Modular High Temperature Pebble Bed Reactor Faculty Advisors Andrew C. Kadak
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Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Modular High Temperature Pebble Bed Reactor Faculty Advisors Andrew C. Kadak Ronald G. Ballinger Michael J. Driscoll Sidney Yip David Gordon Wilson MPBR-1 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Student Researchers • Fuel Performance - Heather MacLean - Jing Wang • Thermal Hydraulics - Chunyun Wang - Tamara Galen • Core Physics - Julian Lebenhaft • Safety - Tieliang Zhai MPBR-2 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Project Objective Develop a sufficient technical and economic basis for this type of reactor plant to determine whether it can compete with natural gas and still meet safety, proliferation resistance and waste disposal concerns. MPBR-3 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Generation IV Reactor • • • • Competitive with Natural Gas Demonstrated Safety Improved Proliferation Resistance Readily Disposable Waste Form MPBR-4 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Modular High Temperature Pebble Bed Reactor • • • • • • • 110 MWe Helium Cooled “Indirect” Cycle 8 % Enriched Fuel Built in 2 Years Factory Built Site Assembled MPBR-5 • On-line Refueling • Modules added to meet demand. • No Reprocessing • High Burnup >90,000 Mwd/MT • Direct Disposal of HLW Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project What is a Pebble Bed Reactor ? • • • • • • MPBR-6 360,000 pebbles in core about 3,000 pebbles handled by FHS each day about 350 discarded daily one pebble discharged every 30 seconds average pebble cycles through core 15 times Fuel handling most maintenance-intensive part of plant Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR Specifications Thermal Power Core Height Core Diameter Pressure Vessel Height Pressure Vessel Radius Number of Fuel Pebbles Microspheres/Fuel Pebble Fuel Fuel Pebble Diameter Fuel Pebble enrichment Uranium Mass/Fuel Pebble Coolant Helium mass flow rate Helium entry/exit temperatures Helium pressure Mean Power Density Number of Control Rods Number of Absorber Ball Systems MPBR-7 250 MW 10.0 m 3.0 m 16 m 5.6 m 360,000 11,000 UO2 60 mm 8% 7g Helium 120 kg/s (100% power) 450oC/850oC 80 bar 3.54 MW/m3 6 18 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Conceptual Design Layout Turbomachinery Module Reactor Module MPBR-8 IHX Module Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Competitive With Gas ? • • • • Natural Gas AP 600 ALWR MPBR 3.4 Cents/kwhr 3.62 Cents/kwhr 3.8 Cents/kwhr 3.3 Cents/kwhr Levelized Costs (1992 $ Based on NEI Study) MPBR-9 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-10 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Improved Fuel Particle Performance Modeling: Chemical Modeling Student: Heather MacLean Advisor: R. Ballinger MPBR-11 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Objective • Model fuel particle chemical environment – particle temperature distributions – internal particle pressure • Model chemical interactions with coatings (SiC) – migration of fission products (Ag) through coatings (SiC) – chemical attack (Pd) of SiC MPBR-12 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Accomplishments • Analyzed likely temperatures in fuel particles in different core locations – ∆T across any particle < 20 °C – peak kernel temperature range: 500-1100 °C • Diffusion experiment in progress – 2 diffusion couples heated, continuing – characterization in progress MPBR-13 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Coated Particle Fuel System Individual Microsphere Fuel Kernel Buffer IPyC SiC OPyC 780 µm nominal diameter Fuel Pebble ~11,000 microspheres per fuel pebble ~350,000 pebbles per core MPBR-14 60 mm diameter Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Thermal Model Calculate temperatures in a pebble: • Linear axial bulk He temperature rise (450-850 °C) • Packed-bed He heat transfer correlation (∆T across He film surrounding a pebble) ⇒ Pebble surface temperature for any core location • Homogenized (volumetric averages) pebble thermal conduction model based on core average power • Thermal conductivity depends on temperature ⇒ Temperature distribution inside a pebble ⇒ Fuel particle thermal model MPBR-15 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fuel Particle Thermal Model Calculate temperatures in a particle: • Particle surface temperature determined by radial location in a pebble • Fuel kernel fission product swelling data 1% volume swelling per 10 GWd/T • Buffer densification to accommodate kernel swelling • Kernel thermal expansion -- 10-6 K-1 MPBR-16 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Bounding Thermal Examples THe(inlet) = 450 °C Low Temperature Case core inlet power: average peak T: 513 °C ∆T: 16 °C High Temperature Case core outlet power: average 2x average peak T: 968 °C 1074 °C ∆T: 17 °C 19 °C THe(outlet) = 850 °C MPBR-17 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Typical Particle Temperatures Pebble Power Axial Location Loc. In Pebble Average Core Inlet Outer Edge Average Core Outlet Center 723 1123 1123 Kernel Center 786 1241 1347 Kernel Outer Edge Buffer Outer Edge IPyC Outer Edge SiC Outer Edge OPyC Outer Edge 779 771 770 770 770 1234 1225 1224 1224 1224 1340 1329 1329 1329 1328 Particle ∆T 16 17 19 Bulk He Temp.(°K) 2x Average Core Outlet Center Temperatures MPBR-18 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Significance of Temperatures • Small ∆T across all particles ⇒ can use average temperature in a particle for chemical analyses • Variation in particle peak temperature ⇒ chemistry phenomena (diffusion) vary exponentially with temperature • Gradient across particle ⇒ significant impact on mechanical phenomena MPBR-19 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Chemical Interactions • Palladium – very destructive, local attack – can open a pathway for fission product release – limited data MPBR-20 • Silver – diffuses through intact SiC – activity / maintenance concern – limited data in MPBR proposed temperature range Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project SiC Diffusion Experiments • Limited data for specific fission products and temperatures of interest • Develop experimental foundation for future study of advanced fission product barrier 3/4 inch OD materials MPBR-21 30 mil thick wall Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Experimental Procedure 1. Sputter Coating Ag or Pd target 2. SiC Overcoating 3. Heat Treatment 4. Characterization Microscopy SIMS ESCA XRD 1000-1600 oC 10-1000 hours Ar gas Graphite Hemisphere (hollow shell) Metal Coating Deposited on Inside of Shell Metal Inner Coating MTS & H2 Diffusion Couple (cross section) 5. Data Analysis DAg(T) DPd(T) DMFP(T) CAg Graphite Shell SiC or ZrC overcoating r MPBR-22 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Status of Experiments • Experimental procedure defined • System operational • 2 diffusion heat treatments completed – 1500 °C, 24 hours, Ag-SiC – 1400 °C, 44 hours, Ag-SiC – other temperatures in progress • Characterization in progress MPBR-23 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Future Work • Continue diffusion couple heat treatments • Collect and analyze diffusion experiment data • Update thermal and pressure models – include UCO data – include radial and axial power peaking MPBR-24 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fuel Performance Modeling — Mechanical Analysis Student: Jing Wang Advisors: Prof. Ballinger & Prof. Yip MPBR-25 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Objective • Develop a mechanical model to predict the mechanical behavior of TRISO fuel particles, including failure, that can be used as a tool in understanding past behavior and in developing advanced particles MPBR-26 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Mechanical Model Stress Analysis Finite Element ABAQUS • Anisotropy • Asphericity • Substructure Analytical Solution ‘FUEL’ code • Isotropy • Fast Speed • MC Sampling Specialized FEM MPBR-27 Failure Model Pure Pressure Vessel Failure Crack Induced Failure • Stress Intensity Factor ( KI ) • Strain Energy Release ( G ) Fracture Strength ( σF ) Fracture Mechanics Failure Criteria Chemistry Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Conclusion • Currently with closed form solutions, the fracture mechanics based failure model, developed as part of this task, yields a good prediction of the failure probability of TRISO fuel particles MPBR-28 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Closed Form Solutions • • System: IPyC/SiC/OPyC Assumptions – Spherical layers – Elastically isotropic – Creep and swelling are treated for IPyC/OPyC – SiC is just elastic shell – Three layers are tightly bonded Layer Outer PyC Thickness (µm) 43 SiC 35 Inner PyC 53 Buffer PyC 100 UCO 195 (diameter) Total Diameter TRISO Fuel Particle MPBR-29 0.66 mm Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Time Evolution of Radial Stress Distribution in TRISO Fuel Particles 60 50 40 40-50 30 30-40 20-30 20 10-20 0-10 10 -10-0 -20--10 0 -30--20 -10 Fl u 1.632 1.428 1.02 1.224 0.816 0.612 0.408 -30 0.204 325.88 0 316.71 307.54 ns) 298.37 i cro 289.2 270.86 s (m OPyC 280.03 261.69 252.52 234.18 Ra d iu MPBR-30 -20 SiC 243.35 225.01 197.5 206.67 215.84 IPyC vt) 21 n 10 ^ ( e enc Radial Stress (MPas) 50-60 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Time Evolution of Tangential Stress Distribution in TRISO Fuel Particles 200 100 0 0-100 -100-0 -200--100 -300--200 -100 -400--300 -200 21 (10 ^ nce e u l F nvt) 1.632 1.428 1.224 1.02 0.816 0.612 0.408 0.204 -400 327.19 0 315.4 303.61 s) 291.82 cro n 280.03 (m i OPyC 268.24 ius 256.45 244.66 Ra d MPBR-31 -300 SiC 232.87 221.08 197.5 209.29 IPyC Tangential Stress (MPas) 100-200 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Finite Element Method • Check with analytical solutions and other calculations • Study the non-ideal particles – anisotropy of material – anisotropy of geometry • Evaluate the effects of crack and debonding • Combine with analytical solutions to predict failure MPBR-32 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fracture Mechanics based Failure Model • Consider the impact of the cracking of IPyC to SiC • Stress distributions come from closed form solutions • Currently use stress intensity factor to evaluate local stresses • Predict failure probability with MC sampling process (Gaussian Distribution : Layer thickness, kernel & buffer densities Weibull Distribution : Fracture strength of IPyC, SiC and OPyC Triangular Distribution : Critical stress intensity factor of SiC ) MPBR-33 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Sketch for FM based Failure Model OPyC K I ( IPyC ) = σ T πa SiC IPyC σT PO MPBR-34 PI K IC (SiC ) Material Property Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Prediction by FM based Failure Model • Inputs SiC layer –– (Sampled with triangular distribution) KIC(SiC) (mean) = 3300MPa·µm1/2 [1] Standard Deviation = 530MPa·µm1/2 IPyC layer –– (Sampled with Weibull distribution) σF(IPyC) (mean) = 384MPa [2] Weibull modulus = 8.6 [2] End-of-life Burnup –– 75% FIMA Particles Sampled –– N=1,000,000 • Outputs Cases with IPyC Failure: 595 Cases with SiC Failure: 17 Failure Probability: 5.95×10-4 Failure Probability: 1.70×10-5 [1] Material Specification No. SC-001, Morton Advanced Materials, 185 New Boston Street, Woburn, MA 01801 [2] J. L. Kaae, et al., Nucl. Tech., 35, 1977, p368 MPBR-35 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Conclusions • The previous mechanical model, based on a pressure vessel failure by overpressure, from INEEL predicts zero fuel failure • New fracture mechanics based failure model gives reasonable prediction of the failure probability of TRISO fuel particles MPBR-36 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Future Work • Use finite element method (ABAQUS) to incorporate non-ideal particles • Improve the fracture mechanics based failure model • Build a more realistic pyrocarbon model • Use specialized finite element method MPBR-37 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-38 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Dynamic Modeling for MPBR Chunyun Wang Advisors: Prof. R. G. Ballinger Dr. H. C. No (Draft) Presentation for INEEL Review MPBR-39 Aug. 01, 00 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Current Design Schematic 803 °C 7.6MPa 850°C 7.6MPa 445°C 7.7MPa 30°C 2.0MPa 401°C 2.1MPa MPBR-40 97°C 8.0MPa Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Objective • Develop a dynamic model as the primary tool for – developing the control system – performing transient analysis – optimizing power conversion system MPBR-41 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Summary • Have developed dynamic models for core , heat exchanger. A simple steady state turbo-machinery model is used. • Verification of core kinetic model • Verification heat exchanger model • Provide control methods and use PID controller to implement them MPBR-42 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Model Structure MPBRSim MPBRSim Turbo-machinery Turbo-machinery T-H T-H MPBR-43 CoreModel Model Core Kinetic Kinetic ControlModel Model Control Poisoning Poisoning Heatexchanger exchanger Heat Gas-Gas Gas-Gas Gas-Liquid Gas-Liquid Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Core Thermal-Hydraulic Model • • • • Nodalization Assumptions – Fuel region is treated as a homogeneous region – Helium heat conduction is negligible – The heat loss from the reactor vessel is negligible Pebble bed effective thermal conductivity (GE correlation, taking into account both conduction