Objectives Flashcards
State the definition of pH.
The negative of the base ten logarithm of the hydrogen ion concentration of a solution given in moles per liter.
State whether a solution is acidic, neutral or basic, given the solution pH value at 25°C.
<7 is acidic. 7 is neutral. >7 is basic
State the definition of General Corrosion
A uniform dissolution or attack of a metal from all surfaces in contact with water.
List the conditions necessary for formation of the magnetite film on stainless steel.
A magnetite film is formed on iron compounds at high temperatures (>400°F) and in the absence of dissolved oxygen (Fe3O4).
State the benefit gained from General Corrosion.
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.
State the direction of change of General Corrosion rate as the following factors change: Temperature, pH, dissolved oxygen.
Temperature: high temps increase the General Corrosion rate.
pH: extreme pH in either direction will increase corrosion rates. A pH of >12 causes caustic embrittlement.
Dissolved oxygen: the more dissolved oxygen, the more General Corrosion.
Describe 3 undesirable characteristics of CRUD.
CRUD will foul heat transfer surfaces; it will tend to collect and then provide a higher radiation source term; CRUD may block flow passages or foul demineralizer surfaces.
State the means by which CRUD bursts are initiated.
A CRUD burst can be caused by changing the ability of CRUD either by pH, temperature or dissolved oxygen changes. It can also be caused by mechanical shock (water hammer, fluid velocity changes).
State the chemical used and the reason for intentionally initiating a CRUD burst prior to shutdown.
A CRUD burst is initiated by addition of H2O2, hydrogen peroxide, to the RCS. We attempt to dissolve the CRUD and transport it to the CVCS demineralizers to “decon” (reduce the source term of) the RCS.
Define Galvanic Corrosion and describe how to minimize it.
Dissolution or attack of a metal which results when 2 dissimilar metals are in contact in an electrolyte. To minimize, use similar metals, remove DOs, maintain high water purity and use a sacrificial anode.
Crevice Corrosion type
Localized attack at or in a mechanical crevice. To minimize, eliminate crevice, perform crevice cleaning and/or reduce contaminants so they cannot concentrate.
Define Pitting Corrosion and describe how to minimize it.
A deep attack in or on a small area of the metal. To minimize, reduce aggressiveness of the environment, use pitting resistant materials, improve system design.
Define Chloride Stress Corrosion and describe how to minimize it.
An intergranular corrosion which occurs in high temperature water for austenitic stainless steel in the presence of oxygen, chlorides and tensile stress. To minimize, maintain low chloride ion and oxygen content, use low carbon steels.
Define Fluoride Stress Corrosion and describe how to minimize it.
An intergranular corrosion which occurs in high temperature water for Inconel and Zircaloy-4 in the presence of oxygen, fluorides and tensile stress. To minimize, maintain oxygen and fluoride concentrations low; stay within Tech Spec limits.
Define Caustic Stress Corrosion and describe how to minimize it.
Where ferrous metals, Inconel and Zircaloy are susceptible at elevated pH and in the presence of tensile stress. To minimize, maintain proper pH.
