Loads on RPV Internals in a PWR due to Loss-of-Coolant Accident considering Fluid-Structure Interaction

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2 Loads on RPV Internals in a PWR due to Loss-of-Coolant Accident considering Fluid-Structure Interaction Dr. P. Akimov, Dr. M. Hartmann, L. Obereisenbuchner Fluid Dynamics Stuttgart, May 24, 2012

3 Content Motivation Fluid-structure interaction Introduction of computer codes used STRAC / HAUPT LOCAFLEX Sample LOCA calculations Summary Interaction Dr. P. Akimov May 24, p.3

4 Motivation In the case of a LOCA (e.g. break at the main coolant line): Allowable deformations of Control Rod Guide Tubes must not be exceeded ensure safe reactor shutdown Control Rod Guide Tubes Upper Support Plate (USP) Upper Support Columns Integrity of the RPV internals Upper Plenum (e.g. Core Support Barrel, Support Plates, Support Columns) ensure sufficient core cooling Downcomer Core Support Barrel Core Upper Core Plate (UCP) Lower Support Plate Take into account the main effects of the fluid-structure interaction in the computational models RPV and internals Interaction Dr. P. Akimov May 24, p.4

5 Fluid-structure interaction (FSI) FSI effects with regard to the Core Support Barrel (CSB): FSI effects in the Upper Plenum: Upper Support Plate Cold Nozzle Hot Nozzle Downcomer RPV CSB Core Postulated break buckling of the CSB deflection of the CSB Zone of reduced pressure Strong reduction of incoming pressure waves due to FSI Upper Core Plate bending of the tubular structures in the Upper Plenum Interaction Dr. P. Akimov May 24, p.5

6 Sequential vs. coupled FSI approaches Sequential approach: FSI approach: Fluid Displacements No FSI effects! Fluid Forces Fluid Structure Structure Displacement & Stresses Assessment of the results Fluid Forces Stresses from displacements Covering global loads, not realistic More realistic, load reduction effects due to structural reaction Interaction Dr. P. Akimov May 24, p.6

7 Computer codes Upper plenum internals Code STRAC / HAUPT Upper Plenum Lower internals, RPV, and Fuel Assemblies (FAs) Code LOCAFLEX Core Support Barrel Core with FAs Lower internals RPV and internals Interaction Dr. P. Akimov May 24, p.7

8 Code STRAC / HAUPT (upper plenum internals)

9 STRAC / HAUPT Main features CSB RPV STRAC is based on code TRAC (Transient Reactor Analysis Code) Loop 1 1D and 3D components PIPE, TEE, VALVE, PUMP, STGEN, VESSEL, CORE Guide Tube for Measurement Loop 1 (hot) Loop 2 (hot) Support Column Control Rod Guide Tube Loop 2 Non-homogeneous, non-equilibrium modelling 2 fluid flow, 2 phase flow Modifications and model extensions Evaluation of forces, valve models, interface to structure programs, e.g., HAUPT Fluid-structure interaction of the upper plenum internals is considered Loop 4 Loop 4 (hot) Loop 3 (hot) 3D grid for the RPV (horizontal cross section) Loop 3 Interaction Dr. P. Akimov May 24, p.9

10 Code LOCAFLEX (RPV, the core, and RPV internals)

11 LOCAFLEX Main features Fluid: The whole primary coolant volume is included. Modeled are: the RPV with internals, the core, steam generators, pumps, etc 1D, 2 phase flow Structure: The model consists of the RPV, the core, and the RPV internals (except for the upper plenum internals) New object-oriented developments allow for complex structural models generated by ANSYS software with nonlinear couplings Fluid-structure interaction in the downcomer is considered Interaction Dr. P. Akimov May 24, p.11

12 LOCAFLEX Fluid model of the RPV Upper Support Plate Cold Nozzle R327 R345 R363 R381 R9 R144 R8 R143 Loop Level R309 R308 R307 Upper Support Plate R310 R328 R346 R364 Hot Nozzle R7 R142 R306 Downcomer R6 R141 R5 R140 R4 R139 R3 R138 R2 R137 R1 R136 R303 R289 R296 R386 R393 R304 R302 Core Bypass R305 R301 R300 R299 R298 R297 Upper Core Plate Core Lower Support Plate Downcomer Lower Support Plate Core RPV and internals Upper Core Plate = 2D Network Interaction Dr. P. Akimov May 24, p.12

