Why is the study of FW/Blanket/Divertor Components Reliability and Lifetime a DEMO R&D Gap?

NCT Discussion Group, FNT-7: Alice Ying, Neil Morley (UCLA)

What is the Broad Issue?

FW/blanket/divertor components performance, reliability, and lifetime must lead to DEMO availability goal ~50-70%, tritium self-sufficiency, high grade heat generation for electricity production, and sufficient radiation shielding for components and personnel.

What Is the R&D gap?

No FW/blanket module or system has ever been built or tested – potential interdependent and synergistic phenomena and failure mechanisms have not necessarily been identified or understood.

Plasma facing components that are capable of withstanding continuous high surface heat load of ~10 MW/m2

are yet to be tested at the Demo-level materials, high temperature, transients,and irradiation.

Blanket example: Typical vision of a ceramic-breeder–based blanket module.

FW/Blanket systems are complex and have many integrated functions, materials, and interfaces

Tritium BreederLi2TiO3 (<2mm)

First Wall

(RAFS)

Neutron MultiplierBe, Be12Ti (<2mm)

Surface Heat FluxNeutron Wall Load

High-P, High-T He coolant

077-05/rs

1. D-T fuel cycle tritium self-sufficiency in a practical system(from El-Guebaly and Sawan, UW)

depends on many physics and engineering parameters / details: e.g. fractional burn-up in plasma, tritium inventories, FW thickness, penetrations, passive coils, doubling time

• Tritium production, extraction and inventory in the solid/liquid breeders under actual operating conditions

• Tritium permeation, control and inventory in blanket and PFC

2. Identification and characterization of performance, failure modes, effects, and rates in blankets and PFC’s • Thermo-magnetic-mechanical-vibration loadings and

response of blanket and PFC components under normal and off-normal operation

• Materials interactions, compatibility, and chemistry• Radiation damage and Plasma driven synergistic effects• Lifetime of blanket, PFC, and other fusion nuclear

components

3. Remote maintenance with acceptable machine shutdown time.

Summary of R&D Issues for FW/Blanket/Divertor

Design Verification & Reliability Data

Theory/Modeling

BasicSeparateEffects

MultipleInteractions

PartiallyIntegrated

Integrated

Property Measurement

Phenomena Exploration

Non-Fusion Facilities

Experiments in non-fusion simulation facilities are essential to establishing FW/Blanket/Divertor scientific foundations …

Design Codes

Component

•Fusion Env. Exploration•Concept Screening•Performance Verification

Testing in Fusion Facilities

(various non neutron test stands, fission reactors and accelerator-based neutron sources)

… and critical to understand & interpret complex, synergistic experiments in the integrated fusion environment

Thermo-mechanical Tritium High Heat Flux Magnetic Plasma/Tokamak …

ITER will provide the first opportunity, through the test blanket module (TBM) program, to perform low fluence integrated environment and phenomena experiments

Vacuum Vessel

Bio-shield

A PbLi loop Transporter located in

the Port Cell Area

He pipes to TCWS

2.2 m

Vision of TBM System

ITER has allocated 3 ITER equatorial ports (1.75 x 2.2 m2) for TBM testing, and space in the reactor hall and TCWS building for support systems

ITER will test and develop the knowledge base for low temperature, water-cooled copper FW and divertor designs. However, DEMO will require different materials, designs, and temperatures.

ITER-TBM can be used tostudy synergistic effects among FW/blanket phenomena and provide data to improve models and benchmark simulation codes.

TBM experiments in ITER can provide a bridge between laboratory and NCT experiments.

There is currently no ITER program for testing advanced divertor designs

A NCT Facility Is Unique in Filling the FW/Blanket/Divertor Reliability and Lifetime Gap in the Following Ways

Provide a true fusion environment ESSENTIAL to activate mechanisms that drive coupled phenomena, integrated behavior, and prototypical failure modes; and thus allow development of engineering performance and growth of reliability. The requirements for testing nuclear components are estimated as:

NWL 1-2 MW/m2, ~ 6 MW.y/m2, ~ 10 m2 test area, and high surface heat load (SHF ~0.5 / 10 MW/m2 for FW / divertor).

