Pre0038-Saibaba Nudurupati

Development of Structural Core Components

for Breeder Reactors

N. SaibabaChief Executive

Nuclear Fuel Complex

Hyderabad, India

International Conference on Fast Reactors and Related Fuel Cycles Safe Technologies and Sustainable Scenarios (FR13)

Paris, France, March 5, 2013

3-STAGE NUCLEAR POWER

PROGRAMME

Dr. Homi Jehangir Bhabhaformulated the three stage Indian

Nuclear Power Programme linking

the fuel cycles of PHWRs and FBRs.

STAGE I

Consists of PHWRs and BWRs.

These reactors produce power

from natural U fuel. Pu239 is also

produced as a bye product.

STAGE II

Consists of FBRs. These reactors

produce power from Pu239 as fuel.

Here fuel breeding is carried out by

converting Th232 to U233 and U238 to

Pu239.

STAGE III

Consists of PHWRs and

AHWRs. These reactors

produce power by using U233

and Pu239 from stage II as

fuel.

500 MWe PFBR CORE

FUEL CLAD TUBES

(6.6 x 0.45 x 2555 mm)

41000/50000 Nos

REFLECTOR CLAD TUBES

(44 x 1 x 1070 mm)

1200/1200 Nos

BLANKET CLAD TUBES

(14.33 x 0.56 x 2350 mm)

6000/8200 Nos

CSR CLAD TUBES

(22.4 x 1 x 1260 mm)

1000/1000 Nos

DSR CLAD TUBES

(21.4 x 0.7 x 1110 mm)

500/500 Nos

IBC CLAD TUBES

(44 x 1 x 3325 mm)

1100/1100 Nos

TUBES FOR CORE STRUCTURALS

01 Main Vessel

02 Core Support Structure

03 Core Catcher

04 Grid Plate

05 Core

06 Inner Vessel

07 Roof Slab

08 Large Rotating Plug

09 Small Rotating Plug

10 Control Plug

11 CSRDM / DSRDM

12 Transfer Arm

13 Intermediate Heat Exchanger

14 Primary Sodium Pump

15 Safety Vessel

16 Reactor Vault

Fuel Cycle Cost vs Burn-up

FR Burn-up (MWd/Kg)

Re

lati

ve f

ue

l cy

cle

co

st

Advantages of high burn-up

IN FBRs, 200 GWd/t BURN-UP IS DESIRED TO

REDUCE THE FUEL CYCLE COST

To Lower Unit Energy Cost

MINIMISE WASTE GENERATION

Less Minor Actinides and

Fission Products per MWe

REDUCE MAN-REM EXPOSURE

per MWe

But…

Radiation damage of the core

components is the major

concern

Core Structural Materials

• Though the desire is to have only fuel in the core, structural material form 25% of the total core

–To support and to retain the fuel in position

– Provide necessary ducts to make coolant flow through & transfer/remove heat

• For 500 MWe FBR with Oxide fuel (Peak Linear Power 450 W/cm), total fuel pins required in the core are of the order 39277 pins (both inner & outer core Fuel SA)

• Considering 217 pins/Fuel SA there are 181 Fuel SA wrapper tubes

• These structural materials see hostile core with max temperature and neutron flux

Sl no Structural components Wt (%)

1 Clad tubes 50

2 Wrapper 40

3 spacer wire 10

STRINGENT IN-SERVICE CONDITIONS IN FBRs

� High energy neutron irradiation leads to displacement of atoms (vacanciesand interstitials)

� Agglomeration of vacancies

� Void formation and swelling

�Density of neutron flux 3·1015 – 1016 n/cm2s

�Rate of He generation 20 – 30 appm/year

�Dose rate 100 – 200 dpa/year

�Temperature 400 – 6500С

Fresh Core Bowed Core BowingDilation(Swelling + Creep)

Irradiation Induced Dimensional Changes

Fuel Subassembly – Clad & Wrapper

Agglomeration

of vacancies

Intense Neutron Flux

(1015n/cm2/s)

