Transcript Document

The ALFRED Project
ESNI+ Summer School
Stockholm, 19-21 May 2014
Luigi Mansani
[email protected]
1
Introduction
Development of a new reactor technology must follow
gradual and progressive steps to reach maturity



Identification of main issues related to the technology
Small scale to Large scale experimental facilities
Irradiation tests, fuel and materials development
and try to:
 Exploit full potential of the coolant
 Include from the beginning Safety in the Design
 Show sustainability of the fuel cycle
 Define and evolve a reference conceptual design of the FOAK
ESNI+ Summer School, Stockholm, 19-21 May 2014
2
LFR Development
The first step in the development of a Lead Cooled Critical Fast Reactor in
Europe started in 2006 with the EU - FP6 ELSY project, on the basis of
previous projects already carried out in the frame of projects dedicated to
Lead-Bismuth/Lead cooled Accelerator Driven Systems (XT-ADS,
EUROTRANS, etc.)
On February 2010 (EU - FP6 ELSY project terminated) a first reference
configuration of an industrial size (600 MWe) LFR was available
On April 2010 the LEADER project started its activities with the main goal to:
•
Develop an integrated strategy for the LFR development
•
Improve the ELSY design toward a new optimized conceptual configuration of
the industrial size plant, the ELFR conceptual design
•
Design a scaled down reactor, the LFR demonstrator – ALFRED, using solutions
as much as possible close to the adopted reference conceptual design but
considering the essential need to proceed to construction in a short time frame
ESNI+ Summer School, Stockholm, 19-21 May 2014
3
Why LEAD? – Some Advantages
 Lead does not react with water or air
Steam Generators installed inside the Reactor Vessel
 Very high boiling point (1745C ), very low vapor pressure (3 10-5 Pa @ 400 C)
Reduced core voiding reactivity risk
 Lead has a higher density
No need for core catcher (molten clad float and breached fuel could float)
 Lead is a low moderating medium and has low absorption cross-section
No need of compact fuel rods (large p/d defined by T/H)
Very low pressure losses (1 bar for core, 1.5 bar for primary loop)
Very high primary natural circulation capability
natural circulation DHR
LEAD COOLANT
PASSIVE SAFETY
ESNI+ Summer School, Stockholm, 19-21 May 2014
4
Why LEAD? – Not Only Advantages
PROVISIONS
High Lead melting point (~ 327 C) – assure Lead T above 340-350 C
Heating system, design and operating procedures
Overcooling transient (secondary side) may cause Lead freezing
FW requirement – diversification and redundancy – Really a safety issue?
Corrosion / erosion of structural materials - Slugging of primary coolant
Coatings, oxygen control, limit flow velocity (Russian approach)
Strategy at low oxygen content, Lead chemistry (alternative approach)
Seismic risk due to large mass of lead
2-D seismic isolators, vessel hanged, specific design
In-service inspection of core support structures
Similar to other HLM reactors but high T, all components replaceable
Fuel loading/unloading by remote handling
Develop appropriate cooling system (active  passive back-up)
Steam Generator Tube rupture inside the primary system
Show no effect on core, provide cover rupture disks to limit max pressure
Flow blockage and mitigation of core consequences
Hexagonal wrapped FAs – outlet temperature continuous monitoring
Full unprotected flow blockage causes cladding damages to a max of 7 FAs
ESNI+ Summer School, Stockholm, 19-21 May 2014
5
Strategy for Sustainability of Nuclear Energy
 Present known resources of Uranium represent about 100 years of consumption
with the existing reactor fleet
 Fast neutron reactors with closed fuel cycle have the potential:
 to multiply by a factor 50 to 100 the energy output from a given amount of uranium (with
a full use of U238),
 to improve the management of high level radioactive waste through the transmutation of
minor actinides
 to provide energy for the next thousand years with the already known uranium resources
 Both fast spectrum critical reactors and
sub-critical ADS are potential candidates
for dedicated transmutation systems
 Critical reactors, however, loaded with
fuel containing large amounts of MAs
might pose safety problems caused by
unfavourable reactivity coefficients and
small delayed neutron fraction
– Core fuelled with only MA (Uranium free)
has no Doppler nor Delayed Neutrons
