1. ALFRED and ELFR system design
Technical Workshop to Review Safety and Design Aspects of
European LFR Demonstrator (ALFRED),
European LFR Industrial Plant (ELFR), and
European Lead Cooled Training Reactor (ELECTRA)
Joint Research Centre, Institute for Energy and Transport,
Petten, the Netherlands, 27–28 February 2013
Luigi Mansani

2. Structural Material and Molten Lead Impact on Design
Selection and qualification of structure and clad materials, for nuclear reactor systems using lead or lead-alloy as coolant, is a key issue
Molten lead and lead-alloy are corrosive for structural materials at high-temperature operation
They can induce/accelerate material failure:
under static loading, such as brittle fracture
under time-dependent loading, such as fatigue and creep
Main parameters impacting the corrosion rate of steels in lead or lead-alloy are :
chemical and metallurgical features of the steel
temperature
liquid metal velocity
dissolved oxygen concentration
Flowing molten lead and lead-alloy are erosive for structural materials
Structural material properties can degrade under irradiation of high energy neutron flux and in contact with liquid metal

3. Structural Material suitable for Molten Lead Environment
Selected candidate materials for nuclear reactor systems using lead or lead-alloy as coolant are:
Austenitic low-carbon steels (e. g. AISI 316L), owing to the available large database, are candidate for components operating at relatively low temperatures and low irradiation flux as is the case of the Reactor Vessel
Corrosion rate remains acceptable up to 450°C (might be 500 °C to be confirmed) for austenitic low-carbon steels
Ferritic-martensitic steels (e.g. T91) are candidate materials for components operating at relatively high temperatures and at high irradiation flux as in the case of the Fuel Cladding
Corrosion rate remains acceptable for ferritic-martensitic steels up to 500 °C with controlled Oxygen environment
Oxidation above 450°C reduces heat transfer capability
15-15/Ti steel, owing to the available large database, is candidate for fuel cladding operating at relatively low temperature

4. Design Provisions to fulfil the Structural Material Corrosion Issue
Prevention of corrosion maintaining a continuous and compact metal oxide film adherent to the metal substrate of the structures
Controlled Oxygen concentration in the melt in a range where the upper limit is the concentration for lead oxide formation (PbO Saturation) and the lower limit is the concentration for iron oxide (magnetite) formation
In the high temperature range (above 500°C), corrosion resistance enhanced by coating
Coating is of great interest mainly for fuel cladding or in general for heat exchanger tubes where protective oxide layer thickness should be limited to not affect significantly the heat transfers characteristics
Coating allows to increase the operating temperature above 550°C
R&D qualification program for the use of the coatings is mandatory in order to demonstrate their mechanical stability, adhesion to the substrate etc. under relevant operating conditions including neutron irradiation
Self-protecting structural materials through coolant chemistry control and corrosion inhibitors
R&D qualification program is necessary

5. Design Provisions to fulfil the Structural Material Erosion Issue
Provisions taken in the design to preserve structural material integrity against erosion phenomena impose an upper limit on the coolant flow velocity
Erosion rate remains acceptable for stainless steels in fluent lead up to velocity of 1 m/s
Erosion rate remains acceptable for ferritic-martensitic steels in fluent lead up to velocity of 2 m/s
Mechanical pumps are exception where the relative flow velocity cannot be limited below 10 m/s
Structural materials, for the pump impeller, resistant to high velocity shall be identified and characterised
Promising candidate materials for pumps are
Silicon Carbide and Titanium (Ti3SiC2) based alloys
Tantalum coated

6. ALFRED – FA and Core Configuration Control/shutdown system
FAs – Same concept of ELFR
171 Fuel Assembly
12 Control Rods
4 Safety Rods
108 Dummy Element
Control/shutdown system
2 diverse, independent and redundant shutdown systems
1° System for Control and Shutdown - Buoyancy Absorbers Rods passively inserted by buoyancy from the bottom of the core
2° Shutdown System - Pneumatic Inserted Absorber Rods passively inserted by pneumatic from the top of core