FAST REACTOR CORE

STRUCTURAL

MATERIALS

High Temperature 400-

700oC- clad 400-600oC

wrapper

DISPLACEMENT

OF ATOMS

VOID SWELLING

Irradiation Creep

Dimensional Changes and Deterioration in

Mechanical Properties

100 – 200 dpa

Vacancies and

Interstitials

Irradiated

Unirradiated

Core

fuel

CRITERIA FOR MATERIAL SELECTION

IRRADIATION

EFFECTS

MECHANICAL

PROPERTIES

CORROSION

PROPERTIES

• Void Swelling

• Irradiation creep

• Irradiation embrittlement

• Tensile Strength

• Tensile Ductility

• Compatibility with Sodium

Materials for Core Structural Components of FBRs

Choice of Materials for Clad Tubes:

�Austenitic Stainless Steels

� F-M Steels

�ODS Steels

�Bi-Metallic

SELECTION OF SS D9 OVER SS 316

1. Higher Nickel: Nickel reduces void nucleation by enhancing vacancy diffusion

coefficient and thus reducing vacancy supersaturation.

2. Lower Chromium: Reducing chromium increases the stability of γγγγ phase against

precipitation of alloying elements that are responsible for reduced void swelling.

3. Solutes: Ti, Si, B and C play a dominant role in improving void swelling resistance

by extending the duration of the transient regime of void swelling.

4. Cold Work (higher dislocation density) improves void swelling resistance by:

• providing sinks for vacancies

• providing nucleation sites for ppts.

• improving phase stability during irradiation.

5. In general, factors that improve void swelling resistance are observed to improve

irradiation creep resistance.

ALLOY D9

• Primary carbides accelerate recrystallization (thusremoving the effect of cold work)

• Increasing Ti/C ratio leads to formation of primarycarbides (restricted to 6).

• 20% prior cold worked hexcans, for better void swellingresistance

– Ti/C = 4 →→→→ best creep resistance

– Ti/C = 6 →→→→ best mechanical properties and acceptable creepresistance

• 20% CW → optimum to avoid recrystallization of coldworked material and retard void swelling.

• Focus on increasing the threshold &

incubation fluence

• Linear swelling rate remains almost

constant

Swe

llin

g

%

Fluence (dpa)

Linear swelling

regime, insensitive to

initial microstructure

Transient swelling

regimeMicrochemical

evolution

Current

austenitic

stainless

steels can

support

up to 150

dpa

DIA

ME

TR

AL D

EF

OR

MA

TIO

N (

%)

3

553500000

1

2

5

4

6

CW 316

7

8

CW 15-15 Ti

1359575

DOSE (dpa)

115

CW Si-MOD 15-15 Ti

CW 316 Ti

Swelling behaviour of different Materials

(irradiation temp ~ 670-870 K)

Strategy for Improving Swelling Resistance in

Austenitic Stainless Steels

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

200 250 300

Stress (MPa)

Min

imu

m C

reep

Rate

(p

er

sec)

έ = A σn exp(−Q / RT )

SS D9 exhibits lower creep rate

as compared to SS 316 at 923 K

Austenitic 316 SS

C Cr Ni Mo Mn Si S P

0.04-0.07 16-18 12-14 2.0-2.5 1.4-2.0 0.75 0.025 0.03

Material for clad

and wrapper

tubes in FBTR

(initial core)

50nm

40 dpaUNIRRADIATED CONDITION

Cold worked

structure

Void – Ppt.

