Page 1/31 CHATS-AS October 9-11, 2013 | Cambridge, MA © 2013, ITER Organization Process Analyses of...

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CHATS-AS October 9-11, 2013 | Cambridge, MA© 2013, ITER Organization

Process Analyses of ITER Toroidal Field Structure Cooling Scheme

R. MAEKAWA, S. TAKAMI*, A. IWAMOTO*, H.S. CHANG, A. FORGEAS, M. CHALIFOUR, L. SERIO

IO/CEP/PED/CSE*National Institute for Fusion Science

At CHATS-AS

October 9, 2013

Disclaimer: The views and opinions expressed herein do not necessarily reflect those of the ITER Organization

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Outline

• Background

• Objective

• Introduction– ITER cryogenic system– ACB-ST and ST modeling

• Nominal operation

• Mitigation

• Disruption

• Conclusion

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ITER TOKAMAK

TF coil/structureNb3Sn/SS: 18

CS Nb3Sn: 6

PF/CCNbTi: 6/63

Cryostat24 m high x 28 m dia.

~4400 tons for ST can be used as thermal damper

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Background

• ITER; – Achieve Q>10 Production of 500MW fusion power– DT phase starting from 2027

– 15 MA baseline -> Substantial dynamic heat load from TOKAMAK ~50 kW variations in 1800s• Eddy current • AC losses• Nuclear heating

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Background

• Substantial Dynamic Heat Load during POS ~50 kW

• Cryoplant has to demonstrate its robustness– Countermeasure

A Cryoplant operation in terms of “Boosting” (40-100kW)B “Mitigation” to surpass peak-to-peak heat load

– Plan A: Cryoplant boosting• Difficulties to balance three CBs operated in parallel

to adjust the refrigeration power of 50 kW in 1800s– Plan B: Mitigation

• Utilization of massive TF ST as thermal buffer– Plan C??

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Objective; Mitigation scheme implementation• Achieve (provide) a quasi-static operating

condition for Cryoplant (plant friendly)

• “Mitigation” with TF-ST, applying different process controls to Auxiliary Cold Box (ACB-ST)

– Developed dynamic simulation model as implementing a classical Proportional-Integral (PI) Control

• ALL ANALYSES ARE BASED ON THE CRYOPLANT POINT OF VIEW

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ITER Cryogenic System

• 75 kW @4.5K (40-110 KW ADAPTATION)

TF PF/CC

CCB

ST

ST

Cold Compressor

SHe LHe heat exchanger

Cold Circulator

Clients

CB1 CB2 CB3

Cryoplant

PFTF

CC

CP

CP

CTCB

CS

CS

LHe Tank LHe Subcooler

ACB

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ACB-ST & ST

ACB-ST

Supply Cryoline (55m)

Return Cryoline (49m)

Supply Feeder (68m)

Return Feeder (38m)

Transit time of SHe~300s

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TF ST Cooling Pipe Layout

BU(20)~17m long

Outer Board Leg: Connected to Gravity Support

BP(14)~18m

AP(20)~16m

AU(20)~19m

Cross section of AU&AP

• Cooling pipe layout for BU

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Massflow Rate for each Segment

# of channel

L (m)

Transit (s)

m (g/s) Re f h(W/m2-K)

Total m (g/s)

AP 20 16.0 38.4 2.7 1.18e5 0.018 616.11 54.0

BP 14 17.7 42.5 2.7 1.18e5 0.018 616.11 37.8

AU 20 19.0 112.0 1.1 4.81e4 0.021 300.39 22.0

BU 20 17.2 101.4 1.1 4.81e4 0.021 300.39 22.0

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ACB-ST w/ ST

• Nominal Operation– PI control

• LHe level (SHE feed)• Subcooler pressure

(LP Return)

• Mitigation– “Inferential” control

1. Speed variation2. HX bypass3. ST bypass

SHeReturn

HX bypass

LICPIC

ST bypassSupply

Return

FIC

AP20

AU20

BU20

BP14

1

2

3

41 2

3

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Modeling

• One cooling channel w/ massive weight piping

• Four spatial divisions with different heat inputs

• SHe Cooling Module is based on 1st law of thermo dynamics

Integrated Cooling Channel in each Segment (h and A_heat

transfer)

BU(1)

BP(1)

AP(1)

AU(1)

dt

dEWQ

dAnvP

edVet

WQ

SCVC

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Heat Load

• Eddy current & Nuclear heating on AP1 & AP3– 17.4 kW nuclear heating to define the upper bound

(13.8kW as baseline)

AP1

AP2

AP3

AP4

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NOMINAL OPERATIONCope w/ Dynamic Heat Load by Adjusting Cooling power

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Nominal Operation-processArrangement of cooling circuit w/ process control

• HX bypass & ST bypass are closed!

• PIC is implemented at LP Return line

SHeReturn

AP20

AU20

BU20

BP14

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Simulation Result-Nominal operation

• 14.2MJ of thermal energy deposition in each POS

• Variation of heat loads & LHe level in the

subcooler

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SHE Loop-Nominal operation

• SHe loop behavior – T & P variations & m variation in each segment

• 1

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Summary-Nominal Operation

• Peak-to-peak variation of heat loads (~10 kW)

w/ 14.2MJ of thermal energy deposition

• Good tracking performance of LHe level and subcooler pressure regulations

• Impact on massflow rate is acceptable for cold circulator operation and TF coil operation; temporary reduction of flow rates

• Feasibility of operation depends on Cryoplant

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MITIGATIONReducing the impact of Cryoplant operation

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SHeReturn

AP20

AU20

BU20

BP14

2

Mitigation; Circulator Speed

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SHeReturn

AP20

AU20

BU20

BP14

2

Mitigation-HX Bypass

HX massflow change

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Mitigation-ST Bypass

Massflow at ST

• Two disturbances for

CC– POS and m regulations

SHeReturn

AP20

AU20

BU20

BP14

3

•

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Mitigation

• Replace peak profile to Flat Topped Peak

• Manipulation of 14.2MJ in 30 min.

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Variation in HX and/or ST

Control Action-MitigationSpeed & HX bypass ST bypass with Supply

valve

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ST Cooling Effect-MitigationEffective cooling for

ST Loop T variation at ST

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Summary; Mitigation

• Three schemes demonstrate comparable results for Mitigation

• Speed variation should be the first choice to implement for the process control

– Pumping energy saving– Constant ST inlet temperature; TF Coil operation– Production of LHe during “Dwell” (as providing the

constant refrigeration power from Cryoplant)

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Disruption• Thermal energy deposition ~10 MJ in 1sec.

• Heat load to Cryoplant is not acceptable– Compressor, turbine, cold compressor trips– Exceed the HX performance

Cooling loop; HX bypass

Not compliant

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Disruption; summary

• The same control logic as Mitigation cannot be applicable in the case of disruption

• Dedicated control logic has to be developed and implemented

– To be compliant with a project requirement

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• Impact from m

regulation

Cold Circulator Operation

Disruption-Nominal ST bypass-Mitigation•

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Conclusion• Nominal operation can be sustained based on

the classical PI control (as long as Cryoplant cope w/)

• Mitigation schemes demonstrate comparable

result

• Circulator speed variation should be implemented based on the energy saving, constant inlet temp. to ST and more LHe accumulation in the Tank

• Circulator operation is enclosed in the high efficiency envelope

• ST bypass demands wider operation field on cold circulator

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Open Issue

• Dedicated control is required in the case of DISRUPTION

• Risk of Cryoplant shutdown– Trip of expansion turbine, compressor station, cold

compressor

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