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1

A Look at Nuclear Scienceand Technology

Larry Foulke

Module 5.5

Energy removal from the core

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Nuclear Engineering Program

Constraints

Least Favorable Local Temperatures &

Coolant Flows Must Be Accommodated Cant Control to Average Parameters

Must Assess Worst-Case Core Conditions

Normal Operation Potential Energy Removal Degradation

Transient & Accident Conditions

Reactor Energy Removal

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Thermal-Hydraulic Analysis

Consider Global Core Power Distributions

Fuel and Clad and Coolant Temperatures

Coolant & Moderator Feedbacks

Local Element Power Density

Fuel-Pin Temperature Distribution

Coolant Flow Conditions

Establish Operating Limits to Prevent Melting

Reactor Energy Removal

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Power Density Peak-to-Average

Power-Shaping (Peak-Reduction) Techniques Reflector

Enrichment Zoning Example: Two Different (Higher/Lower)

Homogeneous EnrichmentBatches

Multiple-Batch Fuel Management

Power Distribution

Fmax(

r

)=

Pmax(r)

P(r)=max(r)

(r)= unitless

,want

itclose

to

1.0

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Calvert Cliffs Assembly Inlet Temp: 560 K (~287 C)

Pressure: 15 Mpa (~2235 psi)

Flow Rate: 103.63 kg/s

50 axial segments of 7 cm

17,850 Thermal Regions

Four control rod locations

One instrument tube (center)

Image Source: See Note 1

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6

Axial Location (cm)

Temperature(

K)

Calvert Cliffs Assembly Axial Temperature Profile (Fuel & Coolant)

Fuel Centerline Temperature

Coolant Temperature

Average Fuel Temperature

Image Source: See Note 1

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AxialPosition(cm)

Tempera

ture(

K)

Calvert Cliffs Assembly Axial Fuel & Coolant Temperature Distributions

Image Source: See Note 1

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AxialPosition(cm)

Tempera

ture(

K)

Calvert Cliffs Assembly Axial Coolant Temperature Distributions

Image Source: See Note 1

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Coolant Temperature Rise Factor

Temperature Parameters

Heat Flux From Surrounding Pins

Coolant Heat Capacity Inlet Temperature

Pressure

FH

(r) =temperature rise in channel at r

temperature rise in core average channel

Peaking Factors

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Reflector Peaking EffectPmaxPmax

PavePave

Image Source: See Note 2

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Enrichment Zoning Effect

Same peak, but raised average

Image Source: See Note 2

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Fuel Pin Heat Transport

We have described the relative powerdistribution on a per fuel pin (or per channel)

basis in the core; now lets consider localheating within a single fuel pin.

Lets cover fuel pin heat transport in aqualitative way.

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Fuel Pin Temperatures depend upon:

Fission Source Distribution

Fuel Pin Heat Transport Properties

Coolant Heat Sink

Fuel Pin Geometry

Fuel Pellet

Gap

Cladding Tube

Coolant

Fuel Pin Heat Transport

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rFOrFcl= 0

rCI

rCO

Fuel Pin Radial Cross Section

Image Source: See Note 2

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Fuel Pin Heat Transport

Assume that fissions occur uniformly throughout thefuel region, therefore heat is produced uniformly in fuelregion.

Heat generated in the fuel must pass through all of thefuel element layers before it is absorbed in the coolant.

Fuel: Conduction (with uniform heat source)

Gap: Convection

Clad: Conduction

Coolant: Convection

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200

300

400

500

600

700

800

0.0 0.2 0.4 0.6 0.8

Temperature

,C

Fuel Pin Radial Distance, cm

Fuel

Gap

CladCoolant

PWR Fuel-Pin Temperature Profile

Image Source: See Note 3

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Nuclear Engineering Program

Nuclear Limits

We want to set operating limits so thatthe maximum centerline fuel temperature

at the hottest axial position of the hottestfuel rod remains below the fuel meltingtemperature.

17

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Departure from Nucleate Boiling (DNB)PWR BWR

Image Source: See Note 2

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Reactor Control

Maximum Hot-Spot

Normal Operation Anticipated Transients

Reactivity Control

Control Rods

Insertion Increases Peaking

Radial

Axial

Feedbacks

Design Considerations

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Axial

Flux w/

ControlRods

Image Source: See Note 2

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Radial Flux w/ Control Rods

Image Source: See Note 2

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1. Reprinted with permission from David Griesheimer, DF Gill, J WLane, DL Aumiller, An Integrated Thermal Hydraulic FeedbackMethod for Monte Carlo Reactor Calculations, Presented at theInternational Conference on the Physics of Reactors (PHYSOR

2010).2. Adapted and reprinted with permission from the American

Nuclear Society. Nuclear Engineering Theory and Technologyof Commercial Nuclear Powerby Ronald Allen Knief, 2ndEdition. Copyright 2008 by the American Nuclear Society, La

Grange Park, Illinois. Figure 7-1 (slide 10), 7-2 (slide 11), 7-3(slide 14), 7-7 (slide 18), 7-9 (slide 20), and 7-10 (slide 21).

3. Reprinted with permission from Ron Knief.

Image Source Notes