Association

M6C ηηηη carbide

Si: 8.1%

Cr: 21.5

Fe: 28.7

Ni: 33.7

Mo 1.7

Ni – Si rich

G phaseDefect formation at

low doses

Precipitation of M23C6

and M6C

Formation of Ni, Si

rich G Phase at high

dose

316 SS has good thermal creep properties

Breakaway swelling beyond 50 dpa

1. Increase nickel

2. Reduce chromium

3. Add titanium

4. Control Silicon

5. Use of phosphorous as

alloying element

C Cr Ni Mo Mn Si S P Ti

316 SS 0.04-0.07 16-18 12-14 2.0-2.5 1.4-

2.0

0.75 0.025 0.03

D9 .035-.045 13.5-

14.5

14.5-

15.5

2.0-2.5 1.4

2.0

0.5-

0.75

0.025 0.01 0.25

D9-I .035-.045 13.5-

14.5

14.5-

15.5

2.0-2.5 1.4

2.0

0.75-

0.8

0.025 0.035-

0.045

0.25

Improvements of Swelling resistance by Change in composition

swelling resistance increases from 50 to 100 to 150 dpa

10010

-11

10-10

10-9

10-8

10-7

10-6

300200

Min

imu

m c

reep

rate

/s

Applied stress,MPa

D9 923 K

316 SS 923 K

D9 973 K

316 SS 973 K

D9 1023 K

316 SS 1023 K

Creep Properties of 316 SS and D9 SS Clad Tubes

9% Cr steels shows minimum shift in DBTT

Ferritic- Martensitic Steels

Mod. 9Cr-1Mo steel shows lower DBTT Shift than HT-9

HT9 Steel for wrapper ( Fe-9Cr-1Mo-0.07C- 0.2-0.6 Si)

Target: to be used for irradiation doses up to 200 dpa

Beneficial to start with materials with high purity to ensure low DBTT

HT91 Steel for cladding of metal fuel reactors (HT9+ Nb- 0.06-0.1, V- 0.18 – 0.25 , N -0.03-0.07)

� Exellent void sewlling resistance dose up to 200dpa

� Inferior High Temperature creep properties above 600 deg. C

� Formation of low melting (725 0C) eutectic phase with Uranium

Bi-metalic clad tube for metallic fuel

UZr

HT91

Effectiveness of Zr liner U-Fe Phase diagram

Eutectic formation at 725oC

U-Zr Phase diagramNo Eutectic formation in U-Zr system

Zr liner

U T91T91

Diffusion couple

• ODS ferritic - martensitic steels (Fe - 9 Cr- 0.1 C- 2W-0.2 Ti + 0.35 Y2O3 )

Combines swelling resistance of ferritic-martensitic steels with high-

temperature creep resistance of austenitic steels

�For use as cladding material for achieving high burn-up targets

�Can be used up to fluence of 200dpa

Final option: Oxide Dispersion Strengthened Ferritic-Martensitic Steels

100 150 200 250Neutron Dose (dpa)

1000

950

900

850

PH Ferritic/

Martensitic

Austenitic

ODS

High TemperatureHigh TemperatureHigh TemperatureHigh TemperatureStrengthStrengthStrengthStrength

RadiationRadiationRadiationRadiationResistanceResistanceResistanceResistance

Maxim

um

Tem

per

atu

re (

K)

Manufacture of

D9 & Mod-9Cr-1Mo Clad tubes

Specifications for D9 and Mod-9Cr-1Mo Fuel Clad Tubes

• Dimensional Tolerances:

� OD : 6.6 + 0.02 mm

� ID : 5.7 + 0.02 mm

� WT : 0.43 min

� Length : 2555 + 1/-0 mm

� Straightness : 0.25/500

• Cold Work : 20 + 4 %

• Grain Size after final annealing : 7-9 (ASTM

E-112)

• IGC: ASTM A 262 Pr A @ 100 X

magnification

• Hardness : 220-290 VHN

• Surface Finish: 0.5 µRa

• ECT: 0.3 + 0.03 mm through holes

• UT: 0.05 + 0.002 mm X 1.5 mm Lg 600 V

Notch


� OD : 6.6 + 0.02 mm

� ID : 5.7 + 0.02 mm

� WT : 0.43 min

� Length : 2555 + 1/-0 mm

� Straightness : 0.25/500

• Hardness : 250 VHN max

• Surface Finish: 0.5 µRa

• ECT: 0.3 + 0.03 mm through holes

• UT: 0.05 + 0.002 mm X 1.5 mm Lg

600 V Notch

Property At Room

Temp.

