alfred and elfr system design technical workshop to review safety and design aspects of european lfr...

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, 2728 February 2013 Luigi Mansani [email protected]

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 450C (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 450C reduces heat transfer capability 15-15/Ti steel, owing to the available large database, is candidate for fuel cladding operating at relatively low temperature

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 500C), 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 550C 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 (Ti 3 SiC 2 ) based alloys Tantalum coated

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED FA and Core Configuration 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 171 Fuel Assembly 12 Control Rods 4 Safety Rods 108 Dummy Element FAs Same concept of ELFR

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR FA and Core Configuration STRATEGY: -Adiabatic core power distribution flattened with two zone different hollow pellets diameters 270 Outer Fuel Assembly 12 Control Rods 12 Safety Rods 132 Dummy Element 157 Inner Fuel Assembly

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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) SCKCEN

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 B 10 ) cooled by the primary coolant Pins have no gas plenum, the small produced gas realised into primary coolant SCKCEN RS2: 2 Shutdown System

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED - Inner Vessel Inner Vessel assembly Upper grid Lower grid Pin

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR Inner Vessel, Core support and Fuel Assembly (Same ALFRED concept larger dimensions)

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED - Steam Generator Bayonet Tube Geometry Steam Generator Geometry Bayonet tube Number of coaxial tubes 4 Slave tube O.D9.52 mm Slave tube thickness1.07 mm Inner tube O.D19.05 mm Inner tube thickness1.88 mm Outer tube O.D25.4 mm Outer tube thickness1.88 mm Outermost tube O.D31.73 mm Outermost tube thickness 2.11 mm Length of exchange6 m Number of tubes510

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED - Steam Generator SGs Tubes, forged plates and shells are made of X10CrMoVNb9-1, as per the RCC-MRx code (equivalent in ASME code to T91 steel) Water Hot Lead Cold Lead Steam

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED - Steam Generator Performances First tubesheet Second tubesheet Third tubesheet Steam outlet Water Inlet Pump casing Tubes Steam Generator Performance 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR Once through Spiral SG: Concept PowerMW187.5 Lead Inlet TemperatureC480 Lead Outlet temperatureC400 Water Inlet TemperatureC335 Steam Outlet temperatureC464 Steam Outlet PressureMPa18

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 ELFR Once through Spiral SG: Concept features

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR - Steam Generator ParameterValue Tubes number218 Outside tube diameter, mm22.22 Tube thickness, mm2.5 Average tube length, m55 Tubes per layer2 Radial & Axial pitches, mm24 Inner shell inner/outer diameters, m1.12/1.22 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 diameters2.44/2.54 Bundle height, m2.62

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 Primary Pump ParametersALFREDELFR Flow rate, kg/s 3247.516250 Head, m 1.5 Outside impeller diameter, m 0.591.1 Hub diameter, m 0.390.43 Impeller speed, rpm 315140 Number of vanes 53 Vane profile NACA 23012 Suction pipe velocity, m/s 1.121.6 Vanes tip velocity, m/s 9.88.7 Meridian (at impeller entrance and exit) velocity, m/s 2.03.1 Primary pump is an axial mechanical pump, always running at constant speed, with blade profile designed to achieve the best efficiency

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 10.13 Inner diameter, m 8 Wall thickness, mm 50 Design temperature, C 400 Vessel material AISI 316L

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR - Reactor Vessel Same concept of ALFRED with more large dimensions Main Dimensions Height, m 12.8 Inner diameter, m 13.77 Wall thickness, mm 50 Design temperature, C 400 Vessel material AISI 316L

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 25 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 TritiumTernary fission From 10 B Total 3 H after 1y (g) 0.290.540.83 PoloniumC00 LeadC1 Lead Po after 40 y (g) 0.030.4 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 1.2 10 -10 Element Volatilized fraction 480C Volatilized fraction 800C 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 ALFRED Primary Cover Gas Activity

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED - Reactor Arrangement

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR - Reactor Arrangement

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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)

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 Courtesy of GE 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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)

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED DHR System Performances 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ELFR Decay Heat Removal Systems DHR N2 DC (1 of the 4 Independent loops) DHR N1 ICS (1 of the 4 Independent loops)

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 4 Loops in operation (Maximum performances) Time to freeze 4 hours 3 Loops in operation (Minimum performances) Time to freeze > 10 hours ELFR DHR N1 System Performances

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 Selected materials for the main components of ALFRED and ELFR Components Material ALFREDELFR Reactor VesselAISI316L Vessel SupportP295GH Safety Vessel (Cavity Liner)AISI316L Reactor CoverAISI316L Inner VesselAISI316LN Core Lower GridAISI316LN Core Upper GridAISI316LN Steam GeneratorT91 Primary Pump: Duct and ShaftAISI316LN Primary Pump: Impellertbd (Maxtal ?) Deep CoolernaAISI316LN Fuel Assembly: Cladding15-15/TiT91 Fuel Assembly: Grids15-15/TiT91 Fuel Assembly: WrapperT91

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED and ELFR Design Options (Differences) ItemsALFRED OptionELFR Option Electrical Power (MWe) 125 MWe (300 MWth) 632 MWe (1500 MWth) Fuel Clad Material15-15Ti (coated)15-15Ti or T91 (coated) Fuel typeMOX (max Pu enrich. 30%)MOX for first load MAs bearing fuel..... Max discharged burnup (MWd/kg-HM)90100100 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 System2 diverse and redundant systems (actively actuated, Passively operated) DHR1Isolation 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 DHR2Duplication of DHR1 260% total power removal Alternate solution to ELSY W-DHR under investigation

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED and ELFR Design Options (Similarities) Primary CoolantPure Lead Primary SystemPool 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 CycleWater-Superheated Steam Feed-water Temperature (C)335 Steam Pressure (MPa)18 Secondary system efficiency (%) 41 Reactor vesselAustenitic SS, Hung Safety VesselAnchored to reactor pit Inner Vessel (Core Barrel) Cylindrical, Integral with the core support grid, Removable Primary pumpsMechanical in the hot collector, Removable

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 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 System2 diverse and redundant systems of the same concept derived from CDT 1 st System for ShutdownBuoyancy Absorbers Rods: control/shutdown system passively inserted by buoyancy from bottom of core 2 nd System for ShutdownPneumatic Inserted Absorber Rods: shutdown system passively inserted by pneumatic (by depressurization) from the top of core Refuelling SystemNo refuelling machine inside the Reactor Vessel Seismic Dumping Devices2D isolator below reactor building

Technical Workshop; Joint Research Centre, Petten, the Netherlands, 2728 February 2013 ALFRED Thank you for your attention

alfred and elfr system design technical workshop to review safety and design aspects of european lfr...

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