CONCEPTUAL DESIGN STUDIES FOR THE LIQUID METAL SPALLATION TARGET META:LIC

Transcription

1 CONCEPTUAL DESIGN STUDIES FOR THE LIQUID METAL SPALLATION TARGET META:LIC J. R. Fetzer, A. G. Class, C. Fazio, S. Gordeev Institute for Nuclear and Energy Technologies () KIT University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

2 Outline European Spallation Source (ESS) META:LIC Concept Window Target Module Conceptual Design first layout Thermohydraulics Structur mechanical Analysis Conceptual Design second layout Feasibiliy of Expansion Volume Windowless Target Module Next steps Conclusion Conceptual Design Thermohydraulics 2

3 European Spallation Source (ESS) ESS key figures: To be build in Lund, Sweden Open in 2019, fully operational in Partner countries Design relevant parameters Proton beam energy 2.5 GeV Proton beam mean current 2 ma Proton beam power 5 MW Long-pulse 2.86 ms Repetition rate 14 Hz Beam footprint assumtion on target: 2D parabolic Total width 140 mm Total height 50 mm 3

4 META:LIC Concept modular concept 3 separately replaceable modules pool LBE target module (window/windowless) pump module heat exchanger module proton beam moderator heat exchanger module proton beam guide target module pool pump module 4

5 Design guidelines Analysis of flow configuration of exitsting LM targets angle between coolant flow and proton beam necessity of flow conditioning flow configuration in ensuring window cooling Pressure inside target compared to ambient pressure Design guidelines keep almost coaxial beam direction omit stagnation points omit flow limiter omit complex flow conditioning, to allow for an analytical predesign 5

6 Window target module first layout Target module - Concept nozzle for flow conditioning and elimination of cavitation channel with15 inclination results in small relatively uniform heating successive beam pulses interact with fluid not subjected to the beam previously lower than ambient pressure flow velocity LBE m/s structure material T91 pressure loss < 0.2 bar nozzle window outflow inflow proton beam inclination of 15 6

7 Window Target Module -Thermohydraulics Calculation conditions: Average jet velocity 2 m/s Inlet temperature: 200 C Fluid properties: LBE (ν,σ,ρ,λ)= f(t) Beam Parameters Repetiton rate: 20 Hz Pulse length: 2 ms Heating power density distribution (Star CCM+) Calculation model: k-ε High Reynolds number TM Boundary conditions: Adiabatic walls Symmetry in z-direction no slip at walls Z X Y Beam axe e e e e e+08 Inlet window Symmetry plane 0 Outlet 7

8 Temperatures Structure mean temperature and transient temperature in structure material window thickness < 1.5 mm for reasonable window coolability RANS simulation with 20 Hz shows temperature oscillation amplitude approx. 20 K 529 C 523 C Mean temperature distribution structure material 516 C Maximum temperature in structure material as a function of time 510 C 8

9 Temperatures LBE mean temperature and transient temperature in LBE acceptable maximum temperatures 375 C 360 C Mean temperature in LBE 355 C 356 C Maximum temperature in LBE as a function of time 9

10 Window target module - Issues Issues of LM targets subjected to pulsed proton beam Instantaneous heat deposition at beginning of pulse constant volumetric increase in liquid metal additional volume blocks the liquid metal flow first positive pressure wave End of the pulse the heat deposition stops volumetric expansion stops liquid metal flow field is conformed to the thermal expansion second negative pressure wave 10

11 Structure mechanical Analysis - J. Wolters FZJ Stressing of the target container due to thermal expansion of LBE in transient condition accumulation of stresses for several pulses 1 st pulse 2 nd pulse 3 rd pulse 11

12 Results structure mechanical Analysis J. Wolters FZJ LBE volume will increase approximately 18 cm³/pulse outlet flow rate is 1.7% higher than inlet flow for normal operation conditions Stressing of the container due to pressure pulses is probably insignificant compared to the stressing due to the thermal expansion of the fluid during one pulse Deformations and stresses will be accumulated for the first pulses after a beam trip. Maximum pressure amplitude ~ 10bar More critical proton beam transients Sudden beam cut-off (beam trip on - off) Start-up (beam trip off - on) 12

