Chapter 1 - Introduction Flashcards
What is the pressure in a PWR?
15 MPa
What is the pressure in a BWR?
7 MPa
What is the temp at a PWR?
300
What is the temp at BWR?
280
Where are the controle rods in the PWR?
Up
Where are the control rods in the BWR?
Bottom
what is the irradiation level in a pwr in n/cm2-sec?
10^14
What type of steel is use for the RPV in a PWR”
308, 309 SS
material used for control rods in pwr?
ss cladding with b4c poison
what is the fuel cladding made of?
zr alloy
what is the fuel made of?
uo2
name fuel material issues?
fission gas release; fission product swelling; thermal conductivity decrease with burnup
name cladding material issues
waterside corrosion and hydriding, embrittlement, growth; pellet-cladding interaction; creep; fretting
name neutorn absorbers material issues
embrittlement; thermal mechanical failiure
name rpv material issues
radiation embrittlement
name the 4 main irradiation effects on structural materials
irradiation hardening and embrittlement
irradiation and thermal creep
volumetric swelling
he embrittlement (fusion)
What is dpa?
displacement per atom
how many dpa in a current gen 2 fission reactor
from 10 o 30 dpa
how many dpa in a msr?
100-190
what is creep?
tendence of solid material to move slowly or deform permanently under influence of persistent mechanical stresses that occurs in long-term exposure to high levels of stress.
Wha is moderate swelling
1-5% swelling leading to volume changes and distortion
what is large swelling
swelling of 10% causing severe embrittlement
What is embrittlement?
decrease of ductility of a material makingit brittle.
Why are SS not use in fast reactor?
14% swelling of 316 SS irradiated at 400 degrees
What is the melting point of 316SS
1400C
MELTING point of al
660 C
What is the transition temperature
temp at which material changes from one crystal state to another
what is the upper shelf energy
it provides margins of safety against fracture
What is the impact on the transition temperature and upper shelf energy of radiation in the rpv?
increase transition temperature and decrease upper shelf energy causing embrittlement.
What does the transition temperature really characterise in the rpv?
The temperature at which ductile to brittle properties happen.
At what temp does the unirradiated RPV material becomes brittle?
Around 0 degrees
At what temperature does the irradiated rpv material becomes brittle, higher or lower?
radiation causes embrittlement by exposure to neutrons which causes the transition temp to increase meaning the temperature rises and the material can become brittle at higher energies.
Is there a way to recover the increase transition temperature in an irradiated RPV?
yes, by annealing
What neutron energy is the major source of dpa damage?
fast neutrons > 0.1 Mev
What is the average fast fission neutrno ernergy?
1-2 mev
What is the primary recoil atoms?
The atoms in direct interacction with the neutron leaving the reaction.
What is the average temperature (energy) for a PRA
10 keV fission and 50 kev in fusion
What does the PRA causes in terms of other atoms?
it displaces them
How many displace atoms are cause by a PRA (the formula)?
v_d = T/2Ed + excitation energy + heat where Ed is the displacement threshold energy
What are the neutron damage dose units?
Displacements per atom (dpa)
What are the primary displacement defects?
vacancies and self interstitial atoms (sia)
are the number of sia the same as the number of vacancies?
Yes, when an atom gets nocked out it may become a self-interstitial atom which then leaves a vacancie which can be ocupy by another atom .
What is a self-interstiaial atom?
an atom which has ocupy a place in between two or more naturally positioned atoms in the crystalline structure.
What is the magnitude of the flux, PKAs, and recolis?
10 to the 6, 4, 2 respectively
What is pka? explain
primary knock-on atom is an atom displaced from its lattice site by irradiation. It is hte first atom that an incident particle encounters
What happens after the prdoduction of a PKA
it can induce subsequent lattice site displacements of other atoms if it posseses sufficient energy or come to rest in the interstitial site.
What three routs can vacancies and SIA along with solute and impurities take?
- V-SIA recombination (damage annihilation
- V-SIA clustering (bubble, void, loop formation)
- V-SIA absorption at sinks (dislocations, clusters)
2 and 3 result in damage accumulation causing dimensional and mechanical property changes.