7. ELFR – FA and Core Configuration
270 Outer Fuel Assembly
12 Control Rods
12 Safety Rods
132 Dummy Element
157 Inner Fuel Assembly
STRATEGY:
-“Adiabatic” core
power distribution flattened with two zone different hollow pellets diameters

8. Reactor Control and Shutdown System
Two redundant, independent and diverse shutdown systems are designed for ALFRED and ELFR (derived from MYRRHA design)
The control rod system RS1 used for both normal control of the reactor (start-up, reactivity control during the fuel cycle and shutdown) and for SCRAM in case of emergency
During reactor operation at power, RS1 rods are most of the time partly inserted allowing reactor power tuning
To avoid risk of reactivity accident, in case of inadvertent rod windrowed, each rod is inserted for a maximum worth less than 1$ of reactivity
RS1 have fast shut down ability build in and act as a first safety shutdown system
The safety rod system RS2 is used only for SCRAM
RS2 rods are fully extracted during operation at power
RS2 rods are fully inserted in case of fast shut down (SCRAM) and act as a second diverse safety shutdown system
Reactive worth of each shutdown system is able to shut down the reactor even if the most reactive rod of the system is postulated to remain stuck
During refuelling both systems are inserted

9. RS1: 1° Control/Shutdown System
Control/Shutdown rods are extracted downward and rise up by buoyancy in case of SCRAM
During normal operation, Control rods are inserted from the bottom of the core to control the reactivity
The buoyancy is driving force for the emergency insertion, it also keep therods inserted
The control mechanism push the assembly down through a ball screw (for accurate positioning - like in BWR) .
The actuator is coupled to long rod by the SCRAM electromagnet
SCRAM triggered by loss of electromagnet electric supply (on SCRAM signal or loss of power)
Absorber bundle constituted by 19 pins with boron carbide (90% enriched in B10) cooled by the primary coolant flow
Pins have a gas plenum collecting the Helium (favourable to buoyancy)
© SCK•CEN

10. Shutdown rods are inserted downward in case of SCRAM
RS2: 2° Shutdown System
Shutdown rods are inserted downward in case of SCRAM
During normal operation RS2 rods are fully extracted over the core
RS2 rods constituted by 2 opposing piston on same shaft, the lift off piston and the insertion piston
The 2 chambers are at the same pressure (same feeding), lift off piston effective area is greater than the insertion piston effective area
Lift off piston is connected through a large section pipe to a fast acting purge valve directly actuated by the feeding line (feeding pressure keeps valve closed)
In case feed line break ►purge valve opens depressurising the lift-off piston, insertion piston remains pressurised forcing the rod to insert
A Tungsten ballast is used to maintain rod inserted
Absorber bundle constituted by 12 pins of boron carbide (90% enriched in B10) cooled by the primary coolant
Pins have no gas plenum, the small produced gas realised into primary coolant
© SCK•CEN

11. ALFRED Upper and Lower Core Support Plates
Upper core support plate
Box structure with two horizontal perforated plates connected by vertical plates.
Plates holes are the housing of FAs foots.
The plates distance assures the verticality of FAs
Box structure as lower grid but more stiff
It has the function to push down the FAs during the reactor operation
A series of preloaded disk springs presses each FA on its lower housing
Hole for Instruments 11

12. ALFRED - Inner Vessel Upper grid Pin Lower grid Inner Vessel assembly12

13. ELFR Inner Vessel, Core support and Fuel Assembly (Same ALFRED concept – larger dimensions)

14. ALFRED - Steam Generator Bayonet Tube Concept
Bayonet vertical tube with external safety tube and internal insulating layer
The internal insulating layer (delimited by the Slave tube) has been introduced to ensure the production of superheated dry steam
The gap between the outermost and the outer bayonet tube is filled with pressurized helium to permit continuous monitoring of the tube bundle integrity
High thermal conductivities particles in the gap to enhance the heat exchange capability
In case of tube leak this arrangement guarantees that primary lead does not interact with the secondary water 14

