modular pebble bed reactor high temperature gas reactor
TRANSCRIPT
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Modular Pebble Bed ReactorHigh Temperature Gas Reactor
Andrew C KadakMassachusetts Institute of Technology
American Nuclear SocietyWinter Meeting - Washington, D.C
November 2002
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AVR: Jülich15 MWe Research Reactor
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THTR: Hamm-Uentrop300 Mwe Demonstration Reactor
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HTR- 10 ChinaFirst Criticality Dec.1, 2000
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What is a Pebble Bed Reactor ?
• 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 10 times• Fuel handling most
maintenance-intensive part of plant
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Modular High TemperaturePebble Bed Reactor
• 110 MWe• Helium Cooled• 8 % Enriched Fuel• Built in 2 Years• Factory Built• Site Assembled• On--line Refueling
• Modules added to meet demand.
• No Reprocessing• High Burnup
>90,000 Mwd/MT• Direct Disposal of
HLW• Process Heat
Applications -Hydrogen, water
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Turbine Hall Boundary
Admin
Training
ControlBldg.
MaintenanceParts / Tools
10
9
8
7
6 4 2
5 3 1
0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
Primary island withreactor and IHX
Turbomachinery
Ten-Unit VHTR Plant Layout (Top View)(distances in meters)
Equip AccessHatch
Equip AccessHatch
Equip AccessHatch
For 1150 MW Combined Heat and Power Station
Oil Refinery
Hydrogen ProductionDesalinization Plant
VHTR Characteristics- Temperatures > 900 C- Indirect Cycle - Core Options Available- Waste Minimization
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Fuel Sphere
Half Section
Coated Particle
Fuel
Dia. 60mm
Dia. 0,92mm
Dia.0,5mm
5mm Graphite layer
Coated particles imbeddedin Graphite Matrix
Pyrolytic Carbon Silicon Carbite Barrier Coating Inner Pyrolytic Carbon Porous Carbon Buffer
40/1000mm
35/1000
40/1000mm
95/1000mm
Uranium Dioxide
FUEL ELEMENT DESIGN FOR PBMR
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Reactor Unit
Helium Flowpath
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Fuel Handling & Storage System
Fuel/Graphite Discrimination system
Damaged Sphere
ContainerG
raph
ite R
etur
n
Fuel
Ret
urn
Fresh Fuel
Container
Spent Fuel Tank
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Equipment Layout
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Modular Pebble Bed Reactor
Thermal Power 250 MWCore Height 10.0 mCore Diameter 3.5 mFuel UO2Number of Fuel Pebbles 360,000Microspheres/Fuel Pebble 11,000Fuel Pebble Diameter 60 mmMicrosphere Diameter ~ 1mmCoolant Helium
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Fuel Handling SystemReactor Vessel in thisArea - Not shown
Fresh FuelStorage
Used FuelStorageTanks
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Power Cycle - Brayton
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Pebble Bed Reactor Designs
• PBMR (ESKOM) South African- Direct Cycle - Two Large Vessels plus two smaller ones
• MIT/INEEL Design- Indirect Cycle - Intermediate He/He HX- Modular Components - site assembly
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Rea
ctor
PBMR Layout
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MIT’s Pebble Bed Project
• Similar in Concept to ESKOM
• Developed Independently
• Indirect Gas Cycle• Costs 3.3 c/kwhr• High Automation• License by Test
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TurbomachineryModule
IHX ModuleReactorModule
Conceptual Design Layout
MIT Design for Pebble Bed
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Project Overview
• Fuel Performance• Fission Product Barrier
(silver migration)
• Core Physics• Safety
Loss of CoolantAir Ingress
• Balance of Plant Design• Modularity Design• Intermediate Heat
Exchanger Design
• Core Power Distribution Monitoring
• Pebble Flow Experiments• Non-Proliferation• Safeguards• Waste Disposal• Reactor Research/
Demonstration Facility• License by Test• Expert I&C System -
Hands free operation
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MIT MPBR Specifications
Thermal Power 250 MW - 115 MweTarget Thermal Efficiency 45 %Core Height 10.0 mCore Diameter 3.5 mPressure Vessel Height 16 mPressure Vessel Radius 5.6 mNumber of Fuel Pebbles 360,000Microspheres/Fuel Pebble 11,000Fuel UO2Fuel Pebble Diameter 60 mmFuel Pebble enrichment 8% Uranium Mass/Fuel Pebble 7 gCoolant HeliumHelium mass flow rate 120 kg/s (100% power)Helium entry/exit temperatures 450oC/850oCHelium pressure 80 barMean Power Density 3.54 MW/m3
Number of Control Rods 6
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TurbomachineryModule
IHX ModuleReactorModule
Conceptual Design Layout
PBMR-Direct Cycle MIT Indirect Cycle
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PBMR - MIT/INEEL Projects
PBMR• Commercial• Direct Cycle• German Technology• Not Modular• German Fuel• NRC site specific
application (exemptions)• Repair Components
MIT/INEEL• Private/Government• Indirect Cycle• US advanced Technology• Truly modular• US fuel design (U/Th/Pu)• NRC Certification using
License by Test• Replace Components
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Features of Current Design
Three-shaft ArrangementPower conversion unit2.96Cycle pressure ratio900°C/520°CCore Outlet/Inlet T126.7 kg/sHelium Mass flowrate
