EPRI Nuclear Power Plant Materials
Exam Questions and Answers
What is Materials Degredation? - Answers -Many passive components in a nuclear
plant such as pipes, valve bodies, pressure vessels that are susceptible to degradation.
Degradation can be cracking of metal by fatigue or stress corrosion, wall loss due to
erosion or general area corrosion. This can lead to a leak/rupture. Principle concern of
degradation is nuclear safety. Can also result in costly outages, more regulatory
oversight, and loss of time for plant.
Components/Programs important to nuclear safety - Answers -PWR/BWR Vessels and
internals, SG, primary pressure boundary components, materials issues related to non
destructive evaluation, chemistry programs, related non destructive evaluation
When does stress corrosion cracking happen? Provide example locations - Answers -
Certain conditions such as High tensile stress, a corrosive environment, and susceptible
materials. (Ex: CRDM penetrations, SG tubing)
What is tensile strength? - Answers -max stress a material can withstand without
breaking while being pulled/stretched
What guideline is required for evaluating and repairing material degradation? - Answers
-NEI 03-08
What is a metal? - Answers -Large collections of millions of crystals composed of
different atoms held together by metallic bonds. Metals are a class of elements and/or
compounds that may have a high melting point, solid at room temp, good conductor of
heat, etc)
What is an alloy? How do they enhance metal? - Answers -A mixture of two or more
materials and at least one of which is metal. Enhance metal generally by: increasing
strength, hardness enhance ductility (ability of mtl to be deformed without fracture),
increase resistance to corrosion, increase machinability, increase wear resistance.
Alloys are usually stronger than pure metals (ex: steel)
What are the two different types of alloys? - Answers -1) Ferrous alloys (contain iron) 2)
Non ferrous alloys (do not contain iron)
What is ferrous alloy? - Answers -Means iron. include iron and alloys of at least 50%
iron such as cast iron, wrought iron, steel, stainless steel. Highly dependent on
possessing key element of carbon.
, What is non ferrous alloys? - Answers -Metals composed of elements other than iron.
Examples: copper, nickel (inconel), cobalt (stellites), and zirconium alloys. Commonly
used in nuclear plants.
What is strength? - Answers -Ability of material to support an applied load. Ability to
resist deformation.
What is ductility? - Answers -Ability of a material to deform easily upon the application of
tensile force without rupture- Prior to fracture
Conductivity? - Answers -Property of conducting heat/electric current
3 different types of crystal structures? - Answers -Body centered cubic (bcc), Face
centered cubic (fcc), Hexagonal close packed (hcp)
What is lattice? - Answers -3 dimensional array of atoms in a metal molecule in which
the array is a regular repeating configuration in all directions
What is BCC? - Answers -8 atoms at corner and one in center. High strength, low
ductility. Ex: iron, chromium
What is FCC? - Answers -8 atoms on corners and one at center of each of the faces of
cube. Lower strength, higher ductility. Ex: iron, aluminum, nickel,. silver, gold
What is HCP? - Answers -3 layers of atoms. top and bottom contain 6 atoms of
hexagon, on at center of each hexagon, etc. Not as ductile as FCC but more than BCC.
Lower strength than BCC. Ex: cobalt, beryllium, magnesium
What is a grain? - Answers -a crystal - merely a crystal without smooth faces because
its growth was impeded with another grain or boundary surface / avg size of grain is
important to the metal as it determines the properties.
What is a ground boundary? - Answers -Interface between grains / grains and grain
boundaries help determine the properties of a material
What does it mean if you have a smaller grain size? - Answers -increases tensile
strength and ductility (faster metal is cooled smaller grain gets)
What is machinability? - Answers -How a metal reacts to mechanical deformation by
removing chips with respect to the amount of metal effectively removed and the surface
finish attainable
What are the 10 properties of metals? - Answers -Brittleness, ductility, elasticity,
hardness, malleability, plastic deformation, strength, strain, stress, toughness
Exam Questions and Answers
What is Materials Degredation? - Answers -Many passive components in a nuclear
plant such as pipes, valve bodies, pressure vessels that are susceptible to degradation.
