Closed Brayton Cycle Power for Pebble Bed Reactors

Jim Kesseli, Brayton Energy, LLC

Kesseli@BraytonEnergy.com

January 30, 2017

CANES

Center for Advanced Nuclear Energy Systems

* A MITEI Low – Carbon Energy Center*

77 MASSACHUSETTS AVE CAMBRIDGE MA 02139-4307

Introductory Notes and Acknowledgements

• Notes from Prof. Jacopo Buongiorno: “focus your talk on Helium Brayton, both the heat compact exchangers and the turbomachinery, with emphasis on readiness, performance, challenges, and importantly cost wrt steam cycle.”

• Acknowledgements:• Portions of this work was sponsored by X-energy (2010-2013) covering the

early studies of the direct Brayton cycles.

• PBMR Inc sponsored Brayton Energy studies 2004-2008, for the development of an alternative recuperator.

• AREVA sponsored Brayton Energy studies of IHX for indirect cycles 2005-2007

Closed Cycle Brayton for Pebble Bed Reactors

GeneratorPre

-coole

r

Turbine Compressor

Recuperator PEBBLE BED

REACTOR

Containment

AC power terminals Containment

Heat

rejection

Principles:• Gas turbine (Brayton cycle) • Working fluid: inert gas (He favored,

non-radioactive release)

Attractions:• Simplicity: “One major moving part”• No water or steam• Simplified pressure boundary for

coding

4

8-stage Axial –

Centrifugal

Compressor

Axial

turbine

(2-stage)

PM Alternator (12 MWe)

Turbomachinery for closed He cycle - high stage count for He. (Pr~3)

• Closed-cycle He working fluid

• Only one moving part

• No mechanical wear – all magnetic bearings

• Shaft speed motor/alternator, for variable power

control.

Cost ~ $500/kWe

State of Readiness: • Conservative aero

design loading • Low stress• Common low

temp alloys • High TRL • Mag bearings • PMA

~600mm diameter turbine rotor Axial compressor diameter~ 400mm, centrifugal ~800mm

10MW Helium Cycle Turbo-Alternator

Reactor inlet temp = 500ºC

Reactor outlet temp = 850ºCPeak Pressure = 4 MPa

He mass fraction = 15%,

Ar mass fraction = 85%

η-electric=0.28

η-electric=0.29

η-electric=0.30

Efficiency trades: Basic cycle ~30% thermal-electric

7

• Step 1- Brayton’s cycle model for trade studies• Step – 2: Concepts NREC Agile™ Software for refined performance

modeler, maps, and blade design for turbine and compressor

Structural ANSYS Aero

FEA

Brayton Turbomachinery Design Sequence - Readiness: Very Mature

Aerodynamic

1. Cycle studies- Pr, N, η …

2. 1-D geometry definition, based on nondimentional parameters (specific speed, head coefficient…(defines speed and rough geometry, stage count)

3. Mean-line analysis: ηc, ηt, map prediction.

4. 2-D Blade geometry generator: stream-line coordinate methods.

5. 3-D full performance analysis and refinements

8

Mechanical

1. Rotor-dynamic analysis (seals an bearings)

2. Cost analysis trade studies

3. AN2 stress / creep life: scoping studies: material selection

4. Preliminary CAD modeling – for polar characteristics for rotor dynamic analysis & bearing design.

5. Detailed FEA: Thermal structural analysis, blade dynamics

6. Final CAD – manufacturing.

Notes on turbine life• Very low TIT (750°C), blade root

temp <<700 °C• Due to low loading coefficient

(best efficiency) low stressTherefore:• No blade cooling • Solid blades (vs cored)• Generic alloys • Blisks possible if size permits 9

Alloy MAR-M 247

Current thinking: Blisk and fully machined first test articles

Modular Pebble Bed Modular Reactor for X-energy

2010-2012

Closed cycle recuperated gas turbine (He)

Almost half the cost was the alternator & bearings

Mass (kg) 10 500

108663 $10,595,296 $9,663,663

Normalized Cost $/kWe $1,060 $966

Item Mass (kg) Low Prod. Cost High Prod. Cost $/kg

RECUPERATOR 5710 $579,626 $325,149 $102

TURBOMACHINERY 7824 $1,047,357 $864,711 $134

ALTERNATOR AND POWER ELECTRONICS 30833 $4,394,597 $4,141,464 $143

HEAT REJECTION TANKS 34395 $542,642 $362,940 $16

MAIN VESSEL & SUPPORTS 29901 $274,499 $259,362 $9

SYSTEM INSTALL 0 $74,775 $42,439

COOLING TOWERS 0 $3,550,000 $3,550,000

INVENTORY CONTROL SYSTEM 0 $131,800 $117,597

CONTROLS & INSTRUMENTATION

TOTAL 108663 $10,595,296 $9,663,663

Cost at Production Level:

