Anne-Marie CHOHO, the senior Executive Vice President in charge of Engineering & Projects from AREVA, exposed the impact of load follow on the design from the ‘A Mode’ in the 1970s to the ‘G Mode’ studies and its industrialization in 1995-1990, until the ‘T Mode’ developed for the EPR.

1. Major Innovations in PWR
Load Follow Operations
by AREVA
Anne-Marie Choho
Senior Executive Vice President,
Engineering & Projects, AREVA
Paris, 21st October 2013

2. Outlines
Requirements from the Grid
Impact of Load Follow on French PWR Design
Industrial Deployment of the Load Follow on French PWR
Conclusions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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3. Outlines
Requirements from the Grid
Impact of Load Follow on French PWR Design
Industrial Deployment of the Load Follow on French PWR
Conclusions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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4. An Exciting Story
that began at the end of the 70s…
From the 900 MW to the EPRTM Units
Tricastin, Rhone Valley, France
EPR Flamanville 3 consruction site,
Normandy, France
A worldwide unique experience in nuclear
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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5. 1975 to 1980
The Starting Point
End of 1970s in France: first PWRs
(CP0) : Operation in Base Load (or
smooth Load Follow) with A Mode
Decision to raise the % nuclear power:
PWRs need to comply with electrical
grid constraints
AREVA conceived an innovative solution to meet
challenging grid constraints
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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6. Overview of the Grid Requirements
The AREVA solution: capable of matching
the daily electricity demand
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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7. Grid Requirements
1) Load Follow Transients
Daily load follow program sent to Nuclear units
100%
100%
70%
SLOW TRANSIENTS ( 12 - 3 - 6 - 3)
50%
30%
3h
3h
6h
100%
3%/min
70%
3%/min
100%
FAST TRANSIENTS (16 - 8)
50%
30%
Ramp up to full
power at 5% per
minute WITHOUT
100%
100%
3%/mn
5%/mn
But… can be interruped by an
INSTANTANEOUS RETURN
to FULL POWER w/o NOTICE
required by the Grid Owner
notice
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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8. Grid Requirements
2) Frequency control
Non predictable power variations: Frequency Control
Power
103
101
99
97
95
93
91
89
87
Time (hours)
1
2
3
4
5
6
7
8
9
10
11
12
Power matching to real time electricity demand
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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9. Outlines
Requirements from the Grid
Impact of Load Follow on French PWR Design
Industrial Deployment of the Load Follow on French PWR
Conclusions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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10. Core Control Principles (1/2)
Power variations
requested by the grid
Opening/closing
of the turbine inlet valves
requierements
Steam flow rate variations
Lead to SG outlet temperature
variations and then to core inlet
temperature modifications
Control Banks automatically move modifying core reactivity accordingly
and keeping the primary average temperature inside the allowed variation
range (→ reactor power and turbine/generator power are correctly balanced)
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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11. Core Control Principles (2/2)
Optimized control
banks efficiency
for better safety
and reactivity
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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12. Some Physics
Variations of the power level lead to variations of reactivity
Nuclear feedbacks (Moderator + Doppler effects)
Xenon concentration variations
Power
<0
Reactivity
>0
Nuclear
Control
Feedbacks
Banks
ACCORDING to the
CORE CONTROL MODE
Xenon
Dilution
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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13. Chronology of the Load Follow
G” Mode “ Development
1975
• 1975-1980:
1980
1985
today
Definition of the Load Follow G Mode core control principles
Design of the core and NSSS control channels (I&C aspects)
•1980-1985: Safety and Mechanical Analyses
Equipment and Fuel Assembly Qualification in Tests Facilities
On Site Load Follow G Mode Qualification Tests
•1985-1990: Load Follow G Mode Industrialization
•1995-2005: Development of the EPR core control mode: so-called “T Mode”
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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14. Impact on Core and Nuclear and Steam Supply
System (NSSS) Control Channels (1/4)
Core Control: creation of “Gray Mode” (G Mode)
Classical “Black” Rod Cluster Control
Assembly (RCCA) design
24 absorbing rods made of
Silver/Indium/Cadmium, B4C or both
High anti-reactivity worth
New “Gray” RCCA design
8 absorbing rods made of Ag/In/Cd
16 rods made of Stainless Steel
Low anti-reactivity worth
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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15. 1975 to 1980
Impact on Core and NSSS Control
Channels (2/4)
Rod Cluster Control Assembly (RCCA) configuration
“Gray” control banks (G1, G2), followed by “black” control banks (N1, N2),
drive load follow power transients
In addition to “Gray” control banks (G1, G2), “Black” control banks (N1, N2),
are necessary for reaching zero power conditions
G1, G2, N1, N2 overlaps are managed to minimize axial power distribution
distortions
Core control principles
G1, G2, N1, N2 control the electrical power
One control bank (“R”) is dedicated to temperature control to
• counter “nuclear feedbacks”
• participate in the control of axial power distribution (axial-offset)
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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16. Impact on Core and NSSS Control
Channels (3/4)
1975 to 1980
I&C Aspects
Need to switch to digital
technology
Set points update via Memory
Chips
The world’s first nuclear digital I&C technology!
