Safety Analyses for Dynamical Events (SADE) SAFIR2018 Interim Seminar Ville Sahlberg

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1 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Safety Analyses for Dynamical Events (SADE) SAFIR2018 Interim Seminar Ville Sahlberg

2 SADE Project SADE produces more reliable answers to safety requirements set in the YVL guides through refining transient safety analysis calculations Adopting CFD calculations Improving neutronics models Transient analyses 2

3 Open core geometry and RPV Internal coupling between HEXTRAN and SMABRE - HEXTRAN computes only the core neutronics and heat transfer inside fuel rods - SMABRE solves thermal hydraulics of the whole circuit One of the tests: Control rod ejection transient for a VVER-440 reactor Evolution of the relative fission power Power distribution in a core crosscutting at the time of the maximum total fission power 3

4 Open core geometry and RPV 1-way coupling of HEXTRAN and PORFLO Time-dependent node-wise 3D heating power pre-computed with HEXTRAN can be applied in PORFLO simulations for thermal-hydraulics Tested in computations for a VVER-1000 transient benchmark (OECD/NEA benchmark V1000CT-2), in which a large break in the main steam line between the steam generator and steam isolation valve is assumed (4 cases for 2 scenarios computed) Coolant temperature (K) (t = 71 s) Coolant temperature (K) in the hot leg 4 4

5 Open core geometry and RPV Full 2-way coupling of PORFLO with HEXTRAN and SMABRE Full couplings of HEXTRAN and SMABRE with PORFLO were implemented and tested. Couplings and data transfer between HEXTRAN, FINIX, SMABRE and PORFLO 5

6 Open core geometry and RPV Full 2-way coupling of PORFLO with HEXTRAN and SMABRE Applicability of the new coupled HEXTRAN-SMABRE-PORFLO simulation framework for nuclear power plants was tested in two transients: Case 1: 7 th dynamic AER benchmark for the start-up of an inoperable cold loop in VVER-440 Green: the CFD domain 6

7 Open core geometry and RPV Full 2-way coupling of PORFLO with HEXTRAN and SMABRE Case 1: 7 th dynamic AER benchmark for the start-up of an inoperable cold loop in VVER s 15 s 19 s 25 s 29 s 39 s T [ C] 7

8 Open core geometry and RPV Full 2-way coupling of PORFLO with HEXTRAN and SMABRE Case 2: VVER-1000 main-steam-line-break transient benchmark (OECD/NEA benchmark V1000CT-2 - Exercise 3) Coupling the CFD modelling domain for RPV with the SMABRE nodalization Coolant temperature: hot leg 4 8

9 Open core geometry and RPV Full 2-way coupling of PORFLO with HEXTRAN and SMABRE Case 2: VVER-1000 main-steam-line-break transient benchmark (OECD/NEA benchmark V1000CT-2 - Exercise 3) Temporal (60 s after the break) core inlet temperature (top) and assembly-wise fission power (bottom) in CFD-coupled HEXTRAN-SMABRE-PORFLO (left) and HEXTRAN-SMABRE (right) simulations With CFD coupling Without CFD coupling 9

10 Open core geometry and RPV New detailed polyhedral meshes created and simulations running VVER-1000 VVER-440 Instrumentation Tubes (blue) Support Plates (yellow) Perforated Plate (red) Control Rod Guide Tubes (purple) Spacers (dark green) Fuel (light green) Perforated Plates (red) Upper Support Plate (yellow) Assembly Inlets (blue) Fuel (light green) Reflector (dark grey) Support Plates (yellow) Control Rod Guide Tubes (blue) Reflector (dark grey) Core Barrel Bottom (red) Core Barrel Bottom (red) ~ cells ~ cells 10

11 Developing the neutronics models The refinement of neutronics models is kind of a follow-up story from pin power reconstruction to the base nodal model EPR core, TRAB3D From node-wise assembly powers to pin powers resolution increase of two orders of magnitude 11

12 Developing the neutronics models To analyze the pin power models, the continuous-energy Monte Carlo reactor physics code Serpent 2 was adopted to produce reference results 12

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14 Developing the neutronics models The relative differences between TRAB3D and Serpent 2 for all 1.39M pin powers for hot zero power (HZP) EPR core case 14

15 Developing the neutronics models Axial heterogeneities in HZP EPR core model with startup load produced notable differences between TRAB3D and Serpent 2. Methodology to generate leakage-corrected axial discontinuity factors was developed Single-assembly 3D Serpent 2 calculations + Assembly-wise TRAB3D calculations Axial discontinuity factors Improved full core TRAB3D calculations 15

16 Developing the neutronics models Reduction in total axial difference: 58.9 % Reduction in maximum (peak) difference: 52.9 % Absolute difference (% of total power) Axial node layer Differences in axial power distributions from TRAB3D and Serpent 2 with and without axial discontinuity factors 16

17 Developing the neutronics models Axial discontinuity factors for assembly #3 in the HZP EPR case for TRAB3D and an AFEN model Conclusion: A sufficiently advanced nodal model would not need axial discontinuity factors. This is investigated further in MONSOON project in

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