Parametric Study of Sloshing Effects in the Primary System of an Isolated LFR Marti Jeltsov, Walter Villanueva, Pavel Kudinov

Transcription

1 1 Parametric Study of Sloshing Effects in the Primary System of an Isolated LFR Marti Jeltsov, Walter Villanueva, Pavel Kudinov Division of Nuclear Power Safety Royal Institute of Technology (KTH) Stockholm, Sweden

2 Outline Sloshing Risk analysis related to sloshing Seismic phenomena in LFRs Parameters relevant to sloshing CFD analysis Modeling assumptions Input data Results Conclusions Future plans 2

3 Sloshing Yung et al., J. Ship Research, 54, 174 (2010). A violent behavior of the liquid content in tanks that are subjected to the external forced motions. Very sensitive to the excitation signature (frequency/amplitude). Impacts on the vertical walls and/or on the horizontal top covers. Hydrodynamic pressure components: impulsive (fluid moving at containers velocity), convective (motion of the free surface slosh ), used in mechanical analog of tank-liquid systems. Maximum pressures can alter by as much as 2 orders of magnitude during an impact event. 3

4 4 Sloshing Flip-through modes Lugni et al., Phys. Fluids, 18, (2006). No gas entrapment Single bubble entrapment Generation of finescale liquid-gas mixture (dispersion)

5 Sloshing related risk assessment Goal: To show that the combination of dominant frequency and amplitude determines the sloshing regime. Development of a sloshing regime map allows: Implement surrogate model e.g. look-up table. Multiple runs needed for IDPSA (e.g. using Monte Carlo) is then achievable. 5

6 Se(g) 6 IDPSA application Spectra selection CFD analysis Floor Response Spectra Bounding frequencies Bounding amplitudes 2D, partial 3D, full 3D FSI Steel wall f(hz) Map of regimes Development of models Development of map of sloshing regimes Wave shapes Hydrodynamic parameters Void formation (characteristics of void) FSI (criteria for structural failure) GE (gas entrainment as a function of seismic character) Map of modes... CFD analysis Gas transport in an LFR primary system Assess the probabilty and extent of core voiding

7 Seismic phenomena in a reactor Heavy liquid metal cooled reactors are usually of pool type. Reactor pools are filled partially with coolant Presence of free surface. Occurs at free levels (gas-liquid interface): Cold plenum (collector), Hot plenum (collector). Sloshing has two distinct consequences 1. Impact forces acting on the vessel, on solid structures inside it and on the roof of it, 2. Entrapment of gas during flip-through of a slosh wave. Isolation 7

8 System analyzed: LFR - ELSY Compact design Economy Safety concerns Seismic load on a partially filled tank Sloshing of heavy liquid metal Risk of structural damage due to FSI Proximity of the SG and the sloshing region (free surface) to the core inlet Positive void effect of Pb at EOC (2 $) Risk of RIA due to core voiding Total mass of the reactor is tons out of which tons is the mass of Pb. 8

9 Parameters relevant to sloshing Sloshing regimes depend on: Geometry Aspect ratios Fill volume Presence of obstructions (baffles, 3D bodies, ceiling) Excitation characteristics 1 st frequency harmonic and respective amplitude Importance of higher harmonics and their amplitudes Duration 9

10 10 Analysis Modeling assumptions Solver: Fluent Geometry: 2D Mesh: Rectangular Time: Unsteady, variable time step (Co=0.5) Momentum: RANS Turbulence: Realizable k-epsilon Energy: No (isothermal) Phases: Eulerian Multiphase, VoF Incompressible liquid lead Compressible argon Surface tension Gas Liquid Gas Liquid

11 Analysis Seismic input Two types of soil analyzed: a) Hard soil (input spectra defined by RG 1.60 extended to Central and Eastern USA) b) Soft soil (input spectrum type 1 and soilt type E accroding to EN1998-1) Three levels of seismicity: a) Operating Basis Earthquake, OBE (1/3 DBE) a) Acceleration 0.2 g b) Displacement 7 cm b) Design Basis Earthquake, DBE a) Acceleration 0.6 g b) Displacement 22 cm c) Beyond Design Basis Earthquake, BDBE (3 DBE) a) Acceleration 1.8 g (however, SILER analysis was done for 1.2 g) b) Displacement 70 cm Maximum acceleration limit of 2.4g have been applied (Japan) Time-histrories for each type of soil and spectrum: a) Displacement b) Velocity c) Acceleration 11

12 12 Analysis Seismic input In NPPs, natural frequencies go from 5-8 Hz to Hz, the latter being in the range of natural frequency of sloshing Study in ELSY project: Isolation led to frequency shift from 2.78 Hz to 0.58 Hz Isolated building maximum acceleration is 0.25 g. Study in SILER project: 0.25 Hz 4.5 Hz (at IP1B and h1 direction only) X Y Z Parameter Non-Isolated Isolated (HDRB) Vessel support Cover center HDS.A 1000 RSB-S Frequency [Hz] 3/10 3/ /3 Sa [g] 4.1/ / /0.16 Frequency [Hz] 3/10 3/ Sa [g] 3.2/ / Frequency [Hz] 3/ /10 5/10 Sa [g] 2.3/ / /1.1 Courtesy of G. Moretti

13 Analysis Simulation matrix Sinusoidal behavior assumed: u = u max sin ωt, ω = 2πf This assumption is justified with irregular nature of seismic excitation. Implemented via UDF based source term in momentum equation Discrete frequency and spectral acceleration values bound the realistic (ELSY) data Excitation is applied in one horizontal direction. 0.1g 0.3g 0.9g 0.25 Hz Case 1 Case 2 Case Hz Case 4 Case 5 Case 6 5 Hz Case 7 Case 8 Case 9 13

14 Analysis Input excitation 14

15 15 Analysis Grid study Case Instantaneous addition of x-momentum source equal to gravity Cell size 10 cm 4 cm 2 cm Number of cells Simulation time 1 h 13 min 3 h 18 min 10 h 30 min Average time step 10 ms 3.4 ms 1.5 ms

16 frequency 5 Hz 2.5 Hz 0.25 HZ Results 0.1g 0.3g 0.9g acceleration Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 Case 8 Case 9 16

17 Results Wave heights 17

18 18 Results Wall pressure 2.3 MPa

19 19 Results Wall pressure 0.75 MPa

20 20 Results Wall pressure 1.2 MPa

21 Results 21

22 22 Extra cases Case10 Case11 Case12

23 Conclusions Sloshing regimes, loads and wave heights Low frequencies and high amplitudes is the problematic region for dynamic loads on the structures High waves, High pressure spikes, Possibility to hit the top wall (producing highest pressures up to 23 bars). Roof is hit in cases located in the upper right of the sloshing regime map High frequency oscillation even at high amplitude results in moderate (up to few bars load) Gas entrapment Length of the domain is not sufficient for development of breaking waves Splashes are observed only when the wave hits the top wall 23

24 Outlook Modeling of seismicity Use higher harmonics Use real time histories Multi-dimensional excitation (h1, h2, v at the same time) Data necessary for validation Advance geometry 3D analysis to be performed in order to compare with 2D analysis results Local congestion of the flow can have significant effects on sloshing Coupling with structural analysis Gas entrapment Evaluate the amount of entrapped gas Analyze velocity vectors since high downward velocities can enhance the transport of the void towards the core. Lagrangian simulation of bubbles in the primary system of ELSY 24

25 Thank you! 25