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Status and Progress for the Pebble-Bed Advanced High
Temperature Reactor (AHTR)
Per F. Peterson
Department of Nuclear Engineering
University of California, Berkeley
March 2, 2009
UC Berkeley
Overview
• Overview of intermediate and long
term nuclear energy options
• Modular PB-AHTR design
– 900 MWth / 410 MWe
– Core power density 20 - 30 MW/m3
– Core inlet/outlet temps 600°C/
704°C
– Uses available ASME Section III
materials
• Modular PB-AHTR development
UC Berkeley
Advanced Nuclear Energy Technology Overview
UC Berkeley
Resource inputs will affect future capital costs and
competition between energy technologies
• Nuclear: 1970’s vintage PWR, 90% capacity factor, 60 year life [1]
– 40 MT steel / MW(average)
– 90 m3 concrete / MW(average)
• Wind: 1990’s vintage, 6.4 m/s average
wind speed, 25% cap. factor, 15 year life [2]
– 460 MT steel / MW (average)
– 870 m3 concrete / MW(average)
• Coal: 78% cap. factor, 30 year life [2]
– 98 MT steel / MW(average)
– 160 m3 concrete / MW(average)
• Natural Gas Combined Cycle: 75%
cap. factor, 30 year life [3]
– 3.3 MT steel / MW(average)
– 27 m3 concrete / MW(average)
Concrete + steel are >95% of construction 1. R.H. Bryan and I.T. Dudley, “Estimated Quantities of Materials Contained in a 1000-MW(e)
PWR Power Plant,” Oak Ridge National Laboratory, TM-4515, June (1974)
inputs, and become more expensive in a 2. S. Pacca and A. Horvath, Environ. Sci. Technol., 36, 3194-3200 (2002).
3. P.J. Meier, “Life-Cycle Assessment of Electricity Generation Systems and Applications for
carbon-constrained economy Climate Change Policy Analysis,” U. WisconsinReport UWFDM-1181, August, 2002.
UC Berkeley
Nuclear power plants require very small natural resource
inputs (even at March 2008 prices)
Quan. Price Cost
Commodity (1) 3/20/08 ($/kW)
Aluminum (metric tons) (2) 18 $2,794 $0.05
Brass (metric tons) (2) 10 $4,950 $0.05
Bronze (metric tons) (3) 25 $4,950 $0.12
Carbon steel (metric tons) (2) 32731 $601 $19.67
Concrete (m^3) (3) 75026 $98 $7.36
Copper (metric tons) (2) 694 $7,634 $5.30
Galvanized iron (metric tons) (2) 1257 $721 $0.91
Iconel (metric tons) (2) 124 $7,000 $0.87
Insulation (thermal) (m. tons) (3) 922 $1,000 $0.92
Lead (metric tons) (2) 46 $2,640 $0.12
Nickel (metric tons) (2) 1 $28,446 $0.03
Paint (gal) (3) 17500 $20 $0.35
Total commodities cost $35.75
The most recent price for a new nuclear plant is $3450 per kilowatt (Westinghouse
AP-1000 contract for Progress Energy) – resource scarcity will never limit the
construction of new nuclear plants (fuel and waste are long-term issues)
(1) R.H. Bryan and I.T. Dudley, “Estimated Quantities of Materials Contained in a 1000-MW(e)PWR Power Plant,” Oak Ridge
National Laboratory, TM-4515, June (1974)
2. Prices for 3/20/08 downloaded from http://www.metalprices.com/FreeSite/metals/cu/cu.asp
3. Assumed price
UC Berkeley
The new supply chain for nuclear infrastructure will be
much different from the 1970’s/1980’s
1978: Plastic models on roll-around carts 2000: 4-D computer aided design
and virtual walk-throughs
McGuire Nuclear Station Reactor Building Models.
