Influence of neutron irradiation parameters on swelling and mechanical properties of stainless steels - materials

of BN-350 fuel assembly ducts

O.P.Maksimkin, M.N.Gusev, K.V.Tsai, O.G.Romanenko, L.G.Turubarova, N.S.Silnyagina, O.V.Tivanova

Almaty, Kazakhstan Republic, 2005

Laboratory of the materials physical-mechanical

properties investigations, maksimkin@inp.kz

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Report contents

• Mechanical properties of investigated steels• Influence of damage dose rate on microstructure

and swelling of investigated steels. • Peculiarities of plastic deformation of highly

irradiated materials.

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Investigated materials

•08Cr16Ni11Mo3•12Cr18Ni10Ti

поток нейтронов

Т, оС

280 450

Object of investigation – hexagonal shroud of fuel assemblies Sample’s sizes:

2020.3mm.

Neutron flux

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Irradiation condition for investigated steels

Assembly, mark.08Cr16Ni11Mo3

N-214(2)

08Cr16Ni11Mo3

V-300

08Cr16Ni11Mo3

V-33712Cr18Ni10Ti,

N-214(1)

0Dose, dpa [T,C] 15.6 [337°] 17.1 [354°]

Damage rate, dpa/s 4.810-8 1.610-7

+500Dose, dpa [T,C] - 11.0 [346°] 12.1 [354°] 7.1 [309°]

Damage rate, dpa/s 2.010-7 2.610-7 2.210-7

-500

Dose, dpa [T,C] 7.08 [309°] 10.8 [302°] 11.9 [305°]

Damage rate, dpa/s 2.210-8 1.910-7 2.610-7

-900Dose, dpa [T,C] 1.27 [281°]

Damage rate, dpa/s 410-9

-1200

Dose, dpa [T,C] 0.25 [280°]

Damage rate, dpa/s 810-10

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Experimental equipment and investigation techniques

Uniaxial tensile mechanical test. (definition of 02 В, full).

Transmission and scanning electron microscopy (concentration and morphology of radiation defects, swelling value).

Metallography and microhardness measurement.Magnitometry and optical extensometry.

Laboratory of the materials physical-mechanical properties investigationsLaboratory of the materials physical-mechanical properties investigations, INP NNC RK, INP NNC RK

Influence of irradiation on mechanical properties of 08Cr16Ni11Mo3 steel

0

200

400

600

800

1000

1200

1400

0 5 10 15 20

dose, dpa.

yiel

d a

nd u

ltim

ate

stre

ss, M

Pa

0

2

4

6

8

10

12

14

16

18

0 5 10 15 20

dose, dpa

elong

ation

, %

B

02

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Correlation between yield stress and microhardness

0

200

400

600

800

1000

1200

0 100 200 300 400 500

Micrihardness, kg/mm^2

Yie

ld s

tres

s, M

Pa

iniBusby et. All(JNM, v.336,2005)

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Changes in density of irradiated 08Cr16Ni11Mo3 steel

7,82

7,84

7,86

7,88

7,9

7,92

7,94

7,96

7,98

0 2 4 6 8 10 12 14 16 18

fluence, dpa

dens

ity,

g/c

m3

N-214(2)

V-300+500

V-337+500

V-300-500

V-337-500

0,25%

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Swelling of irradiated 08Cr16Ni11Mo3 steel

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0 2 4 6 8 10 12 14 16 18

fluence, dpa

swel

ling,

%

N-214(2)

V-337V-300

"low" dpa rate

"high" dpa rate

T<310 C

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Voids in irradiated 08Cr16Ni11Mo3 steel

N-214, «-900», 1.27 dpa., 410-9dpa/s N-214(2), «-500», 7.08 dpa. 2.210-8

N-214(2), «0», 15.6 dpa. 2.210-8dpa/sТВС «V-337», 11.9 dpa, 2.610-

7dpa/s

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Voids in irradiated 12Cr18Ni10Ti, assembly N-214(1)

50 nm

Dose 0.67 dpa,Dose rate 0,1210-8 dpa/s,Tirr = 281°С

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Influence of dose rate on yield stress of 08Cr16Ni11Mo3

0

5

10

15

20

0,0E+00 5,0E-08 1,0E-07 1,5E-07 2,0E-07 2,5E-07 3,0E-07 3,5E-07

dose rate, dpa/s

do

se

, dp

a 1010960

920

871

914

550711

low dose rate high dose rate

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Peculiarities of plastic deformation and fracture of high irradiated samples

SEM image of fracture surface for specimen from «-1200mm» mark (08Cr16Ni11Mo3 steel).

The deformation relief develops in zone of localized deformation

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Method of mark extensometry for miniature irradiated samples

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Distribution of strains and stresses on on deformed sample of 08Cr16Ni11Mo3 steel

σист,кг/мм2

Рабочая длина образца

ε, %

Рабочая длина образца

V-337, -500.

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Engineering curves and dependences “true stress – conditional strain”

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140

deformation, %

true

str

ess,

kg/

mm

^2

Unirradiated steel

Irradiated (V-337, -500)

«true» curves

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Relationship between true stress and true strain for irradiated 08Cr16Ni11Mo3 steel

0

200

400

600

800

1000

1200

1400

1600

1800

0 0,2 0,4 0,6 0,8 1 1,2

true strain

true

str

ess,

MPa

Irr, V-337, 11,9dpa

unirradiated

Irr., V-300, 10,8dpa

N-214, -900mm (1.27dpa)

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Conclusion

The changes in structure and mechanical properties of 08Cr16Ni11Mo3 and 12Cr18Ni10Ti steels – as materials of spent fuel assemblies of BN-350 reactor – irradiated up to damage doses 0.25 – 15.6 dpa at dose rate from 810-10 to 2.610-

7dpa/s were investigated.

•It was found that the dose rate is one of important factors influencing on void formation and development as well as on formation of mechanical properties of investigated materials.

•The void formation at low dose rates and low damage doses (1.27 dpa for 08Cr16Ni11Mo3 steel and 0.67 dpa for 12Cr18Ni10Ti steel) was observed.

•The method of mark extensometry was proposed and applied for investigation of peculiarities of plastic deformation of miniature specimens irradiated at various dose rates.•It was shown that relation between true stresses and true strains at localized deformation of high irradiated steel samples can be described by equation =k0.5+0.