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TRANSIENT EVALUATION OF A GEN-IV LFR DEMONSTRATION PLANT THROUGH A LUMPED-PARAMETER ANALYSIS OF COUPLED KINETICS AND THERMALHYDRAULICS ANALYSIS OF COUPLED KINETICS AND THERMALHYDRAULICS Sara Bortot, Antonio Cammi LEADER PROGRESS MEETING, W.P. 4 TASK 4.4 Preliminary definition of the Control Architecture CIRTEN - POLITECNICO DI MILANO November 18 th, 2010, Bologna

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OUTLINE Context and goals Reactor configuration Analysis approach Mathematical model Simulation results Conclusions WORK PROPOSAL – TASK 4.4

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CONTEXT and GOALS ►Lead-cooled Fast Reactor (LFR) selected by the Generation IV international Forum (GIF) as one of the candidates for the next generation of nuclear power plants ►significant technological innovations need of a demonstrator reactor (DEMO) study of plant global performances refining/finalizing the system configuration REACTOR DYNAMICS design of an appropriate control system

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REACTOR CONFIGURATION ParameterValueUnit Thermal Power300MWth Average Coolant Outlet T480°C Coolant Inlet T400°C Average Coolant Velocity3.0m s -1 Clad Max T600°C Clad Out Diameter6.00mm Clad Thickness0.34mm Pellet Outer Diameter5.14mm ParameterValueUnit Pellet Hole Diameter1.71mm Fuel Column Height650mm Fuel Rod Pitch8.53mm Number of Pins/FA744- SS box beam inner width45.65mm SS box beam outer width48.65mm Number of Inner/Outer FAs10/14- Pu Enrichment Inner/ Outer29.3/32.2vol.% CORE LAYOUT

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ANALYSIS APPROACH (1) H Ψ C i CORE T f T c T l T in δρ(t) δψ(t) δT in (t) δT f (t) δT c (t) δT l (t) δq(t) δT out (t) δT in (t) δH(t) δT f (t) δT c (t) δT l (t) δρ(t) δH(t) Kinetics Thermal-hydraulics Reactivity Input T out

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ANALYSIS APPROACH (2) MAIN ASSUMPTIONS - NEUTRONICS -neutron time fluctuations independent of spatial variations -spectrum independent of neutron level -core lumped source of neutrons with prompt heat power -neutron population and neutron flux related by constants of proportionality POINT-KINETICS APPROXIMATION

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ANALYSIS APPROACH (3) MAIN ASSUMPTIONS – THERMAL-HYDRAULICS -average channel representation -single-node heat-exchange model -3 distinct temperature regionsfuel cladding coolant -energy balance over the fuel pin surrounded by coolant -reactor powerinput retrieved from reactor kinetics LUMPED-PARAMETER APPROACH

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MATHEMATICAL MODEL (1) NEUTRON KINETICS EQUATIONS - - ASSUMPTION t ≤ 0 steady state - - perturbation around steady state solution - - linearization SMALL-PERTURBATION APPROACH with: - - ψ = n(t)/n 0 = q(t)/q 0 - - η i = C i (t)/C i0

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MATHEMATICAL MODEL (2) THERMAL-HYDRAULICS EQUATIONS ASSUMPTIONS: - - constant properties - - axial conduction neglected - - T l = (T in + T out )/2 SMALL-PERTURBATION APPROACH Time constants: - - f = M f C f /k fc - - c1 = M c C c /k fc - - c2 = M c C c /h cl - - l = M l /Γ

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MATHEMATICAL MODEL (3) REACTIVITY EQUATIONS - - α D = Doppler coefficient - - α L = coolant density coefficient - - α Z = axial expansion coefficient - - α R = radial expansion coefficient - (Linked option) - α H = CR-related coefficient - - Function of fuel average temperature cladding average temperature coolant average temperature coolant inlet temperature externally introduced reactivity (ideal control rod)

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REACTIVITY COEFFICIENTS CALCULATION DOPPLER LEAD DENSITY RADIAL EXPANSION AXIAL EXPANSION MATHEMATICAL MODEL (4)

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SIMULATIONS (1) SOLUTION TECHNIQUE – MIMO (Multiple Input Multiple Output) SYSTEM modelling equations state-space representation: state vector: output vector: input vector:

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SIMULATIONS (2) ERANOS-2.1, JEFF-3.1 data library calculations

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RESULTS (1) LEAD INLET TEMPERATURE PERTURBATION (+10 K) Reactivity Lead average temperature Power Fuel average temperature Clad average temperature Core outlet temperature

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RESULTS (2) CONTROL ROD EXTRACTION (+50 pcm) Reactivity Power Fuel average temperature Lead average temperature Clad average temperature Core outlet temperature

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RESULTS (3) REACTOR CORE OPEN-LOOP STABILITY Study of the system representative TRANSFER FUNCTION qualitative insights into the response characteristics of the system STABILITY all the system poles with negative real parts

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CONCLUSIONS ►preliminary evaluation of DEMO core dynamics ►coupling of NEUTRONICS and THERMAL-HYDRAULICS ►prediction of DEMO reactions to 10°C increase of lead inlet T 50 pcm insertion by ideal CR ►stable system ►significant impact of reactivity insertion on reactor power (steady state: + 32/25 % nominal value at BoC/EoC) and fuel temperature (+ 276/220 K at BoC/EoC) ►model with satisfactory capability of predicting the system response to both perturbations (small errors figured) ►generally slight impact of assuming the fuel linked to the cladding or the radial expansion driven by the coolant average temperature ►useful tool allowing a relatively quick, qualitative analysis of fundamental dynamics and stability aspects

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WORK PROPOSAL ►Primary loop modeling ►Secondary loop modeling ►Coupling between primary and secondary loops ►Sensitivity analysis ►Control and measured variables definition ►Control strategy assessment (SISO loops and Multi-variable control, e.g. MPC) TASK 4.4 Preliminary definition of the Control Architecture

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