Effects of High Dose Neutron Irradiation on Reduced-activation Ferritic/Martensitic Steels

Effects of High Dose Neutron Irradiation on Reduced-activation

Ferritic/Martensitic Steels

T. Hirose

, Y. Katoh

, H. Tanigawa

, K.G. Field

, H. Sakasegawa

, B.K. Kim

, M. Ando

, D.T. Hoelzer

, L. Tan

, L.L. Snead

, R.E. Stoller

1

Japan Atomic Energy Agency

2

Oak Ridge National Laboratory

This work is part of the U.S. DOE – JAEA collaboration on Fusion Materials.

Research sponsored by the Office of Fusion Energy Sciences, U.S. Department of Energy, and Japan Atomic Energy Agency under contracts DE-AC05-00OR22725 and

NFE-10-02779, respectively, with UT-Battelle, LLC. ¹

OUTLINE

1. Background

– Reduced activation ferritic/martenitic steel (RAFM), F82H – Irradiation testing for F82H

2. Experimental

– JAEA-DOE collaborative research

– Non-instrumental capsules, JP-28 & JP-29 – Post-irradiation tensile tests

3. Results

4. Discussion

5. Summary

Reduced-Activation Ferritic/Martensitic (RAFM) Steel

Fe - 8

9Cr - 1 ∼ 2W - V,Ta (F82H, JLF-1, EUROFER, CLAM, ARAA etc.)

 Fully tempered martensitic steel, based on Mod9Cr (Gr.91: Fe 9Cr-1Mo V, Nb).

 Good swelling resistance was demonstrated as the candidate material for FBR fuel cladding material.

 Mo replaced with W, Nb replaced with Ta to reduce activation.

 8 to 9 Cr was selected due to its minimum ductile-brittle transition temperature (DBTT) shift after irradiation.

 Compared to the other candidate fusion blanket structural material, RAFM has sound technological background on its reproducibility and weldability.

A. Kohyama, J. Nucl. Mater. 233-237 (1996) 138

Swelling resistance Reduced activation Post-irradiation DBTT shift

obtained by Charpy impact test

Irradiation tests for F82H

• Post irradiation tensile tests on F82H have been conducted over 20 years under Japan/US collaboration.

• Irradiation hardening is significant at 300 ^oC, above 400^oC small hardening or softening.

• BOR-60 data shows tendency of saturation in hardening beyond 30 dpa at 300 ^oC.

• Available high-dose data is limited to fast breeding reactor such as FFTF and BOR-60.

• High dose irradiation tests using a mixed spectrum reactor, High Flux Isotope Reactor (HFIR) has been conducted at 300, 400 and 500 ^oC.

Post irradiation tensile tests on F82H

4

Irradiation test matrix for F82H

*E. Gaganidze, J. Aktaa, Fusion. Eng. Des. 88 (2013) 118– 128.

High dose irradiation tests using HFIR

• The specimen has been prepared from a certain batch of F82H-IEA heat (5,000kg). Same material

• Neutron irradiation has been conducted in the High Flux Isotope Reactor, HFIR at Oak Ridge National Laboratory.

Same reactor

• Common holder design was employed for 6 capsules.

 Irradiation data with minimized disturbance.

Capsule Dose (dpa) Temp. (^oC) Note

JP-26 9 300/400/500 Hardening level is comparable w/ instrumented capsule JP-27 21 300/400 Hardening is greater than FFTF at 400^oC

JP-28 87 300/400/500

The highest dose on RAFM in HFIR

JP-29 87 300/400/500

JP-30 20 300/400/650 RAFM joints (to be tested) JP-31 20 300/400/650 RAFM joints (to be tested)

Specimen positions in JP-28, JP-29

Position Specimen Temp. (oC)

1 Tensile 400

2 Bend-bar 500

3 Tensile 300

4 Compact 300

5 Bend-bar 300

6 Compact 400

7 Tensile 400

8 Compact 400

9 Tensile 500

10 Bend-bar 300

11 Bend-bar 300

12 Bend-bar 300

13 Bend-bar 300

14 TEM 300

Position Specimen Temp. (oC)

1 TEM 400

2 Tensile 400

3 Tensile 500

4 Bend-bar 300

5 Compact 300

6 Bend-bar 300

7 Tensile 300

8 Bend-bar 400

9 Bend-bar 500

10 Tensile 300

11 Bend-bar 300

12 Tensile 300

13 Tensile 300

14 TEM 500

JP-28 JP-29

Horizontal mid-plane

Tensile and toughness

specimen have been positioned to receive

equivalent dose.