48.1% (Not take into account cooling IHX and HPT. if considering, it is believed > 45%)
Plant Net Efficiency120.3 MWNet Electrical Power132.5 MWGross Electrical Power250 MWThermal Power
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Current Design Schematic
Generator
522.5°C 7.89MPa 125.4kg/s
509.2°C 7.59MPa 350°C
7.90MPa
Reactor core
900°C
7.73MPa
800°C
7.75MPa
511.0°C 2.75MPa
96.1°C 2.73MPa
69.7°C 8.0MPa
326°C 105.7kg/s
115 °C
1.3kg/s69.7°C
1.3kg/s
280 °C520°C 126.7kg/s
Circulator
HPT 52.8MW
Precooler
Inventory control
Bypass Valve
Intercooler
IHX
Recuperator
Cooling RPV
LPT 52.8MW
PT 136.9MW
799.2 C 6.44 MPa
719.°C 5.21MPa
MPC2 26.1 MW
MPC1 26.1MW
LPC 26.1 MW
HPC 26.1MW
30 C 2.71MPa
69.7 C 4.67MPa
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Mechanical Design Constraints
• Size/Modularity– Manufacturing off site– Transportation to construction site– Maintenance during operation
• ASME Boiler & Pressure Vessel Codes– Section III for Nuclear Components– Section VIII for Balance of Plant
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IHX Outer Configuration
12O 6
Units U.S. Customary
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IHX Outer Pictorial
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IHX Internal Pictorial
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MPBR Modularity
Marc V Berte Prof. Andrew Kadak
MIT Nuclear Engineering Department
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Modularity Progression
• Conventional Nuclear Power Systems• Assembled on site• Component-level transportation• Extensive Site Preparation
• Advanced Systems• Mass Produced / “Off the Shelf” Designs• Construction / Assembly Still Primarily on Site
• MPBR• Mass Produced Components• Remote Assembly / Simple Transportation &
Construction
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MPBR Modularity Plan
• Road- Truck / Standard-Rail Transportable– 8 x 10 x 60 ft. 100,000 kg Limits
• Bolt-together Assembly– Minimum labor / time on site required– Minimum assembly tools– Goal: Zero Welding
• Minimum Site Preparation– BOP Facilities designed as “Plug-and-Play” Modules– Single Level Foundation– System Enclosure integrated into modules
• ASME Code compliant– Thermal expansion limitations– Code material limitations
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Design Elements
• Assembly• Self-locating Space-frame Contained Modules and Piping.• Bolt-together Flanges Join Module to Module• Space-frame Bears Facility Loads, No Additional Structure
• Transportation / Delivery• Road-mobile Transportation Option
– Reduces Site Requirements (Rail Spur Not Required)• Module Placement on Site Requires Simple Equipment
• Footprint• Two Layer Module Layout Minimizes Plant Footprint• High Maintenance Modules Placed on Upper Layer
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IHX Module
ReactorVessel
Recuperator Module
Turbogenerator
HP Turbine
MP Turbine
LP Turbine
Power Turbine HP Compressor
MP Compressor
LP Compressor
Intercooler #1
Intercooler #2
Precooler
~77 ft.
~70 ft.
Plant Footprint
TOP VIEWWHOLE PLANT
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Total Modules Needed For Plant Assembly (21): Nine 8x30 Modules, Five 8x40 Modules, Seven 8x20 Modules
Six 8x30 IHX Modules Six 8x20 Recuperator Modules
8x30 Lower Manifold Module8x30 Upper Manifold Module
8x30 Power Turbine Module
8x40 Piping & Intercooler #1 Module
8x40 HP Turbine, LP Compressor Module
8x40 MP Turbine, MP Compressor Module
8x40 LP Turbine, HP Compressor Module
8x40 Piping and Precooler Module
8x20 Intercooler #2 Module
PLANT MODULE SHIPPING BREAKDOWN
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Space Frame Technology for Shipment and Assembly
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Reactor Vessel Intermediate Heat Exchangers
Turbo-generator
Recuperators
High Pressure Turbine and Compressor
Low Pressure Turbine and Compressor
Precooler
Current MIT/INEEL Design Layout
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Turbine Hall Boundary
Admin
Training
ControlBldg.
MaintenanceParts / Tools
10
9
8
7
6 4 2
5 3 1
0 20 40 60 80 100 120 140 160
0
20
40
60
80
100
Primary island withreactor and IHX
Turbomachinery
Ten-Unit MPBR Plant Layout (Top View)(distances in meters)
Equip AccessHatch
Equip AccessHatch
Equip AccessHatch
For 1150 MW Electric Power Station
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AP1000 Footprint Vs. MPBR-1GW
~400 ft.
~200 ft.
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Fuel The Key Safety System
• Develop Fuel Performance Model• Identify Barriers to Diffusion of Silver• Understand impact of Palladium on SiC• Develop an optimized design for reliability• Work with manufacturer to optimize• Make fuel and test
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Coated TRISO Fuel Particles
IPyC/SiC/OPyC: structural layers as pressure vessel and fission product barrier
Buffer PyC: accommodate fission gases and fuel swelling
From Kazuhiro Sawa, et al., J. of Nucl. Sci. & Tech., 36, No. 9, pp. 782. September 1999
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Fuel Performance Model
• Detailed modeling of fuel kernel• Microsphere• Monte Carlo Sampling of Properties• Use of Real Reactor Power Histories• Fracture Mechanics Based• Considers Creep, stress, strains, fission
product gases, irradiation and temperature dependent properties.