13 Window target module Second layout Target module Expansion chamber in U-bend Spoiler enforcing flow detachment Two internal free surfaces Expansion chamber Outflow duct Outflow is decoupled from inflow 13

14 Design measures - effects Beam trip off - on wall stresses add from 2 3 pulses Beam trip on - off time for the low pressure/ cavitation zone to be neutralized at the free surfaces: approx. 2 pulses thermally expanded volume/ cavitation zone low pressure/ cavitation zone 14

15 Feasibility of Expansion Volumes 15

16 Feasibility of Expansion Volumes VOF Phase Fraction 1(LBE) colored by velocity magnitude [m/s] t = 0-3 s 16

17 Feasibility of Expansion Volumes Filling of the META:LIC target module Boundary & Initial Conditions 2 dimensional OpenFOAM V. 2.1 Solver: InterFoam VOF Phase alpha1 0: air (T= 525K) Phase alpha1 1: LBE (T =525K) Grid: blockmesh hexahedral elements 17

18 Feasibility of Expansion Volumes Filling of the target module 2d t=0-7s alpha1 = 1: LBE alpha1 = 0: air 18

19 Conclusion window target module channel walls stay at low temperature acceptable maximum temperature dedicated design measures limit the accumulation of stresses due to the thermal expansion of LBE to 2-3 pulses free surfaces can be established at the expected locations no negative feedback of the free surface in the expansion volume on the fluid flow in the proton beam interaction zone 19

20 Windowless target module Target module Concept design nearly identical to window option (1 st layout) window is removed beam does not directly hit any solid structures no design measures needed limit effects of proton beam induced pressure waves splashing from free surface can be collected in proton beam guide proton beam guide proton beam 20

21 Window Target Module -Thermohydraulics Calculation conditions: Average jet velocity: 2 m/s Inlet temperature: 200 C Fluid properties: LBE (ν,σ,ρ,λ)= f(t) Beam Parameters Repetiton rate: 20 Hz Pulse length: 2 ms Heating power density distribution (Star CCM+) Calculation model: k-ε High Reynolds number TM Volume-of-Fluid (VOF) Boundary conditions: Adiabatic walls Symmetry in z-direction no slip at walls Free surface Free surface Z X Y Beam axe e e e+08 Inlet e e+08 Symmetry plane 0 Outlet 21

22 Window Target Module -Thermohydraulics Flow velocity at nozzle outlet 2 m/s Instantaneous free-surface flow determined by VOF

23 Conclusion Windowless target module stable supercritical free surface channel walls stay at low temperature (max 340 C) acceptable maximum temperature 23

24 Next steps Implementation of the MPV (Multiple Pressure Variables) Method in OpenFOAM to simulate thermally induced pressure waves at reasonable numerical costs in real geometries MPV (Multiple Pressure Variables) approach: use of multiple pressure variables Thermodynamic pressure Acoustic pressure Balance pressure to satisfy incompressible continuity use of a underlying base grid for the flow simulation and a coarse grid for the acoustic phenomena 24

25 Conclusion The META:LIC concept exploits previous experience. This has allowed to freeze the nozzle design at an early stage Key results window option: For the first implementation phase (gain experience) appropriate window cooling can be achieved. Design measures to limit accumulation of stresses due to thermal expansion of LBE Key result windowless option: For upgrading to higher power level stable supercritical free surface acceptable maximum temperatures Window/windowless target modules geometrically and thermohydraulically nearly identical; ancillaries are independent of window/windowless target option Acknowledgement: BMBF Design Update ESS AREVA Nuclear Professional School (ANPS) 25

26 Thermohydraulic Simulations use previous baseline parameters (20 Hz, 2 ms) Maximum time averaged power density does not change significantly effect on time averaged stationary results is small Lower repetition rate increase of energy deposition per pulse could have effect on fatigue due to thermal stresses 26