Mass (kg) 10 500

108663 $10,595,296 $9,663,663

Normalized Cost $/kWe $1,060 $966

Item Mass (kg) Low Prod. Cost High Prod. Cost

RECUPERATOR 5710 $579,626 $325,149

RECUPERATOR CORE 3072 $523,155 $285,923

RECUPERATOR TIE ROD 208 $8,664 $4,870

RECUPERATOR CASE 838 $9,872 $7,948

HP EXHAUST MANIFOLD 1591 $37,935 $26,409

NO. CORES 18

TURBOMACHINERY 7824 $1,047,357 $864,711

TURBINE MODULE 3144 $253,132 $190,654

COMPRESSOR MODULE 2487 $200,167 $154,912

SHAFT UNIT 73 $8,100 $6,917

BEARING ASSEMBLY 36 $514,160 $457,585

SUPPORT AND MOUNTING 2084 $30,253 $24,333

FINAL ASSEMBLY 0 $41,545 $30,311

ALTERNATOR AND POWER ELECTRONICS 30833 $4,394,597 $4,141,464

ALTERNATOR 18636 $2,040,120 $1,927,620

MOUNTING 12196 $208,247 $185,966

POWER ELECTRONICS 0.00 $2,146,230 $2,027,878

UTILITY INTERFACE $540,000 $510,222

LOAD BANK $2,160,000 $2,040,889

CABLES AND WIRING $54,000 $51,022

ENCLOSURE $54,000 $51,022

HEAT REJECTION TANKS 34395 $542,642 $362,940

PRESSURE VESSEL 7251 $66,996 $25,078

INTERNAL FIN MODULE 15449 $239,313 $170,639

EXTERNAL FIN MODULE 10784 $221,332 $155,309

INSTALLATION 912 $15,000 $11,913

MAIN VESSEL & SUPPORTS 29901 $274,499 $259,362

VESSEL 24498 $247,920 $234,249

SUPPORT STRUCTURE 5403 $26,579 $25,114

SYSTEM INSTALL 0 $74,775 $42,439

FACTORY ASSEMBLY 0 $15,845 $8,743

RIGGING & TRANSPORT 0 $14,396 $9,124

ON SITE ASSEMBLY 0 $44,534 $24,572

COOLING TOWERS 0 $3,550,000 $3,550,000

DRY COOLING TOWERS & FANS $3,400,000 $3,400,000

COOLANT PUMPS $50,000 $50,000

PLUMBING $100,000 $100,000

INVENTORY CONTROL SYSTEM 0 $131,800 $117,597

COMPRESSOR 0 $105,000 $93,685

AFTERCOOLER 0 $1,200 $1,071

CONTROLS AND PIPING 0 $25,600 $22,841

CONTROLS & INSTRUMENTATION

TOTAL 108663 $10,595,296 $9,663,663

Cost at Production Level:

