 ppm

Fluoride <= 0.15 ppm

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6
Q

What conditions are necessary for formation of the magnetite film on stainless steel

A
  • High temperatures (> 400 degrees Fahrenheit)
  • No dissolved oxygen
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7
Q

What conditions much exist to cause crevice corrosion

A

The crevice becomes a concentration cell

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8
Q

What controls can be used to prevent or minimize pitting corrosion

A

Eliminate/minimize dissolved oxygen and chlorides

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9
Q

What benefit is gained from general corrosion

A

If general corrosion results in a film of magnetite being created, this will slow down future corrosion as ferrous ions must pass through the film to react with water

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10
Q

What controls are used to prevent or minimize crevice corrosion

A
  • Eliminate crevices
  • Perform crevice cleaning
  • Reduce contaminants so they cannot concentrate
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11
Q

What conditions must exist to caustic stress corrosion

A

High pH and tensile stress

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12
Q

What conditions must be present to cause chloride stress corrosion

A
  • High temperature water
  • Presence of Oxygen and Chlorides
  • Tensile stress
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13
Q

What is the relationship between dissolved oxygen and general corrosion

A

As dissolved oxygen increases general corrosion increases

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14
Q

What chemical is used to intentionally initiate a CRUD burst

A

Hydrogen peroxide added to the RCS

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15
Q

What controls can be used to prevent or minimize caustic stress corrosion

A

Maintain system pH to prevent caustic levels from rising to a corrosive point

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16
Q

Why is a CRUD burst intentionally initiated

A

CRUD burst is initiated to dissolve the CRUD and transport it to the CVCS demineralizers to lower dose rates during an outage.

17
Q

Define FLUORIDE STRESS CORROSION

A

Intergranular corrosion which occurs in high temperature water, stainless steel, and the presence of oxygen and fluorides

18
Q

What is the relationship between temperature and general corrosion

A

As temperature increases general corrosion increases

19
Q

What is hydrogen embrittlement

A

Monatomic hydrogen diffuses into the Zircaloy resulting in a loss of ductility and tensile strength at pH values greater than 11.3

20
Q

What controls can be used to prevent or minimize fluoride stress corrosion

A

Minimize or eliminate fluorides

21
Q

What conditions must exist to cause pitting corrosion

A

Chemical activity that begins at the metal at the bottom of the pit acts as an anode and loses electrons forming corrosion products and deepens the pit

22
Q

What is the relationship between pH and general corrosion

A

pH at extremes will increase general corrosion (pH > 12 or pH <4)

23
Q

Define GALVANIC CORROSION

A

Dissolution or attack of a metal which results when two dissimilar metals are in contact in an electrolyte

24
Q

What are the TRO limits for transient RCS chemistry

A

TRM 8.4.1

Dissolved O2 <= 1 ppm

Chloride <= 1.5 ppm

Fluoride <= 1.5 ppm

25
Q

What is hydrogen blistering

A

Monatomic hydrogen combines to form H2 which will not diffuse and causes bulges in the cladding at pH values greater than 11

26
Q

What controls are used to prevent galvanic corrosion

A
  • Use metals that are generally corrosion resistant
  • Select metals that are close to each other in electronegativity
  • Maintain high water purity as pure water is a poor electrolyte
27
Q

Define CHLORIDE STRESS CORROSION

A

Intergranular corrosion which occurs in high temperature water, stainless steel, and the presence of oxygen and chlorides

28
Q

What conditions must exist to boric acid corrosion

A

Boric acid in contact with carbon steel

29
Q

What controls can be used to prevent or minimize boric acid corrosion wastage

A
  • Minimize RCS leaks
  • Cladding carbon steel
  • Substitute Stainless steel for carbon steel
30
Q

What conditions must be present for galvanic corrosion to occur

A

A difference in electrical potential between two metals which creates an electrical current flow

31
Q

State the definition of pH

A

The negative of the base ten logarithm of the hydrogen ion concentration of a solution given in moles per liter.

pH = -log (+H)

32
Q

Define BORIC ACID CORROSION WASTAGE

A

Localized attack of ferritic steel (carbon steel) due to high concentrations of boric acid resulting in metal wastage

33
Q

By what means can CRUD bursts can be initiated

A
  • Changing solubility by either pH, temperature, or dissolved oxygen changes
  • Mechanical shock (e.g., water hammer, velocity changes, etc.)
34
Q

Define CREVICE CORROSION

A

Localized attack at/in a mechanical crevice

35
Q

Define PITTING CORROSION

A

A type of corrosion attack that involved a deep attack in/on a small area of the metal

36
Q

Define CAUSTIC STRESS CORROSION

A

Corrosion that occurs in the presence of high pH levels

37
Q

What are three undesirable characteristics of CRUD

A
  • Fouls heat transfer surfaces
  • Collects and then provide higher radiation source term
  • Blocks flow passages or foul demineralization surfaces

RO32 ILT GFE Foundational Topics (12 decks)

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