Degradation can be cracking of metal by fatigue or stress corrosion, wall loss due to
erosion or general area corrosion. This can lead to a leak/rupture. Principle concern of
degradation is nuclear safety. Can also result in costly outages, more regulatory
oversight, and loss of time for plant.
Components/Programs important to nuclear safety - Answers -PWR/BWR Vessels and
internals, SG, primary pressure boundary components, materials issues related to non
destructive evaluation, chemistry programs, related non destructive evaluation
When does stress corrosion cracking happen? Provide example locations - Answers -
Certain conditions such as High tensile stress, a corrosive environment, and susceptible
materials. (Ex: CRDM penetrations, SG tubing)
What is tensile strength? - Answers -max stress a material can withstand without
breaking while being pulled/stretched
What guideline is required for evaluating and repairing material degradation? - Answers
-NEI 03-08
What is a metal? - Answers -Large collections of millions of crystals composed of
different atoms held together by metallic bonds. Metals are a class of elements and/or
compounds that may have a high melting point, solid at room temp, good conductor of
heat, etc)
What is an alloy? How do they enhance metal? - Answers -A mixture of two or more
materials and at least one of which is metal. Enhance metal generally by: increasing
strength, hardness enhance ductility (ability of mtl to be deformed without fracture),
increase resistance to corrosion, increase machinability, increase wear resistance.
Alloys are usually stronger than pure metals (ex: steel)
What are the two different types of alloys? - Answers -1) Ferrous alloys (contain iron) 2)
Non ferrous alloys (do not contain iron)
What is ferrous alloy? - Answers -Means iron. include iron and alloys of at least 50%
iron such as cast iron, wrought iron, steel, stainless steel. Highly dependent on
possessing key element of carbon.
, What is non ferrous alloys? - Answers -Metals composed of elements other than iron.
Examples: copper, nickel (inconel), cobalt (stellites), and zirconium alloys. Commonly
used in nuclear plants.
What is strength? - Answers -Ability of material to support an applied load. Ability to
resist deformation.
What is ductility? - Answers -Ability of a material to deform easily upon the application of
tensile force without rupture- Prior to fracture
Conductivity? - Answers -Property of conducting heat/electric current
3 different types of crystal structures? - Answers -Body centered cubic (bcc), Face
centered cubic (fcc), Hexagonal close packed (hcp)
What is lattice? - Answers -3 dimensional array of atoms in a metal molecule in which
the array is a regular repeating configuration in all directions
What is BCC? - Answers -8 atoms at corner and one in center. High strength, low
ductility. Ex: iron, chromium
What is FCC? - Answers -8 atoms on corners and one at center of each of the faces of
cube. Lower strength, higher ductility. Ex: iron, aluminum, nickel,. silver, gold
What is HCP? - Answers -3 layers of atoms. top and bottom contain 6 atoms of
hexagon, on at center of each hexagon, etc. Not as ductile as FCC but more than BCC.
Lower strength than BCC. Ex: cobalt, beryllium, magnesium
What is a grain? - Answers -a crystal - merely a crystal without smooth faces because
its growth was impeded with another grain or boundary surface / avg size of grain is
important to the metal as it determines the properties.
What is a ground boundary? - Answers -Interface between grains / grains and grain
boundaries help determine the properties of a material
What does it mean if you have a smaller grain size? - Answers -increases tensile
strength and ductility (faster metal is cooled smaller grain gets)
What is machinability? - Answers -How a metal reacts to mechanical deformation by
removing chips with respect to the amount of metal effectively removed and the surface
finish attainable
What are the 10 properties of metals? - Answers -Brittleness, ductility, elasticity,
hardness, malleability, plastic deformation, strength, strain, stress, toughness