Mass (kg) 10 500

108663 $10,595,296 $9,663,663

Normalized Cost $/kWe $1,060 $966

Item Mass (kg) Low Prod. Cost High Prod. Cost

RECUPERATOR 5710 $579,626 $325,149

RECUPERATOR CORE 3072 $523,155 $285,923

RECUPERATOR TIE ROD 208 $8,664 $4,870

RECUPERATOR CASE 838 $9,872 $7,948

HP EXHAUST MANIFOLD 1591 $37,935 $26,409

NO. CORES 18

TURBOMACHINERY 7824 $1,047,357 $864,711

TURBINE MODULE 3144 $253,132 $190,654

COMPRESSOR MODULE 2487 $200,167 $154,912

SHAFT UNIT 73 $8,100 $6,917

BEARING ASSEMBLY 36 $514,160 $457,585

SUPPORT AND MOUNTING 2084 $30,253 $24,333

FINAL ASSEMBLY 0 $41,545 $30,311

ALTERNATOR AND POWER ELECTRONICS 30833 $4,394,597 $4,141,464

ALTERNATOR 18636 $2,040,120 $1,927,620

MOUNTING 12196 $208,247 $185,966

POWER ELECTRONICS 0.00 $2,146,230 $2,027,878

UTILITY INTERFACE $540,000 $510,222

LOAD BANK $2,160,000 $2,040,889

CABLES AND WIRING $54,000 $51,022

ENCLOSURE $54,000 $51,022

HEAT REJECTION TANKS 34395 $542,642 $362,940

PRESSURE VESSEL 7251 $66,996 $25,078

INTERNAL FIN MODULE 15449 $239,313 $170,639

EXTERNAL FIN MODULE 10784 $221,332 $155,309

INSTALLATION 912 $15,000 $11,913

MAIN VESSEL & SUPPORTS 29901 $274,499 $259,362

VESSEL 24498 $247,920 $234,249

SUPPORT STRUCTURE 5403 $26,579 $25,114

SYSTEM INSTALL 0 $74,775 $42,439

FACTORY ASSEMBLY 0 $15,845 $8,743

RIGGING & TRANSPORT 0 $14,396 $9,124

ON SITE ASSEMBLY 0 $44,534 $24,572

COOLING TOWERS 0 $3,550,000 $3,550,000

DRY COOLING TOWERS & FANS $3,400,000 $3,400,000

COOLANT PUMPS $50,000 $50,000

PLUMBING $100,000 $100,000

INVENTORY CONTROL SYSTEM 0 $131,800 $117,597

COMPRESSOR 0 $105,000 $93,685

AFTERCOOLER 0 $1,200 $1,071

CONTROLS AND PIPING 0 $25,600 $22,841

CONTROLS & INSTRUMENTATION

TOTAL 108663 $10,595,296 $9,663,663

Cost at Production Level:

12

H2

H3

H4

H5

H1

C1

C2

C3

C4

Helium cycle

SCO2 Recompression Cycle-Top

SCO2 Cycle-Bottom

NHS boundary

IHX

-1

IHX

-2

Emer

gen

cy b

y-p

ass

cir

cuit

Butterfly valve

Start heater

HeliumCO2Water/glycol

Brayton-sCO2 Combined Cycle PCS System

Gen

com

pre

sso

r

turbine

Sole

no

idva

lve

Safe

ty b

y-p

ass

valv

e

Gen

Gen

Fan cooler

Fan cooler

• Economics highly leveraged by cycle efficiency

• Potentially 40 to 50% efficiency

• State of Readiness for sCO2 cycles: low TRL

13

H2

H3

H4

H5

H1

C1

C2

C3

C4

Helium cycle

SCO2 Recompression Cycle-Top

SCO2 Cycle-Bottom

NHS boundary

IHX

-1

IHX

-2

Emer

gen

cy b

y-p

ass

cir

cuit

Butterfly valve

Start heater

HeliumCO2Water/glycol

Brayton-sCO2-ORC Combined Cycle PCS System

Gen

com

pre

sso

r

turbine

Sole

no

idva

lve

Safe

ty b

y-p

ass

valv

e

Gen

Gen

Fan cooler

Fan cooler

• Economics highly leveraged by cycle efficiency

ORC

20%

25%

30%

35%

40%

45%

50%

55%

300 400 500 600 700 800 900

Turbine Inlet Temp, C

Effi

cien

cy

MIT papers

Aspen CaseStudy atPR=4.2

Published SCO2 Efficiency Studies

14

ASPEN Case Study

• Pressure Ratio = 4.17

• Compressor polytropic eff = 0.84

• Turbine polytropic eff = 0.88

• Alternator efficiency = 0.96

• Power Electronics (or gear )

efficiency or 0.97

• Cooling system parasitic = 0.97

• Heat Addition DP/P = 2%

• Recup HX eff = 0.90

& SNLA papers

TIP 250 bar

TOP, bar Efficiency

Split

Fraction

Pressure

Ratio

40 40.84% 0.196 6.25

45 42.39% 0.196 5.56

50 43.89% 0.196 5

55 45.29% 0.191 4.55

60 50.48% 0.326 4.17

65 49.77% 0.315 3.85

70 48.87% 0.288 3.57

75 47.96% 0.258 3.33

80 46.94% 0.206 3.13

85 46.05% 0.169 2.94

90 45.13% 0.098 2.78

95 43.62% 0.005 2.63

100 41.48% 0 2.5

Estimated cost for Combined Cycle PCUHigher vs basic direct cycle, but lowered full power plant cost

Note: Budgetary costs for sCO2 cycle based on rough engineering estimates and not substantiated by suppliers