13 LOCAFLEX Structural model (RPV) Rigid beam model of the RPV Coupling to the CSB Flange Coupling of the RPV support to the building fixpoint Coupling to the Lower Support Plate 10 1 Parts of the RPV and internals that are in this model Interaction Dr. P. Akimov May 24, p.13

14 LOCAFLEX Structural model (Lower internals) Extended FE-model with over 2000 MDOFs *) Hold-Down HOLD-DOWN-SPRING Spring USP Hold-Down Spring CRGA-C Control assemblies UCP USP Core HR schroud CRGA-C Control assemblies CSB CB UCP LSP *) MDOFs = Master Degrees of Freedom Parts of the RPV and internals that are in this model Interaction Dr. P. Akimov May 24, p.14

15 LOCAFLEX Structural model (Upper plenum internals) The fluid forces due to the pressure waves (from STRAC/HAUPT) are applied in LOCAFLEX directly to the tubular structures Control Rod Guide Tubes Upper Support Plate USP CRGA-C Control assemblies UCP Fluid forces on the tubular structures Upper Core Plate Realistic coupling mechanism between the UCP and the USP thanks to the detailed FE models of the upper plenum internals RPV and internals Interaction Dr. P. Akimov May 24, p.15

16 Horizontal row models of Fuel Assemblies (FAs) (5 row models for 1 direction are shown with colors) LOCAFLEX Structural model (Core) Loop 1 (hot) Core-Y Loop 2 (hot) Impact couplings Shroud / FA and FA / FA Coupling to UCP Loop 1 Loop 2 Core-X Loop 4 Loop 3 Loop 4 (hot) Loop 3 (hot) Coupling to LSP Interaction Dr. P. Akimov May 24, p.16

17 LOCAFLEX Coupling between fluid & structure models Downcomer Downcomer inside CSB By means of Fluid CSB RPV CSB Control Rod Guide Tubes Upper Support Plate Upper Support Columns Fixpoint CSB Flange LSP UCP RPV By means of Structure RPV FAs FAs Building fixpoint Downcomer Core Support Barrel Lower Support Plate Core Upper Core Plate Core Shroud RPV and internals Interaction Dr. P. Akimov May 24, p.17

18 Sample LOCA calculations

19 LOCA calculation: Cold leg break Results Scaled force (CSB/CSBmax) without FSI X direction Y direction TIME (S) RPV Loop 3 (hot) Loop 3 Loop 2 Y Loop 4 (hot) RPV with 4 loops CSB Loop 4 Loop 1 Loop 1 (hot) Deflection of the CSB due to rapid decompression X Total Force on the CSB Interaction Dr. P. Akimov May 24, p.19

20 LOCA calculation: Cold leg break FSI effects without FSI with FSI Scaled force (CSB/CSBmax) X direction Y direction Scaled force (CSB/CSBmax) X direction Y direction TIME (S) TIME (S) With FSI more realistic analysis as to peak loadings & frequencies Interaction Dr. P. Akimov May 24, p.20

21 Summary Accurate and reliable numerical tools STRAC / HAUPT and LOCAFLEX for loads analyses in the assessment of safety for nuclear power reactors Allowing for Fluid-Structure Interaction and a complete consideration of dynamics lead to more realistic analyses of loads on the RPV internals New developments in LOCAFLEX allow for more realistic and accurate calculations Interaction Dr. P. Akimov May 24, p.21

22 [Editor and Copyright, 2011]: AREVA NP GmbH Paul-Gossen-Straße Erlangen, Germany. It is forbidden to reproduce the present publication in its entirety or partially in whatever form without prior written consent. Legal action may be taken against any infringer and/or any person breaching the aforementioned conditions. Subject to change and error without notice. Illustrations may differ from the original. The statements and information contained in this brochure are for advertising purpose only and do not constitute an offer of contract. They shall neither be construed as a guarantee of quality or durability, nor as warranties of merchantability or fitness for a particular purpose. These statements, even if they are future-oriented, are based on information that was available to us at the date of publication. Type, quantity and characteristics of goods and services are subject to formal individual formal contracts. Interaction Dr. P. Akimov May 24, p.22

23 Loads on RPV Internals in a PWR due to Loss-of-Coolant Accident considering Fluid-Structure Interaction Dr. P. Akimov, Dr. M. Hartmann, L. Obereisenbuchner Fluid Dynamics Stuttgart, May 24, 2012 Weitere Fragen? Besuchen Sie uns am AREVA-Stand (HS 5) Further questions? Visit us at the AREVA booth (HS 5)