GFES Thermo Flashcards by Finn Alexander

Conversion from ft to psi
(at atmospheric pressure and “normal” temps)

1 ft = 0.433 psi

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Level Indication and DP

Reference Leg is HP side

Level inversely proportional to DP

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Level Indication and DP

Reference Leg is LP side

Level directly proportional to DP

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Combined Gas Law

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Turbine Process

isentropic

straight down on Mollier diagram

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Throttling

isenthalpic

straight across on Mollier diagram

includes steam leaks, relief valves, throttled valves

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Core Thermal Power

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Heat Exchangers Temperature Trends

Q̇-hot = Q̇-cold

ṁ-hot ↑, all temps ↑ (except T-cold in)

ṁ-cold ↓, all temps ↓ (except T-cold in)

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Departure from Nucleate Boiling Ratio
(DNBR)

DNBR = CHF/AHF

(CHF = Critical Heat Flux, AHF = Actual Heat Flux)

DNBR goes up → farther from DNB
DNBR goes down → closer to DNB

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Critical Heat Flux

If pressure ↑, then…

CHF ↑

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Critical Heat Flux

If flux ↑, then…

CHF ↓

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Critical Heat Flux

If temperature ↑, then…

CHF ↓

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Critical Heat Flux

If flow rate ↓, then…

CHF ↓

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What is the equation for pressure from water level?

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What are the three pump laws and how do we remember them?

Very Hard Problems are as easy as 1-2-3

V̇ ∝ n

H ∝ n^2

P ∝ n^3

V̇ = volumetric flow rate
H = pump head
P = pump power (amps)
n = pump speed

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Does water hammer (pressure spike) dissipate faster in a longer or shorter pipe?

shorter

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Is water hammer (pressure spike) worse in a hotter or colder fluid?

colder
(cold water is more dense, so mass flow rate is higher, meaning more mass is contained in the sonic wave causing the pressure spike)

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What is the temperature limit for fuel cladding?

2200°F

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How do we calculate the average linear power density for an entire core?

Heat Flux ∝ Power Density

What is the Linear Power Density Limit for Steady State Operation?

13.9 kW/ft

What is the limit for the departure from nucleate boiling ratio (DNBR)?

1.3

What is the nuclear heat flux hot channel factor?

a measure of the relationship between peak linear power density to the average linear power density in the core at a particular elevation
(basically describes the neutron flux profile of the core)

What is the limit for the nuclear heat flux hot channel factor?

2.5

(limits placed to prevent excessive heat production)

What is a stress?

a force intensity or a force per unit area

What is strain?

elongation per total length

What is elastic deformation?

the material returns to its original shape after stresses are removed

What is plastic deformation?

the material stays deformed after the stresses are removed

What is a brittle material?

materials that break or fracture under stress before they have the chance to permanently deform (e.g. ceramic) (failure unpredictable because there is no elongation)

What is ductility?

a relative measure of how much something stretches before it breaks (e.g. soft metals like copper are very ductile)

What is the yield point?

the transition point where elastic deformation ends and plastic deformation begins

What is ultimate tensile strength (UTS)?

the maximum stress supported by a material before it fractures

What is the RT-NDT?

reference temperature for nil-ductility transition (a.k.a. the nil-ductility transition temperature) the temperature below which metal fails by brittle fracture

What is brittle fracture, and what conditions must be present for it to happen?

rapid catastrophic failure of a metal below tensile limit with little or no plastic deformation →metal must be below RT-NDT →there must be a pre-existing flaw in the material →must be applied tensile stress (pressure stress is always tensile)

What is neutron embrittlement?

changes caused to metal by neutron irradiation →raises the ductile-to-brittle transition temperature so that brittle fracture happens more easily →causes hardening to the metal which increases tensile strength but makes it more brittle

What are the characteristics of heat-up stress?

→inside wall compressed due to temperature stress →outside wall has tensile stress

What are the characteristics of cooldown stress?

→inside wall has tensile stress due to temperature →outside wall compressed →cooldown stress is more limiting than heat-up stress

What is pressurized thermal shock (PTS)?

rapid cooldown with sudden pressure rise, e.g. a steam break accident

Which component do we consider the limiting component for material failure?

the reactor vessel

What are the common derivations of the mass flow rate equation?

Why is bulk boiling in the tubes of a single-phase heat exchanger undesirable?

turbulence will restrict fluid flow through the heat exchanger tubes

What is critical heat flux?

the heat flux that causes DNB for given pressure and temperature conditions

From the bottom to the top of the core, CRITICAL heat flux...

decreases continually

From the bottom to the top of the core, ACTUAL heat flux...

increases, then decreases

If a steam cycle is 33% efficient, how much heat is rejected in the main condenser?

the other 67%

Where is DNBR typically at its minimum (closest to DNB)?

slightly above the core midplane

Where is DNBR typically at its maximum (farthest from DNB)?

bottom of core

What happens in reflux core cooling?

→happens after significant reduction in RCS inventory →loop circulation breaks down →cooling occurs by steam condensation in the steam generator →vapor generated in the core flows through top of hot leg piping and condenses in both the up-flow and down-flow sides of the S/G →on up-flow side, condensed liquid returned to the reactor through the bottom of the hot leg piping →on down-flow side, liquid and any uncondensed steam flows into the cold leg suction piping (smaller mass flow rates and primary to secondary temperature differences than with natural circulation)