In October 2008 Westinghouse and Shaw
announced the construction of an AP-1000
module factory at Lake Charles, LA; Areva a
collaboration with Northrop Grumman at 1000 MW Reactor (Lianyungang Unit 1)
Newport News shipyard UC Berkeley
Three primary options exist for long-term, sustainable
nuclear energy systems
• Fast neutron spectrum reactors
– Uranium-238 based fuel cycle
– Increased fission/capture probability (good neutron economy)
– Large transuranic inventories and complex reactivity control
• Thermal neutron spectrum reactors
– Thorium-232 based fuel cycle
– Requires highly efficient neutron economy (liquid fuels best)
– Small transuranic inventories and simple reactivity control
• Fission/fusion thermal spectrum hybrid reactors
– Uranium-238 or Thorium-232 based fuel cycle
– Abundant neutrons
– Small transuranic inventories and simple reactivity control
– Requires workable fusion power source
UC Berkeley
Recent activity in the development of innovative,
advanced reactor technologies
UC Berkeley
Two innovative, interesting nuclear power plant designs
are now in USNRC pre-application review
Pebble Bed Modular Reactor (PBMR) NuScale reactor module
Modular helium reactor Pressurized water reactor
165 MW electric 45 MW electric
UC Berkeley
Technology-neutral licensing requires demonstrating that
a new nuclear plant design creates sufficiently low risk
PBMR Event Frequency Versus Consequence Graph
UC Berkeley
PB-AHTR safety assessment and licensing involves the
systematic identification of Licensing Basis Events
10
Acceptable
1
Example
10-CFR50.20 Anticipated operational
10-1 AOO
Unacceptable
occurrences
10-2
Example
DBE
10-3 10-CFR50.34
Design basis events
10-4
10-5 Example
BDBE
Latent Beyond design basis
QHO
10-6
events
10-7 Isorisk line
10-8
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104
DOSE (TEDE REM) AT EXCLLUSION AREA BOUNDARY (EAB)
• PB-AHTR LBE’s may be generated by internal or external events
• PB-AHTR LBE’s are categorized by frequency
• For conceptual design, LBE’s for PB-AHTR include Loss of Forced Circulation
(LOFC), Loss of Heat Sink (LOHS), and Anticipated Transient Without Scram
(ATWS) with LOFC or LOHS
UC Berkeley
Response to Licensing Basis Events involves rapid
phenomena (seconds to days)
10
Acceptable
1
10-CFR50.20
Example
10-1 AOO
Unacceptable
10-2
Example
DBE
10-3 10-CFR50.34
10-4
10-5 Example Latent
BDBE QHO
10-6
10-7 Isorisk line
10-8
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104
DOSE (TEDE REM) AT EXCLLUSION AREA BOUNDARY (EAB)
• With recent advances, university scale research is now capable of
developing experimentally validated modeling tools for reactor
transient response (for water, liquid salt, and helium coolants).
UC Berkeley
Frequency of Licensing Basis Events involves slow
phenomena (intervals of of months to millions of years)
10
Acceptable
1
10-CFR50.20
Example
10-1 AOO
Unacceptable
10-2
Example
DBE
10-3 10-CFR50.34
10-4
10-5 Example Latent
BDBE QHO
10-6
10-7 Isorisk line
10-8
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104
DOSE (TEDE REM) AT EXCLLUSION AREA BOUNDARY (EAB)
• LBE frequency analysis depends upon slowly evolving phenomena
– PB-AHTR development strategy minimizes fuels and materials risk
• The PB-AHTR development path would include separate effects tests
(material and fuel irradiation, etc.) and reliability testing of major system
components in the Component Test Facility, to provide data for PRA models
• AOO frequency prediction is also important for economics (affects the plant
capacity factor)
UC Berkeley
AHTR Technology Overview
UC Berkeley
Advanced High-Temperature Reactors (AHTRs)
combines two older technologies
Coated particle fuel
max.
PB-AHTR 1600°C Liquid fluoride salt coolants
temp Excellent heat transfer
Transparent, clean fluoride salt
Boiling point ~1400ºC
Reacts very slowly in air
No energy source to pressurize
containment
Fuel failure fraction vs. temperature UC Berkeley
Liquid fluoride salts have fundamentally different
properties than other reactor coolants
• High volumetric heat capacity provides high thermal inertia
– High power density, low pressure operation possible compared to
helium cooled reactors
– High efficiency, compact primary loop equipment compared to
water cooled reactors
– Transparent coolant, low thermal shock, low chemical reactivity
compared to sodium cooled reactors
UC Berkeley
Fluoride salts are of interest for multiple applications