Unit Number Mass (kg) 10 500

RECUPERATOR -

TURBOMACHINERY 9,708 $880,235 $695,130

ALTERNATOR AND POWER ELECTRONICS 8,393 $1,319,321 $1,244,995

MAIN VESSEL & SUPPORTS 11,213 $102,937 $97,261

SYSTEM INSTALL - $74,775 $42,439

COOLING TOWERS (INSTALLED) - $4,167,391 $4,167,391

INVENTORY CONTROL SYSTEM -

CONTROLS & INSTRUMENTATION -

TOTAL PCS 29,314 $6,544,660 $6,247,216

SCO2 POWER MODULE (no heat addition or rejection HXs) $16,400,000 $11,480,000

INTERMEDIATE HEAT EXCHANGERS 19,320 $1,126,384 $957,426

TOTAL PCS 48,634 $24,071,044 $18,684,643

Power, MWe 15 15

Normalized cost $/kWe 1,592,000$ 1,235,757$

Actually just over 17MW-e

16

A Joint Venture between ESKOM and British Nuclear Fuels Corp./Westinghouse Corporation

PBMR: Direct Cycle He gas-cooled nuclear reactor (2002-2007)

Brayton Energy was sponsored to develop a low cost, strain-tolerant recuperator

17

BRAYTON’s PBMR Recuperator

Shut-off Disk

BRAYTON

Energy, LLC

Factory assembled module,

Recup- welded stack

of cells

Recup cell -

brazed

HP gas interface

We have worked on every aspect of the integrated

PBMR recuperator package

Recup core

w/integral

manifolds

LP gas interface

Recup module 3x6 m

18

Brayton Recuperator PBMR highlights• Compact containment vessel diameter: 2.8 meters

• Factory install recup into Class-1 vessel • Full factory acceptance test• Vessel transport width suitable for highway truck, • Arrives at PBMR power plant needing only external connections.

• No internal support structure (“cradle”)– Recup cores supported from cool HP pipes

• Cumulative damage factor for PBMR maneuvers and full mission profile = 0.0 (infinite fatigue life) – based on 12-mo. of ANSYS analysis

• Demonstrated hermetic pressure boundary and creep resistance exceeding 30-yr life (ongoing full-scale cell tests employing Larsen-Miller time extrapolation)

• Weight: HX core – 29,000 kg (common 304 or 316 stainless)• ½ to ⅓ of Heatric core

• Manufacturing plans for GEA, in Germiston So. Africa

19

Integration and assembly

• Preliminary layout and integration

• Review of specifications vs design - TBD

20

2.8m

5.3m

This integration design requires no internal support structures, as the cores are suspended from the ring manifolds by their integral manifolds.

Annular module, 1 of 4)

PBMR Recuperator Assembly

Recup cores: 61 per row or module4 modules totaling 244 cores

High-pressure (HP) piping and toroidal ring manifolds – delivers cool HP

21

Top of assembly – co-axial HP duct per PBMR specification.

Interconnecting vertical distribution pipes connect feeder to ring manifolds (omitted for clarity)

Cores hang from ring manifold on short rigid HP pipes transitioning to the integral core manifold pipes (50 mm dia,)

Hot flex pipes tolerate differential growth and provide interface to central collector pipe

Ring manifold

HP gas inHP gas outHP gas in

22

Core to core annular seal(keeps hot LP within the annulus and the cooler LP exit on the Class-1 vessel interior surface

Large (2.2m) bellows surrounds core modules on cool side, permitting the cores to move axially with the growth of the central hop HP pipe. This AISI316 bellows was quotes at a price of $5,000.

Hot LP gas enters co-axial pipe at bottom

LP in

LP out

LP out

Class-1 pressure vessel bathed in LP out gas

23

LP Seals bridge core to core annulus.Insulation to fill between cores (omitted for clarity)

Coaxial HP duct – as specified by PBMR

HP Flex piles on hot side – 50 mm dia, 2mm wall thickness

HP –cool intake pipes support core weight

insulation

24

50 mm diameter HP flex pipes staggered.

Compensating bellows and tie bar on cool 106°C HP side).

Insulation

510 C LP gas in

25

Testing in Phase 1- Brayton addressed critical design and life issues

1. Manifold flow distribution measurement and model validation

2. Wavy fin and straight fin friction factor measurements

3. Brazed folded wire matrix pressure drop characterization vs. braze parameters

4. Rupture tests-coupons (at room temp, to qualify manufacturing processes)

5. Rupture tests – cells (at room temp)

6. Long duration creep tests at peak PBMR temps

26

A battery of test performed for PBMR recuperatorTest specimen (52 folds, 100-mesh folded screen)

Suction port

Static pressure taps

Ambient air in port

Rubber sealRubber seal

Test Section volume1100x700x150mm

Microprocessor controller and safety monitor

Gas bottles (N2)

• P = 17MPa

• P = 41.3 MPa

Pressure

control

switches

(Bread-

board)

Regenerative Blower

Manometer Bank

Flow Meter

Cell InletCell Outlet

Regenerative Blower

Manometer Bank

Flow Meter

Cell InletCell Outlet

Brazed high-density formed screen flow test Header & manifold flow distribution measurements

High-temp high-pressure cell creep

High pressure destructive tests for braze strength characterization

27

• Photo shows SN048 and

SN056 in creep test rig

• Photos taken at

approximately 600 hours

@ 17.2 MPa, 510°C

• Two additional cells (S/N

83 and 85 were later

installed at 24.2 MPa gas

pressure.

