Corrosion and Deuterium Pickup in Zr-2.5Nb: Twenty Years ... · Twenty Years of In-Reactor Testing at the OECD Halden Boiling Water Reactor H.M. Nordin, R. Szőke ... Two vacuum arc

-1-UNRESTRICTED / ILLIMITÉ

Corrosion and Deuterium Pickup in Zr-2.5Nb:

Twenty Years of In-Reactor Testing at the OECD

Halden Boiling Water ReactorH.M. Nordin, R. Szőke

19th International Symposium on Zirconium in the Nuclear Industry

May 19 - 23, 2019, Manchester, UK.


Outline

1. Introduction

• CANDU Reactor

• Pressure Tube

• Pressure Tube Fabrication

• Corrosion and Deuterium Ingress

2. Experiment

• Materials

• Test Loop

3. Results

4. Summary

UNRESTRICTED / ILLIMITÉ -3-

CANDU Reactor


CANDU Reactor Fuel Channel

Pressuretube

Calandriatube

Feederpipe

Temperature

Flow

Fast neutron flux

[D]

•Temperature: 250°C – 310°C

•Pressure: 10 MPa

•Flux: 0 – 3.5x1017 n/m2s


Pressure Tube Fabrication1990’s

Zirconium Feedstock

Two vacuum arc melts (Double Melt)

ingot

1960 – 1980’s

Press forge at 1015°CRotary forge at 815°C

Heat to 1015°C and β-Quench

Extrude at 815°C

Cold draw 27%

Steam Autoclave at 400C for 24 hours

1980’s

1970’s

Four vacuum arc melts (Quad Melt)

ingot

Press forge at 1015°CRotary forge at 815°C

Heat to 1015°C and β-Quench

Extrude at 815°C

Cold draw 27%


Pressure Tubes• Historically, extensive research programs have been under

taken to fabricate improved pressure tubes:

• ~ 1960’s started investigating Zr-2.5Nb – improved mechanical properties and corrosion

• ~ 1980’s introduced β-quenching – improve strength

• ~ 1990’s introduced quad melting and lowered initial hydrogen content – reduce Cl and F for improved fracture toughness

• ~ 2000’s increased Fe concentration to 1080 ppm and reduced C concentration to 80 ppm – improve corrosion, deformation and fracture toughness


Pressure Tubes• The extrusion process is known to result in microstructure and

texture variations along the pressure tube which in turn affects deformation, mechanical properties, oxidation and deuterium pickup.


Corrosion and D Ingress• Corrosion and the associated deuterium ingress may be life

limiting degradation mechanisms in Zr-2.5Nb pressure tubes.

• Corrosion and deuterium uptake in pressure tubes can be influenced by:

- environmental factors (flux, temperature or pH).

- material properties (microstructure, microchemistry, texture and state of the β-phase) which are influenced by fabrication processes.

• To support pressure tube improvement programs, in-reactor corrosion and deuterium ingress studies were conducted at the OECD Halden Boiling Water Reactor over a 20 year period.

• Effect of environment and fabrication variables investigated:

- ingot melting (double melted or quadruple melted)- non--quenched versus -quenched- cold work (12% or 27%)- pH- In-flux versus out-flux


Materials• Corrosion test coupons were machined from twenty-one different

Zr-2.5Nb pressure tubes.

- variations in fabrication history (e.g. β-quenched) and minor element concentration, illustrating the development history of pressure tube fabrication processes.

• The machined coupons tested had different surface finishes:

Machined coupons ~ 10 mm wide, 30 mm long and 1 mm thick

Machined

PickledHF, HNO3 and H2SO4 solution

Pickled + Pre-filmed400°C steam for 24 hours

Machined + Pre-filmed400°C steam for 24 hours

Note: Many variables!


Schematic Diagram of In-Flux Test Loop 9

• Operates under CANDU HTS conditions (pHa 10.2-10.8)

• Two independently heated in-flux test channels, three out-flux autoclaves

• Temperature range: 250°C – 335°C

• Neutron flux: 3-5x1013 n/cm2/s

• Ratio of thermal flux\fast flux: 2:1


Oxygen and Deuterium Pickup

• Oxidation kinetics were linear after 150 days.


Effect of Flux on Oxide Growth Rate

• The in-flux oxide growth rate tends to be greater than the out-flux oxide growth rate (P-value = 0.0004).

• Enhancement of in-flux oxide growth rate dependent on initial microstructure and surface finish.


• No effect of flux on deuterium pickup (P-value = 0.96).

Effect of Flux on D Pickup Rate


• Oxide growth and deuterium pickup rate similar between Kroll and electrolytic.

• Larger extruded tube front-back differences in Kroll ingots.

Ingot Production


Effect of Ingot Melting

• Quad melting result in lower deuterium ingress rates.


Effect of β-Quenching

• β-quenching results in lower deuterium ingress rate.


Effect of β-Quenching

Non-β-Quenched β-Quenched

• More uniform grain structure in β-quenched material.• Curly nature of non-β-quenched grains may cause β-Zr filaments to be

oriented perpendicular to free surface leading to faster oxidation along these filaments.


Comparison of Fabrication Methods

• Fabrication modifications reduced oxide growth rate.

1960 - 1980 1980 - 1990 1990 - 2000 2000 - 2005


Comparison of Fabrication Methods

1960 - 1980 1980 - 1990 1990 - 2000 2000 - 2005

• Deuterium ingress reduced by a factor of 5.


Discussion• A large number of confounding variables in tests making

comparison of data and interpretation of the results difficult.

• The synergistic interactions between fabrication processes, microstructure, texture, the state of the β-phase and the resulting pressure tube properties are difficult to assess.

• With the tube improvements, the net total concentration of hydrogen isotopes has been significantly reduced making Zr-2.5Nb pressure tubes much less susceptible to the deleterious effects of hydrides on fracture properties.


Conclusions• Research programs undertaken to improve pressure tube

properties were successful in reducing corrosion and deuterium ingress.

• Deuterium ingress reduced by a factor of 5.

• This reduction should make Zr-2.5Nb pressure tubes much less susceptible to the deleterious effects of hydrides on fracture properties.


Acknowledgements• CNL’s (formerly AECL’s) in-reactor corrosion test program lasted for

approximately 20 years. • The contributions of many individuals need to be acknowledged:

• From AECL/CNL (including former employees): V. F. Urbanic, R.A. Ploc, G. McDougall, I. J. Muir, G.A. McRae, A. A. Bahurmuz, A.J. Elliott, A. Shaddick, S. Bergin, V. Hilton, C. Davis, M. Seguin, D. Wilkins, R. MacLeod, A. Britton, R. Stuthers, P. Sullivan, D. Irvine, R. Beier, J. Hamel, Y. Andrews and M. Godin.

• From the Halden Reactor Project (including former employees): M. A. McGrath, K-L Moum, I. Thoresen, H. Devold, H. Valseth, H. Thoresen, C. Helsengreen, M. Lundgren, K-W. Eriksen, C. Vitanza.


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Corrosion and Deuterium Pickup in Zr-2.5Nb: Twenty Years ... · Twenty Years of In-Reactor Testing at the OECD Halden Boiling Water Reactor H.M. Nordin, R. Szőke ... Two vacuum arc