UC Berkeley1

Raluca Scarlat, Per F. PetersonDepartment of Nuclear Engineering

University of California, Berkeley

TEA Conference, Washington, DC12 May 2011

The Pebble-Bed Advanced High Temperature Reactor (PB-AHTR),a Fluoride Salt Cooled High Temperature Reactor (FHR)

900 MWth, 410 MWe PB-AHTR

UC Berkeley2

The PB-AHTR is a compact pool-type reactor with passive decay heat removal

UC Berkeley3

Potential Benefits of Radially-Zoned, Annular Seed/Blanket Core Configuration

• Zoning allows use of thorium blanket pebbles

– External Pa-233 decay storage

– Closed and once-through seed-blanket fuel cycles being studied

• Effective neutron shielding of outer radial reflector

• Greatly reduced core pressure drop (using a combination of axial and radial flow)

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Fluoride salt cooled High Temperature Rectors (FHRs) Combine Two Older Technologies

Liquid fluoride salt coolantsExcellent heat transferTransparent, clean fluoride saltBoiling point ~1400ºCReacts very slowly in airNo energy source to pressurize containmentBut high freezing temperature (459oC)And industrial safety required for Be

FHRs have uniquely large fuel thermal margin

Coated particle fuel(TRISO Fuel)

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Reactor Safety: PB-AHTR Defense in Depth

HVAC Zones1 - Reactor cell

(Low-LeakageInerted

Containment)2 - Reactor citadel

(Filtered Confinement)3 – Reactor quipment

hallways (Ambient air)

4 - Turbine hall(Ambient air) –

additional hold-up

TRISO ParticlesMicro-containment

vessels (>10,000 per fuel element)

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Modular PB-AHTR EconomicsMuch more compact equipment than Gas Cooled Reactors

1. D. T. Ingersoll, et al., "Status of Preconceptual Design of the Advanced High-Temperature Reactor (AHTR)," ORNL/TM-2004/104, pp. 69, 2004.

900 MWthPB-AHTR

400 MWthPBMR

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PB-AHTR Materials

• Metallic components

– ASME Section III alloys include 316 SS, Hastelloy N, Alloy 800H

» 316 SS (high neutron tolerance, well developed code case for up to 800oC, low corrosion with clean flibe & Be metal redox control, additional corrosion testing needed)

» Hastelloy N (lower neutron tolerance, incomplete code case, excellent corrosion performance, higher cost)

• Reflectors are graphite

– Compatibility with fluoride salts excellent

– Recent scoping experiment shows that fluoride salt can be an excellent lubricant for graphite pebbles sliding on graphite

• Carbon composite and/or SiC composites could also be valuable

– e.g., shut-down rod channel liners

† Hastelloy N modified with 2% titanium shows excellent corrosion and neutron embrittlement resistance,“The Development Status of Molten-Salt Breeder Reactors,” ORNL-4812, pp. 205, August 1972.

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PB-AHTR Development Program and Licensing Approach

Viability phase --> Performance phase --> Demonstration phase

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Licensing FrameworkGenerating the Frenquency-Response Plot

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

DOSE (TEDEREM) AT EXCLLUSION AREABOUNDARY (EAB)

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

LatentQHO

10-CFR50.34

10-CFR50.20

Unacceptable

Isorisk line

Acceptable

ExampleAOO

ExampleDBE

ExampleBDBE

• Transient response codes must be validated against Separate Effect Test and Integral Effect Test experiments

• Understanding of plant transient response and resulting safety should be broadly based and non-proprietary

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Licensing FrameworkGenerating the Frenquency-Response Plot

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

DOSE (TEDEREM) AT EXCLLUSION AREABOUNDARY (EAB)

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

LatentQHO

10-CFR50.34

10-CFR50.20

Unacceptable

Isorisk line

Acceptable

ExampleAOO

ExampleDBE

ExampleBDBE

• LBE frequency analysis depends upon slowly evolving phenomena

• Materials testing, component design and testing, and reliability engineering are critical in affecting event frequency and plant availability/economics

• Integrated design solutions that can demonstrate predictable and high reliability have commercial value (see NuScale example)

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The FHR Development Program has three phases

Viability Phase (nominally 3 to 4 years)

• Simulant Fluids SET and IET Experiments performed

Major end products:

• Conceptual design for a 16-MWth Test Reactor

• NRC pre-application review submittal

Performance Phase (nominally 4 years)

• Component Test Facility operates, and Fuel Qualification underway

Major end products:

• Construction authorization for a 16-MWth Test Reactor

• Submittal of NRC Design Certification Application for a commercial prototype

Demonstration Phase (nominally 5 years)

• 16-MWth AHTR Test Reactor operates

Major end products:

• NRC Design Certification

• NRC Combined Construction and Operating License for a commercial-scale PB-AHTR Pilot Plant

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Systematic Methodology for Guiding PB-AHTR Development

The Role of Modeling and Experimentation

System Design

Characterization of Individual Phenomena

Separate Effects Tests

(SETs)

DominantPhenomena

System Model

Integral Effects Tests(IETs)

Construction

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Systematic Methodology for Guiding PB-AHTR Development:

Hierarchical System Decomposition

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Major AHTR Experimental Program Elements

• Integral Effects Tests

– Compact Integral Effects Test (CIET) facility

» Scaled simulant fluid IET to study system response to LOFC, ATWS, and other transients

– Pebble Recirculation Experiment

» Scaled simulant fluid IET to study pebble recirculation hydrodynamics

– Czech EROS zero power critical tests (w/ salt) (Viability phase)

» Validate predictions for negative coolant void reactivity

• Separate Effects Tests

– Scaled High Temperature Heat Transfer (S-HT2) facility

» Heat transfer coefficient measurements using simulant fluids

– Fuel irradiation and post-irradiation examination

– Other SET experiments

» Materials corrosion test loop

» Pebble friction coefficients

» Confirmatory data during component test experiments

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Dowtherm A is a useful simulant fluid for fluoride salts

Prandtl Number for flibe and Dowtherm A

Dowtherm A is an excellent simulant coolant fluid for flibe molten fluoride salt.