JP28 & JP29

• A pair of non-instrumented capsule was prepared for high dose irradiation.

• Specimen from 400 and 500 ^oC showed rusty surface, it was found at the previous capsules.

300 ^oC irradiated (JP29 #13) 400 ^oC irradiated (JP28 #7) 500 ^oC irradiated (JP28 #9) ⁷

JP-28 JP29

Start April, 2005 Jan., 2005 Finish July, 2013 July, 2013 Temperature (^oC) 300/400/500 300/400/500

Max dose (dpa) 87 87

# of reactor cycles 46 46 Exposure (MWd) 91569 92334

EFPD 1077 1086

Summary of JP-28 & JP-29

Experimental procedure, PIE

• Materials

– F82H IEA: 0.1C -8Cr-2W-0.2V-0.04Ta – F82H mod3: 0.1C -8Cr-2W-0.2V-0.09Ta

– F82H 1.4%Ni: 0.07C-8Cr-2W-0.3V-0.02Ta-1.4Ni

»

Ni58 and Ni60 isotopes were prepared

Transmutation Helium (11appm/dpa )

• Post irradiation tensile tests

– SS-J3 (0.76

x 1.25

x 5

mm

) sheet tensile specimen with shoulder loading

– Tensile tests were conducted at irradiation temperature in vacuum

– Cross-head speed controlled at 0.2%/s in gauge

RESULTS OF POST IRRADIATION TENSILE

TESTS AT IRRADIATED TEMPERATURE

Tensile properties of F82H (>80dpa)

• All specimen demonstrated hardening.

• Hardening was significant at lower temperature.

• Tensile properties of mod3 (0.1%Ta) is comparable with IEA.

• Ni58 including 900appm He demonstrated significant hardening at 300^oC, but drastically decreased with temperature.

Tensile properties of F82H (>80dpa)

• All specimen demonstrated less elongation.

• Although Ni58 steel which includes 900appm of helium demonstrated minimum ductility, Ni60 kept its ductility >10 %.

• The minimum elongation (7.5 %) was found at 300-400 ^oC, where unirradiated F82H show minimum elongation.

T_irr = T_test T_irr = T_test T_irr = T_test

Dose dependence of Hardening

• >80dpa, all specimen demonstrated hardening even above 400

o

C where softening was observed at the specimen irradiated in the FFTF.

• Hardening at 300

C demonstrated tendency of saturation.

• Hardening increased with dose above 400

C (HFIR).

*E. Gaganidze, J. Aktaa, Fusion. Eng. Des. 88 (2013) 118– 128. 12

Helium effects on Hardening

• F82H w/ 1.4%Ni58 steel produced up to 920appm of He.

–

At 300

C, larger hardening than the others.

• He w/ immobile vacancy enhanced the hardening.

–

At 400

C, no difference between 240 and 920ppm He.

–

>80 dpa above 400

C, hardening is smaller than the others.

Dose dependence of Ductility loss

14 TP Reactor Gauge

length

Gauge

width Thick.

RBT JMTR 25 mm φ 4mm

SS-3 HFIR,

JMTR 7.5 mm 1.5 mm 0.75 mm SS-J FFTF 5 mm 1.2 mm 0.25 mm SS-J3 HFIR 5 mm 1.2 mm 0.75 mm

RBT

Gauge cross section

SS-J SS-J3

Dose dependence of Ductility loss

• >80dpa, ductility is below unirradiated level. No saturation was observed.

• Specimens w/ less aspect ratio, SS-3 & SS-J give less ductility.

• The minimum ductility (7.5 %) was found at 300-400 ^oC, where unirradiated F82H demonstrates the minimum ductility.

• Total elongation around 300-400 ^oC should be monitored as well as embrittlement at <300 ^oC. It might limit the use of RAFM.

HFIR vs FFTF (dpa rate)

• No significant difference in damage rate is observed between FFTF and HFIR.

• Difference in damage rate between HFIR and FFTF is within factor of 2.

• Difference between HFIR and FFTF?

