R&D of ferritic-martensitic steel

EP450 ODS for fuel pin claddings

of prospective fast reactors

Joint Stock Company "High-technological Institute of Inorganic Materials"

(JSC VNIINM), Moscow, Russia

IAEA Technical meeting on “Design, Manufacturing and Irradiation Behaviour

of Fast Reactors Fuels”, 10 May-03 June 2011, IPPE

V.S. Ageev, A.A. Nikitina, A.P. Chukanov,

N.P. Porezanov, V.V. Tsvelev, O.A. Kruglov

Exploitation conditions for fuel pin

cladding materials of fast reactors

Large difference in temperatures along fuel pin cladding (370-700 °С)

High fluence of neutrons (~2 × 10²³ n/сm² @ Е>0,1 МeV)

Influence of stresses from gaseous debris of fuel fission and from mechanical interaction with swelling fuel rod.

Aggressive corrosion environment (coolant on outside surface of fuel pin cladding and products of fuel fission: Cs, Te, I and other – on inner surface of cladding)

Besides, material for fuel cladding must be corrosion resistant during long-term water storage of worked-out test assemblies in cooling pond

Technological scheme of receiving of

ODS steels

Receiving of matrix steel powder with

spherical or scaly shape of particles by the

centrifugal atomization of melt from revolving

crucible in inert gas (He) atmosphere.

Mechanical alloying of received powder by

particles of Y2O3 in vibration high-energy mill.

Vibro-infill of steel cans by received

powder blend, decontamination and sealing

of cans.

Hot pressing of steel cans with powder on

hydraulic press with tonnage 600 tons at

1100 °C into compact billets with maximum

possible density.

Hot extrusion at 1150 °С of compact billets

in hot-extruded bars with drawing no more

than 10-12 and subsequent mechanical

treatment

Structure and chemical composition of steel EP450

a – optical microscopy

b – transmission electron microscopy

Element content, wt. %

С Si Mn Cr Ni Mo Nb V B P

0,10-

0,15

<0,5 <1,0 11,0-

13,5

0,05-

0,30

1,5-

2,0

0,15-

0,40

0,1-

0,3

0,005-

0,015

<

0,025

a b b a b

Powder of matrix steel EP450

b a a b

a – external view;

b – microstructure of powder received by TEM

Powders of yttrium oxide

External view of yttrium oxide powder of industrial production (SEM) and microstructure of separate agglomerate (TEM) of yttrium oxide crystallites

Yttrium oxide powder, received with application of special technology: external view (TEM) and histogram of distribution of particles by sizes

Microstructure of powder of steel EP450 mechanically alloyed by

0,3 wt.% of Y2O3 and 0,4 wt.% of TiH

а b а b

c

а, b – structure in initial state;

c – structure after annealing at 1150 ºС

during 30 min

Hot extrusion

Bars

Tube shells

Microstructure of a bar from steel EP450 ODS, received with use of yttrium oxide

powder of industrial production (a-c) and histogram of distribution of oxide

particles by sizes in it (d)

а а b b

c

d

а а b b

c c

d

Microstructure of a bar from steel EP450 ODS, received with use of yttrium oxide

received by special technology (a-c) and histogram of distribution

of oxide particles by sizes in it (d)

а b

а а

а b b

c d

Microstructure of steel EP450 ODS (SEM) (a) and images of microstructure

in characteristic X-ray emissions of titanium and yttrium

Material Test

temperature, оС

Stress, MPа Creep rate,

%/h

EP450 650 140 1,18*10-2

EP450 ODS 650 140 2,38*10-4

EP450 700 120 9,1

EP450 ODS 700 120 1,82*10-3

Thermal creep curves of plate samples from steels EP450 and EP450 ODS

@ temperatures 650 and 700°С

Microstructure of hot rolled plate

from steel EP450 ODS

Temperature dependence of impact toughness of specimens of steels

EP450 and EP450 ODS

Specimens for impact toughness tests :

L = 55 mm

В = 2±0,05 mm

H = 8 mm

Н1 = 6±0,1 mm

Mechanical properties of plates 0,4 mm from EP450 ODS steel with different

initial deformation ratio

def. ratio, % elongation, % YS , MPа UTS, MPа

20 7,1 839 885

30 6,6 868 909

40 6,2 881 922

50 5,0 893 945

60 4,6 912 960

70 3,8 1086 1169

Specimens of thin-walled tubes

6,9х0,4х1000 mm

from steel EP450 ODS

Structure (a – optical microscopy; b, c – TEM) of thin-walled tube from steel EP450 ODS

after finish heat treatment 1150 ºС, 1,5 h, then 740 ºС, 2h and histogram of distribution

of oxide particles, which present in structure of tubes (d)