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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17. Impact on Core and NSSS
Control Channels (3/4)
1980 to 1985
NSSS Systems
Pressurizer Surge Line
CVCS charging line nozzle
Control system modified to minimize mechanical constraints
on pipes and nozzles
Major Safety improvements
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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18. 1980 to 1985
Impact on Safety & Design Analyses
Four additional shut down black control banks
No new accident initiating events
New core and NSSS initial conditions before possible accidents
were analyzed
Design File Transients were updated with the new equipment
loadings
The behavior and capacity of concerned systems were verified
for the load follow transients: no design change
Balance of Nuclear Island: no change
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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19. Outlines
Requirements from the Grid
Impact of Load Follow on French PWR Design
Industrial Deployment of the Load Follow on French PWR
Conclusions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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20. 1980 to 1985
Equipment and
Fuel Assembly Qualification Tests (1/2)
Confirmation of resistance calculations in
Tests Facilities:
Control Rod Drive Mechanisms
• Tested in the CEA “Superbec Loop”
Core baffle: Fatigue resistance of bolting
Extensive testing on mock-ups led to industrial
solutions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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21. 1980 to 1985
Equipment and
Fuel Assembly Qualification Tests (2/2)
Theoretical Approach
Fuel Assembly response to power variations
Experimental Approach
Power ramps and cycling variations in CEA “CAP” reactor
International R&D programs
In-reactor fuel surveillance program
Fuel Cladding Rupture risk by Pellet Clad Interaction (PCI)
Above tasks showed this risk does not exist in Load Following
Extensive testing on mock-ups led to industrial
solutions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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22. On Site Qualification Tests
1980 to 1985
Tricastin Unit 3 First of A Kind
Load Follow control system co-existed with traditional control mode
Load Follow mode feasible both manually and automatically
Three successful testing Campaigns
• October 1981
• November 1982
• March 1983
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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23. 1985
Industrialization of the Load
Follow “G Mode”
The 900 MW CPY power plants were designed as “bi-mode units”
The first units of TRICASTIN, GRAVELINES, DAMPIERRE,
BLAYAIS (1, 2) were commissioned in base load
They switched to load follow “G” Mode after Safety Authorities
authorization
The other units started up directly in load follow “G” mode
No significant modifications implemented later on
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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24. 1985 To today
EPRTM Reactor and
ATMEA1 Features
Best combination of “G mode” and German load follow
practices = Advanced load follow “T Mode”
Full automatic Control Mode including boration and dilution
Choice of operating strategy available to operator:
Instantaneous return to full power without notice capability, or
Liquid effluents saving strategy (automatic countering of xenon
effect by control banks)
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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25. Comparison of Core
Control Modes
1985 To today
A Mode
Control Channels
Banks control
Temperature
Reactivity (Nuclear
Feedbacks)
Mainly Boron
G Mode
G1,G2,N1,N2 Banks
control Power
R bank controls
Temperature
Control Banks (G1, …
N2)
T Mode
Banks control
Temperature, AxialOffset and Return to
Full Power Capability
Control Banks
Boron
Boron
Control Banks or Boron
according to the
Operator Strategy
Manual by Operator (via
Control Banks
repositioning thanks to
Boron Concentration
manual Changes
AO Distortions
minimized thanks to G
Mode Design Residual
effects manually
controlled by Operator
Automatic by Control
Banks
Advantages
Control Banks close to
the top of the Core
Nice for Neutronics
Fits fast and
Unscheduled Power
Changes
Fully Automatic
including
Boration/Dilution
Full Return to Full
Power Capability or
Liquid Wastes saving
Strategies
Drawbacks
Fits slow Power
Changes only
Limited by CVCS
Capability
Periodic Calibration of
(G1,…N2) vs. Power
Risk of CRDM Wear
Secondary Side
Interface
More Complex
Xenon
Axial-Offset Control
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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26. Outlines
Requirements from the Grid
Impact of Load Follow on French PWR Design
Industrial Deployment of the Load Follow on French PWR
Conclusions
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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27. 1975 to 1985
High Flexibility Level
since Decades
Load follow license was obtained in 1983
Frequency Control license was obtained
in 1984
48 Nuclear Units are presently operated
in load following conditions according to
the G Mode principles
Thanks to AREVA’s innovative solutions, EDF is the first and
only to perform load follow since 30 years!
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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28. Worlwide Robust Experience
1975 to today
AREVA Load Follow experience in Foreign Countries
L Mode
Daya Bay 1-2
Ling Ao I 1-2
Ling Ao II 3-4
G Mode
Taishan 1-2 (T Mode)
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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29. 1975 to 1985……..Next
Flexibility of the Energy Mix
The T Mode is the fruit of a continuous development aiming at
providing Utilities with the highest flexibility level
Capable to meet new grid requirements induced by renewable energies
AREVA anticipates future needs for both nuclear &
renewable energies
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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30. EPR Olkiluoto 3
THANK YOU for YOUR ATTENTION!
EPR Flamanville 3
EPR Taishan 1&2
A-M. CHOHO – SEVP Engineering & Projects - SFEN Young Generation, Paris, 21st Oct. 2013
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