15. ALFRED - Steam Generator Bayonet Tube Geometry
Steam Generator Geometry
Bayonet tube
Number of coaxial tubes 4
Slave tube O.D
9.52 mm
Slave tube thickness
1.07 mm
Inner tube O.D
19.05 mm
Inner tube thickness
1.88 mm
Outer tube O.D
25.4 mm
Outer tube thickness
Outermost tube O.D
31.73 mm
Outermost tube thickness
2.11 mm
Length of exchange
6 m
Number of tubes
510

16. ALFRED - Steam Generator
Water
Hot Lead
Cold Lead
Steam
SGs Tubes, forged plates and shells are made of X10CrMoVNb9-1, as per the RCC-MRx code (equivalent in ASME code to T91 steel)

17. ALFRED - Steam Generator Performances
Removed Power [MW]
37.5
Core outlet Lead Temperature [°C]
480.0
Core inlet Lead Temperature [°C]
401.5
Feedwater Temperature [°C]
335.0
Immersed bayonet steam outlet T [°C]
451.5
Steam Plenum Temperature [°C]
450.1
SG steam/water side global ∆p [bar]
3.3
First tubesheet
Second tubesheet
Third tubesheet
Steam outlet
Water Inlet
Pump casing
Tubes

18. ELFR Once through Spiral SG: Concept
Power MW
187.5
Lead Inlet Temperature °C
480
Lead Outlet temperature
400
Water Inlet Temperature
335
Steam Outlet temperature
464
Steam Outlet Pressure
MPa 18

19. ELFR Once through Spiral SG: Concept features
Compact with reduced Volume
Reactor vessel kept at constant temperature
Positioned in the upper part of the Reactor Vessel
No constraint from main vessel leakage accident and from steam entrainment
Adequate natural circulation in case of LOF
No risk of catastrophic primary system pressurization
Feed water and steam collectors installed outside the reactor vessel
Effect of SGTR mitigated by:
Feed water tubes with Venturi nozzle and steam tubes with check valve for leak-flow limitation
Reactor cover gas plenum depressurization by rupture discs
Water/steam release near the lead free level
No industrial experience, manufacturability not yet demonstrated 19 19

20. ELFR - Steam Generator Parameter Value Tubes number 218
Outside tube diameter, mm
22.22
Tube thickness, mm
2.5
Average tube length, m 55
Tubes per layer 2
Radial & Axial pitches, mm 24
Inner shell inner/outer diameters, m
1.12/1.22
Inner companion shell Inner/outer diameters, m
1.23/1.24
Outer companion shell inner/outer diameters, m
2.42/2.43
Outer shell inner/outer diameters
2.44/2.54
Bundle height, m
2.62

21. Primary Pump
Primary pump is an axial mechanical pump, always running at constant speed, with blade profile designed to achieve the best efficiency
Parameters
ALFRED
ELFR
Flow rate, kg/s
3247.5
16250
Head, m
1.5
Outside impeller diameter, m
0.59
1.1
Hub diameter, m
0.39
0.43
Impeller speed, rpm
315
140
Number of vanes 5 3
Vane profile
NACA 23012
Suction pipe velocity, m/s
1.12
1.6
Vanes tip velocity, m/s
9.8
8.7
Meridian (at impeller entrance and exit) velocity, m/s
2.0
3.1

22. ALFRED - Reactor Vessel
Cylindrical vessel with a torospherical bottom head anchored to the reactor pit from the top
RV is closed by a roof that supports the core and all the primary components
RV upper part is divided in two branches by a “Y” junction: the conical skirt (cold) that supports the whole weight and the cylindrical (hot) that supports the Reactor Cover
A cone frustum welded to the bottom head has the function of bottom radial restraint of Inner Vessel
Inner Vessel radial support
Support flange
Cover flange
Main Dimensions
Height, m
Inner diameter, m 8
Wall thickness, mm 50
Design temperature, °C 400
Vessel material AISI 316L

23. Same concept of ALFRED with more large dimensions
ELFR - Reactor Vessel
Same concept of ALFRED with more large dimensions
Main Dimensions
Height, m
Inner diameter, m
Wall thickness, mm 50
Design temperature, °C 400
Vessel material AISI 316L

