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ALFRED
Alessandro Alemberti
Consultants’ Meeting: Education Training Seminar on Fast Reactors
Science and Technology ITESM Campus Santa Fe, Mexico City -
29 June -03 July 2015 m
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SUMMARY
• Main Goals of ALFRED
• ALFRED Design from LEADER project
• Core
• Safety Systems
• General lay-out
• Summary of recent developments
• Primary arrangement
• New Decay heat removal
• Safety vessel
• DHR-1 with non-condensable
AL
FR
ED
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ALFRED – MAIN DESIGN GUIDELINES
ALFRED will be connected to the electrical grid (Reactor Power ~125 MWe)
ALFRED design should be as much as possible based on available technology to speed up the construction time
ALFRED shall use structural materials compatible with the corrosive Lead used as coolant (Selected material AISI 316LN, T91, 15-15/Ti)
ALFRED design shall limit coolant flow velocity compatible with the erosive Lead used as coolant
ALFRED design solutions shall allow components to be removed from the Reactor Vessel to facilitate inspection, maintenance, replacement
ALFRED design solutions (especially for Safety and Decay Heat Removal function) should be characterized by very robust and reliable choices to smooth the licensing process
ALFRED Decay Heat Removal Systems shall be based on passive technology to reach the expected high Safety level (low primary system pressure drops to enhance natural circulation)
AL
FR
ED
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MAIN
COOLANT
PUMP
REACTOR
VESSEL SAFETY VESSEL
FUEL ASSEMBLIES
STEAM
GENERATOR
ALFRED - Reactor Configuration
ALFRED Main Characteristics
Electrical capacity: 125MWe
Thermal capacity: 300MWth
Primary Coolant Lead
Primary Circulation
Normal Operation
Accident Conditions
Forced (8mechanical pumps)
Natural
Primary System Pressure: < 0.1MPa
Primary System Temperature: 400÷480 °C
Primary System Flowrate 26000 kg/s
Secondary Coolant: Water/Superheated-Steam
Secondary System Pressure: 18 MPa
Superheated Steam
Temperature:
450 °C
Secondary Coolant Flowrate 193 kg/s
Fuel Material: MOX
Fuel Cycle/Residence time: 12 Months / 5 Years
Residual heat removal
systems:
2 DHR systems, 4 loops each -
Passive
Design Life: 40 Years
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ALFRED - Core Configuration
Power (MWth) 300
Fuel Assemblies Inner core Outer core
171 57
114
Fuel type MOX
Pu enrichment Inn/Out (at %)
21.7/27.8
Control/shutdown Rods
12
Safety Rods 4
Dummy elements 110
Fuel Batches 5
Fuel cycle length 365 EFPD
Peak/avg BU (MWd/t) 103/73.3
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ALFRED – Fuel Pin & Assembly
1390
Overall length 8000
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ALFRED - Reactor Control and Shutdown System
• Two redundant, independent and diverse shutdown systems
are designed for ALFRED (derived from MYRRHA design)
• The Control Rod (CR) system used for both normal control of
the reactor and for SCRAM in case of emergency
– CR are extracted downward and rise up by buoyancy in case of
emergency shutdown (SCRAM)
– During reactor operation at power CR are most of the time partly
inserted allowing reactor power tuning (each rod is inserted for a
maximum worth less than 1$ of reactivity)
• The Safety Rod (SR) system is the redundant and diversified
complement to CR used only for emergency shutdown SCRAM
– SR are fully extracted during operation at power
– SR are extracted upward and inserted downward by the actuation
of a pneumatic system (insertion by depressurization – fail safe)
– A Tungsten ballast is used to maintain SR inserted
• Reactive worth of each shutdown system is able to shutdown
the reactor even if the most reactive rod of the system is
postulated stuck CR SR
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ALFRED - Upper and Lower Core Support Plates
Lower 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.
