Status and Progress for the Pebble-Bed Advanced High Temperature

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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 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/
   – Uses available ASME Section III

• 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
     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-CFR50.20                        Anticipated operational
      10-1      AOO
      10-3                                              10-CFR50.34
                                                                              Design basis events

      10-5             Example
                                                                  Latent      Beyond design basis
      10-7                                         Isorisk line

          10-7 10-6 10-5 10-4 10-3 10-2 10-1   1       10    102 103    104

•    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)
                  10-1      AOO

                  10-3                                              10-CFR50.34


                  10-5             Example                                    Latent
                                     BDBE                                      QHO

                  10-7                                         Isorisk line

                      10-7 10-6 10-5 10-4 10-3 10-2 10-1   1       10    102 103    104

• 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)
                       10-1      AOO

                       10-3                                              10-CFR50.34


                       10-5             Example                                    Latent
                                          BDBE                                      QHO

                       10-7                                         Isorisk line

                           10-7 10-6 10-5 10-4 10-3 10-2 10-1   1       10    102 103    104

• 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

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
  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
      – 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

    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

                               Primary Pumps

                                                                  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)


      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
        – 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
        – 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

                  Parameter                 LWR                PBMR

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

                                                 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
                                       Intermediate Heat

                       DRACS Heat


                       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

   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
• 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
• 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
• 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
    – EROS zero power critical tests (w/ salt) (Viability phase)
• Separate Effects Tests
    – Scaled High Temperature Heat Transfer (S-HT2) facility (Viability
        » 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

• 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

                                             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

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

                               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
    – e.g. pebble bed heat transfer coefficients, pebble friction coefficients,
• 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/
     – 1:1 effective height (1:2 actual)
     – 1:190 effective flow area (1:756 actual)
     – 1:190 effective power (1:9000 actual, 100
     – 1:(2)1/2 time
     – reduced temperature / pressure
     – reduced heat loss
     – small distortion from thermal radiation
                                                                                 Semiscale, INL
  See 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
• 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
    – 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

 PBMR Helium Test Facility (HTF) in Pelindaba, SA
                                                    UC Berkeley

• 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

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