ESNI+ Summer School, Stockholm, 19-21 May 2014
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Sustainability:
Example of Closed Fuel Cycle in Fast Reactors
MOX first loads
Fabrication
LFR
Adiabatic
Reprocessing
FP
+ losses
MOX equilibrium
Unat/dep
All Actinides
 LFR can be operated as adiabatic:
 Waste only FP, feed only Unat/dep
 Pu vector slowly evolves cycle by cycle
 MA content increases and its composition drift in the time
 LFR is fully sustainable and proliferation resistant (since the start up)
 Pu and MA are constant in quantities and vectors
 Safety - main feedback and kinetic parameters vs MA content
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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 hightemperature 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
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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
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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
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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
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ALFRED - DESIGN GUIDELINES
ALFRED will be connected to the electrical grid
Power close to 125 MWe (300 MWth)
ALFRED design should be based as much as possible on available
technology to speed up the construction time
ALFRED design solution (especially for Safety and Decay Heat
Removal function) should be characterized by very robust and
reliable choices to smooth as much as possible the licensing
process
ALFRED Decay Heat Removal System based on passive
technology to reach the expected high Safety level
12
ALFRED - Reactor Configuration
FUEL ASSEMBLIES
Power:
Primary cycle:
Secondary cycle:
MAIN
COOLANT
PUMP
300 MWth
400-480 °C
335-450 °C
STEAM
GENERATOR
MAIN
COOLANT
PUMP
STEAM
GENERATOR
REACTOR
CORE
REACTOR
VESSEL
SAFETY VESSEL
13
ALFRED - Core Configuration
FAs – Same concept of ELFR
171 Fuel Assembly
4 Safety Rods
12 Control 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
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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
Cover
Inner Vessel
Support flange
flange
Main Dimensions
Height, m
10.13
Inner diameter, m
8
Wall thickness, mm
50
Design temperature, C 400
Vessel material
AISI 316L
Inner Vessel radial
support
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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
Upper core support plate
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
ESNI+ Summer School, Stockholm, 19-21 May 2014
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ALFRED - Inner Vessel
Upper grid
Pin
Lower grid
ESNI+ Summer School, Stockholm, 19-21 May 2014
Inner Vessel assembly
17
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
(start-up, reactivity control during the fuel cycle and shutdown) and for
SCRAM in case of emergency
– CR are extracted downward and rise up by buoyancy in case of 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 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 shut down the
reactor even if the most reactive rod of the system is postulated stuck
• At refuelling both systems are inserted
18
ALFRED - 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)
ESNI+ Summer School, Stockholm, 19-21 May 2014
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© SCK•CEN
ALFRED - 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
ESNI+ Summer School, Stockholm, 19-21 May 2014
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© SCK•CEN
ALFRED - Steam Generator
 Bayonet vertical tube with
external safety tube and
internal insulating layer
Water
Bayonet Tube Concept
 The internal insulating layer
(delimited by the Slave tube)
has been introduced to
ensure the production of
superheated dry steam
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
Hot Lead
Cold Lead
 In case of tube leak this
arrangement guarantees that
primary lead does not interact
with the secondary water
 Flexibility of materials in
terms of compatibility with
Lead and Water
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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
1.88 mm
Outermost tube O.D
31.73 mm
Outermost tube
thickness
2.11 mm
Length of exchange
6m
Number of tubes
510
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ALFRED - Steam Generator Performances
