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ALFRED and ELFR system design

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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 assembly
12

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


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