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Mechanical Analysis
• System: IPyC/SiC/OPyC
• Methods: Analytical or
Finite Element
• Viscoelastic Model
• Mechanical behavior
– irradiation-induced dimensional changes (PyC)
– irradiation-induced creep (PyC)
– pressurization from fission gases
– thermal expansion
Stress contributors to IPyC/SiC/OPyC
Dimensional changes
Creep
Pressurization
Thermal expansion
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Integrated Fuel Performance ModelPower Distribution in the Reactor Core
Sample a pebble/fuel particle
Randomly re-circulate the pebble
Get power density, neutron flux
t=t+∆t
T distribution in the pebble and TRISO
Accumulate fast neutron fluence
FG release (Kr,Xe)PyC swelling
Mechanical model
Failure modelMechanical ChemicalStresses FP distributionStrength Pd & Ag
Failed
In reactor core
Y
10 times
1,000,000 times
MC Outer Loop
MC inner loop
N
N
Y
MC outer loop:
samples fuel particles of statistical characteristics
MC inner loop:
implements refueling scheme in reactor core
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Stress Contributors
Internal Pressure
IPyC Irr. Dimensional Change
OPyC Irr. Dimensional Change
SiC
SiC
IPyC
IPyC
Low Burnup
High Burnup
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Barrier Integrity
• Silver Diffusion observed in tests @ temps• Experiments Proceeding with Clear
Objective - Understand phenomenon• Palladium Attack Experiments Underway• Zirconium Carbide being tested as a
reference against SiC.• Focus on Grain SiC Structure Effect• Will update model with this information
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Silver Diffusion CouplesSpherical Shells
• Graphite substrate 760 µmchemical conditioning~15% porosity
• Fission product insidepowder
• SiC or ZrC coating ~50 µm thicksilver can ONLY diffusethrough graphite and barrier
3/4 inch OD 30 mil thick wall
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SiC(light gray)
Silver(bright white)
Graphite(dark gray)
Silver Migration -- Ag20Backscatter Electron Image
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SiC Microstructure -- Ag29Optical Microscopy (1000x)
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Calculated Diffusion Coefficients
1.E-19
1.E-18
1.E-17
1.E-16
1.E-15
1.E-14
1.E-13
3.5 4.5 5.5 6.5 7.5 8.5104/T (K)
Diff
usio
n C
oeffi
cien
t (m
2 /s)
S1 (2-5)
S2 (2-8)
S3 (2-6)
S4 (2-12)
S5 (2-11)
S6 (2-10)
S7 (2-9)
S8
S9
S10
S11 (2-7)
S12
Z1 (2-14)
Ag20 XPS
Ag20 Auger
1000 oC1200 oC1600 oCPlot Label (Eqn. #)
Data points
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SiC
Interaction Zone
mount
Pd-SiC Interaction
Pd : 32Si : 14C : 54
Pd : 22Si : 10C : 68
Pd : 9Si : 26C : 65
Sample PdS01, Backscatter Electron ImageAtomic %
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Core Physics• Basic tool Very Special Old Programs (VSOP)• Developing MNCP Modeling Process • Tested Against HTR-10 Benchmark• Tested Against ASTRA Tests with South
African Fuel and Annular Core• VSOP Verification and Validation Effort
Beginning• Working on International Benchmark
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MCNP4B Modeling of Pebble Bed ReactorsSteps in Method Development
MIT Nuclear Engineering Department
startup coreMCNP vs. VSOP
PBMRSouth Africa
mockup of PBMRannular core
ASTRA critical experiments @ KI
predict criticalitycf. measurement
HTR-10 physics benchmark
simple coresstochastic packing
PROTEUS critical experiments @ PSI
4
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MIT Nuclear Engineering Department
Modeling ConsiderationsPacking of Spheres
Spheres dropped into a cylinder pack randomly
Packing fraction ~ 0.61
Repeated-geometry feature in MCNP4B requires use of a regular lattice
SC, BCC, FCC or HCP?
BCC/BCT works well for loose sphere packing
Random Close Packed
Body Centered Cubic
5
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MIT Nuclear Engineering Department
HTR-PROTEUS (PSI)Zero-power critical facility:
Graphite reflectorCore: Rc ≈ 60 cm, H ≈ 150 cmFuel/mod sphere: Rs = 3 cmTRISO fuel with 5.966 g U/FS16.76% U235; F/M = 1
[6] JAERI calculation using version of MCNP with a stochastic geometry feature.
7
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MIT Nuclear Engineering Department
HTR-10 (Beijing)10 MW Pebble Bed Reactor:
Graphite reflectorCore: Rc = 90 cm, H ≤ 197 cmTRISO fuel with 5 g U/Fuel Sphere17% U235F/M sphere ratio = 57:43, modeledby reducing moderator sphere sizeInitial criticality December 2000
1.00081±0.00086K-eff
128.5 cmCritical Height
16,890Actual Loading
16,830Calculated Loading
MCNP4B Results
9
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MIT Nuclear Engineering Department
HTR-10 MCNP4B Model
12
Reactor
TRISO fuel particle Core
Fuel sphere Core lattice
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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
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MIT Nuclear Engineering Department
MCNP4B/VSOP Model Output
Top ofcore
top
0
161
242
402
483
644
725
0 108 13
4 175
0
1
2
3
4
5
6
7
8
MW
/m3
Axial Position (cm)
Radial Position
(cm)
Power Density in PBMR Equilibrium CoreControl Rods 1/4 Inserted (z = 201.25 cm)
7.00E+00-8.00E+006.00E+00-7.00E+005.00E+00-6.00E+004.00E+00-5.00E+003.00E+00-4.00E+002.00E+00-3.00E+001.00E+00-2.00E+000.00E+00-1.00E+00
Power density in annular core regions
25
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MIT Nuclear Engineering Department
IAEA Physics Benchmark Problem MCNP4B Results
B1 h = 128.5 cm critical height (300 K)
B20 k = 1.12780 ± 0.00079 300 K UTX†
B21 k = 1.12801 293 K | UTX, no expansionB22 k = 1.12441 393 K | (curve fit of k-eff @B23 k = 1.12000 523 K | 300 K, 450 K, 558 K)
B3 k = 0.95787 ± 0.00089 300 K UTX∆ρ ≈ 157.3 mk total control rod worth
(∆ρ ≈ 152.4 mk INET VSOP prediction)
† Temperature dependent cross-section evaluation based on ENDF-B/VI nuclear data by U of Texas at Austin.
