APEX Mechanical Design Considerationsfor Liquid Wall Concepts

presented by B. Nelson

APEX MeetingSandia National Laboratory

July 27, 1998

Presentation Outline_______________________________________________________________________

• Status of Activities for mechanical design and availability group

• General Design Requirements

• Description of design point and evaluation criteria progress

• Availability / Maintenance / Vacuum Boundary Considerations

• Status of FRC configuration

Status of Activities________________________________________________________________________

Progress:

• Took first pass at incorporating thick liquid wall in ARIES RS configuration

• Assembled evaluation criteria data input for one case

• Developed FRC configuration CAD model for comment

• Developed draft plan of activities for FY99

Plan:

• Continue to assist design advocates with specific designs

• Continue to review vacuum topology

• Identify availability issues and possible improvements for specific designs

Goal and Scope____________________________________________________________________

General Goal:

Develop attractive Fusion Power Technology system

Fusion Power Technology, FTP, is defined to include*:

• Vacuum environment• Plasma exhaust• Power extraction from plasma particles and radiation• Power extraction from neutrons and secondary gammas• Tritium breeding• Tritium extraction and processing• Radiation protection (shielding + confinement)

APEX is focused on power extraction, but other items must be considered

* ref. M. Abdou, APEX kick-off meeting, Oct. 15, 1997

General Mechanical Design Approach________________________________________________________________________

• Develop Requirements

• Develop Generic configurations

- ARIES - RS- FRC

• Produce strawman design for each concept

- Identify main features of concept- Provide 3-D layouts with space blocked out for piping, special components, etc.- Identify changes to generic configuration, if any- Determine if any requirements must be relaxed

General Design Requirements________________________________________________________________________

Function Requirement Value/Goal

Power Extraction Neutron Wall Load

Surface Heat Flux

7 MW/m^2 avg*10 MW/m^2 peak*

2 MW/m^2*

Tritium Breeding Self Sufficient TBR > 1

Shielding Radiation exposure of coils (insulation)Nuclear heating of coils (sc cable)Reweldable confinement boundary

< 1x109 Rad< 1kW/m3

< 1 appm He

Vacuum Compatible with plasma- Base partial pressure, non-fuel- Base pressure, fuel (H,D,T)

< 1x10-9 Torr< 1x10-7 Torr

Safety confinement boundaries At least 2

* Values are minimum goals for steady state operation

Other Design Assumptions________________________________________________________________________

Function Requirement Value/Goal

Plasma Exhaust Divertor required to remove helium

Penetrations Plasma Heating Power Density - NBI - ICH

Diagnostics

~4 MW/m2

~6 MW/ m2

TBD

Operating Parameters Pulse LengthNumber of pulsesDisruptions

Steady State< 3,000

TBD

Availability Maximize total availability Aplant > .75

Ablanket/FW > .98

ARIES RS Parameters and APEX modifications_______________________________________________________________________ref http://aries.ucsd.edu/PUBLIC/ariesrs.html

ARIES APEX

Major Radius 5.52 sameMinor Radius 1.38 samePlasma Aspect Ratio 4 sameNumber of Sectors 16 same

Fusion power (MW) 2170.5 ~ 4000Neutron Power (MW) 1735.5 ~ 600Alpha power (MW) 433.1 ~ 3400

Fusion power density (MW/m3) 6.38 ~ 12

Average neutron load (MW/m2) 4.03 7 peak neutron load (MW/m2) 5.67 10

Average FW surface heat flux (radiative), MW/m2 0.4 1.5Peak FW surface heat flux, MW/m2 0.47 2

Liquid Wall Concept_______________________________________________________________________

• Thin layer of fast flowing liquid intercepts surface heat flux

• Thick layer of slower flowing liquid intercepts neutron flux

• Liquid walls have big payoff if they work, since leaks will no longer be an issue

Goals:

Nothing inside vacuum vessel but liquid

Cooler fast stream to keep vapor pressure low

Hotter thick stream for more efficient heat recovery

Sufficient shielding to protect vacuum vessel, allow re-welding

Simplified, modular maintenance

Mechanical Design Approach for Liquid Wall concept_______________________________________________________________________