@ 5400C

YS (Mpa) 420 Min 275

UTS (Mpa) 558-760 320

% e (min) 20 To be reported

Property At Room

Temp.

@ 5400C

YS (Mpa) 550-760 430-585

UTS (Mpa) 700-830 500-690

% e (min) 20 10

Basic Manufacturing Process

HOT EXTRUSION To Obtain Mother Hollows.

Cold Pilgering

Cold Drawing

(only for D9)

With high reductions up to75% with reduced number of cold working passes.

Final Process to obtain very close dimensional tolerances with higher rates of production where limited final cold work of 20% specified.

Heat treatment

Final Annealing at 1050 to 1080C/ 2min followed by fast cooling (175C/min) for D9

Normalizing at 1050-1080C/ 30min/ Air cooling followed by tempering at 760-780C/60min/Air cooling for Mod-9Cr-1Mo Grade

Stringent Specifications at

ET & UT

CHALLENGES DURING

MANUFACTURING

CLAD TUBES

CONTROLLED

CHEMISTRY

C - pick up problem

N- pick up problem

Nitrogen Pick up upto 450 ppm

Cracked

Ammonia

Ar + H2

Controlling Nitrogen and Carbon Pick up

0

50

100

150

200

250

300

350

1 2 3 4 5 6

N V

alu

es in

PP

M

Number of Annealing

N PICKUP VS NO. OF ANNEALING

100% CA 20% Ar + 80% CA

50% Ar + 50% CA 100% Ar

88% Ar + 12% H2

� Carbon pick up was controlled by Special vapor Degreasing system to ensurethorough cleaning of lubricants used during cold working operations such asPilgering and Drawing.

� Nitrogen pick up was controlled by modifying Furnace Atmosphere

Tensile properties Specified value Result obtained

UTS (MPa) 700 - 830 793

YS(MPa) 550 - 760 691

% Elg.(Gl=5.65√A) 20 min. 23

Hardness (VHN) 220 - 290 271

HIGH TEMPERATURE (AT 5400C) MECHANICAL PROPERTIES

ROOM TEMPERATURE MECHANICAL PROPERTIES

Tensile properties Specified value Result obtained

UTS (MPa) 500 - 690 615

YS(MPa) 430 - 585 579

% Elg.(Gl=5.65√A) 10 min. 11

Typical Mechanical Test Results of D9 Tubes

Characterization of Mod-9 Cr- 1 Mo Clad Tubes

Pinning of Sub-grain

boundaries during Creep

Microstructure of modified 9Cr-1Mo (a) Optical (b) TEM (c) Particle size distribution

MX : Nb(C,N) & VN

Parameter Specified Value Result Achieved

Y.S.( Mpa) 420 Min. 535 - 578

UTS (MPa) 585 - 760 695 -714

Hardness HB 250 Max. 243 - 248

% Elongation 20 Min. 23 - 26

Simulated heat treatment values

Y.S.( Mpa) RT 420 min. 470 - 520

UTS (MPa) RT 585 - 760. 660 - 710% Elongation RT 20 min. 25 - 26

Y.S.( Mpa) HT 275 min. 370 - 420UTS (MPa) HT 370 min. 465 - 525

% Elongation HT To be reported 20 - 22

Manufacturing of ODS Clad Tube

Challenges In Processing ODS

� size and uniform distribution of yttria (Y2O3) duringmechanical alloying.

� Selection of Deglassing techniques after extrusionrequiring chemical compatibility

� Detection and removal of MS patches from the surface.

� Machinability of extruded mother hollow surface

� Selection of cold working parameters Ex: Feed rate, inputlength, reduction per pass, Tool design etc.

� Selection of Heat Treatment parameters e.g., soakingtime and temperature & furnace atmosphere.