* A.M. Ermi, et al., DOE/ER-0313/18 (1995) 27-62. ** J.P. Robertson, et al., DOE/ER-0313/21 (1996) 249-252. 16 dpa dpa

/MWD Irradiation period (h) FFTF/MOTA

2B* 20 4.4E-04 5.2E+03 HFIR JP-27 21.2 9.1E-04 7.5E+03 FFTF/MOTA

2A* 39 5.1E-04 8.1E+03 HFIR

JP-14** 33.9 8.7E-04 - FFTF/MOTA

2A+2B 59 4.0E-04 1.3E+04 JP-28 & 29 87 9.5E-04 2.4E+04

Irradiation parameters

Softening or Hardening above 400 ^o C

HFIR irradiated materials demonstrated hardening FFTF irradiated materials demonstrated softening

• Softening

– Thermal Aging: Recovery, Segregation (loss of solute)

• Hardening

– Defects induced by irradiation – Irradiation induced segregation – Transmutation (W => Os)

– Lower irradiation temperature

• Increase of heat transfer between specimen and holder, but surface oxide was observed at specimen irradiated at higher temperature

• Decreasing gap between holder and sleeve?

• Post irradiation properties reflects the results of competing processes above.

• Detailed analysis on microstructure and chemical composition including gas element are required.

HFIR vs FFTF

R.E. Stoller, L.R. Greenwood., J. Nucl. Mater. 271-272 (1999) 57-62.

• No significant difference in damage rate is observed between FFTF and HFIR.

• Effects of neutron energy?

dpa dpa

/MWD Irradiation period (h) FFTF/MOTA

2B 20 4.4E-04 5.2E+03

HFIR JP-27 21.2 9.1E-04 7.5E+03 FFTF/MOTA

2A 39 5.1E-04 8.1E+03 HFIR JP-14 33.9 8.7E-04 -

FFTF/MOTA

2A+2B 59 4.0E-04 1.3E+04 JP-28 & 29 87 9.5E-04 2.4E+04

Irradiation parameters

W186

HFIR vs FFTF

R.E. Stoller, L.R. Greenwood., J. Nucl. Mater. 271-272 (1999) 57-62.

• No significant difference in damage rate is observed between FFTF and HFIR.

• Effects of neutron energy?

• Ex) W transmutation to

Os (HFIR) or Re (FFTF)

L.R. Greenwood et al., J. Nucl. Mater. 212-215 (1994) 635-639

dpa dpa

/MWD Irradiation period (h) FFTF/MOTA

2B 20 4.4E-04 5.2E+03

HFIR JP-27 21.2 9.1E-04 7.5E+03 FFTF/MOTA

2A 39 5.1E-04 8.1E+03 HFIR JP-14 33.9 8.7E-04 -

FFTF/MOTA

2A+2B 59 4.0E-04 1.3E+04 JP-28 & 29 87 9.5E-04 2.4E+04

Irradiation parameters

Impact of Re and Os to tensile properties

• Reduction of W seems small impact on tensile properties of martensitic steel.

–

If W in laves phase (reduction of solute W) transmuted to Os, it could raise the strength.

*R.L. Klueh et al. / J. Nucl. Mater. 279 (2000) 91-99. ₂₀

Summary

• Reduced activation ferritic/martensitic steel, F82H were

irradiated up to ~87 dpa at 300, 400 and 500

C in the HFIR.

Post irradiation tensile tests have been conducted at irradiation temperature.

–

Irradiation hardening & loss of ductility were observed even at 400 and 500

C

• It is noted specimen irradiated in the FFTF demonstrated softening at the temperature.

• Difference between FFTF and HFIR should be investigated including transmutation effects.

• Lower irradiation temperature due to deformation of capsule material is possible.

–

Hardening was significant in the specimen irradiated at 300

C.

The increment gradually decreased w/ dose, but the strength was obviously larger than previous works.

–

Ductility after irradiation was minimum at 300-400

C, and dose

dependence of ductility loss does not show saturation up to

87dpa.

Summary (continued)

– F82H w/ Ni58 isotope, which has 900 appm of transmutation helium, demonstrated significant hardening at 300

C. However, the difference was diminished at 400 and 500

C.

• The difference between Ni58 and Ni60 should be

carefully investigated using microstructural analysis.