11
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MIT Nuclear Engineering Department
ASTRA Critical Experiments
Sidereflector
Central h l
Core
Mixing zone
Internalreflector
Experimentalchannels
CR - Control dMR1 - Manual control dSR - Safety dE1-E6 - Experimental chambers
h l1-9 - Experimental channels for d t tPIR,ZPT,ZII,ZRTA - Ionization chambers and neutron
tNeutron source channel
SR2
SR3 CR5 SR7
E5SPU2
PIR
PIR
E6
ZII2ZRTA4
E1
SPU3
E2
ZIIЗ ZRTA1
E3
E4
ZII1
SPU1ZRTA2
ZPT2
ZII1ZRTA3
CR4
SR6
MR1
SR5
CR3
SR4SR8 CR2
SR1
CR1
a b c d e f g h j k l m n i o
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
A
B
Kurchatov Institute, MoscowMockup of PBMR annular core
Inner reflector: graphite spheres (M)10.5 cm ID 72.5 cm OD
Mixed zone: 50/47.5/2.5 (M/F/A)105.5 cm OD
Fuel zone: 95/5 (F/A)181 cm OD (equiv.)
Core height: 268.9 cm
packing fraction = 0.64 2.44 g U/FS, 21% U235, 0.1 g B/AS 5 CRs, 8 SRs, 1 MRCR = 15 s/s tubes with B4C powder6 in-core experimental tubes
13
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ASTRA Conclusions
• Criticality Predictions fairly close (keff = .99977)
• Rod Worth Predictions off 10%• Analysis Raises Issues of Coupling of Core
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Safety Issues
• Fuel Performance - Key to safety case• Air Ingress• Water Ingress• Loss of Coolant Accident• Seismic reactivity insertion• Reactor Cavity Heat Removal • Redundant Shutdown System• Silver and Cesium diffusion
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Safety Advantages
• Low Power Density• Naturally Safe• No melt down • No significant
radiation release in accident
• Demonstrate with actual test of reactor
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Safety
• LOCA Analysis Complete - No Meltdown• Air Ingress now Beginning focusing on
fundamentals of phenomenon• Objectives
- Conservative analysis show no “flame”- Address Chimney effect - Address Safety of Fuel < 1600 C- Use Fluent for detailed modeling of RV
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Massachusetts Institute of TechnologyDepartment of Nuclear Engineering
Advanced Reactor Technology Pebble Bed Project
MPBR-5
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Fig-10: The Temperature Profile in the 73rd Day
0
200
400
600
800
1000
1200
1400
1600
0 1 2 3 4 5 6 7 8 9 10 11
Distance to the Central Line
Tem
pera
ture
(C)
Vessel
Core Reflector Cavity Soil
ConcreteWall
Temperature Profile
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The Prediction of the Air Velocity(By Dr. H. C. No)
Fig-14: Trends of maximum temperature for 0, 2, 4, 6 m/s of air velocity in the air gap region
0
200
400
600
800
1000
1200
1400
1600
1800
0 30 60 90 120 150 180 210Time (hr)
Tem
pera
ture
(C)
Hot-PointTemperature of thecore(0m/s)Hot-PointTemperature of theVessel (0m/s)Hot-PointTemperature of theConcrete Wall (0m/s)Hot-PointTemperature of theCore (2m/s)Hot-PointTemperature of theVessel (2m/s)Hot-PointTemperature of theConcrete Wall (2m/s)Hot-PointTemperature of theCore (6m/s)Hot-PointTemperature of theVessel (6m/s)Hot-PointTemperature of theConcrete Wall (6m/s)Limiting Temperaturefor the Vessel
Limiting Temperaturefor the Containment
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Air Ingress• Most severe accidents
among PBMR’sconceivable accidents with a low occurrence frequency.
• Challenges: Complex geometry, Natural Convection, Diffusion, Chemical Reactions
Vary Choke Flow
Bottom Reflector
Air In
Air/COx out
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The Characteristics the Accident
Important parameters governing these reactionsGraphite temperature
Partial pressures of the oxygen
Velocity of the gases
Three Stages:Depressurization (10 to 200 hours)
Molecular diffusion.
Natural circulation
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Overall Strategy
• Theoretical Study (Aided by HEATING-7 and MathCad)
• Verification of Japan’s Experiments (CFD)
• Verification of Germany’s NACOK experiments(CFD)
• Model the real MPBR(CFD)
Level 1: In-Vessel model
Level 2: In-Cavity model
Level 3: In-Containment model
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Graphite Combustion
• Robust, self-sustaining oxidation in the gas phase involving vaporized material mixing with oxygen
• Usually produces a visible flame.
