Evolution of ACR Physics from CANDU 6

By Peter Chan, ACR Fuel & Physics Section Head

Presented to US Nuclear Regulatory CommissionOffice of Nuclear Reactor Regulation

December 4, 5, 2002 at CRL

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Outline

� Major differences between ACR and CANDU 6 CoreDesigns� Coolant� Fuel� Lattice Pitch

� Core Physics of ACR� High Power Output in a Compact Core� Negative Power Feedback Reactivity Coefficients� Negative Coolant Void Reactivity� Unique LOCA features

� Summary

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Major Differences betweenCANDU 6 and ACR

� Coolant� CANDU 6 (D2O )� ACR (H2O)

� Fuel� CANDU 6 (NU in 37-element bundle)� ACR (2.0 % SEU in 42 pins, Central Pin Dy/NU, CANFLEX

bundle)

� Lattice Pitch� CANDU 6 (28.575 cm, 11.25 inches)� ACR (22.0 cm, 8.66 inches)

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Comparison of CANDU 6 and ACR Lattices

CANDU 6 Lattice

ACR Lattice

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CANDU 6728 MWe380 channelsDiameter = 760 cm ( 299 inches)

ACR 731 MWe 284 channelsDiameter = 520 cm ( 205 inches)

Core Size Comparison

Calandria volume reducedby a factor of 2.5 (smallerlattice pitch).By using H2O coolant, lessthan 25% of D2O used in C6is required.

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Reactivity Effects in ACR-700 and CANDU 6(Equilibrium Core)

+10 to +15 mk-3.0 mkFull-Core Coolant-VoidReactivity

~ 0-0.07 mk/% powerPower Coefficient (95% -105% full power)

small negative-0.008 (mk/ �F)Fuel Temperature effect

positive-0.006 (mk/�F )Coolant Temperature(including density) effect

slightly positive-0.013 (mk/�F )Moderator Temperature(including density) effect

CANDU-6ACR-700

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Safety & Control Parameters in ACR-700 and CANDU 6

14 Controllers in7 Assemblies

18 Controllers in9 Assemblies

Bulk & Spatial Control

0.920.33Prompt Neutron Lifetime( millisecond)

6 Poison Nozzles(core region)

6 Poison Nozzles(reflector region)

Shutdown System (SDS2)

28 AbsorberRods

20 AbsorberRods

Shutdown System (SDS1)

4 MechanicalAbsorber rods

4 MechanicalAbsorber Rods

Fast Power Reduction

0.00580.0056Total Delayed NeutronFraction ( ß )

CANDU 6ACR-700

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Effect of Prompt Neutron Lifetime on Power Transients

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0

Time (second)

Rel

ativ

e Po

wer

l*=0.33 ms +1 mk Stepl*=0.90 ms +1 mk Stepl*=0.33 ms +3 mk Stepl*=0.90 ms +3 mk Stepl*=0.33 ms +0.5 mk Stepl*=0.90 ms +0.5 mk Stepl*=0.33 ms -3.0 mk Stepl*=0.90 ms -3.0 mk Step

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Characteristics of ACR-700 and CANDU 6

7.520.5Core-AveragedBurnup (MWd/kgU)

165.8Fueling Rate(Bundles per Day)

23Channel Visits/Day

37 NU pins2.0% in 42 pinsCentral NU/Dy pin

Fuel Enrichment

728731Gross ElectricalPower ( MW)

20641982Reactor ThermalPower ( MW)

380284Fuel Channels

CANDU 6ACR-700

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CANDU Fuel Bundle Designs

37-Element37-Element BundleBundleC6 Fuel ChannelC6 Fuel Channel

CANFLEXCANFLEXBundleBundle (43 elements) (43 elements)ACR Fuel ChannelACR Fuel Channel

Dy

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Effects of CANFLEX SEU Fuel in ACR� Enables the use of H2O Coolant� Allows the reduction of moderator to reduce Coolant Void

Reactivity ( CVR)� Allows the use of neutron absorber in the central fuel pin to

further reduce CVR to target of – 3 mk� High fuel burnup and high power output� Flat radial channel power profile ( 0.93 form factor)� Reduction in maximum fuel element rating� Inlet skewed axial power profile improves thermalhydraulic

margin

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Element Ratings ( ACR vs CANDU-6)for 900 kW bundle power at mid-burnup

-15.2 **57.248.5Ring 4

-18.546.537.9Ring 3

+ 6.141.343.8Ring 2

- 52.139.719.0Ring 1(Central)

% ChangeACR vs C-6

C-6 ( 37-el NU)(kW/m)

ACR (Canflex SEU) ( kW/m)

** lower element rating allows higher power and higher burnup

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End-View of ACR-700

Pg 14 Schematic Face View of CANDU 6 Reactor

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Radial Thermal Flux Profiles

ACR-700 CANDU-6

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Axial Thermal Flux Profiles

ACR-700 CANDU 6

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Channel Power Profiles in ACR-700 and CANDU 6