and radiation). Helium convection:KFA correlation MPBR-44 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Core neutronics, product poisoning and verification • One effective group point kinetics equation (Fig. 1) • Fission product poisoning (Fig.2) • Temperature coefficient of reactivity(Doppler effect) γI 135I Fission λI γX λX 135Xe σaφ MPBR-45 135Cs 136Xe Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig. 1 Numerical result versus analytical result for one effective group kinetics equation 5 P/P0 Normalized Power 4 Analytical (0.22% Reactivity) 3 Analytical(-0.22% Reactivity) Numerical (0.22% Reactivity) Numerical (-0.22% Reactivity) 2 1 0 0 5 10 15 Time (sec) MPBR-46 20 25 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig.2 135Xe buildup following the core shutdown 6 Xe-135 Concentration (Normalized) Normalized Concentration 5 I-135 Concentration (Normalized) 4 3 2 1 0 0 20 40 60 Time (Hour) MPBR-47 80 100 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Heat Exchanger Model • Heat exchanger model – For counter flow heat exchanger – Divide it into many equally length sections – In each section, for gas side, ignore the gas mass, therefore ignore the gas stored energy MPBR-48 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig. 3 Recuperator steady state temperature distribution Recuperator steady-state temperature distribution 400 350 Temperature (C) 300 250 Hot Side Steel Wall Cold Side 200 150 100 50 0 2 4 6 8 10 Axial Positions (m) MPBR-49 12 14 16 18 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig. 4 Recuperator transient response to a step temperature increase of 200 C at hot helium inlet side 700 Temperature (C) 600 500 Hot helium inlet Hot helium outlet Cold helium inlet Cold helium out 400 300 200 100 0 0 500 1000 1500 Tiem (sec) MPBR-50 2000 2500 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig. 5 Helium energy storage’s effect on the recuperator performance 25 Model including helium energy storage Time Constant (sec) 24.8 24.6 Model excluding helium energy storage 24.4 24.2 24 23.8 23.6 23.4 23.2 23 0 2 4 6 8 10 Hehlium Pressure (MPa) MPBR-51 12 14 16 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Control Model • Control methods – – – – Control rod motion Primary circulator speed Bypass control in the power conversion system Inventory control in the power conversion system • Controller: PID MPBR-52 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Summary • Have developed dynamic models for core , heat exchanger. A simple steady state turbo-machinery model is used • Verification of core kinetic model • Verification of heat exchanger model • Provide control methods and use PID controller to implement them MPBR-53 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Future Work • Use programmed turbo-machinery characteristic maps (Cooperate with NREC) in the model • Develop valve model • Simulate electric load ramp MPBR-54 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Comparison Between Air and Helium for Use as Working Fluids in the EnergyConversion Cycle of the MPBR Student: Tammy Galen Faculty: D. G. Wilson MPBR-55 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Objective: To assess the relative advantages of using air and helium for the working fluid in the MPBR energy-conversion cycle. Comparisons: •Cycle efficiency •Component design •Size •Efficiency •Possible development work required MPBR-56 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Conclusion Use of helium in a closed-cycle configuration is best suited to the modularity requirement of the MPBR. It results in the smallest sized components, high efficiency, and implements well established turbomachinery technology. MPBR-57 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Three cycles investigated •Air open cycle •Air closed cycle •Helium closed cycle Closed Cycle Open Cycle HX Tb C HX MPBR-58 HX C Tb Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Influence of choice of working fluid Working Fluid Component Efficiency Development Work MPBR-59 Component Design Cycle Efficiency Component Size Component Cost Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Thermophysical Properties of Helium and Air at 700K and 2MPa Turbines and Compressors ↑ Specific heat ↑ Number of stages Air Helium ↓ Viscosity, ↑Re # ↑ Efficiency Molecular weight 28.97 4.003 Specific heat (J/kgK) 1074 5193 ↑ Sonic velocity, ↑ Compressor blade speed ↓ Mean diameter Sonic velocity (m/s) 590 1500 Thermal conductivity .056 (W/mK) Viscosity (10-5) 3.33 .273 3.56 Density (kg/m3) 1.42 ↑ Density ↓ Mean