• True burning of graphite should not be expected below 3500 °C. (From ORNL experiments)
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Critical Parameters for Air Ingress
• Temperature of reacting components• The concentration of oxygen• Gas flow rates• Pressure (partial pressure and total pressure
in the system)
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The Assumptions for theoretical Study
The gas temperature is assumed to follow the temperature of the solid structures.The reaction rate is proportional to the partial pressure of the oxygenThere is enough fresh air supply.The inlet air temperature is 20 °C.
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The Procedures for Theoretical Study
1. Calculate the resistance of the pebble bed
2. Calculate the chemical reaction rate
3. Add the heat by chemical reaction
4. Run heating-7
5. Calculate the the air velocity and other
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Key Functions
P_buoyancy=(ρ_atm-ρ_outlet)*g*H
P_resistance=ψ(H/d)*[(1-ε)/ε3]ρu2/2
ψ=320/[Re/(1-ε)]+6/[(Re/(1-ε))0.1]
Re=duρ/η
Q_transfer=hc*360000*(d/2)2*(T_graphite-T_gas)
hc=0.664(k/d)(Re/ε)1/2Pr1/3
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Figure 1: The Initial Temperature of the Channels
500
550
600
650
700
750
800
850
900
950
1000
-4 -3 -2 -1 0 1 2 3 4
Z (m)
Tem
pera
ture
(C)
Channel 1Channel 2Channel 3Channel 4Channel 5
Initial Temperature Distribution
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Fig-2: Air Inlet Velocity Vs. the Average Temp. of the Gases
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0 400 800 1200 1600 2000 2400 2800 3200
the Average Temp. of the Gases (C)
Air
Inle
t Vel
ocity
(m/s
)
Air Ingress Velocity f(temperature)
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Preliminary ConclusionsAir Ingress
For an open cylinder of pebbles:
• Due to the very high resistance through the pebble bed, the inlet air velocity will not exceed 0.08 m/s.
• The negative feedback: the Air inlet velocity is not always increase when the core is heated up. It reaches its peak value at 300 °C.
• Preliminary combined chemical and chimney effect analysis completed - peak temperatures about 1670 C.
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The Chemical Reaction
The Chemical Reaction Rate:(From Dave Petti’s Paper)
Rate=K1*exp(-E1/T)(PO2/20900)When T<1273K: K1=0.2475, E1=5710;When 1273K<T<2073K, K1=0.0156, E1=2260
The production ratio of CO to CO2(R):R=7943exp(-9417.8/T)
• For C + zO2 = xCO + y CO2z=0.5(R+2)/(R+1), x=R/(R+1), y=1/(R+1)
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Figure 3: The peak temperature
800
900
1000
1100
1200
1300
1400
1500
1600
1700
0 50 100 150 200 250 300 350 400
time(hr)
Tem
pera
ture
(C)
Simplified HEATING7 Open Cylinder AnalysisPeak Temperature
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PBR_SIM Results with Chemical Reaction
• Considering only exothermic C + O2 reactions• Without chemical reaction - peak temperature 1560 C @ 80
hrs• With chemical reaction - peak temperature 1617 C @ 92 hrs• Most of the chemical reaction occurs in the lower reflector• As temperatures increase chemical reactions change:
– C + O2 > CO2 to– 2C + O2 > 2C0 to– 2CO + 02 > 2 CO2
• As a function of height, chemical reactions change• Surface diffusion of O is important in chemical reactions
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Verify the Chemical Model (FLUENT 6.0)
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Verify the Chemical Model
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Model for Database Generation
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Testing Model Using Simplified Geometry
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Testing Model Using Simplified Geometry (cont.)
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Testing Model Using Simplified Geometry (cont.)
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The Detailed Model in Progress
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Detailed Bottom Reflector
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Typical Treatment
• Assume that after blowdown (Large break) that the reactor cavity is closed limiting the amount of air available for ingress.
• Assume that all the air is reacted - mostly in the lower reflector - then chemical reaction stops consuming only several hundred kilograms of graphite.
• Need to cool down plant - fix break - stop air ingress path.
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Summary• Air Ingress is a potentially serious event for high
temperature graphite reflected and moderated reactors (prismatic and pebble).
• Realistic analyses are necessary to understand actual behavior
• Based on realistic analyses, mitigation strategies are required.
• Good news is that long time frames are involved at allow for corrective actions (70 to 200 hours).
• MIT working on detailed analysis of the event with baseline modeling and testing with German JulichNACOK upcoming tests on air ingress.
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Competitive With Gas ?