Liquid-Salt-Cooled VHTR
(Advanced High-Temperature Reactor;
Coated-Particle Fuel; Salt Coolant) Liquid Fluoride Thorium
Reactor (Molten Salt Reactor)
Liquid-Salt Fast Reactor Fission/Fusion Heat-Transport Systems
(Metal-Clad Fuel; Salt Coolant Hybrid For H2 Production
UC Berkeley
The Modular PB-AHTR is a compact pool-type reactor
with passive decay heat removal
UC Berkeley
The PB-AHTR uses well understood materials and fuel
• TRISO based fuel is well understood
– Peak temperature during normal operation and accidents < 1000°C
– Capability to manufacture being reestablished
– Uses special pebble design (see later slide), rapid burn up (210 day)
enables very short fuel development program schedule
• Metallic components are Alloy 800H clad with Hastelloy N for
corrosion resistance
– The baseline design has a conservatively low 704°C core outlet
temperature to assure high corrosion resistance (extensive test data
available)
– Alloy 800H provides structural strength and is ASME Section III code
qualified for use up to 760°C; ORNL now extending code case to 900°C
– Hastelloy N has well understood corrosion resistance with fluoride salts
• Reflectors are graphite
– Capability to manufacture nuclear-grade graphite has been
reestablished
The baseline PB-AHTR fuel and materials have moderate development risk
UC Berkeley
In September 2007 UCB published 3 key papers on the
Pebble Bed AHTR
• Neutronics analysis, verifying that the PB-AHTR
– can be designed with negative void reactivity
– can achieve high discharge burn up, comparable to MHRs
• Thermal hydraulic analysis, using RELAP5-3D
to verify that the PB-ATHR
– has very gentle response to Loss of
Forced Cooling Transient
– can be designed to have acceptable response
to Anticipated Transient Without Scram
– Power levels up to 4800 MWth possible
• Results from the Pebble Recirculation
Experiment (PREX-1), verifying
– pebble injection into the reactor cold leg
– lower plenum pebble landing dynamics
– pebble defueling from the top of the reactor core
PREX-1 with 8300 pebbles
UC Berkeley
Modular 410-MWe PB-AHTR Design Overview
UC Berkeley
The PB-AHTR power conversion system design is
derived from the PBMR/Mitsubishi design
Generators
Compressors
Turbines
Recuperator
Primary Pumps
Reactor
Intercoolers
Precoolers
Helium heaters
Intermediate drain tank
Intermediate pumps
Intermediate heat exchangers
168-MWe PBMR/Mitsubishi 410-MWe PB-AHTR
helium cooled HTR liquid cooled HTR
To scale
UC Berkeley
The Modular PB-AHTR uses seismic base isolation
Hearst Mining Building, UCB
Grade level
• Structure isolated with resonant
period of 3.6 seconds
• Isolators filter out higher frequency
seismic energy
UC Berkeley
GT-MHR and PB-AHTR reactor buildings (to scale)
81m
36m
GT-MHR reactor building AHTR reactor/turbine building
(287MWe) (410 MWe)
Typical LWR and SFR buildings are ~75m high
UC Berkeley
The current Modular PB-AHTR plant design is compact
compared to LWRs and MHRs
Reactor Type Reactor Reactor and Turbine Ancillary Total
Power Auxiliaries Building Structures Building
Volume Volume Volume Volume
(MWe) (m3/MWe) (m3/MWe) 3
(m /MWe) (m3/MWe)
1970’s PWR 1000 129 161 46 336
ABWR 1380 211 252 23 486
ESBWR 1550† 132† 166 45 343
EPR 1600 228 107 87 422
GT-MHR 286 388 0 24 412
PBMR 170 1015 0 270 1285
Modular PB-AHTR 410 105 115 40 260
†
The ESBWR power and reactor building volume are updated values based on the Design
Certification application arrangement drawings.
UC Berkeley
The new Modular PB-AHTR is designed
to maintain superior economics with a
modular HTR design
• Comparison of PB-AHTR with the
PBMR:
– 2 x power output per reactor
– ~30 MWth/m3 core power density
versus 4.8 MWth/m3
– large reduction in vessel size
– atmospheric pressure operation
– 4 x reduction in spent fuel volume
per unit of electricity/process steam
produced
– maximum fuel temperature during
transients/accidents reduced from 900 MWth 400 MWth
1600°C to 1000°C PB-AHTR PBMR
The smaller size and low mass of major components (reactor vessel
weight < 180 tons) has implications for the construction schedule
UC Berkeley
PB-AHTR uses less uranium than LWRs and PBMRs
Integral
Parameter LWR PBMR
PB-AHTR
Discharge burn up (MWt-day/kg) 55 117 80
Fuel enrichment (%) 5.0 10.0 8.1
Tails assay (%) 0.3 0.3 0.3
C/HM 0 363 425
Thermal efficiency (%) 33 46 42
Natural uranium consumption (kg/MWe-day) 0.630 0.439 0.565
Separative work consumption (SWU/MWe-day) 0.397 0.321 0.399