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12

Channels from Centre of Reactor Core (Central Row)

Cha

nnel

Pow

er (

MW

)

ACR-700CANDU-6

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Axial Power Profiles in ACR and in C6

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6 7 8 9 10 11 12

Bundle Position from Inlet End ( Channel Power = 7.5 MW)

Bun

dle

Pow

er (k

W)

ACR 2-bundle-shift

C6 8-bundle-shift

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Effect of Coolant Void in ACR� ACR lattice is under-moderated with normal H2O coolant� H2O acts as both coolant and moderator� LOCA further reduces moderation from the lattice� Coolant Void Reactivity (CVR) is a combined effect due to loss of

absorption (positive) and loss of moderation (negative) from H2O� Increase in fast flux and decrease in thermal flux upon LOCA� U238 and Pu239 generate negative components in CVR

� Increase in Resonance Absorption (1 eV to 100 keV) in U238� Decrease in Fission (0.3 eV resonance) in Pu239

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Physics Innovations to achieve slightlynegative CVR ( H2O Coolant)

� Large Moderator/Fuel ratio (Vm/Vf) means high CVR� Current Lattice Pitch ( LP) 28.575 cm ( 11.25 inches ) Vm/Vf =16.4 CVR = + 60 mk� Target CVR = -3 mk requires Vm/Vf < 6.0, 0 LP < 20 cm (7.87 inches)� Minimum LP = 22 cm ( 8.66 inches) required to provide space for feeders

between channels Vm/Vf = 8.4

� Use larger CT, OR =7.8 cm (3.07 inches) to displace more moderator� Vm/Vf = 7.1� Add Dy (4.6% ) to central NU pin CVR = - 3 mk

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Neutron Flux Averaged over Fuel and Coolant within thePressure Tube (MCNP Model)

0

0.01

0.02

0.03

0.04

0.05

0.06

1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Neutron Energy, MeV

Nor

mal

ized

flux

per

uni

t let

harg

y

normal void

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Absorption Cross Section of 238U

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Fission Cross Section of 239Pu

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Change in Power/Flux Profile due to LOCAfor 900 kW bundle power at mid-burnup of ACR CANFLEX Fuel

- 6.845.248.5Ring 42 % SEU

+ 4.039.437.9Ring 32 % SEU

+ 17.250.243.8Ring 22 % SEU

+ 21.1 **23.019.0Ring 1 (Central Pin)NU + 4.6 wt% Dy

% Changedue to LOCA

ACR Voided( kW/m)

ACR Cooled( kW/m)

** current CVR design target is – 3 mk -10 mk CVR can be achieved by using less than 10 wt% Dy in the central pin

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Typical Power Pulses in CANDU 6 for Individual Bundle and for Broken- &Intact-Loop Core Halves

• Fast power rise due to positive CVR

• Power transient quickly terminated by

• Fast response neutron detectors

• 2 independent fast acting shutdown systems

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Unique LOCA Features in ACR

• Power in reactor core region drops upon LOCA due tonegative void reactivity

• LOCA power transients not sensitive to trip time(relative to CANDU 6)

• Rapid rise in thermal neutron flux in the reflector regiondue to migration and subsequent thermalization of fastneutrons from the core region

• Fast neutronic trip is available from neutron detectors inthe reflector region

• Slower process trip is sufficient to terminate LOCA

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Effect of Trip Time on LOCA TransientACR 100% RIH LOCA Transient

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Time after break ( second)

Rel

ativ

e Po

wer

CVR -3 mk, Trip at 1 s, 1.36 FPS

CVR -3 mk, Trip at 2 s, 2.11 FPS

CVR -3 mk, Trip at 3 s, 2.81 FPS

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0

0.5

1

1.5

2

2.5

3

3.5

4

0 50 100 150 200 250 300 350 400 450 500 550

Distance from Edge of Reflector (cm)

Ther

mal

Flu

x ( 1

0E14

)

T=0.0s

T=0.010s

T=0.015s

T=0.020s

T=0.030s

Thermal Neutron-Flux Distributionsin ACR-700 after LOCA

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Thermal Flux Profile upon LOCA at t=0 s

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Thermal Flux Profile upon LOCA at t=0.015 s

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Thermal Flux Profile upon LOCA at t=0.02 s

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Thermal Flux Profile upon LOCA at t=0.03 s

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Thermal Flux Profiles in ACR-700 upon LOCA( click picture to start animation )

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Thermal Flux Ratios in ACR-700 upon LOCA( click picture to start animation )

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Summary� ACR is an evolutionary design of current CANDUs

� Common features between ACR and current CANDUs:� Horizontal fuel channels� D2O moderator� On-power fueling� Simple fuel bundle design

� ACR specific features:� H2O coolant� Smaller lattice-pitch and compact reactor core� High burnup SEU fuel� High power output� Negative coolant void reactivity� Negative power feedback coefficients

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