• Natural Gas 3.4 Cents/kwhr• AP 600 3.6 Cents/kwhr• ALWR 3.8 Cents/kwhr• MPBR 3.3 Cents/kwhr
Relative Cost Comparison (assumes no increase in natural gas prices) based on 1992 study
ESKOM’s estimate is 1.6 to 1.8 cents/kwhr (bus bar)
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MPBR PLANT CAPITAL COST ESTIMATE(MILLIONS OF JAN. 1992 DOLLAR WITH CONTINGENCY)
Account No. Account Description Cost Estimate
20 LAND & LAND RIGHTS 2.521 STRUCTURES & IMPROVEMENTS 19222 REACTOR PLANT EQUIPMENT 62823 TURBINE PLANT EQUIPMENT 31624 ELECTRIC PLANT EQUIPMENT 6425 MISCELLANEOUS PLANT EQUIPMENT 4826 HEAT REJECT. SYSTEM 25
TOTAL DIRECT COSTS 1,275
91 CONSTRUCTION SERVICE 11192 HOME OFFICE ENGR. & SERVICE 6393 FIELD OFFICE SUPV. & SERVICE 5494 OWNER’S COST 147
TOTAL INDIRECT COST 375
TOTAL BASE CONSTRUCTION COST 1,650CONTINGENCY (M$) 396
TOTAL OVERNIGHT COST 2,046UNIT CAPITAL COST ($/KWe) 1,860AFUDC (M$) 250
TOTAL CAPITAL COST 2296
FIXED CHARGE RATE 9.47%LEVELIZED CAPITAL COST (M$/YEAR) 217
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MPBR BUSBAR GENERATION COSTS (‘92$)
Reactor Thermal Power (MWt) 10 x 250Net Efficiency (%) 45.3%Net Electrical Rating (MWe) 1100Capacity Factor (%) 90
Total Overnight Cost (M$) 2,046Levelized Capital Cost ($/kWe) 1,860Total Capital Cost (M$) 2,296Fixed Charge Rate (%) 9.4730 year level cost (M$/YR):Levelized Capital Cost 217Annual O&M Cost 31.5Level Fuel Cycle Cost 32.7Level Decommissioning Cost 5.4
Revenue Requirement 286.6
Busbar Cost (mill/kWh):Capital 25.0O&M 3.6FUEL 3.8DECOMM 0.6
TOTAL 33.0 mills/kwhr
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O&M Cost
• Simpler design and more compact• Least number of systems and components• Small staff size: 150 personnel• $31.5 million per year• Maintenance strategy - Replace not Repair• Utilize Process Heat Applications for Off-
peak - Hydrogen/Water
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Graph for Income During Construction60,000
30,000
00 40 80 120 160 200 240 280 320 360 400
Time (Week)
Income During Construction : MostLik l
Dollars/Week
INCOME DURING CONSTRUCTION ?
likely
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Generating CostGenerating CostPBMR vs. AP600, AP1000, CCGT and CoalPBMR vs. AP600, AP1000, CCGT and Coal
(Comparison at 11% IRR for Nuclear Options, 9% for Coal and CCGT(Comparison at 11% IRR for Nuclear Options, 9% for Coal and CCGT11))
(All in (All in ¢¢/kWh)/kWh) AP1000 @AP1000 @ CoalCoal22 CCGT @ Nat. Gas = CCGT @ Nat. Gas = 33
AP600AP600 3000Th3000Th 3400Th3400Th PBMRPBMR ‘‘CleanClean’’ ‘‘NormalNormal’’ $3.00$3.00 $3.50$3.50 $4.00$4.00
FuelFuel 0.5 0.5 0.50.5 0.5 0.5 0.480.48 0.60.6 0.60.6 2.1 2.45 2.82.1 2.45 2.8
O&MO&M 0.8 0.52 0.46 0.8 0.52 0.46 0.230.23 0.80.8 0.60.6 0.25 0.25 0.250.25 0.25 0.25
DecommissioningDecommissioning 0.1 0.1 0.10.1 0.1 0.1 0.080.08 -- -- -- -- --Fuel CycleFuel Cycle 0.1 0.1 0.1 0.1 0.10.1 0.1 0.1 --__ --__ -- -- --__
Total Op CostsTotal Op Costs 1.5 1.22 1.16 1.5 1.22 1.16 0.890.89 1.41.4 1.21.2 2.35 2.70 3.052.35 2.70 3.05
Capital RecoveryCapital Recovery 3.4 3.4 2.5 2.5 2.12.1 2.2 2.2 2.02.0 1.51.5 1.0 1.0 1.0 1.0 1.01.0
TotalTotal 4.9 3.72 3.26 4.9 3.72 3.26 3.093.09 3.43.4 2.72.7 3.35 3.70 4.053.35 3.70 4.05
11 All options exclude property taxesAll options exclude property taxes22 Preliminary best case coal options: Preliminary best case coal options: ““mine mouthmine mouth”” location with $20/ton coal, 90% capacity factor & 10,000 BTU/kWlocation with $20/ton coal, 90% capacity factor & 10,000 BTU/kWh heat rateh heat rate33 Natural gas price in $/million BtuNatural gas price in $/million Btu
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MIT Nuclear Engineering Department
Nuclear Nonproliferation
Pebble-bed reactors are highly proliferation resistant:
small amount of uranium (9 g/ball)high discharge burnup (80 MWd/kg)TRISO fuel is difficult to reprocesssmall amount of excess reactivity limitsnumber of special production balls
Diversion of 6 kg Pu239 requires:
157,000 spent fuel balls – 1.2 yrs258,000 first-pass fuel balls – 2+~20,000 ‘special’ balls – 1.5 +
Spent Fuel
Pu238 1.9%Pu239 36.8Pu240 27.5Pu241 18.1Pu242 15.7
First Pass
Pu238 ~0 %Pu239 82.8Pu240 15.2Pu241 1.9Pu242 0.1
30
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Extrinsic Safeguards ProtectionSystem for Pebble Bed Reactors
Proposed Concept
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Extrinsic Safeguards System for Pebble Bed Reactors
WastePackage
Fresh Fuel Room
ScrapWaste Can
Typical Waste Storage Room
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Waste Disposal Conclusions
• Per kilowatt hour generated, the space taken in a repository is less than spent fuel from light water reactors.
• Number of shipments to waste disposal site 10 times higher using standard containers.
• Graphite spent fuel waste form ideal for direct disposal without costly overpack to prevent dissolution or corrosion.
• Silicon Carbide may be an reffective retardant to migration of fission products and actinides.