PrePrePrePre----alloyed Powderalloyed Powderalloyed Powderalloyed Powder

YYYY2222OOOO3333 PowderPowderPowderPowder

Mechanical Alloying (MA)(Ball Milling)

Hot Extrusion at 1150 C

Raw MaterialPowder

CanningDegassing at 400 C

Dispersoid Size Control

Mother Tube

36363636mm OD x mm OD x mm OD x mm OD x 4444mm WT mm WT mm WT mm WT

Annealing

(Φ14mm)

Drilling

Powder Metallurgy (PM) Process for Mother Tubes

NDE for Detection of MS patches

Ph

oto

gra

ph

Th

erm

al

Ima

ge

�NDE techniques could reliably detect MS patches

�Small MS patches could also be detected

Uncoated region

Coated with black paint

A.U

.

36mm OD X 4 mm WT ODS

steel mother tubes

NDE could detect sub-surface MS inclusion

� EC and MBE revealed less sensitivity but could reliably detect the sub-surface

MS inclusions

�Thermal imaging could not detect the sub-surface MS inclusion.

0 10 20 30 40 50 60 70 80 90 100

30

40

50

60

70

MB

E R

MS

Valu

e, A

U

Scan position, mm

Synthesis &

consolidation

Pass schedule for manufacture of ODS clad

tubes: 11 stages of cold pilgering with three

intermediate annealing and a final normalising-

tempering heat treatment, from mother tube

to clad tube.

Development of 9Cr-2W-0.1C-0.2Ti-0.35Y2O3 ODS Clad Tube by Rod extrusion Synthesis and Processing

Nano Yttria powder

35µm

Atomized alloy powder

(Fe-9Cr-0.13C-0.2Ti-2W)

150µm

Mechanical Alloying

Canning and Degassing

Upsetting

Hot extrusion to blank

Pilgering (11passes)

Evaluation of tubes

Nano Yttria powder

35µm

Atomized alloy powder

(Fe-9Cr-0.13C-0.2Ti-2W)

150µm

Mechanical Alloying

Canning and Degassing

Upsetting

Hot extrusion to blank

Pilgering (6 passes)

Evaluation of tubes

OD/ID machined

billet 36 mm OD X 28 mm ID extruded and

machined mother blank

MANUFACTURING OF ODS CLAD TUBE BY HOLLOW MOTHER BLANK

Pass schedule for manufacture of

ODS clad tubes: 6 stages of cold

pilgering with five intermediate

annealing and a final normalising-

tempering heat treatment, from

mother tube to clad tube.

Upset Billets

Preheated Billet

undergoing OD lubrication with glass powder

Billet transferred into extrusion press

container vertically630 T Extrusion Press24 Ø mm rod in red hot condition

MATERIAL UTS (MPa) YS (MPa) % ELONG.

SPECIFICATION FOR D9 700 - 830 550 - 760 20

D9 PROPERTIES (TYPICAL) 724 600 21

ODS PROPERTIES (TYPICAL)959 811 -

921 830 22.7

MATERIAL UTS (MPa) YS (MPa) % ELONG.

SPECIFICATION FOR D9 500 - 690 430 - 580 10

D9 PROPERTIES (TYPICAL) 548 488 14

ODS PROPERTIES (TYPICAL) 554 519 14

ROOM TEMPERATURE PROPERTIES

HIGH TEMPERATURE PROPERTIES(540OC)

Mechanical Properties of ODS Steel Clad Tube

17.75 Ø mm X 1.75 mm WT

machined & polished ODS

Tube

Finished ODS Steel Clad tube

6.6mm OD X 0.45mm WT

Alloy powder, Plate-like,

varying sizes <300 µµµµm

=20 µm; IPF Coloured; Step=0.8 µm; Grid146x115

{111}Pole Figures

[Project4.cpr]

Iron bcc (old) (m3m)

Complete data set

16737 data points

Equal Area projection

Upper hemispheres

Half width:10°

Cluster size:5°

Exp. densities (mud):