24. ALFRED – Primary Cover Gas System
Primary Cover Gas is Argon
Primary Cover Gas System main functions:
to guarantee cover gas confinement during normal plant operation (Primary Boundary)
to maintain cover gas volume in under-pressure (90 kPa)
to provide cover gas purification during normal operations
to detect fuel assemblies cladding failure by monitoring increased cover gas activity
to purge Nitrogen and to restore Argon after any Reactor Vessel opening for refueling or components maintenance/replacement

25. ALFRED – Primary Cover Gas Activity
Activity in the Cover Gas comes from a fraction of the radionuclides present in the primary lead coolant that have vaporized into the gas phase
Radionuclides in the primary lead have two different sources:
coolant activation products resulting from neutrons irradiation
radionuclides released from damaged fuel rods
Due to the retention property of Lead the more significant radionuclides present in the Cover Gas are Noble Gases and Tritium
Tritium
Ternary fission
From 10B
Total 3H
after 1y (g)
0.29
0.54
0.83
Element
Inventory (g)
Ne 23
Ar 37
Ar 39
Ar 41
Ar 42
Element
Volatilized fraction 480°C
Volatilized fraction 800°C I Cs Sr Po
Polonium
C00 Lead
C1 Lead Po
after 40 y (g)
0.03
0.4 25

26. ALFRED - Reactor Arrangement

27. ELFR - Reactor Arrangement

28. Decay Heat Removal Systems
Several systems for the decay heat removal function have been conceived and designed for both ELFR and ALFRED
One non safety-grade system, the secondary system, used for the normal decay heat removal following the reactor shutdown
Two independent, diverse, high reliable passive and redundant safety-related Decay Heat Removal systems (DHR N1 and DHR N2): in case of unavailability of the secondary system, the DHR N1 system is called upon and in the unlike event of unavailability of the first two systems the DHR N2 starts to evacuate the DHR
DHR N1:
Both ELFR and ALFRED rely on 4 Isolation Condenser (IC) system connected to 4 out of 8 SGs
DHR N2:
ELFR rely on 4 Isolation Condenser systems connected to 4 Dip Coolers (DCs) immersed in the cold pool
ALFRED rely on other 4 Isolation Condenser system connected to the other 4 SGs
Considering that, each SG is continuously monitored, ALFRED is a demonstrator and a redundancy of 266% is maintained, the Diversity concept could be relaxed
DHR Systems features:
Independence obtained by means of two different systems with nothing in common
Diversity obtained by means of two systems based on different physical principles
Redundancy is obtained by means of three out of four loops (of each system) sufficient to fulfil the DHR safety function even if a single failure occurs
Passivity obtained by means of using gravity to operate the system (no need of AC power)

29. Isolation Condenser History
In 1992 Ansaldo Nucleare designed the so called “Isolation Condenser” as part of the cooperation for the development of the SBWR design
Recently GE used the component developed by Ansaldo Nucleare for the ESBWR design
Ansaldo Nucleare successfully proposed the same type of arrangement for the IRIS Westinghouse reactor
The Isolation Condenser has been already tested in Italy by SIET (ENEA) at full scale SBWR conditions
Courtesy of GE

30. DHR Systems (Isolation Condenser)
ALFRED
DHR Systems (Isolation Condenser)
8 Independent loops
DHR N1 4 loops
DHR N2 the other 4 loops
Each Isolation Condenser loop is comprehensive of:
One heat exchanger (Isolation Condenser), constituted by a vertical tube bundle with an upper and lower header
One water pool, where the isolation condenser is immersed (the amount of water contained in the pool is sufficient to guarantee 3 days of operation)
One condensate isolation valve (to meet the single failure criteria this function shall be performed at least by two parallel valves)
1 loop (typical)

31. ALFRED Isolation Condenser Heat Exchanger
Upper and lower spherical header diameter 560 mm
Tube diameter mm
Number of tubes 16
Average tube length 2 m
Material Inconel 600

