Neutronic Challenges in SCWR Core Design. T. K. Kim Argonne National Laboratory

Transcription

1 Neutronic Challenges in SCWR Core Design T. K. Kim

2 Key Differences between SCWR and LWR Normalized Eφ(E).8.7 FBR RMWR SCR. BWR Neutron energy(ev) Density (g/cm ) Specific heat and density of water at 25 MPa Temperature (K) Specific heat (kj/kg/k) Coolant Density Severe coolant density change axially Coolant density is very sensitive to coolant temperature Operating Condition High pressure and high temperature Cladding Material High temperature resistant material Higher neutron absorption Zr Ni-58 Fe-56 1

3 A Sample System Code for SCWR Core Design WIMS8 used for lattice calculations 172-group library (based on JEF2.2) employed for self-shielding shielding calculations Zonal cross sections are functionalized by state parameters, o o o o σ σ σ ( ρm, Tm, Tf, SB) = σ ( ρm, Tm, Tf, SB ) + ρm + T ρ T SOLTRAN used for core calculations Interface current nodal formulation of simplified P 2 equation in multi- dimensional hexagonal geometry Multi-group, -Dimensional geometry σ + SB SB Single-phase heat balance equation was adopted for T/H condition update, T i, k 1, out ) p i, k i k = Tin + q ( z dz i, k w c m m m σ + T f T f 2

4 Algorithm of WIMS8/SOLTRAN System Lattice Calculation (WIMS8) Read Input for XS calculations Write XS (ISOTXS format) files Read XS (ISOTXS format) files Initialize T/H properties Core Calculation (SOLTRAN) Loop of T/H update Update node-wise XS Solve diffusion (or SP ) equation 2 Flux converged? yes Loop of outer iteration Update T/H properties T/H converged? yes Edit solution

5 Eigenvalue Iteration PWR SCWR Diff Eigenvalue changes in T/H property updating Convergence Problem Difference from 1.1, pcm Eigenvalue of typical PWR converges easily Eigenvalue of SCWR oscillates during calculation of T/H condition update T/H properties are very sensitive to coolant temperature Oscillatory behavior is dependent on coolant mass flow rate, core power, inlet temperature, etc 4

6 Comparison between SCWR and PWR Normalized power SCWR-1.2 SCWR-1.4 PWR-14.5 Coolant temperature, K SCWR-1.2 SCWR-1.4 PWR-14.5 Coolant density,g/cm SCWR-1.2 SCWR-1.4 PWR-14.5 Specific heat, kj/kg/k SCWR-1.2 SCWR-1.4 PWR-14.5 Numbers in legends denotes coolant mass flow rate in kg/sec/mwe 5

7 Sensitive to Coolant Mass Flow Rate 4 8 Normalized Power Coolant temperature,k Pseudo Core Height, cm Core Height, cm.9 8 Coolant density, g/cm Specific heat, kj/kg/k Core Height, cm Core Height, cm Numbers in legends denotes coolant mass flow rate in kg/sec/mwe Pseudo means pseudo-critical temperature at 25MPa 6

8 Coolant Pressure Effect Normalized power Coolant temperature, K Coolant density, g/cm Specific heat, kj/kg/k Numbers in legends denotes coolant pressure in MPa 7

9 Effect of Active Core Height Normalized power Coolant temperature, K Coolant density, g/cm Specific heat, kj/kg/k Numbers in legends denotes active core height in cm 8

10 Whole Core Calculation Inner core Blanket Inner core Blanket Outer core Outer core Reflector Reflector A: Normalized 2D power B: Assembly averaged coolant temperature, K C: Assembly averaged coolant density, g/cm D: Exit coolant temperature, K A B C D 2 5 Power and coolant density are very sensitive to the coolant temperature Power fluctuation is due to the non- uniform radial power shape Neutronic instability may happen during depletion, moving of control rods, perturbation of coolant mass flow, etc. 2 9

11 Accuracy of codes Challenges Lattice codes for cross section generation Intermediate neutron spectrum (need benchmark) Need higher actinide cross sections for burner design Core calculation code Challenges Multi-group calculation is necessary Convergence problem due to high sensitive T/H properties Axial power shape control Water-rod, rod, solid-rod, axial enrichment zoning, etc Radial power shape control (or coolant flow rate control) Reactivity coefficient control Pan-cake type core, Zr-H H layers, Thorium fuel, etc Neutronics and T/H coupling calculation for instability analysis Advances core concepts Burner, Breeder, Multi-purpose reactors, etc 1

12 Multi-purposed Mixed Spectrum SCWR Control rod Coolant outlet Coolant outlet Coolant inlet ~.7g / cm ~.1g / cm ~.7g / cm Coolant inlet Inner core (fast spectrum) Outer core (thermal spectrum) Thermal shield Core plate ~.4g / cm 11

13 Reactivity Control with Thorium-base Fuel 6 5 SCR with 9.98 fissile Void Coefficient(pcm) (Th+Pu)O 2 with fissile (Th+Pu)O 2 with 9.98 fissile Burnup(GWD/t) 12