Hole for
Instruments
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
Upper core support plate
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ALFRED - Inner Vessel
Inner Vessel assembly
Upper grid
Lower grid Pin
Inner Vessel has the main functions of core support and hot/cold plena separation. Fixed to the cover by bolts and radially restrained at bottom (replaceable). Core Support plate is mechanically connected to the IV with pins for easy removal/replacement
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ALFRED - Steam Generator
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 conductivities particles are added to 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
Water
Hot Lead
Cold Lead
Steam
Bayonet Tube Concept
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ALFRED - Steam Generator Geometry &Performances
Steam Generator Performance
Removed Power [MW] 37.5
Inlet Lead Temperature [C] 480
Outlet Lead Temperature [C] 400
Feed-water Temperature [C] 335
Steam Temperature [C] 450
SG steam/water side global ∆p [bar] 3.3
Steam Generator Geometry
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 1.88 mm
Outermost tube O.D 31.73 mm
Outermost tube thickness
2.11 mm
Length of exchange 6 m
Number of tubes 510
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ALFRED - Primary Pump – LEADER Option
Parameters Value
Flow rate, kg/s 3250
Head, bar 1.5
Outside impeller diameter, mm 590
Hub diameter, mm 390
Impeller speed, rpm 315
Number of vanes 5
Vane profile NACA 23012
Suction pipe velocity, m/s 1.1
Vanes tip velocity, m/s 9.8
Meridian (at impeller entrance and exit) velocity, m/s
2.0
Axial Mechanical Pump Type
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ALFRED - Primary Pump – New Option
Screw Pump Type
• Promising design
• Low relative speed
• Good performance
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ALFRED - Reactor Vessel
Cylindrical Vessel with a torispherical bottom head
Anchored to the reactor cavity from the top
Cone frustum, welded to the bottom head, provides radial support of the Inner Vessel
Inner Vessel radial
support
Support flange Cover
flange
Main Dimensions
Height, m 10.13
Inner diameter, m 8
Wall thickness, mm 50
Design temperature, C 400
Vessel material AISI 316L
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ALFRED - Decay Heat Removal Systems
• DHR Systems – One non safety-grade system, the secondary system, used for
normal decay heat removal – Two independent, 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 system N1
is called to operate and • in the unlike event of unavailability of the first two systems, the DHR
system N2 is called to operate
• DHR N1: – Isolation Condenser system connected to 4 out of 8 SGs
• DHR N2: – Isolation Condenser system connected to the other four 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: two different systems with nothing in common Redundancy: three out of four loops (of each system) sufficient
to fulfil the DHR safety function even if a single failure occurs Passivity: using gravity to operate the system (no need of AC
power)
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ALFRED - Isolation Condenser Heat Exchanger
• Upper and lower spherical header
diameter 560 mm
• Tube diameter 38.1 mm
• Number of tubes 16
• Average tube length 2 m
• Material Inconel 600
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ALFRED - DHR System Performances
300
320
340
360
380
400
420
440
460
480
500
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
°C
s
Core inlet temp
Core outlet temp
300
350
400
450
500
550
0 5,000 10,000 15,000 20,000 25,000°C
s
Core inlet temp
Core outlet temp
3 Loops in operation (Minimum performances)
Lead Peak Temperature 500C
Time to freeze > 8 hours
4 Loops in operation (Maximum performances)
Lead temperature < nominal
Time to freeze 4 hours
Freezing temperature Freezing temperature
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ALFRED - Secondary System
• Power conversion system based on superheated
cycle
• with dual turbine configuration, three extractions in
the HP and in the LP with an axial outlet
• Net cycle efficiency greater than 41%
Plant net output, MWe 125
Cycle Net Efficiency, % 41
Mass Flow, kg/s 193
Pressure, MPa 18
Steam Temperature, C 450
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ALFRED - Reactor Building: Vertical Section
20 09/07/2015
ALFRED – RECENT DEVELOPMENTS
From the end of the LEADER project we performed a
complete review of the main primary arrangement and
components following also recommendations received
from TSOs and suggestions of the partners of a
consortium (FALCON) dedicated to ALFRED development
and construction.
The main modifications are illustrated in the following
slides concerning the following aspects:
• Primary arrangement
• Safety vessel
• New Decay heat removal (DHR-2)
• DHR-1 with non-condensable
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ALFRED – NEW PRIMARY ARRANGEMENT
The main modification are:
• 4 primary pumps
• 4 Steam Generators
• Elimination of direct
connection between SG and
Core (the SG outlet do not
feed directly the lower
plenum below the core)
• Introduction of DHR-2 HX
22 09/07/2015
ALFRED – SAFETY VESSEL MODIFICATION
No more Safety Liner Safety Vessel
• Enlargement of the Reactor cavity (+800 mm);
• Concrete refractory layer (~770 mm) between the Safety Vessel
and the concrete structure;
• additional air gap placed between the Safety Vessel and the
refractory concrete (~30 mm) (thermal expansion);
• Reduction of the Vessel’s gap dimension (-150 mm);
• Implementation of a Reactor Cavity Cooling System;
• Change of the Reactor Support;
Main Requirements: Refractory Insulating Uncompressible (as needed) Formable by casting
4 intakes 4 chimneys new vessel support
to chimney
from intake
hot collector
hot collector
refractory filler
safety vessel Lightweight concrete
reactor vessel
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ALFRED – SAFETY VESSEL MODIFICATION
CFD analysis
confirm that
structural concrete
temperatures are
acceptable
heat losses from
vessel (normal
operation are close
to 200 KW)
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ALFRED DHR CONFIGURATION IN LEADER
• Main problem to be solved is the short time to freezing when ICs are called to operate
• Ansaldo registered a patent….
Steam
Generators
DH
R-1
an
ti-f
ree
zin
g s
ys
tem
26 Piacenza 17 - 04 -
2014
“Anti-freezing” system for DHR in HLM-cooled reactors:
• Noncondensable gas tank connected to IC lower header;
• When power removed by ICS > primary coolant power ICS depressurises noncondensable gas expands NC-Gas reach IC tubes heat exchange is reduced
• pICS stabilised;
• Tprimary stabilised > Tfreezing
Pb pool
Steam Generator
Condenser
Noncondensable gas tank
ANSALDO “ANTI-FREEZING” SYSTEM
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ALFRED – New DHR1 – grace time to freezing
300
350
400
450
500
550
600
0 1 2 3 4 5 6 7 8 9 10
Te
mp
era
ture
[°C
]
time [days]
(d) Pb temperature at SG outlet
SG outlet TPb freezing point
300
350
400
450
500
0 50 100 150 200 250
Te
mp
era
ture
[°C
]
time [min]
(c) Pb temperature at SG outlet
SG outlet T
Pb freezing point
Innovative DHR System Old DHR System
ALFRED: Lead temperature during Station Black Out
OLD DHR1- about 4 hours to freezing
NEW DHR1 with NC – 4-5 Days (judged sufficient for
operator action)
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ALFRED