Depleted uranium generation (kg/MWe-day) 0.575 0.420 0.535
HM mass (g/pebble) - 10.06 9
Relative natural uranium consumption 1.00 0.70 0.90
Relative SWU consumption 1.00 0.81 1.00
Relative spent fuel volume - 0.56 1.00
UC Berkeley
The Modular PB-AHTR uses pebble channel assemblies
Elevation View Plan Views
UC Berkeley
Viability phase R&D includes construction of
PREX-2 to verify pebble recirculation in a PCA
Baseline design for lower half of PCA
showing configuration of pebble
channels
UC Berkeley
Modularity enables simple scaling from Pilot to
Modular to Central-Station power levels
UC Berkeley
Equipment hallways and turbine hall act as an external
events shell for the PB-AHTR reactor citadel
UC Berkeley
RELAP5-3D Modeling of 900 MWth PB-AHTR
transient response to LOFC and LOHS transients, with
and without scram
UC Berkeley
RELAP5-3D model for 900 MWth Modular PB-AHTR
Hot Leg
Primary
Pump
Intermediate Heat
Exchanger
DRACS Heat
Exchanger
Reactor
Core
Fluidic Diode
Cold Leg
UC Berkeley
Transient response of 900 MWth PB-AHTR to LOFC
PB-AHTR thermal response
(annular pebbles)
• Response is gentle even with 30 MW/m3 power density
UC Berkeley
Results for LOHS without scram for 900 MWth Design
Transient initiated:
Complete heat sink
removal
Fission and decay power PB-AHTR thermal response
• Under LOHS without scram, coolant outlet temperature increases
until reactor shuts down on negative temperature feedback
• Results are sensitive to the fuel and coolant temperature reactivity
feedback
• UCB has developed a passive reactivity shutdown system to
address ATWS
UC Berkeley
Development Approach for the Pilot and Modular PB-
AHTR Designs
UC Berkeley
A PB-AHTR Development Program has four phases
• Viability Phase
Gen IV
– Major end product is a NRC Pre-Application
Submittal Viability Phase
• Performance Phase
Gen IV
– Major end product is a NRC Design Performance
Certification Submittal
Phase
• Licensing Phase
– Major end product is NRC Design
Certification and a NRC Combined
Construction and Operating License for a Pilot
PB-AHTR Plant Gen IV
Demonstration
• Construction and Testing Phase Phase
– Major end product is operational experience to
support commercial deployment of Modular
PB-AHTR plants
UC Berkeley
PB-AHTR Experimental Program
Viability phase --> Performance phase --> Demonstration phase
UC Berkeley
The Modular PB-AHTR Experimental Program
• Integral Effects Tests
– Compact Integral Effects Test (CIET) facility (Viability phase)
» Scaled simulant fluid IET to study system response to LOFC,
ATWS, and other transients
– Pebble Recirculation Experiment (Viability phase)
» Scaled simulant fluid IET to study pebble recirculation
hydrodynamics
– EROS zero power critical tests (w/ salt) (Viability phase)
• Separate Effects Tests
– Scaled High Temperature Heat Transfer (S-HT2) facility (Viability
phase)
» Heat transfer coefficient measurements using simulant fluids
– Other SET experiments (Viability/Performance phases)
» Pebble confirmatory irradiation experiments, etc.
» Materials corrosion test loop experiments
UC Berkeley
The Modular PB-AHTR Experimental Program (con’t)
• Component Tests
– Various scaled component tests with simulant fluids (water)
(Viability phase)
– Component Test Facility (CTF) (Performance phase)
» Major non-nuclear facility to test primary, intermediate and
DRACS loop components under prototypical liquid salt
conditions
• Pilot Plant Tests (Demonstration phase)
– nuclear fuel loading and pre-critical (zero power) testing
– low-power (<5%) testing and operation
– power ascension testing and operation not in excess of 100%
– interim operation
– maintenance and in-service inspection procedures
UC Berkeley
The current UCB test program has 3 facilities
PREX S-HT2 PRISM
Pebble recirculation IET Salt heat transfer SET Passive shutdown rod IET
Match Re, Fr, pebble/salt Match Re, Fr, Pr, Gr Match Re, Fr, rod/salt density
density ratio w/ water w/ Dowtherm A ratio w/ sugar water
UC Berkeley
Collaboration with Czech Republic NRI to validate
AHTR neutronics models in the LR-0 Zero Power Critical
Test facility
LR-0
UC Berkeley
EROS Test Assembly
The design of the test
assembly is a hexagonal
block with a pitch of 23.6cm
with 19 channels drilled for
uranium pins surrounded by
salt.
Fuel pins are .753 cm
diameter (without cladding)
3.6% enriched and clad with
zirconium alloy.
Initial design uses 60%
natural LiF and 40% NaF
salt.