diameter Heat Exchangers ↑ Thermal conductivity ↓ Size MPBR-60 9.96 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Turbomachinery industrial experience • • • Air open-cycle experience – Majority of gas-turbomachinery experience – Combustion-gas turbines: power and aircraft industries Air closed-cycle experience – Less popular demand and less industrial experience to date – First built in 1939 by Escher Wyss in Switzerland – 20 plants built in Europe following WW2 ranging in power under 20MWe Helium experience: – 2 facilities part of HHT international high temperature gas reactor project • Oberhausen II (50MWe, 2MPa), HHV(90MWe, 5MPa) – Circulators from previous gas reactors MPBR-61 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Industrial experience conclusions •Open-cycle air plant •Least amount of development work required for MPBR deployment •Closed-cycle helium and closed-cycle air plants •Comparable amount of development work required •Technology has been tested and judged successful* •Open-cycle turbomachinery design methodology and operating experience is directly applicable *IAEA Summary report on technical experiences from high-temperature helium turbomachinery testing in Germany, 1995 MPBR-62 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Busbar Efficiency • Deducts – Primary circulator work, 7.7 MW – 3.5 MW station load – 98% electric generator efficiency MPBR-63 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Baseline Thermodynamic Comparison Helium Air closed Air open 3.0 4.7 4.6 Busbar efficiency 45.2% 46.9% 47.7% Reactor Tin (K) 767 792 797 Turbine Tin (K) 1101 1101 1101 Pressure ratio Reactor inlet temperature constrained to 718K* Helium Pressure ratio 3.7 Busbar efficiency 44.8% Turbine Tin (K) 1101 Air closed 7.4 46.0% 1101 Air open 7.3 46.8% 1101 *Permissible using 9Cr-1-Mo-V as the vessel material according to ASME Class 2 &3 pressure-vessel in Codes Case N-47 MPBR-64 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Turbine Design Choices MPBR-65 Maximum blade speed at tip (m/s) 550 Work Coefficient (Ψ) 1 and 2 Flow coefficient (φ) 0.5 Reaction (%) 50 Hub shroud ratio at turbine outlet 0.6 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Component volumes (m3) IHX HP turbine LP turbine LP compressor Recuperator Precooler Intercooler 1 Intercooler 2 Sum MPBR-66 Helium 17 0.27 0.58 0.35 13 50 41 41 Air-closed 86 0.06 0.22 0.13 61 97 80 80 Air-open 260 2.2 13 2.7 180 --180 180 160 400 820 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Final Cycle Conclusions Pressure ratio Busbar efficiency Turbine Tin (K) 3 Component volume (m ) Number of flatbed trucks* Helium 3.7 45.3% 1101 160 1 Air-closed 7.1 47.1% 1101 400 2 Air-open 7.1 47.3% 1101 820 N/A *Based on volume analysis, carries all components except IHX and ducting MPBR-67 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Conclusion Use of helium in a closed-cycle configuration is best suited to the modularity requirement of the MPBR. It results in the smallest sized components, high efficiency, and implements well established turbomachinery technology. MPBR-68 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-69 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Pebble-Bed Reactor Physics Research at MIT Julian Lebenhaft Professor Michael Driscoll MPBR-70 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Overview Statement of progress Program goals Neutronic design methodology • MCNP/VSOP model of PBMR • Preliminary results Proliferation resistance of PBMR Path forward MPBR-71 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Progress MCNP4B benchmark of HTR-10 completed VSOP94 fuel management code implemented Procedure established for linking MCNP and VSOP for core neutronic calculations MCNP/VSOP model of PBMR developed and preliminary analysis performed Proliferation resistance of PBMR investigated MPBR-72 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Program Goals • Establish a Monte-Carlo based methodology for modeling neutron and photon transport in PBRs • Ability to model cores with fuel burnup • Integrated computer-aided design tools • Perform preliminary design calculations • Investigate fuel cycles and assess their proliferation resistance • Validation of codes and methods MPBR-73 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Neutronic Design Methodology • Monte Carlo method for accurate analysis of: – – – – – control rod worth void effects geometry changes shielding heat deposition diffusion code composition of fuel • Diffusion-theory code for burnup calculation A versatile