Min= 0.38, Max= 2.45

1

2

NO TEXTURE

EBSD/ pole figures

0

100

200

300

400

freq

uen

cy o

f th

e d

isp

ers

oid

s

Size (nm)2.5 4.5 6.5 8.5 10.5 12.5 15

Metallurgical Characterization

Element C Cr W Ti Y2O3 Mn N O (Total)

Spec. 0.11 - 0.13 8.8 - 9.2 1.9 - 2.1 0.19 - 0.22 0.32 - 0.35 0.04 max < 0.01

Typical 0.12 8.85 2.01 0.21 0.36 0.01 0.01 0.12

100 1000 10000

30

40

50

60708090

200

300

Grade 91

India ODS clad tube

9Cr-ODS Japan

Alloy D9

Ap

pli

ed

str

es

s,

MP

a

Rupture life, hour

700 oCTest in progress

Clad-tubes with 6.6 mm O.D., 0.45 mm thick and 4.2 m length have been successfully produced

Rupture Life

Chemical Composition

�Better creep strength than Austenitic SS.

�DBTT is close to room temperature.

�No carbon leaching in sodium environment.

�Ferritic structure provides better resistance to

neutron damage and has better void swelling

resistance (Compared to austenitics).

Ferritic Steel Vs Austenitic Stainless Steel

for FBR Applications

Development of Double Clad Tubes for Metallic Fuel

Advantages of Metallic Fuels

�higher burn-up-

�higher breeding ratio (i.e. shorter doubling

time)

�Improved safety, as the reactor can be

safely shut down without operator assistance.

METHODS OF FABRICATION

�Co-extrusion

�Zr-2 clad tube lined with Zr-4 for high burn

up in PHWRs.

�Co-Pilgering

�9Cr-1Mo clad tube lined with Zr-4 for

metallic fuel in fast breeders.

�Co-Drawing

�SS tube lined with Zircaloy for chemical

applications

�Explosive Cladding

Route adopted

Co-Pilgering

9Cr-1Mo clad tube lined with Zr-4 for

metallic fuel in fast breeders

Schematic of Double Clad Tube

Fabricated at NFC

Fabrication Criticalities

�End Fusing of T91 & Zr-Alloy tubes is to be

done so as to prevent relative slip between

inner & outer tubes and ingress of oil during

pilgering. (Achieved by Electron Beam

Welding)

�T91 & Zr alloy show different deformation

behavior in pilgering. Hence, fixing of

dimensions of T91 & Zr tubes at pre-final stage

is very critical to achieve the finished

dimensions after co-pilgering.

CO-PILGERING TECHNIQUE FOR MANUFACTURE OF DOUBLE

CLAD TUBE OF SIZE 6.6 MM OD X 0.6 MM WT

SEM PHOTOS OF DOUBLE CLAD TUBE

X-SECTION

Tube Section showing Outer & Inner

Walls of T91 & Zr Alloy

Enlarged View showing no gap at

T91-Zr Interface along with wall

thickness measurement

NDT Examination in Tubing

• Immersion Ultrasonic Testing (L & T): 100%

for deep defects.

• Eddy Current Testing (Saturation field):

100% Surface and sub-surface defects.

• Visual Examination: 100% OD surface

defects

Effectiveness of Zr liner at different temperatures

700oC/1500h 750oC/1500h 850oC/1000

U ZrU Zr T91 U Zr T91 T91

Line spectra on white

phase on Zr liner

� T91, Zr, U strongly bonded at interfaces.

� No interfacial gap ensuring no resistance to heat transfer during reactor

operation.