Long pulse / continuous plasma operation Large module to sector size tests for prototypic geometry

Meet testing needs with practical machine and cost: reasonable fusion power / tritium consumption high base availability and capacity for fast replacement of failed test components

Performing these tests in large fusion device (e.g. ITER, early DEMO) leads to large tritium consumption and cost

e.g., A 1000 MW fusion power facility, even at a low availability will consume the projected CANDU tritium supply in just a few years

THEREFORE, NCT should be done at low power, <150MW (hence driven plasma), or breed/recover much of its own T

0

5

10

15

20

25

30

1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045

Year

Pro

ject

ed O

nta

rio

(O

PG

) T

riti

um

Inve

nto

ry (

kg)

CANDU Supply

w/o Fusion

1000 MW Fusion

10% Avail, TBR 0.0

ITER-FEAT(2004 start)

Backups…

• Initial exploration of coupled, prompt phenomena in a fusion environment

• Uncover unexpected synergistic effects, Calibrate non-fusion tests

• Impact of rapid property changes in early life

• Integrated environmental data for model improvement and simulation benchmarking

• Develop experimental techniques and test instrumentation

• Screen and narrow the many material combinations, design choices, and blanket design concepts

• Uncover unexpected synergistic effects coupled to radiation interactions in materials, interfaces, and configurations

• Verify performance beyond beginning of life and until changes in properties become small (changes are substantial up to ~ 1-2 MW · y/m

2)

• Initial data on failure modes & effects

• Establish engineering feasibility of blankets (satisfy basic functions & performance, up to 10 to 20 % of lifetime)

• Select 2 or 3 concepts for further development

• Identify lifetime limiting failure modes and effects based on full environment coupled interactions

• Failure rate data: Develop a data base sufficient to predict mean-time-between-failure with confidence

• Iterative design / test / fail / analyze / improve programs aimed at reliability growth and safety

• Obtain data to predict mean-time-to-replace (MTTR) for both planned outage and random failure

• Develop a database to predict overall availability of FNT components in DEMO

Sub-Modules/Modules

Stage I

Fusion “Break-in” & Scientific Exploration

Stage II Stage III

Engineering Feasibility & Performance

Verification

Component Engineering Development &

Reliability Growth

Modules Modules/Sectors

D E M O

1 - 3 MW-y/m2 > 4 - 6 MW-y/m2

0.5 MW/m2, burn > 200 s1-2 MW/m2,

steady state or long pulseCOT ~ 1-2 weeks

1-2 MW/m2,steady state or long burn

COT ~ 1-2 weeks

0.1 – 0.3 MW-y/m2

Role of ITER TBM

Gap?

Stages of FW/Blanket/Divertor Testing in Fusion Facilities

Fluence

NWL

Exp type

077-05/rs

10

Blanket Functions (including first wall)

A. Power Extraction– Convert energy of neutrons and secondary gamma rays into heat

– Absorb plasma radiation on the first wall

– Systems to Extract the heat (at high temperature, for energy conversion)

B. Tritium Fuel Replacement– Tritium breeding, must have lithium in some form

– Tritium extraction and control systems

C. Radiation Shielding of the Vacuum Vessel

D. Physical Boundary for the Plasma– Physical boundary surrounding (surface facing) the plasma, inside

the vacuum vessel

– Share space with / Provide access for plasma heating, fueling

– Part of greater electomagnetic environment – conducting materials, ferromagnetic materials, induced currents

077-05/rs

Fusion environment is unique and complex:multiple fields and varied environments

Neutrons (fluence, spectrum, temporal and spatial gradients)

• Radiation Effects (at relevant temperatures, stresses, loading conditions)

• Bulk Heating• Tritium Production• Activation

Heat Sources (magnitude, gradient)

• Bulk (from neutrons and gammas)• Surface Heat Flux (steady, MARF, Disruption)

Particle Flux (energy and density, gradients)

Steady/Blobs Unsteady

Magnetic Field (3-component with gradients)

• MHD from Steady Fields with and without Plasma Current

• Currents from unsteady fields/disruptions

Mechanical Forces• Pressurization• Thermal stresses• EM forces• Weight• Vibrations

Chemical Environment• Hydrogen, Transmutation,

Corrosion

Multi-function, multi-material, multi-interface blanket in multi-component field environment leads to:

- Multi-Physics, Multi-Scale Phenomena - Synergistic effects

Blanket systems are complex and have many integrated functions, materials, and interfaces

Tritium BreederLi2TiO3 (<2mm)

First Wall(RAFS, F82H)

Neutron MultiplierBe, Be12Ti (<2mm)

Surface Heat FluxNeutron Wall Load

[18-54] mm/s

PbLi flow scheme

[0.5-1.5] mm/s

There are Many Blanket Concepts Proposed Worldwide They all have feasibility issues and attractive features

