Term
| What are the thermal limits for fuel melting and clad oxidation. |
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Definition
Fuel melting - 4700F Clad Oxidation - 2200F |
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Term
| What is a peaking factor? |
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Definition
| The ratio of local maximum power produced to the average power produced, also known as HOT CHANNEL |
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Term
| What is radial peaking factor? |
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Definition
| Peak power at a selected core height divided by the average power at that selected core height |
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Term
What is axial peaking factor? |
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Definition
| Average power at a selected core height divided by the average core power. |
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Term
| What is local peaking factor? |
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Definition
| Aka measured heat flux hot channel factor - ratio of maximum power at a hot spot to average core power |
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Term
| What is Total peaking factor? |
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Definition
AKA Heat flux hot channel factor - product of radial and local peaking factor - the ratio of maximum power at a hot spot to average core power |
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Term
| What is Nuclear Enthalpy rise hot channel factor (NKA)? |
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Definition
The measure of maximum total power produced in a fuel rod. Max integrated power rod/ average integrated power rod |
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Term
| Describe the operators role in protecting core thermal limits. |
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Definition
Monitor and control RCS temperature and pressure. |
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Term
| Explain the diff between stress and strain. |
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Definition
Stress is force applied over area when material is loaded. Strain is the degree of deformation that a material undergoes due to stress. |
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Term
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Definition
| The maximum amount of stress that a material can take before plastic deformation will occur. |
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Term
| Explain Ultimate tensile strength. |
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Definition
| The maximum limit of stress before a material fails. |
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Term
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Definition
| Relatively low force will cause failure with little to no deformation. |
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Term
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Definition
| A relative measure of how much a material will stretch before it fails. |
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Term
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Definition
| failure below ultimate tensile stress due to repeated cycling of stress. |
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Term
Explain stress intensity factor. |
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Definition
how much force needs to be applied before a crack will propagate. |
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Term
| Explain fracture toughness. |
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Definition
Given a metal with a flaw, how much energy it will take before failure. |
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Term
| Describe the brittle fracture mode of failure. |
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Definition
| Failure with little energy absorbtion. Little to no deformation and cracks propagate at up to 5000ft/sec. |
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Term
| What are the three conditions necessary for brittle fracture? |
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Definition
| A pre exsisting flaw - A tensile stress - a low temperature (temp must below the reference temp for Nil-Ductility transition) |
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Term
| Explain Nil-Ductility transition temp. |
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Definition
| the temp at which a material transitions from ductile mode of failure to brittle mode of failure. |
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Term
| Reference temp for Nil-Ductility transition (RTndt). |
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Definition
| The higher of two temps found from the drop test and the Charpy-V notch test. |
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Term
| Decribe the drop weight test. |
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Definition
A weight is dropped at 0oF if specimen does not break temperature is lowered until same weight breaks specimen. [image] |
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Term
| Explain Charpy-V notch test |
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Definition
| A weighted pendulum hammer strikes the edge and fractures a specimen at a notched point. Starts at NDT+60oF and is lowered until 35mils of deformation occurs. That temp is Tcv. |
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Term
| Which temp is used from the Drop weight test and the Charpy-V notch test? |
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Definition
| The higher of the two to be conservative. |
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Term
| Explain the effects of fast neutron irradiation on a reator vessel metals. |
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Definition
It causes grain growth in metal, the impact of the neutrons causes interstitial point defects in the lattice and results in increased brittleness. Simple answer - causes the metals to become more brittle. |
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Term
Describe and differentiate between the stresses induced in a reactor vessel wall during heat-up and cooldown. |
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Definition
There are a lot of stresses during both heat-up and cool down, pressure stress, embrittlement stress, temperature induced stress. The difference is that during heat-up the tensile stress will be concentrated at the outer wall and well below the max allowable. During cool down the tensile stress will be concentrated at the inner wall and much closer to the maximum allowable limit. Heatup illustration - slide 77 Cooldown - slide 78 |
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Term
Explain the methods used to minimize the possibility of brittle fracture by using operating limitations |
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Definition
The cool down rate of the RCS is controlled so it cannot cool down to fast The pressure that can be reached when the RCS is cold is limited to prevent Pressurized Thermal Shock (PTS) |
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Term
Describe the 3 things needed for pressurized thermal shock (PTS) and the associated safety concerns. |
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Definition
-High pressure and rapid cool down of reactor vessel walls -High neutron radiation embrittlement -A pre-existing flaw Will result in failure of reactor vessel wall |
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Term
Explain the operational concerns of uncontrolled cooldown. |
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Definition
Can cause PTS, resulting in a brittle fracture of the reactor vessel wall. |
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