• Start with ARIES-RS as basic configuration, but try to adapt the geometryto liquid metal flow characteristics

• Try to incorporate features for thinner, fast moving FW stream

• Keep several options open for slower, thicker stream

- fluid wall – “pockets design” (GMD)- semi permeable walls that maintain head pressure (CLIFF - A)- conventional design with solid boundary (CLIFF – B)

• Evaluate various metal and structure combinations from mechanical design and availability standpoint

• Hold off on the magnetically restrained option as information becomes available

Mechanical Design Features for Liquid Wall concept_______________________________________________________________________

The following features must be included:

• Convective layer forming device

• Convective layer collecting system

• Concept for starting system

• Concept for providing heating and diagnostic penetrations

• Vacuum pumping concept

• Divertor concept

• Piping arrangement

ARIES device as modified for Liquid Wall_______________________________________________________________________

Convective Layer Forming Device_______________________________________________________________________

• Located at top of blanket/maintenance module

• Performs several functions

- Splits stream into inboard and outboard paths- Distributes stream uniformly in toroidal direction- Imparts sufficient velocity (at least 20 m/s) in poloidal direction- Does not interfere with shielding function at top of machine

• Is designed for independent maintenance as a unit for refurbishment and maintenance of exposed surfaces, nozzles

Convective Layer Collecting System / Divertor_______________________________________________________________________

• First wall liquid flows to collection trough in bottom of machine

- Trough surface is separately cooled and- Can be removed independently from primary module and- Directs flow toward divertor pumping duct

• First wall forms part of divertor surface

• Design appears possible only with single null divertor

Divertor / Vacuum Pumping_______________________________________________________________________

• Opening in fluid is formed with deflection device, which can be removed independently from primary blanket/shield module

• Liquid flows as open stream down pump duct

- 1 meter I.D.- ~1/3 full for <5 m/sec^2 velocity

• Pumping duct is protected with removable sleeve

• Exiting liquid from first wall can be

- pumped into blanket region (flibe)- routed through separate power conversion loop (lithium)

Thick Liquid Blanket - Pockets_______________________________________________________________________

• Pocket design uses multiple fast streams to form convective pocket

- liquid in pocket is primarily restrained by feed stream- fast first wall stream prevents any leakage toward plasma

• Liquid enters top front of pocket, spirals to center of pocket and then toroidally

• Minimum amount of structure in breeding blanket regions

• Minimum amount of structure in high fluence / high damage zone

• Pockets are made from refractory alloy, eg tungsten

• Each pocket must be individually fed from manifold system

Piping, GMD/flibe case_______________________________________________________________________

• Separate circuits are needed for feeding each flow pocket

• Piping is withdrawn with blanket/shield module assembly

Pipe # and o.d., minboard outboardREGIONno. i.d. no. i.d.

First Wall – inlet 2 .4 2 .4 outlet na na na naBlanket /shieldinlet 8 .22 8 .28 outlet 2 .4 4 .40Divertor collector, Inlet na na 1 .28 outlet na na 1 .28v.p. duct deflector, inlet na na 1 .28 outlet na na 1 .28

Performance Criteria for GMD Flibe/Flibe DesignConcept: Thick Liquid Wall ( Pockets )

Surface Heat Flux (Peak) 2 Mw/m2

Assumptions: Surface Heat Flux (Average) 1.5 Mw/m2

Neutron Wall Load (Peak) 10 Mw/m2

Neutron Wall Load (Average) 7 Mw/m2

TF Coil W inding

Tf Coil Cas e

Vacuum Ve s s e l Sh ie ld Blank e t Firs t W all Firs t W all Blank e t Sh ie ld

Vacuum Ve s s e l

TF Coil Cas e

TF Coil W inding

Materials %Coolant liq He water flibe/40 flibe/100 flibe flibe flibe flibe water liq He

20 40 100 100 100 tbd (100) 40Structure Cu,Nb-Sn SS316 SS316 FSS 0 0 0 0 FSS SS316 SS316

100 80 60 60 80 100VoidThickness (cm) 98 9.1-10.1 20 53 40 2 2 40 85 20 18-20 99.5

