Multi-Physics Simulation of Fuel Rod Failure during Accidents in Sodium Fast Reactors

1. Multi-Physics Simulation of Fuel Rod Failure during Accidents in Sodium Fast Reactors Roman Samulyak AMS Department, Stony Brook University and Computational Science Center Brookhaven National Laboratory Collaborators: Michael Podowski, Ken Jansen (RPI), Lap Cheng (BNL) James Glimm, Xiaolin Li, Shuqiang Wang, Lingling Wu (Stony Brook) Paul Parks (General Atomics)

2. Project Objectives NERI consortium of Rensselaer Polytechnic Institute, Stony Brook University, Columbia University, and Brookhaven National Laboratory The overall objective is to develop a multiple computer code platform for advanced multiscale/multiphysics simulations of Generation IV reactors Apply proposed methodology to accident analysis for Sodium Fast Reactor (SFR) 2014/8/10 NERI PROJECT NO. 08-033 2

3. Fuel degradation and transport in SFR during fuel rod failure accidents

4. Project Work Scope MD simulations of reactor fuel Multicomponent material (gas, solid, melt) distribution inside fuel elements and ejection through cladding breach Cladding heatup and failure Gas (volatile fission products) and fuel particle injection into liquid metal coolant Multicomponent/multiphase fluid transport inside coolant channels Computational issues: development, implementation and testing of higher order solution algorithms Development of multiple-code computational platform for Blue Gene 2014/8/10 NERI PROJECT NO. 08-033 4

5. Project Overview Flow of liquid sodium coolant and fission gas around l reactor fuel rods Prediction of fuel properties evolution NPHASE-CMFD code uses Reynolds-Averaged Navier Stokes (RANS, e.g. k-ε model) approach to multiphase modeling Fuel rod overheating and melting of cladding in case of coolant-blockage accident Jet of high pressure fission gas entering coolant channels Molecular Dynamics approach analyses the irradiated fuel properties FronTier is a front tracking code capable of simulating multiphase compressible fluid dynamics PHASTA uses direct numerical simulation (DNS) with Level Set method to track the interface between gas and liquid phases 2014/8/10 NERI PROJECT NO. 08-033 5

6. Interaction between component-codes NPHASE domain (RANS) Determines the effects on the reactor fuel due to thermal loads and provides temperature- and irradiation-dependent thermal conductivity, density, effective porosity of fragmented/fractured fuel, diffusive properties of irradiated fuel Molecular Dynamics fuel Simulates the fuel rod heating and melting of stainless steel cladding. Computes the fission gas properties and escape velocity during the meltdown as well as the shape of the damaged cladding MD FronTier PHASTA domain (DNS) P fission gas U, shape of melted cladding Performs a two-phase direct numerical simulation of fission gas jet entering the liquid sodium coolant. The fluctuating velocity field is post-processed to provide the two-phase flow turbulence parameters downstream of fuel rod: mean velocity, turbulent kinetic energy, turbulence dissipation rate and gas volume fraction fission gas PHASTA CU Linear Solver FronTier domain P U,k,ε,α Performs a multiphase RANS simulation of a coolant flow during the accident scenario around several fuel rods using the detailed information provided by PHASTA and FronTier coolant NPHASE-CMFD Improves the ability of NPHASE, PHASTA and FronTier to solve large systems of linear equation in parallel environments 8/10/2014 NERI PROJECT NO. 08-033 6

7. Main Ideas of Front Tracking Front Tracking: A hybrid of Eulerian and Lagrangian methods • Two separate grids to describe the solution: • A volume filling rectangular mesh • An unstructured codimension-1 Lagrangian mesh to represent interface • Major components: • Front propagation and redistribution • Wave (smooth region) solution • Advantages of explicit interface tracking: • No numerical interfacial diffusion • Real physics models for interface propagation • Different physics / numerical approximations in domains separated by interfaces

8. The FronTierCode • FronTier is a parallel 3D multiphysics code based on front tracking • Being developed within DOE SciDAC program • Adaptive mesh refinement • Physics models include • Compressible fluid dynamics, MHD • Flows in porous media • Phase transitions and turbulence models Turbulent fluid mixing. Left: 2D Right: 3D (fragment of the interface)

9. Role of FronTier Code in Fuel Rod Simulations • Using material data from MD, simulate overheating scenarios in nuclear fuel rods and predict the shape and size of cracks in the steel clad and the fission gas and melted fuel flow into the coolant reservoir. Provide input to the PHASTA code. • Research tasks of the FronTier team: • Develop new algorithms for the phase transition (melting and vaporization) in the nuclear fuel rod • Develop algorithms for the crack formation and failure of solid materials • Perform simulations of the fuel rod failure and provide input to the PHASTA code 2014/8/10 NERI PROJECT NO. 08-033 9