Explain the timelaps starting from primary damage
primary damage -> long range diffusion -> loss at sinks and by recombination -> enourmous SIA and vacancy supersaturations
What is the primary concern of irradation of RPV?
the large shifts in transition temperature and the upper shelf energy can limit the life of some plants due to pressurized thermal shock and impact operating flexibility.
what is pressurized thermal shock
scenario in which a large amount of cold water would be injected into the reactor resulting in rapid cooling of the RPV
What does the transition temperature depend on?
synergistic combination of many metallurgical and envirionmental variables including:
- elements used and resulting microstructure
- heat treatment
- flux
- temperature
Is it possible to recover transition temperature?
Yes, by anhealing but re-embrittlement issue.
What is the difference betwen a metal and a ceramic?
Metals are solid substances, which are opaque in nature and having an excellent electric conductance. A nonmetallic inorganic material made up of a mixture of metal and non-metal compounds is known as ceramic
What is the difference between steel and iron?
Steel is an alloy and iron is an element
Name the elements in nuclear fuel for LWR?
URANIUM OXYGEN
What does dpa stand for?
displacements per atom.
At what temperature does irradiation harderning and embrittlement and decreased in uniform elongation begging relative to a material?
<0.4Tm where Tm is the melting temperature
At what temperature does volumetric swelling happen?
0.3 - 0.6 Tm
What is the melting temperature of aluminium?
660 C
What is creep?
sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of (usually long-term) persistent mechanical stresses that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and generally increases as they near their melting point.
At what temperature does irradiation and thermal creep being at?
<0.45Tm for irradiation creep and >0.45Tm for thermal creep
Why is aluminium not used in RPV?
Because of the melting temperature. The operating temperature of the reactor presents ideals scenarios for swelling, creep and hardening and embrittlement to ocurr
How deap do neutrons usually penetrate?
a couple cms
What does PRA stand for?
primary recoil atom
What is the average energy of PRA in fission
T = 10 keV
What do PRA cause to surrouning atoms?
displacement cascades
What determines if an incoming particle will displace the particle which is interacting with?
The displacement threshold energy Ed
How is the damage does measured?
in displacements per atom (dpa)
For stainless steel 316 how does the dpa cross section vary with energy? What are the dpa cross section ranges?
In a log scale linearly. It varies from 10 to 1000 barns from 10-3 to 10 MeV
What does dislocations prefer to absrobe? Interstitials or vacancies? What is the aftermath?
Interstitials. This means that there is clustering of vacancies.
What is one of the msot important design criteria with respect to failiure
bend before break
Difference between bwr and pwr?
control rod positions, number of loops, steam generator and much more.
What is the difference between 300 steels and 400 steels?
300 contain nickel and 18% chromium while 400 series contain 12% and no nickel making it less corrosion resistant.
What is the difference between 308 and 309 SS?
309 HIGHER CHROMIUM AND NICKEL and FERRITE percentage. Ferrite prevents hot cracking
Why is nickel use in SS
It gives corrosion resistance just like chromium and allows SS to remain ductile at very low temperatures and at the same time be use in high temperature applications.
How does nickel work in SS?
Changes the crystal structure of SS to an austenitic FCC structure while conventional steel has ferritic BCC structure.
Why is chromium used in SS?
Resistance to oxidation (corrosion resistance) due to the formation of a passive layer of chromium oxide on the surface of the SS.
What is corrosion?
When most or all of the atoms on the metal surface oxidized damaging the entire surface. Metals tend to lose electrons to oxygen in air or water and as oxygen is reduced it forms an oxide with the metal.
What is hardening?
Increase the hardness of a metal (higher resistance to plastic deformation and a reduction in bend before break (higher embrittlement)
How long does it take for a reaction particle-atom collision to take place? Time scale
10^(-13) -> 10^(-11)g
How does yield strength behave with temperature? What if you add irradiation
The higher the temperature the slighly lower the YS. It is almost a constant line. The YS increases drastically by around 400 MPa for 2-20 dpa and behaves almost linearly.
How does the YS behave with neutron dose (dpa)?
As the dose increases the YS increases also.
How does strain to necking percentage behave with neutron dose (dpa)?
As dose increases the strain to nocking % decreases meaning it requires higher yield strength to cause fracture but the elongation capacity decreases
How does the fracture toughness K behave with neutron dose (dpa)?
it decreases with dose
What is the damage dose dpa formula?
dpa = fluxtimexs_dpa
What is the fluence?
flux*time
What is fretting?
refers to wear and sometimes corrosion damage at the asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration.