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Pebble Flow
• Issue is the central graphite column and its integrity
• Don’t want fuel pebble in graphite or graphite pebble in fuel
• How to assess flow to assure high power peaks do not occur that could lead to fuel failure
Conducted Experiment to determine flow
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Radial Fuel DistributionRadial Fuel Distribution
•• A central core of pure A central core of pure graphite reflector graphite reflector pebbles is surrounded pebbles is surrounded by an annulus of a by an annulus of a 50/50 fuel50/50 fuel--andand--reflector mix, and a reflector mix, and a larger annulus of pure larger annulus of pure fuel pebbles.fuel pebbles.
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Flow DiffusionFlow Diffusion
•• Several mathematical Several mathematical models for granular flow models for granular flow exist, with different exist, with different amounts of diffusion and amounts of diffusion and different velocity profiles.different velocity profiles.
•• The neutron physics of the The neutron physics of the core relies on the core relies on the assumption of laminar assumption of laminar flow and low diffusion flow and low diffusion levels during flow down.levels during flow down.
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Molecular Dynamic Simulationof Pebble Flow in Reactor
PBMR Analysis
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Dropping DiffusionDropping Diffusion
•• The radial spread of The radial spread of pebbles dropped into pebbles dropped into the core is also an the core is also an important factor in important factor in keeping the fixed keeping the fixed radial distribution of radial distribution of the pebbles, as the pebbles, as refueling is onrefueling is on--line line during reactor during reactor operation.operation.
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Half Model Design
81
28.5
12
Measurements in centimeters
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Half Model Data Collection
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Comparison to Design Profile
0
10
20
30
40
50
60
70
80
90
0 10 20 30Width (cm)
Hei
ght (
cm)
-Velocity Profile very similar
- Very flat until the funnel region
30°, 4 cm exit
07.mpg 09.mpg
Movie Clips
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Trial with Central Column
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Video Demo 19.mpg
20.mpg
21.mpg
22.mpg
23.mpg
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StreamlinesConfirmed by 3D Experiment
-5 0 5
0
5
10
x (cm)
y (c
m)
0 5 10150
20
40
60
80
100
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Radial Dispersion of Fuel and Radial Dispersion of Fuel and Graphite Pebbles During Refueling Graphite Pebbles During Refueling in the Pebble Bed Modular Reactorin the Pebble Bed Modular Reactor
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Full 9Full 9--location droplocation drop
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MIT’s Project Innovations
• Advanced Fuels• Totally modular - build in a factory
and assemble at the site• Replace components instead of repair• Indirect Cycle for Hydrogen
Generation for fuel cells & transportation
• Advanced computer automation• Demonstration of safety tests
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Sequence of Pebble Bed Demonstration
• China HTR 10 - December 2000• ESKOM PBMR - Start Construction 2002• MIT/INEEL - Congressional Approval to
Build 2003 Reactor Research Facility• 2007 ESKOM plant starts up.• 2010 MIT/INEEL Plant Starts Up.
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Highlights of Plan to Build
• Site - Idaho National Engineering Lab (maybe)• “Reactor Research Facility”• University Lead Consortium• Need Serious Conceptual Design and Economic
Analysis• Congressional Champions• Get Funding to Start from Congress this Year
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Modular Pebble Bed ReactorOrganization Chart
Industrial SuppliersGraphite, Turbines
Valves, I&C,Compressors, etc
Nuclear SystemReactor Support
Systems includingIntermediate HX
Fuel Company UtilityOwner Operator Architect Engineer
Managing GroupPresident and CEO
Representatives of Major Technology ContributorsObjective to Design, License and Build
US Pebble Bed CompanyUniversity Lead Consortium
Governing Board of DirectorsMIT, Univ. of Cinn., Univ. of Tenn, Ohio State, INEEL, DOE, Industrial Partners, et al.
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Reactor Research FacilityFull Scale
• “License by Test” as DOE facility• Work With NRC to develop risk informed
licensing basis in design - South Africa• Once tested, design is “certified” for
construction and operation.• Use to test - process heat applications, fuels,
and components
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Why a Reactor Research Facility ?
• To “Demonstrate” Safety• To improve on current designs• To develop improved fuels (thorium, Pu, etc)
• Component Design Enhancements• Answer remaining questions• To Allow for Quicker NRC Certification
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License By Test
• Build a research/demonstration plant-reactor research facility
• Perform identified critical tests• If successful, certify design for
construction.
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Risk Informed Approach
• Establish Public Health and Safety Goal• Demonstrate by a combination of deterministic
and probabilistic techniques that safety goal is met.
• Using risk based techniques identify accident scenarios, critical systems and components that need to be tested as a functional system.
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Cost and Schedule
• Cost to design, license & build ~ $ 400 M over 7 Years.
• Will have Containment for Research and tests to prove one is NOT needed.
• 50/50 Private/Government Support• Need US Congress to Agree.