design tool! MPBR-74 Monte Carlo code Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Why MCNP? • Solves the Boltzmann equation • • • • by the Monte-Carlo method Exact representation of neutron and photon transport Continuous-energy cross sections Detailed geometry specification Millions of n-histories used to generate ensemble averages accurate calculations MPBR-75 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project VSOP Very Superior Old Programs Widely used for PBRs Diffusion theory Comprehensive code suite: - Neutronics - Thermal hydraulics - Fuel cycles - Economics • Installed at MIT • Verification in progress • • • MPBR-76 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP/VSOP Model of PBMR Detailed MCNP4B model of ESKOM Pebble Bed Modular Reactor: • • • • reflector and pressure vessel 18 control rods (HTR-10) 17 shutdown sites (KLAK) 36 helium coolant channels Core idealization based on VSOP model for equilibrium fuel cycle: • 57 fuel burnup zones • homogenized compositions MPBR-77 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B Model of Core reflector coolant control reflector fuel shutdown pressure vessel MPBR-78 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B Model of Control Rod B4C vertical view s/s helium graphite horizontal view MPBR-79 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B Model of Shutdown Site 1 3 1) empty channel 2) channel filled with absorber balls 3) 0.25 in. absorber ball with graphite coating 2 MPBR-80 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B/VSOP Model Output Power Density in PBMR Equilibrium Core Control Rods 1/4 Inserted (z = 201.25 cm) 8 Power density in annular core regions 7 MW/m 3 6 5 4 3 7.00E+00-8.00E+00 2 6.00E+00-7.00E+00 5.00E+00-6.00E+00 1 4.00E+00-5.00E+00 top0 MPBR-81 175 134 108 0 725 ion (cm ) 644 2.00E+00-3.00E+00 483 Pos it 402 Ax ia l 242 Top of core 161 0 3.00E+00-4.00E+00 Radial Position (cm) 1.00E+00-2.00E+00 0.00E+00-1.00E+00 Massachusetts Institute of Technology Department of Nuclear Engineering Bottom of core Advanced Reactor Technology Pebble Bed Project MCNP4B/VSOP Model Output .. 2 Thermal Neutron Flux in PBMR Equilibrium Core Control Rods 1/4 Inserted (z = 201.25 cm) 4.E+14 Average flux in annular Average flux core regions in annular core regions 3.E+14 2.E+14 3E+14-3.5E+14 2.5E+14-3E+14 2.E+14 2E+14-2.5E+14 MPBR-82 73 108 0 top 134 0 156 (c m ) 161 os itio n 0.E+00 242 Ax ial P 402 0-5E+13 483 5E+13-1E+14 5.E+13 644 1E+14-1.5E+14 1.E+14 bottom 725 1.5E+14-2E+14 Radial Position (cm ) Neutrons.cm -2.s -1 3.E+14 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B/VSOP Model Output .. 3 Fast Neutron Flux in PBMR Equilibrium Core Control Rods 1/4 Inserted (z = 201.25 cm) 2.E+14 2.E+14 1.E+14 Average flux in annular core regions 1.E+14 1.E+14 8.E+13 6.E+13 1.8E+14-2E+14 4.E+13 1.6E+14-1.8E+14 2.E+13 1.4E+14-1.6E+14 0.E+00 MPBR-83 0 73 108 134 156 0 81 161 242 al P osit i on (cm ) 322 403 8E+13-1E+14 483 A xi 1E+14-1.2E+14 564 644 805 bottom Bottom ofofcore core 1.2E+14-1.4E+14 bottom 725 Neutrons.cm-2.s-1 2.E+14 Radial Position (cm) 6E+13-8E+13 4E+13-6E+13 2E+13-4E+13 0-2E+13 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Nonproliferation Pebble-bed reactors are highly proliferation resistant: • small amount of uranium (9 g/ball) • high discharge burnup (100 MWd/kg) • TRISO fuel is difficult to reprocess • small amount of excess reactivity limits number of special production balls Diversion of 8 kg Pu requires: • 260,000 spent fuel balls – 2.6 yrs • 790,000 first-pass fuel balls – 7.5 • ~50,000 ‘special’ balls – 3 MPBR-84 Spent Fuel Pu238 Pu239 Pu240 Pu241 Pu242 5.5% 24.1 25.8 12.6 32.0 First Pass Pu238 Pu239 Pu240 Pu241 Pu242 ~0 % 64.3 29.3 5.6 0.8 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MCNP4B Analysis of Heavy Balls Supercell Model 1 Ball with depleted U 2 Surrounded by BCC lattice of driver balls 3 Spherical driver core with fuel composition from VSOP model • Critical core (keff = 1) • 238U(n,γ)239U MPBR-85 1 UO2 2 R = 2.1 cm 3 driver fuel R = 1.75 m Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Path Forward • Complete implementation of MCNP/VSOP link • Improve model of PBMR ⇒ ESKOM input • Validate MCNP4B using PROTEUS criticals & VSOP predictions of PBMR startup core • Investigate proliferation resistance of PBR fuel cycles using VSOP (Th/LEU, OTTO-PAP2) • Assess applicability of Monteburns to modeling burnup in PBRs using MCNP4B and ORIGEN2 MPBR-86 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-87 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Safety