UC Berkeley
Thermal hydraulics integral test program
—
The Compact Integral Effects Test
UC Berkeley
Dowtherm heat transfer oil will be used as the principal
simulant fluid for PB-AHTR IET/SET experiments
Scaling parameters to match Pr, Re, Gr, and Fr for flibe and Dowtherm A
•Note that Pr, Re, Gr and Fr can be matched at < 2% of
prototypical heater power
•Water can be used for hydrodynamics experiments
UC Berkeley
The Compact Integral Effects Test (CIET) facility will
validate the PB-AHTR transient thermal hydraulics code
during Viability Phase R&D
• The Compact Integral Effect Test (CIET) facility (located at UC
Berkeley) will be a reduced height, reduced area, reduced power
scaled 100 kW (70 V DC) IET that will:
– provide low-distortion IET data for transient code validation
– exceed the quality of data produced by earlier IET’s for light water
reactors (e.g. Semiscale) (100 kW in CIET is equivalent to 4.7 MW
with the prototypical coolant)
• Additional SET experiments will be performed to study specific
phenomena
– e.g. pebble bed heat transfer coefficients, pebble friction coefficients,
etc.
• A primary purpose of the NRC Pre-Application Review will be to
review and approve use of the IET/SET test program data for
safety code validation
UC Berkeley
CIET can be compared to the INL Semiscale facility
• Semiscale simulation of PWR LOCA
– 1:1 height
– 1:1705 flow area
– 1:1705 power (2 MW)
– 1:1 time
– prototype temperature / pressure
• CIET simulation of the PB-AHTR LOFC/
ATWS
– 1:1 effective height (1:2 actual)
– 1:190 effective flow area (1:756 actual)
– 1:190 effective power (1:9000 actual, 100
kW)
– 1:(2)1/2 time
– reduced temperature / pressure
– reduced heat loss
– small distortion from thermal radiation
Semiscale, INL
See http://users.owt.com/smsrpm/nksafe/testfac.html for a list of other LWR IET’s
UC Berkeley
Component Reliability Test Program
UC Berkeley
The PB-AHTR uses highly reduced salt conditions to
maintain very low solubility for structural materials
• PB-AHTR uses a corrosion resistant cladding (Hastelloy N or similar)
with an ASME Section III code qualified structural material (e.g., Alloy
800H)
• Highly reduced conditions maintained by contacting salt with Be metal
UC Berkeley
The Component Test Facility (CTF) will confirm
operational reliability and maintenance methods for PB-
AHTR components during Performance Phase RD&D
• The CTF is a Performance-phase, non-nuclear test facility generating
prototypical salt conditions, to test the following components and
systems:
– Primary pump (full scale Pilot Plant pump)
– Defueling and pebble injection machines, pebble transfer system, spent/fresh pebble
storage canister system
– Reactor vessel (isothermal)
» Single Pebble Channel Assembly (PCA) with minimum thickness reflector
» Demonstrate procedures for initial heat up and salt filling, pebble fueling and
defueling, PCA replacement
– Control/safety rod drive assemblies, maintenance methods (heated)
– Reduced area intermediate heat exchanger (heated)
– DRAC heat exchangers and heat removal system (heated)
– Seismic snubbers
– Reactor cavity insulation and heating/cooling system
– Salt chemistry control system
– Cover gas chemistry and thermal control system
– In service inspection and on-line monitoring equipment and methods
– Temperature, pressure and flow and control instrumentation
UC Berkeley
The CTF performs the same major functions as the
PBMR Pty. Helium Test Facility
UC Berkeley
The smaller physical size of liquid salt equipment
reduces the size and cost of a CTF
• The PBMR HTF is a 40-m prototypical
height experimental facility, that tests
very large and bulky equipment
• Liquid salt uses small, thin-walled, low
pressure components
• Creates implications for schedule and
cost
PBMR Helium Test Facility (HTF) in Pelindaba, SA
UC Berkeley
Conclusions
• Work at UC Berkeley and elsewhere has identified attractive
features of liquid-salt cooled high temperature reactors
– Potential for high power density (20-30 MWt/m3)
– Low pressure operation, chemically inert coolant
– Use of available ASME Section III code qualified materials
– Safety code validation using integral effects tests with simulant fluid
– Capability to operate on both LEU and TRU fuels
– Reduced spent fuel volume
– Likely attractive economics compare to LWRs and MHRs
More information: Philippe Bardet, Edward Blandford, Massimiliano Fratoni, Aurelie Niquille,
Ehud Greenspan, and Per F. Peterson, “Design, Analysis and Development of the Modular PB-
AHTR,” 2008 International Congress on Advances in Nuclear Power Plants (ICAPP '08), Anaheim
CA, June 8-12, 2008.
UC Berkeley