Steam Generator Performance
Pump casing
Water Inlet
Third
tubesheet
Steam outlet
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
Tubes
Second
tubesheet
First tubesheet
ESNI+ Summer School, Stockholm, 19-21 May 2014
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ALFRED - Primary Pump
Primary pump is an axial mechanical pump, always running at constant
speed, with blade profile designed to achieve the best efficiency
Parameters
Flow rate, kg/s
Head, m
Outside impeller diameter, m
Hub diameter, m
Impeller speed, rpm
Number of vanes
Vane profile
Suction pipe velocity, m/s
Vanes tip velocity, m/s
Meridian (at impeller entrance
and exit) velocity, m/s
ESNI+ Summer School, Stockholm, 19-21 May 2014
ALFRED
3247.5
1.5
0.59
0.39
315
5
NACA 23012
1.12
9.8
2.0
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ALFRED - Decay Heat Removal Systems
– One non safety-grade system, the secondary system, used
for the normal decay heat removal following the reactor
shutdown
– 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 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:
– 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)
ESNI+ Summer School, Stockholm, 19-21 May 2014
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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
26
ALFRED - DHR System Performances
500
550
480
460
500
440
450
400
Core inlet temp
°C
°C
420
Core inlet temp
Core outlet temp
380
Core outlet temp
400
360
340
350
Freezing temperature
320
Freezing temperature
300
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
s
4 Loops in operation (Maximum performances)
Lead temperature < nominal
Time to freeze  4 hours
300
0
5,000
10,000
15,000
20,000
25,000
s
3 Loops in operation (Minimum performances)
Lead Peak Temperature  500C
Time to freeze > 8 hours
27
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
28
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
0.29
0.54
0.83
3H
after 1y (g)
Polonium
Po
after 40 y (g)
C00 Lead
0.03
C1 Lead
0.4
Element
Inventory
(g)
Ne 23
5.5 10-11
Ar 37
3.4
10-4
Ar 39
4.7 10-5
Ar 41
9.9 10-12
Ar 42
10-10
1.2
Element
Volatilized
fraction
480°C
Volatilized
fraction
800°C
I
9.5 10-8
3.0 10-5
Cs
2.4 10-7
4.9 10-6
Sr
7.5 10-16
5.3 10-16
Po
2.1 10-10
2.9 10-7
ESNI+ Summer School, Stockholm, 19-21 May 2014
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29
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
SG Mass Flow, kg/s
192.7
SG Pressure outlet, MPa
18.2
SG Pressure inlet, Mpa
18.8
SG Temperature outlet, C
450
ESNI+ Summer School, Stockholm, 19-21 May 2014
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ALFRED - Reactor Building: Vertical Section
17/07/2015
ESNI+ Summer School, Stockholm, 19-21 May 2014
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ALFRED - Implementation plan
ALFRED realisation includes several phases
 First of all set-up of an international consortium (2013)
 Site for construction has been already chosen (Pitesti in Romania)
 First consortium act, according to ESNI Implementation plan, is to search funding
 Several design steps have been individuated:




Conceptual design, LEADER project (2010-2013)
Basic design, siting and pre-licensing
Detailed design and licensing
components construction, civil engineering, on site assembly and commissioning
 Support R&D program will provide answers to remaining technical
challenges
2013: Consortium
2010
Conceptual
Design
(LEADER)
2020
Detailed design, siting
&
licensing
ESNI+ Summer School, Stockholm, 19-21 May 2014
2025
Construction
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ALFRED - Consortium (FALCON)
2011 – Romanian option
Romanian Government approved the
Memorandum “Option to host ALFRED
demonstrator", initiated by Ministry of Economy,
Trade and Business Environment
Ansaldo, INR and ENEA signed the MoU for ALFRED
2012 – MoU
2013 - ALFRED Consortium
FALCON
Ansaldo, INR and ENEA signed in December 2013
the FALCON (Foster ALfred CONsortium)
Consortium Agreement
Other organizations ready to sign the CA or a MoU
based on technology development
Phase 1
18 months, in-kind contributions, to optimize the cooperation
between the PARTIES, through strategic management, governance,
financial and technical work
Phase 2
Detailed Design
ESNI+ Summer School, Stockholm, 19-21 May 2014
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ALFRED
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