Analysis of PBMR Student: Tieliang Zhai Advisors: Prof. A. Kadak Dr. W.Y. Kato MPBR-88 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Objectives • Identification of the Safety Issues for MHTGR • Analysis of a Major Accident • The Temperature Distribution Calculation After the Depressurization With the Failure of RCCS MPBR-89 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Identification of the Safety Issues • Review of Safety Literature on HTGR • Based on a Specific Design Concept, Identified the Critical Safety Issues: A. Fuel Performance B. Completely Passive System for Ultimate Heat Sink C. Air Ingress D. Lack of Containment E. Calculation of Source Term MPBR-90 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Air Ingress Accident • Important parameters governing these reactions: Gas flow rates Temperature Pressure • 3 steps • Mainly Depends on Possibility of Enough and continuous air supply MPBR-91 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-92 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Specific areas for additional research: • Chimney effect • Airflow rate • The extent that a below-grade confinement building could limit the supply of air MPBR-93 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Temperature Distribution Calculation After the Depressurization With the Failure of RCCS • The Code “Heating-7” Heating-7 is a general-purpose 3-D conduction heat transfer program written in Fortran 77. It can solve steady-state and/or transient heat conduction problems MPBR-94 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Model Established • 20-Region 3-Dimensional model. The core void is filled with stagnant helium at atm. • The air in the confinement is steady and heat transfer only through conductivity and radiation. • The outer radius of this model is 28.4m, i.e. all the heat transfer happen only in this huge volume. • The Materials and their thermal properties (Conductivity, Density and Specific Heat): In the case that the thermal properties could not been fully determined, the conservative values would be selected MPBR-95 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project MPBR-96 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Conclusion • The core peak temperature is 15570C. This is below the 1600 C SiC fuel temperature target and No Core Melt is predicted assuming only conduction. • 192 hours (8 days) later, the peak temperatures of the pressure vessel and the Concrete Wall will be 1348 °C and 1322°C , respectively. The temperatures of the vessel and the concrete wall are out of the design capability range . • • The sensitivity analyses of the initial temperature of the core, the conductivity of the air, the initial temperature of the air gap, the conductivity of the concrete wall and the soil indicate that: The key factors that determine the temperatures of the pressure vessel and concrete wall are the conductivity and heat capacity of the concrete and soil. Some convection cooling will be required to keep the temperature of the vessel and concrete within acceptable ranges - conduction alone is not sufficient. MPBR-97 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project The Temperature Curve of the Hot-Points 1600 the HotPoint of the Core 1400 Te m pe ra ture (C ) 1200 The HotPoint of the Vessel 1000 The HotPoint of the Concrete Wall 800 600 400 200 0 0 50 100 150 200 250 Time (hr) MPBR-98 300 350 400 450 500 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Fig-3: Temperature Distribution on the 8th Day 1600 1400 1200 1400-1600 1000-1200 800-1000 600-800 400-600 200-400 0-200 Temperature (C) 1200-1400 1000 800 600 400 MPBR-99 -8.1 -7.7 -7.3 -4.5 -2.5 -0.5 1.5 3.5 5.5 7.1 7.5 7.9 6.4 8.3 4.4 3.2 2.8 2.4 Distance to the Central Line of the Core r (m) 2 1.6 1.2 0.8 0.4 0 0 -6.5 200 The Depth Z (m) Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Temperatures with Convection 1400 Temperature (K) 1200 1000 800 Vessel Temperature (v=0.0) Vessel Temperature (v=0.5) Vessel Temperature (v=1.0) Vessel Temperature (v=2.0) Concrete Temperature (v=0.0) Concrete Temperature (v=0.5) Concrete Temperature (v=1.0) Concrete Temperature (v=2.0) 600 400 200 0 50 100 150 200 Time(Hrs) MPBR-100 250 300 350 Massachusetts Institute of Technology Department of Nuclear Engineering Advanced Reactor Technology Pebble Bed Project Future Work • The perfection of the model, especially how to model the core of the reactor and the heat transfer through convection and how to obtain the accurate initial condition of the accident. • Air ingress accident simulation. MPBR-101