Tin ToutTmelt, flibe

Tmelt, Dowtherm

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Dowtherm A is a useful simulant fluidResults and Comparison of Dowtherm Data with Flibe Data

ORNL FLiBe Correlation4 < Pr < 14

Turbulent Flow Correlations

S-HT2 Correlation8 < Pr < 36

Dowtherm A data matches available flibe dataORNL flibe data covers a narrower Pr range, and underestimates Nu at higher Pr

ORNLflibe Pr

Range

ORNLflibe

Re Range

Cooke J.W., Cox B. “Forced Convection Heat Transfer Measurements with a Molten Fluoride Salt Mixture Flowing in a Smooth Tube.” March 1973. Oakridge National Laboratory. ORNL-TM-4079.

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PREX 3.0 PREX 3.1

Dry experimental/simulation demonstration for radially-zoned pebble

motion

Wet experiment scaled to match Re and Fr

Blowing

Suction

Pebble injection

Pebble bed dynamics modeling can be validated

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Availability of a simulant fluid reduces the size and cost of a IET Facility

PB-AHTR CIET facility, 0.1MW, under construction at UC Berkeley

1:1 effective height (1:2 actual)1:190 effective power (1:9000 actual, 100 kW)reduced temperature / pressuresmall distortion from thermal radiation

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Major AHTR Experimental Program Elements

• Component Tests

– Various scaled component tests with simulant fluids (water)

– Component Test Facility (CTF)

» Major non-nuclear facility to test primary, intermediate and DRACS loop components under prototypical liquid salt conditions

• Test Reactor (DOE)

– 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

• Commercial Pilot Reactor (Industry)

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Summary PB-AHTR Technology and the Path Forward

– AHTR achieves substaintial reduction in capital cost compared to ALWRs, primarily through compact size, no high pressure, and higher temperature/power conversion efficiency

– Excellent simulant fluids for molten fluoride salts allow for obtaining experimetal data at much lower costs than using prototypical fluids

– PB-AHTRs maintain uniquely large thermal margins for damage to fuel, and Coolant temperature limit is established by thermal limits on primary loop metallic structures

– Key issues relate to demonstrating predictable and high reliability, and confirming safety characteristics

– Development path involves pre-application review and subsequent Design Certification by NRC, and it has \clear roles for national laboratories, universities, and industry

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Acknowledgements

Professor Peterson’s

Research Group

Tommy Cisneros – neutronic analysis

Mike Laufer – pebble dynamics and hydrodynamics

Cristhian Galvez, Nicolas Zweibaum –thermal-hydraulic system modeling in RELAP5-3D

Ed Blandford – licensing methodology and passive shut-down rod hydrodynamics

Lakshana Huddar, Jeff Bicket, AJ Gubser –SET and IET experiments

Minarets (tall towers) with small windows are used to allow for natural circulation cooling of buildings.

This picture looks up into a minaret atAlhambra Palace, Granada, Spain(built in the 14th century)

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“Now look, boys, I ain't much of a hand at makin' speeches, but I got a pretty fair idea that

something doggone important is goin' on back there. And I got a fair idea the kinda personal emotions that some of you fellas may be thinkin'. […] I tell you something

else, if this thing turns out to be half as important as I figure it just might be, I'd say that you're all in line for some important promotions and personal

citations when this thing's over with. That goes for ever' last one of you regardless of your race,

color or your creed. Now let's get this thing on

the hump - we got some flyin' to do.“

(Dr. Strangelove, or How I Learned to Stop Worrying and Love the Bomb, 1964)

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Back-up Slides

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Construction of theCompact Integral Effects Test (CIET) Facility

Facility ConfigurationKey Components: Heater Element

Facility Infrastructure

Scaffold

Equipment Support Rack

Cooling Water and Drain Lines

Seismic Anchoring

Drip Tray

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The new UCB Compact Integral Effects Test (CIET) facility 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

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Safety: AHTRs have unique defense in depth

• Ceramic TRISO fuel

• Over 500°C temperature margin to fuel failure under transients and accidents (unique among all solid-fuel reactor concepts)

• Immersion in chemically inert coolant with high fission product sorption capacity makes air/steam ingress impossible

• Negative coolant void/temperature reactivity feedback

• Passive natural-circulation decay heat removal

• Reactor cavity acts as a low-pressure, low leakage containment

• No stored energy sources topressurize containment

• Large thermal inertia of cavityprovides long time constantto primary coolant freezing

• Reactor citadel acts as a filteredconfinement

• External event shell and turbinehall provide additional hold up

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With active-metal redox control, 316 SS has excellent compatibility with clean flibe

† J. R. Keiser, J. H. DeVan, and E. J. Lawrence , "Compatibility of Molten Salts with Type 316 Stainless Steel and Lithium," Journal of Nuclear Materials, pp. 295-298 (1979).

316 SS has excellent corrosion resistance with flibe with Be metal redox

control †

316 SS has an existing ASME Section III code case for use up to 800°C

8 mm/yr

• Issues include potential interactions with graphite surfaces in primary loop, and salt choice/corrosion control for intermediate loop (U. Wisc. experiments give 1.8 mm/yr 316 SS corrosion for KCl/MgCl2 with Mg metal control)

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AHTRs use reduced salt conditions to maintain very low solubility for structural materials

• AHTR’s can use 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

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Dowtherm heat transfer oil can be used as the principal simulant fluid for 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