10. New Phase Transition Algorithms for FronTier • Developed Embedded Boundary Elliptic Interface method for the heat transfer problem in nuclear fuel rods • Implemented and fully tested front-tracking-based solver of Stefan problem in FronTier • Applied the new solver to the phase transition problem in fuel rods (fuel and clad melting) • Developed algorithms for dynamic creation of boiling/vaporization nucleation centers in regions that exceed critical conditions 8/10/2014 NERI PROJECT NO. 08-033 10

11. Calculations of normal operating conditions • Performed calculations of normal operating conditions for metallic and oxide fuels • Assumed empirical models for effective heat transfer coefficients in the gas gap and turbulent fuel flow Coolant Cladding Gas gap Fuel Ideal (top) and real gas gap 8/10/2014 NERI PROJECT NO. 08-033 11

12. Simulation of fuel rod melting • Performed calculations of the heat transfer and phase transitions (melting) in a nuclear fuel rod at • Increased power production rate (transient overheating accident) • Increasing coolant temperature (loss of coolant accident) 8/10/2014 NERI PROJECT NO. 08-033 12

13. Development of mesoscale solid failure models for FronTier • Finite element meshes conforming to interfaces of solid structures • The medium is represented by a network of nodes connected by bonds satisfying some stress - strain relation • Bonds are present with the probability p. The probability of initial defect is p-1 • The process consists of the energy minimization and sequential breaking of bonds which exceed the critical stress threshold 8/10/2014 NERI PROJECT NO. 08-033 13

14. Fuel clad failure • Performed simulations of the failure of cladding • The failure was caused by the increased pressure and fuel rod deformation. Thermal changes of clad properties were ignored • Future work will focus on the implementation of more realistic stress-strain relations for bonds that include the plastic region and thermal changes of material properties 8/10/2014 NERI PROJECT NO. 08-033 14

15. Fission Gas Flow from Plenum to Sodium Pool • At the time of clad failure, fission gas transport inside fuel pin is first modeled using flow in porous medium equations • Then, FronTier calculations are performed to simulate pressure-driven ejection through cracked cladding wall of multiphase/ multicomponent mixture of fission gasses and molten/solid fuel into reactor coolant channel 8/10/2014 NERI PROJECT NO. XX-XXX 15

16. Ejection of the gas jet into sodium pool PHASTA simulation FronTier simulation 8/10/2014 16

17. PHASTA/NPHASE Link Channel flow DNS at Reτ = 180, Rehd = 11,200 High Re k-ε model Low Re k-ε model 8/10/2014 NERI PROJECT NO. 08-033 17

18. Simulation of processes in materials at extreme conditions in other energy applications 2014/8/10 18

19. ITER Fueling by Pellet Injection • ITER is a joint international research and development project that aims to demonstrate the scientific and technical feasibility of fusion power • ITER will be constructed in Europe, at Cadarache in the South of France in ~10 years Our contribution to ITER science: Models and simulations of tokamak fueling through the ablation of frozen D2 pellets

20. Main results of ITER fuelling simulations • ITAPS Front tracking was used for first systematic “microscale” MHD studies of pellet ablation physics • Simulations revealed new propertied of the ablation flow: • Supersonic rotation of the ablation channel • Resolution of this phenomenon greatly improves the agreement with experiments • Strong dependence of the ablation rate on plasma pedestal properties • Simulations suggested that novel pellet acceleration technique (laser or gyrotron driven) are necessary for ITER Isosurfaces of the rotational Mach number in the pellet ablation flow

21. Work in Progress • Current work focuses on the study of striation instabilities • Striation instabilities, observed in all experiments, are not well understood • We believe that the key process causing striation instabilities is the supersonic channel rotation, observed in our simulations Striation instabilities: Experimental observation (Courtesy MIT Fusion Group)

22. Inertial Confinement Fusion • National Ignition Facility • Construction started in 1997 • Official opening ceremony: May 29, 2009 • 500 Terawatt flash of light within a few picoseconds • 192 laser beams focused on the target

23. New Ideas in Nuclear Fusion: MTF

24. Mercury Jet Target for Neutrino Factory / Muon Collider • Target is a mercury jet interacting with a proton pulse in a magnetic field • Target converts protons to pions that decay to muons and neutrinos or to neutrons (accelerator based neutron sources) • Understanding of the target hydrodynamic response is critical for design • Studies of surface instabilities, jet breakup, and cavitation • MHD forces reduce both jet expansion, instabilities, and cavitation Jet disruptions Top: experiment Bottom: simulation Target schematic