A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016

Self-passivating smart tungsten alloys as an intrinsic safety for the future fusion

power plant

A. Litnovsky, T. Wegener, F. Klein, Ch. Linsmeier, M. Rasinski and J.W. Coenen

Slide 2 of 15A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3‐5, 2016

0 20 40 60 80 100Time, days

Temperature*,oC

200

400

600

800

1000

1200

Motivation

*Final Report of the European Fusion Power Plant Conceptual Study, EFDA RP-RE 5.0, 2005

Conceptual study of the fusion power plant

Mobilization of radioactive elements must be prevented

Accidental loss of coolant:

peak temperatures of first wall

up to 1200 °C due to nuclear decay heat

Additional air ingress: formation of highly

volatile WO3 (Re, Os)

>1000°C in a reactor

1000 m2 surface

Evaporation rate: 10 -100 kg/h

Radioactive WO3 may leave hot vessel

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 3 of 15

Intrinsic safety

Picture is the courtesy of DIFFER NL

Intrinsic safety is the most reliable measure

No immediate access to water and/or coolant No electricity Difficult logistics Lack of manpower

In case of major accident:

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 4 of 15

Smart tungsten alloysAdjust their properties to the environment conditions1

Normal operation (730°C->550°C2):Formation of tungsten surface bydepletion of alloying element(s)

due to preferential sputtering by plasma

structural material

W & alloying element(s)

Tungsten

Accidental conditions:(air ingress, up to 1200°C)

Formation of protective barrier layer

Tungsten-based “smart” alloys

Behave like tungsten during plasma operation

Suppress oxidation during accident

structural material

W & alloying element(s)

Protective layer

PlasmaAtmosphere

2Yu. Igitkhanov et all, Design Strategy for the PFC in DEMO Reactor, Report-Nr. KIT-SR 7637.

1F. Koch and H. Bolt, Phys. Scr. 128(2007)100

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 5 of 15

Choice of alloying elements

+ Low volume increase by oxidation

Good adhesion of the oxide to the alloy

High melting point of alloys and oxides

Cr, Ti, Mn, Y

Requirements Low neutron activation

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 6 of 15

Yttrium as an active element

[1] K. Przybylski, A. J. Garratt-Reed, and G. J. Yurek. Grain boundary segregation of yttrium in chromia scales. Journal of The Electrochemical Society, 135(2):509517, 1988.

[2] M.F. Stroosnijder, et al. The inuence of yttrium ion implantation on the oxidation behaviour of powder metallurgically produced chromium. Surface and Coatings Technology, 83:205 211, 1996. 9th International Conference on Surface Modication of Metals by Ion Beams.

[3] N. Birks, G.H. Meier, and F.S. Pettit, Introduction to the High-Temperature Oxidation of Metals. Cambridge University Press, 2006.[4] R. Buergel, H. J. Maier, and T. Niendorf. Handbuch Hochtemperatur-Werkstofftechnik. PRAXIS, 2011[5] I. A. Kvernes, The Role of Yttrium in High-Temperature Oxidation Behaviour of Ni-Cr-Al Alloys, Oxidation of Metals, Vol. 6, No. 1, 1973

Y at the grain boundaries1,2

Y at the oxide-alloy interface2,3

Reactivity towards impurities3

Smaller grains1,3,4

Thinner oxide layer

Oxidation pegs, good adhesion1,3,4

Oxidation inwards to the surface3

Less pores5

More stable oxide

Y

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 7 of 15

High temperature oxidation: tungsten vs. smart alloys

Best passivation behavior of W-Cr-Y alloy

0 20 40 60 80 100 1200,0

0,1

0,2

2,0

2,51000oCW: Oxidation and evaporation

W-Cr-Y:• Even lower oxidation rate • No delamination/evaporation

W-Cr-Ti:Performance improvementW-Cr:

• Reduced oxidation rate • Delamination after 15´

Mass change, mg/cm2

Exposure time, min.

Oxidation constants:

W:

0.52

W-Cr-Y:

3*10-6

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 8 of 15

Structure of protective layer

W-Cr W-Cr-Y

Smooth thin oxide layer in W-Cr-Y

No visible pores

Pores

Cr2O3

Cr2WO6

Internal oxidation

80 vol.% Ar + 20 vol.% O2 1 bar 1000oC 15’

No W-containing oxides

Suppressed internal oxidation

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 9 of 15

High temperature oxidation of smart alloys: first results

Oxidation time, minutes

W-Cr fails

Mass change, mg2*cm-4

W-Cr-Y oxidizes faster

at 1200oC

Still parabolic behavior of W-Cr-Y after 15 minutes@1200oC

1000oC and 1200oC

4 6 8 10 12 140,00

0,05

0,10

0,15

0,20 W-Cr W-Cr-Y@1200C W-Cr-Y@1000C

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 10 of 15

Oxidation in steam and humid air

W oxidizes immediately

W remains rather inert in humid argon

Smart alloy reacts with water No water cooling in DEMO?

No pure tungsten in DEMO?

0 20 40 60 80 1000,0

0,1

0,2

0,8

1,0

W in humid air W with steam Smart alloy in humid air Smart alloy with steam

Exposure time, min.

Mass change, mg/cm2

Pure W vs.

W-Cr-Y smart alloy

Steam:Ar + 70%

humidity@40oC

Humid air:80 vol.% Ar

+ 20% vol.% O2+70% humidity

@40oC

Exposure at 1000oC, 1 bar

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 11 of 15

Smart alloys: future challenges

Technology

Smart alloys

Mechanical properties

Plasma performance*

Engineering constraints

Other safety interfaces

* A. Litnovsky et al., "Smart alloys for a future fusion power plant: first studies under stationary plasma load and in accidental conditions“, 22nd PSI, Rome, Italy, May 30 - June 3, 2016

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 12 of 15

Safety interfaces: examples

Power plant integrity Reliability of structural elements Stability of PFCs

This presentationCorrosion of coolant pipes3

In-vessel and

ex-vessel LOCA in DEMO1,2

Possible hazards Tritium in VV and in coolant W-dust Activated corrosion products Volatile radioactive rests of PFCs

Joint effort required

[1] M. Nakano et al., Fus. Eng. And Design 89 (2014) 2028[2] M. Nakano et al., Nucl. Fus. 55 (2015) 123008[3] S. Wikman et al. 25 IAEA FEC St. Petersburg, 2014 MPT/P4-23

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 13 of 15

Summary

New advanced materials are required for future power plant

Safety aspect is of prime importance

Tungsten-based smart alloys: a promising combination

of intrinsic safety and plasma performance

Further qualification is underway

First results are encouraging:

Suppressed oxidation of tungsten

Stability of smart alloy system

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 14 of 15

Outlook

Manufacture of bulk samples

Tests of plasma performance

Mechanical properties: optimization

Implementation of advanced technologies: Wf/W

Working on safety interfaces

A. Litnovsky et al., Smart alloys, First IAEA TM on the Safety, Design and Technology of Fusion Power Plants, Vienna, Austria, May 3-5, 2016 Slide 15 of 15

Thank you