• All four cells are still

operating, each with over

2400hrs accumulated –

Brayton will maintain

experiment to 8,000 hrs

High Temp creep testing - full scale Recup cells (5 mm x 480 mm), integral manifold omitted for these tests

Cells pressurized through capillary tubes with N2

28

0

50

100

150

200

250

300

350

400

450

500

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

Time, HRS

MP

a

ASME Code N-47-30, Section III,

Div 1, ASME Boiler & Pressure

Vessel Code, Creep Stress

Rupture

σ_F/A for SN83, S/N85

σ_F/A for SN79, S/N83

σ_F/A for SN048, SN056

F/A fin stress for pressure allowable

PBMR spec,

30-year

Design point,

30-years

P=6MPa

σ_F/A=29 MPa

510 C

Yield,Special Metals

Four samples past 2000-hour mark in early March 07 – Test still in progress; Based on Larsen-Miller time-temp extrapolation of this data – cells will easily meet 30-year creep requirement

(17.2MPa)

(24.1 MPa gas pressure)

29

• The Larson-Miller theory of creep enables the extrapolation of metal failure data to different pressures, temperatures, and times. Applying the known theory to a sample failing at our design conditions of 262,800 hours, 510 C (783K) and 6MPa gas pressure (28 MPa fin tensile stress), enables the prediction of failures at other conditions. Since it is impractical to conduct a creep test at 6MPa, 510C and wait for 30 years to prove viability, Larson-Miller provides a means for predicting the relative pressure increase associated with shorter time intervals. Applying this theory for theses conditions is the basis for extrapolation shown on the previous slide. The reference line in red, emanating from the theoretical design point predicts shorter rupture times, at increasing pressures (or fin stress) for a comparable safety margin. A failure below this reference line indicates that the target conditions are unattainable. Operating above the reference line implies some measure of safety margin.

Explanation of creep life extrapolation

30

PBMR Recuperator cost modelProcess $/Cell

Parting sheets Materials 1.85

Parting Sheet processing 0.07

Braze materials 1.52

Braze application 1.13

Fin materials 3.47

Fin processing 1.60

Manifold Rings materials 1.01

Manifold Rings Processing 3.14

Cell Assembly 1.29

Braze processing (furnace charges) 1.59

Braze processing labor 2.09

Cell to core weld assembly 1.42

Total cell cost 20.17

Number of cells 80820

Total Factory Cost, $ 1,630,427

• Price excludes tooling, and is appropriate for second full recup order.

• Based on material prices quoted in March 2007 from ZAPP rolling mill

• Labor rates based on US rate of $75/hr

The design point for each

Recuperator (2 each)

Primary inlet temperature, C 512.5

Primary inlet pressure, kPa 2977

Primary mass flow, kg/s 101.1

Secondary inlet temperature,

C 108.5

Secondary inlet pressure, kPa 8927

Secondary mass flow, kg/s 95.54

Effectiveness 97.26%

Pressure drop (sum dp/p) 1.00%

Cycle pressure ratio 3.00

$, USD Weight , kg $/kg

Recuperator core & tooling 1,630,427 29,000 56.22

Manifolds, flex pipe, bellows 199,384 11,846 16.83

Vessel , 2.8 m x 6 m

Total, US$ 1,829,811

Power, electric, MW 120 from 400 MWthermal

Inflation 2007-2016 1.16 US labor statistics

Normalized cost, FY2016

$/kWe 17.69

Recup module, less

vessel

The Recuperator represents a small fraction of the PBMR cost

2 each required

31

A Joint Venture between ESKOM and British Nuclear Fuels

Corp./Westinghouse Corporation

Noble gas-cooled nuclear reactor

Brayton turbomachinery and heat exchangers

Cost ~ 35 $/kWe

BRAYTON performed

preliminary design of

the Intermediate Heat

Exchanger “IHX” for

AREVA/Framatome

(2005/2006)

850 C IHX• State of Readiness: High • Costs: please call