32. ALFRED DHR System Performances
Freezing temperature
Freezing temperature
4 Loops in operation (Maximum performances)
Lead temperature < nominal
Time to freeze  4 hours
3 Loops in operation (Minimum performances)
Lead Peak Temperature  500°C
Time to freeze > 8 hours

33. Decay Heat Removal Systems
ELFR
Decay Heat Removal Systems
DHR N1 – ICS
(1 of the 4 Independent loops)
DHR N2 – DC
(1 of the 4 Independent loops)

34. ELFR DHR N1 System Performances
4 Loops in operation (Maximum performances) Time to freeze  4 hours
3 Loops in operation (Minimum performances) Time to freeze > 10 hours

35. ELFR DHR N2 System Performances
4 Loops in operation (Maximum performances) Time to freeze  6 hours
3 Loops in operation (Minimum performances); Time to freeze > 10 hours

36. Selected materials for the main components of ALFRED and ELFR
Reactor Vessel
AISI316L
Vessel Support
P295GH
Safety Vessel (Cavity Liner)
Reactor Cover
Inner Vessel
AISI316LN
Core Lower Grid
Core Upper Grid
Steam Generator
T91
Primary Pump: Duct and Shaft
Primary Pump: Impeller
tbd (Maxtal ?)
Deep Cooler na
Fuel Assembly: Cladding
15-15/Ti
Fuel Assembly: Grids
Fuel Assembly: Wrapper

37. ALFRED and ELFR Design Options (Differences)
Items
ALFRED Option
ELFR Option
Electrical Power (MWe)
125 MWe (300 MWth)
 632 MWe (1500 MWth)
Fuel Clad Material
15-15Ti (coated)
15-15Ti or T91 (coated)
Fuel type
MOX (max Pu enrich. 30%)
MOX for first load
MAs bearing fuel .....
Max discharged burnup (MWd/kg-HM)
90÷100
100
Steam generators
Bayonet type with double walls, Integrated in the reactor vessel, Removable
Spiral type or alternate solution, Integrated in the reactor vessel, Removable
DHR System
2 diverse and redundant systems (actively actuated, Passively operated)
DHR1
Isolation Condenser connected to Steam Generators: 4 units provided on 4 out of 8 SGs
Isolation Condenser connected to Steam Generator: 4 units provided on 4 out of 8 SGs
DHR2
Duplication of DHR1
260% total power removal
Alternate solution to ELSY W-DHR under investigation

38. ALFRED and ELFR Design Options (Similarities)
Primary Coolant
Pure Lead
Primary System
Pool type, Compact
Primary Coolant Circulation: Normal operation
Emergency conditions
Forced
Natural
Allowed maximum Lead velocity (m/s) 2
Core Inlet Temperature (°C)
400
Steam Generator Inlet Temperature (°C)
480
Secondary Coolant Cycle
Water-Superheated Steam
Feed-water Temperature (°C)
335
Steam Pressure (MPa) 18
Secondary system efficiency (%)
 41
Reactor vessel
Austenitic SS, Hung
Safety Vessel
Anchored to reactor pit
Inner Vessel (Core Barrel)
Cylindrical, Integral with the core support grid, Removable
Primary pumps
Mechanical in the hot collector, Removable

39. ALFRED and ELFR Design Options (Similarities)
Fuel Assembly
Closed (with wrapper), Hexagonal, Weighted down when primary pumps are off, Forced in position by springs when primary pumps are on
Maximum Clad Temperature in Normal Operation (°C)
550
Maximum core pressure drop (MPa)
0.1 (30 min grace time for ULOF)
Control/Shutdown System
2 diverse and redundant systems of the same concept derived from CDT
1st System for Shutdown
Buoyancy Absorbers Rods: control/shutdown system passively inserted by buoyancy from bottom of core
2nd System for Shutdown
Pneumatic Inserted Absorber Rods: shutdown system passively inserted by pneumatic (by depressurization) from the top of core
Refuelling System
No refuelling machine inside the Reactor Vessel
Seismic Dumping Devices
2D isolator below reactor building

40. Thank you for your attention
ALFRED
Thank you for your attention