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Cost Estimate for First MPBR Plant Adjustments Made to MIT Cost Estimate for 10 Units
Estimate Category Original Estimate Scaled to 2500 MWTH New Estimate
21 Structures & Improvements 129.5 180.01 24.53
22 Reactor Plant Equipment 448 622.72 88.75
23 Turbine Plant Equipment 231.3 321.51 41.53
24 Electrical Plant Equipment 43.3 60.19 7.74
25 Misc. Plant Equipment 32.7 45.45 5.66
26 Heat Rejection System 18.1 25.16 3.04
Total Direct Costs 902.9 1255.03 171.25
91 Construction Services 113.7 113.70 20.64
92 Engineering & Home office 106 106.00 24.92
93 Field Services 49.3 49.30 9.3
94 Owner's Cost 160.8 160.80 27.45
Total Indirect Costs 429.8 429.80 82.31
Total Direct and Indirect Costs 1332.7 1684.83 253.56
Contingency (25%) 333.2 421.2 63.4
Total Capital Cost 1665.9 2106.0 317.0
Engineering & Licensing Development Costs 100
Total Costs to Build the MPBR 417.0
For single unit
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Annual Budget Cost EstimatesFor Modular Pebble Bed Reactor Generation IV
Year Budget Request
1 52 203 404 405 1006 1207 100
Total 425
Annual Budget Request
5
20
40 40
100
120
100
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7
Years
$ M
illio
ns
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Key Technical Challenges
• Materials (metals and graphite)• Code Compliance• Helium Turbine and Compressor Designs• Demonstration of Fuel Performance• US Infrastructure Knowledge Base• Regulatory System
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Technology Bottlenecks
• Fuel Performance• Balance of Plant Design - Components• Graphite• Containment vs. Confinement• Air Ingress/Water Ingress• Regulatory Infrastructure
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Regulatory Bottlenecks
• 10 CFR Part 50 Written for Light Water Reactors not high temperature gas plants
• Little knowledge of pebble bed reactors or HTGRs - codes, safety standards, etc.
• Fuel testing• Resolution of Containment issue• Independent Safety Analysis Capability
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International Application
• Design Certified & Inspected by IAEA
• International “License”• Build to Standard• International Training• Fuel Support• No Special Skills
Required to Operate
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Collaborative Research Areas
• Air Ingress• Accident Performance
of TRISO Fuel• Water Ingress• Burnup Measurements• Power Distribution
Measurements• Graphite Lifetime
• Defueling Systems• Verification of
Computer Codes -VSOP, Tinte
• Xenon Effects• Modeling of Pebble
Flow• Mixing in Lower
Reflector
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Research Areas Continued
• Containments• Terrorist Impacts• Burning Potential• Advanced I&C -
Computer Control• Safeguards• International
Standards• Materials - ASME
• Blowdown Impacts• Release Models• Break Spectrum• Water Ingress• Seismic Impacts• Post Accident
Recovery• “License By Test”
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A “New” Question
• Can Nuclear Plants withstand a direct hit of a 767 jet with a plane load of people and fuel ?
• Can it deal with other Terrorist Threats?- Insider- Outsider- General Plant Security
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Pebble Advantages• Low excess reactivity - on line refueling• Homogeneous core (less power peaking)• Simple fuel management• Potential for higher capacity factors - no
annual refueling outages• Modularity - smaller unit • Faster construction time - modularity• Indirect cycle - hydrogen generation• Simpler Maintenance strategy - replace vs repair
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Generation IV• Very High Temperature Gas Reactors (VHTR)
– Pebble or Prismatic– > 1100 C– Large Materials Challenges
• Fast Gas Reactors– Fast Spectrum - need to manage reactivity coefficients– Pressurized Containment - decay heat removal– Need new fuel type (pebble or prismatic)– Need to develop full fuel cycle (reprocessing)
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Very High Temperature ReactorPebble or Prismatic
• Reactor power 600 MWth• Coolant inlet/outlet temperature 640/1000°C• Core inlet/outlet pressure Dependent on
process• Helium mass flow rate 320 kg/s• Average power density 6–10 MWth/m 3• Reference fuel compound ZrC-coated
particles in blocks, pins or pebbles• Net plant efficiency >50%
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Fast Gas Reactor
• Advantage of Sustainability• Disadvantage - post shutdown decay heat
removal• Need new fuel development - for either
pebble or prismatic - cermet or composite metal fuels
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Design Features of the GFR Concept
Reactor Design Parameter Conceptual Datawer plant 600 MWth
et efficiency (direct cycle helium) 48 %oolant pressure 90 barutlet coolant temperature 850 °C (Helium, direct cycle)let coolant temperature 490 °C (Helium, direct cycle)ominal flow & velocity 330 kg/s & 40 m/sore Volume 10.9 m3 (H/D ~1.7/2.9 m)ore pressure drop ~ 0.4 barolume fraction (%) Fuel/Gas/SiC 50/40/10 %verage power density 55 MW/m3
eference fuel compound UPuC/SiC (50/50 %)17 % Pu
eeding/Burning performances Self-Breederaximum fuel temperature 1174 °C (normal operation)
< 1650 °C (depressurization)core heavy nuclei inventory 30 tons
ssion rate (at %); Damage ~ 5 at%; 60 dpauel management multi-recyclinguel residence time 3 x 829 efpdoppler effect (180°C-1200°C) -1540 10-5
elayed neutron fraction 356 10-5
otal He voidage effect +230 10-5
verage Burn up rate at EOL ~ 5 % FIMAimary vessel diameter < 7 m
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Figure 5. Schematic diagram of possible core layout with inner reflector for a modular, helium-cooled fast nuclear energy system with ceramics fuel (cercer), or ceramics/metal (cermet) orcomposite metal (metmet) as back-up solutions. Could also be a smaller pebble bed .
Coolant holes Cercer fuel for
modular gas cooled fast reactors.
Active core
Replaceable outer reflector
Replaceable low-density reflector or void
Permanent side reflector
Schematic of a Fast Gas Reactor
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Summary• Pebble Power Appears to Meet Economic, Safety
and Electricity Needs for Next Generation of Nuclear Energy Plants
• Eskom to decide in December whether to build protoype plant in South Africa.
• MIT Project aimed at longer term development with focus on innovation in design, modularity, license by test, using a full scale reactor research facility to explore different fuel cycles, process heat applications, and advanced control system design, helium gas turbines and other components.
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