0

5

10

15

20

25

30

35

40

Vo

lum

e f

racti

on

,%

1-3 4-6 7-10 10-20 20-40 40-100

Particle size, nm

a b

c

d

c

a b b

Material Test

temperature, °С

Stress, MPа Internal

pressure,

kg/mm2

Time to rupture,

h

EP450

700

120

150

20

ChS139 85

EK181 90

EP450 ODS 200

Thermal creep curves of tube specimens of steels EP450 and EP450 ODS

at temperatures 650 и 700 °С

Data of long-term tests on tube specimens under internal pressure of steels

EP450, EP450 ODS and heat-resistant precipitation-hardening martensitic steels

Material

Test

temperature, оС

Stress,

MPа

Time to

rupture, h

Creep rate,

%/h

Comment

EP450 650 140 0 1,18*10-2 Ruptured

during loading

EP450

ODS

650 140 9086 2,38*10-4 δ=7,92%

EP450 700 120 23 9,1 δ=2,83%

EP450

ODS

700 120 1080 1,82*10-3 δ=7,08%

Thermal creep curves, received on microspecimens with 0,4×2,5×7 mm gauge

length cut from experimental tubes from steel EP450 ODS in longitudinal direction

Рис. . Кривые ползучести образцов ЭП-450-Y2O3

Т исп. = 650°С

1 - σ=140 Мпа

2 - σ=170 Мпа

3 - σ=210 МПа

0

0,5

1

1,5

2

0 2000 4000 6000 8000 10000 12000 14000 16000

t, час

Dl,

мм

2

1

3

Thermal creep curves of steel EP450ODS

(experimental batch of tubes)

at 650°С and stresses 140 (1), 170 (2)

and 210 (3) MPа

Рис. . Кривые ползучести образцов ЭП-450-Y2O3Т исп. = 700°С

1 - s=120 Мпа

2 - s=140 МПа

3 - s=160 МПа

4 - s=170 МПа

0

0,5

1

1,5

2

2,5

3

3,5

4

0 2000 4000 6000 8000 10000 12000 14000 16000

t, час

Dl,

м

м

1

3

4

2

Thermal creep curves of steel EP450ODS

(experimental batch of tubes)

at 700°С and stresses 120 (1), 140 (2)

160 (3), 170 (4) MPa

Type of specimen Тtest., °С UTS, MPa YS, MPа Elongation, %

Ring

(transverse direction)

20 740±62 677±40 3,1±0,6

Tube

(longitudinal direction)

910±10 707±6 16,6±0,9

Ring

(transverse direction)

650 407±23 390±10 3,1±1,9

Tube

(longitudinal direction)

420±17 363±21 20,1±0,8

Ring

(transverse direction)

700 297±49 280±52 4,5±0,5

Tube

(longitudinal direction)

307±12 273±15 21±2

Mechanical properties of tube specimens of steel EP450 in

longitudinal and transverse directions after finish heat treatment

а – optical microscopy;

b, c – TEM

Microstructure of thin-walled tubes from steel EP450 ODS, pilot batch

of which was received in JSC «Machine Building Plant» (MSZ)

c

а b b

melting

zone

steel EP450 ODS

Microstructure of welded joint between cladding tube and plug from steel

EP450 ODS received with use of argon arc welding (optical microscopy)

changes structural state of ODS steel

tube

plug

Microstructure of welded joint between plug and cladding tube from steel

EP450 ODS, received by pressurized resistance welding (optical microscopy)

Equipment for pressurized resistance welding

External view of technological specimen from steel

EP450 ODS received by pressurized

resistance welding

welded

joint

scanning

line

joint of cladding tube and plug from steel

EP450 ODS after pressurized

resistance welding

Graphics of distribution of intensity of X-ray

characteristic emission of titanium and

yttrium in welded joint of cladding tube and

plug from steel EP450 ODS after pressurized

resistance welding

welding zone

cladding tube

Quality of welded joint received by

pressurized resistance welding

Estimated by biaxial tension under

internal pressure 120 MPa at temperature

700 ºС.

Typical kind of rupture – outside of

welding zone

Specimens which were put in material test

assembly of BN-600 in the beginning of 2010

механические свойства

physical properties

fracture toughness

mechanical properties

Irradiation conditions for specimens

in material test fuel assembly of BN-

600:

Irradiation temperature: 375-700ºC

Stage 1.

Maximum damage dose 80 d.p.a

Stage 2.

After replacement in new material

test fuel assembly

Maximum damage dose 140-160d.p.a

Flowing and static sodium

environment

Conclusion

• In the course of presented works over research and development of steel EP450 ODS the possibility of significant increase of heat resistance of ferritic-martensitic steels by dispersion strengthening them by nanoparticles of yttrium-titanium oxides was shown.

• Technological schemes of receiving powders, tube shells and thin-walled tubes from steel EP450 ODS were worked out.

• Principle possibility of hermetization of thin-walled tubes from steel EP450 ODS by method of pressurized resistance welding was shown.

2010

Road map of a project “Development of nanostructured oxide dispersion strengthened

(ODS) heat-resistant steels for elements of cores of fast reactors of new generation

(with different types of coolant) and elements of fusion reactor

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Development of experimental technology of receiving the ODS steels

Fabrication of experimental batches of tubes from ODS steels and investigation of their properties

Development of industrial technology and receiving of industrial batches of tubes

Imitating investigations on accelerators

Reactor tests of ODS steels in material test assembly and irradiation device of reactors BOR-60 and BN-600

Postreactor investigations of irradiated cladding tubes from ODS steels

Analysis of experimental data and choice of ODS steels for fuel claddings of reactors with sodium,

lead and lead- bismuth eutectic coolants