Material or Configuration Options

Structural Materials Reduced Activation Ferritic Steel Alloys (including ODS), Vanadium Alloys, SiC Composites

Coolant Media Helium, Water, Liquid Metals, Molten Salts

Breeder MediaLithium-Bearing: Ceramic Breeders (Li4SiO4, Li2TiO3, Li2O); Liquid Metals (Li, PbLi, SnLi); Molten Salts (FLiBe, FLiNaBe); Varying enrichments in Li-6

Neutron Multiplier Materials Beryllium, Be12Ti, Lead

MHD/Thermal Insulator Materials SiC composites and foams, Al2O3, CaO, AlN, Er2O3, Y2O3

Corrosion and Permeation Barriers

SiC, Al2O3, others

Plasma Facing Material Beryllium, Carbon, Tungsten alloys, others

HX or TX Materials Ferritic Steels, Refractory Alloys, SiC, Direct Gas Contact

Blanket Configurations He or Water Cooled Ceramic Breeder/Be; Separately Cooled, Self-Cooled, Dual-Coolant LM or MS

Ceramic Breeder Configurations Layered, Mixed, Parallel, Edge-On (referenced to FW)

Liquid Breeder Configurations Radial-Poloidal Flow, Radial-Toroidal Flow, others

MHD/Thermal Insulator Config. Flow Channel Inserts, Self-Healing Coatings, Multi-Layer Coatings

Structure Fabrication Routes HIP; TIG, Laser and E-beam Welding; Explosive Bonding; Friction Bonding; Investment Casting; and others

Tritium breeding blankets are complex, integrated Tritium breeding blankets are complex, integrated systems critical to the feasibility of D-T fusion energysystems critical to the feasibility of D-T fusion energy

He-cooled RAFS FW

Poloidal flowPbLi channel

Dual-Coolant PbLi Liquid Breeder Module

He-cooled RAFS FW

Be Pebbles

Purge gas pipe

Helium-Cooled Li2TiO3 Ceramic Breeder Module

SiC FCIs

The Blanket provides the mechanisms by which: – tritium is generated for

fuel self-sufficiency – high grade heat is extracted for

efficient energy production

Breeding blankets are complex, heterogeneous, highly integrated systems, with: – Multiple functions, materials and

material interfaces– Integrated Plasma facing FW, tritium

breeder, neutron multiplier, specialized insulators and permeation barriers, structure, and high temperature coolant

Yet, no fusion blanket has ever been built or tested. ITER has always been planned as the facility to begin blanket testing.

Ceramic breeder pebbles

All blanket concepts have feasibility issues!

Simulation capabilities continue to advance and can play a larger role

Example – 3D MHD PbLi flow through and expansion maniflold

17-44% flow mismatch between center and side channels (controlled by MHD)

Ha = 929, Re = 1500, N = 575 (based on Parallel Channel Half-Width)

Electric current

Stream linesVelocity profiles

Component Number

Failure rate in hr-1

MTBF in years

MTTR for Major failure, hr

MTTR for Minor failure, hr

Fraction of failures that are Major

Outage Risk Component Availability

Toroidal Coils

16 5 x10-6 23 104 240 0.1 0.098 0.91

Poloidal Coils

8 5 x10-6 23 5x103 240 0.1 0.025 0.97

Magnet supplies

4 1 x10-4 1.14 72 10 0.1 0.007 0.99

Cryogenics 2 2 x10-4 0.57 300 24 0.1 0.022 0.978

Blanket 100 1 x10-5 11.4 800 100 0.05 0.135 0.881

Divertor 32 2 x10-5 5.7 500 200 0.1 0.147 0.871

Htg/CD 4 2 x10-4 0.57 500 20 0.3 0.131 0.884

Fueling 1 3 x10-5 3.8 72 -- 1.0 0.002 0.998

Tritium System

1 1 x10-4 1.14 180 24 0.1 0.005 0.995

Vacuum 3 5 x10-5 2.28 72 6 0.1 0.002 0.998

Conventional equipment- instrumentation, cooling, turbines, electrical plant --- 0.05 0.952

TOTAL SYSTEM 0.624 0.615

Assuming 0.2 as a fraction of year scheduled for regular maintenance. Demo Availability = 0.8* [1/(1+0.624)] = 0.49 (Blanket Availability must be .88)

DEMO Availability of 50% Requires Blanket Availability >85%(Table based on information from J. Sheffield’s memo to the Dev Path Panel)