Nuclear Heating (w/cm3)Coolant Min 0.001 2.80E-04 5.37 54.6 70.21 60.4Coolant Max 0.011 0.013 50.4 60.2 64.8 6.7Structure Min 7.40E-04 4.20E-03 3.44 5.60E-04 4.50E-05Sturcture Max 4.70E-04 3.13E-03 4.10E-02 7.7 0.042 4.70E-04 3.30E-05

Nuclear Damage 30yrs 30yrs 30yrs 3 yrs 3yrs n/a n/a 3yrs 3 yrs 30yrs 30yrs 30yrsdpa 0.00552 0.0138 1.23 18.57 62.73 0.252 0.00276 0.000375appm He 0.126 8.07 62.73 0.51 0.0051

Outboard RegionInboard Region

7.376.976.95

4.094.07

3.67

Performance Criteria for GMD Flibe/Flibe Design , cont’d

TF Coil W inding

Tf Coil Cas e

Vacuum Ve s s e l Sh ie ld Blank e t Firs t W all Firs t W all Blank e t Sh ie ld

Vacuum Ve s s e l

TF Coil Cas e

TF Coil W inding

Coolant Velocity (m/s)MinimumAverage 0.4 20 20 0.4Maximum

Coolant Pressure (MPa)Inlet <1e-4? <1e-4?Outlet <1e-4? <1e-4?

Coolant FlowMass Flow (kg/s) 1138 1138 2140 2140Vol Flow (m3/s) 0.5 0.5 1.17 1.17Pumping Power (MW)

Temperatue (C)Coolant In 522 515 515 522Coolant Out 557 521.1 522.7 566Structure MinStructure Max

Stresses (Mpa)PrimaryTotal

PipingDiameter I.D. (cm) 22 40 40 28Quantity per sector 8 2 2 8

Inboard Region Outboard Region

Maintenance, Availability and Vacuum Topology_______________________________________________________________________

Strawman design point focused on the following goals:

1. Modular maintenance for everything, with increased ease of access for high risk andhigh damage components – avoid maintenance inside machine, if possible

2. High tolerance of minor failures, such as leaks from shield, blanket region(All liquid wall concepts may have this feature)

3. Protect the vacuum vessel and coil set, as these are life-time components

Maintenance, Availability and Vacuum Topology, cont’d_______________________________________________________________________

Vacuum Vessel must be protected

- Rewelding limit for vessel of 1 appm

If vacuum vessel must be breached to maintain coils, it is prudent that it can be a localrepair, and not require the full replacement of the vessel.

- Limit structural damage to allow use of non-irradiated properties for design

We should try not to complicate design, licensing, and maintenance by cooking thefirst safety barrier

Mechanical Design Group will continue to review vacuum topology issue

Remove Forming, Diverting and Collecting Cassettes

Remove Internal Blanket Shield module______________________________________________________

Design Issues for Liquid Wall concept_______________________________________________________________________

A few of the issues include:

• How to move ~105 kg/s of Li or Flibe in and out of the machine

• How to separate the thin and thick flow regimes

• How to start the two streams

• Does stream develop a toroidal velocity component and come off of the inboard wall?

• How do the passive stability currents move the surfaces around?

• How to protect nozzles and deflectors from plasma, and

• How to protect liquid from exposed surfaces (ie excessive vapor pressure if liquid hits hot spots)

• What are the failure modes and what can be done to compensate?

FRC Concept Configuration_______________________________________________________________________

An FRC configuration has been modeled based on input from Ralph Moir

FRC Concept Configuration_______________________________________________________________________

• Overall length (as drawn) is 72 m, plasma is 8 m long and 2 m in diameter

FRC Concept Configuration –Flibe region_______________________________________________________________________

Summary

• Liquid metal concepts require minor mods to ARIES RS Design

- Changed from double to single null- Modified shape of first wall- Expanded maintenance port

• GMD pocket concept incorporated into modified ARIES RS

- Components/piping fit within ARIES envelope- Entire blanket/shield structure can be withdrawn as single module, or- High exposure components can be separately maintained- Many issues remain

• Assembled performance criteria data input for one GMD case

• FRC configuration model is now available