HTGR Technology Course for the Nuclear R l t C i i

HTGR Component Technology –

Regulatory Commission May 24 – 27, 2010HTGR Component Technology

Steam Cycle Power Conversion SystemHTR Training Course Module 10bModule 10d

Reactor Cavity Cooling System

Lew LommersLew LommersAREVA

1

Outline

• RCCS functions and requirementsq• Passive heat removal in modular HTGRs• RCCS configurationg• RCCS design concepts• RCCS performance

2

RCCS System Functions and Requirements

• Normal operation– Control cavity concrete temperaturesControl cavity concrete temperatures– Cool reactor vessel (for some concepts)

• Accident conditions– Control cavity concrete temperatures– Control reactor vessel temperatures– Residual heat removal

• Passive operation during accidents (typical)• Safety-related heat removal system (typical)• Redundant loops (typical)

3

Outline

• RCCS functions and requirementsq• Passive heat removal in modular HTGRs• RCCS configuration• RCCS design concepts• RCCS performance

4

Overview of Passive Decay Heat Removal in Modular HTGRs

• In reactor vessel– Conduction– Radiation– Convection

( i )(pressurized)– Heat capacity

• In reactor cavity– Radiation– Convection

• In RCCS– Conduction– Convection– Evaporation

5

apo a o

Outline

• RCCS functions and requirementsq• Passive heat removal in modular HTGRs• RCCS configurationg• RCCS design concepts• RCCS performance

6

General RCCSConfiguration Considerations

• RCCS heat absorber structures shield cavity wall surrounding reactor vessel active core height

Air ducts– Air ducts– Panels– Stand pipes

• RCCS fluid circulates through heat absorber structures to remove heat from cavity

• RCCS fluidRCCS fluid– Air– Water

RCCS i l ti f t h• RCCS isolation from atmosphere– Open to atmosphere– Separated by HX

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• Passive and/or active operation

Outline

• RCCS functions and requirementsq• Passive heat removal in modular HTGRs• RCCS configuration• RCCS design concepts

– MHTGR– NP-MHTGR– PBMR-DPP

AREVA– AREVA• RCCS performance

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RCCS Concepts

• A large variety of possible RCCS conceptsA large variety of possible RCCS concepts

• Current vendor approaches provide examplespp p p

9

Overview of Air-Cooled RCCS Concept

10

MHTGR RCCS Concept

• Air-cooled• Natural circulation• Multiple flow pathsp p• Intake/exhaust

structure to mitigate t l ff texternal effects

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MHTGR RCCS Arrangement

• Staggered riser channels create “black” surface

• Riser channels form t f it part of cavity

boundary

• Leaks provide Leaks provide escape path

• No loss of coolant

• Activation of air impurities considered during design

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during design

NP-MHTGR RCCS Concept

• Water loop in cavity

• Heat pipes transfer heat to air in chimneychimney

• Redundant loops

• All natural • All natural circulation

• Head requirements • Head requirements for water and air loops leads to tall t t

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structure

PBMR-DPP RCCS Concept

• Water-cooledBoil-off tanks

• Standpipes surround vessel

• 18 independent circuits

1 t k– 1 tank– 4 standpipes

• Active and passive • Active and passive modes

Stand Pipes

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PBMR-DPP RCCS Water Curtain Arrangement

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PBMR-DPP RCCS Active Mode

From EPCC

Steam outlet to atmosphereFilter

AB

P

MODULE ROOF

NRV

COMMON INLET HEADER

A

H

J

W

W

TANK

NRV

To EPCC C

N

Y

KCRAWLWAY

TANK ROOM

COMMONOUTLETHEADER

D G

F

TANK ROOMUPPER CAVITY

RADIATION SHIELDING FLOOR

E

F

LOWER CAVITY

ONLY ONE OF THE

RCCS ACTIVE MODE

16

ONLY ONE OF THEFOUR STANDPIPESARE SHOWN FOR

CLARITY

PBMR-DPP RCCS Passive Mode

From EPCC

Steam outlet to atmosphereFilter

AB

P

COMMON INLET HEADER

MODULE ROOF

NRV

H

J

W

W

TANK

NRV

To EPCC C

N

Y

KCRAWLWAY

TANK ROOM

COMMONOUTLETHEADER

D G

F

TANK ROOMUPPER CAVITY

RADIATION SHIELDING FLOOR

RCCS PASSIVE MODE

E

LOWER CAVITY

ONLY ONE OF THEFOUR STANDPIPES

RCCS PASSIVE MODE

17

FOUR STANDPIPESARE SHOWN FOR

CLARITY

AREVA RCCS Concept

Water Storageand Heat

ExchangerExchanger

Forced flowOutlet

Headers

• Water-cooled system• Redundant loops• System in red is safety-related

Natural Convection Flow System in red is safety related

– Operates in normal and accident modes

– Natural circulation driven

Panel wall Cavity Cooler

Reactor Vessel

• System in black is non-safety– Operates during normal

operationF d i l ti

Inlet Headers

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– Forced circulation

AREVA RCCS Panel Wall Concept

• Cavity lined with ypanels of welded “finned” tubes

• Comparable to panels for HTR-Modul and HTR-Modul and NP-MHTGR

Wall panel sectionPanel tube cross section

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Wall panel section

Outline

• RCCS functions and requirementsq• Passive heat removal in modular HTGRs• RCCS configurationg• RCCS design concepts• RCCS performance

20

Overall RCCS Performance Factors

• Performance for each function– Vessel heat removal

Cavity “cooling”– Cavity cooling– Concrete surface protection

• Heat removal mechanisms– Thermal radiation (~80%)– Convection (~20%)

• Overall reactor heat removal– Depends on reactor size and operating temperature– Typically 1-2 MWt during normal operation– Typically 1-3 MWt at accident peakyp y p

• Local effects– Local reactor effects– RCCS discontinuities

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– RCCS discontinuities

RCCS Operating Modes

• Normal operation• Accident conditions• Accident conditions• Single loop operation• Active cooling• Active cooling• Passive cooling• Dryout (and refill)• Dryout (and refill)

– Typically BDBE• Failed RCCSFailed RCCS

– Typically BDBE

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Performance Sensitivity

• RCCS heat removal rate is similar during normal operation and accidentsnormal operation and accidents– On-line monitoring of RCCS performance

confirms system status• Accident fuel temperatures are insensitive to

RCCS performancel i i • Vessel temperatures are more sensitive to

RCCS performance but still not a strong functionfunction

• Reactor cavity concrete temperatures are a strong function of RCCS performance

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g p

Other Considerations

• Failure modes– Leaks– Blockage

Dryout– Dryout• Environmental effects

– Emissivity– Emissivity– Cavity atmosphere

• Performance monitoringPerformance monitoring– Overall heat removal– Local temperatures

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Summary

• RCCS maintains cavity wall and reactor vessel temperaturestemperatures

• RCCS is a simple system• A wide variety of potential RCCS A wide variety of potential RCCS

configurations is possible• Fuel temperatures are insensitive to RCCS

performanceperformance• Concrete temperatures are a strong function

of RCCS performancep• Normal operation provides confirmation of

system status

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