EPMA Scan along U/Zr/T91 Interface

700ºC,1505 hrs

Zr

Fe

U

Cr

T91Zr4

Development & Manufacture of D9 Hexcan

wrapper using Hex-Hex Pilgering

SCHEMATIC OF HEXCAN PILGERING

MANDREL

ROLLER

CRTM 60 -160 Pilger Mill Fuel subassembly wrapper tube

Consistency Of Hardness(VHN) & Strength on Hex-can,

manufactured by Hexcan To Hexcan Pilgering Route

500

550

600

650

700

750

800

16 17 18 19 20 21

Percentage Cold Work

Strength

(M

Pa)

UTS

YS

Variation of UTS and YS with cold work in hexcans of SS D9

Specifications for D9 Hexcan Wrapper Tubes

• Chemical CompositionElement Wt% Element Wt%

C 0.035-0.05 Ta 0.02 max

Cr 13.5-14.5 Ti 5C-7.5 C

Ni 14.5-15.5 Al 0.05 max

Mo 2-2.5 Si 0.5-0.75

Mn 1.65-2.35 Co 0.05 max

N 0.005 max Cu 0.04 max

S 0.01 max As 0.03 max

P 0.02 max V 0.04 max

B 10-20 ppm Fe balance

Nb 0.05 max


� Width A/F (outside) : 131.6 + 0.3mm

� Width A/F (Inside) : 124.9 + 0.3mm

� WT : 3.2 + 0.3min

� Length : 3600 + 5/-0 mm

� Straightness : 1/2500

� Twist: 15’/ cross-section apart by 1m

• Cold Work : 20 + 4 %

• Grain Size after final annealing prior to

cold drawing : 5-9 (ASTM E-112)• Surface finish : 2µ Ra in OD & ID

• IGC: ASTM A 262 Pr A @ 100 X magnification

• Hardness : 220-290 VHN

• UT: 0.1 + 0.01 mm X 10 + 0.15 mm Lg

600 V Notch

• LPT : As per ASTM E 165 on the OD of the

tube

Property @ Room Temp. @ 5400C

YS (Mpa) 550-760 430-585

UTS (Mpa) 700-830 500-690

% e (min) 20 10

Mechanical Properties:

Development of process route for Manufacture of Hexcan

Machined Ingots

Extrusion to Rods

Deep Hole Drilling, Expansion

Extrusion to Blanks

Blank Conditioning

Blank Heat Treatment

First pass pilgering

circular tube 146mm OD

x 4mm WT

Heat Treatment

2nd pass pilgering to Hexagonal

Tube

134.0 mm (A/F) x 3.3 mm WT

Heat Treatment

Final pass pilgering Hexcan to

Hex-Can

131.6 mm(A/F) x 3.2 mm WT

Inspection and Testing

3780T Horizontal Extrusion Press

Hot Extruded SS D9 Blank

DRX WINDOWS

Practical zone of

working in Extrusion

Process Maps for D9 Stainless Steel

Extrusion of SS D9

As extruded TD Micrograph As extruded LD Micrograph

Hot extruded Modified D9 Blanks Size : 160mm OD X 9mm WT

Temperature

range: 1140oC to

1180oC

Ram Speed: 80 to

100mm/sec

Challenges during fabrication of D9 Hexcans

� Formation of twist

� Formation of bow

� Wall variation

HEXCAN TO HEXCANEQUIPMENT MODIFICATION

Mandrel Rod

Earlier mandrel rod is made with a circular cross section. This was

modified by providing a hexagonal adaptor (350mm) for fixing the

mandrel at the end of mandrel rod. In addition, hexagonal half cup bushes

of soft aluminum bronze (to avoid lines on ID) were brazed on the mandrel

rod at periodic intervals of 1m with appropriate alignment. These

measures were necessary to ensure that the hexagonal profile of the

ingoing tube matches with that of the hexagonal mandrel.


• Inlet Bushes: Old inlet bushes had a circular cross section and were fixed.

These were replaced by inlet bushes with a hexagonal cross section to

guide the hexagonal ingoing tube. The new bushes were free to rotate in

their groove to mach the rotation of the ingoing hexagonal tube during

feed-and-turn. These bushes were made of copper to avoid lines on OD

surface of tubes.

Circular Bush

For Fixing the BushHexagonal Copper Bush

– Free to Rotate


• Inlet Chuck Jaws: The old inlet chuck jaws had a circular profile. These

were replaced by jaws with a hexagonal profile. The mill was designed for

circular to hexagonal pilgering, where the orientation relationship of the

inlet chuck and hexagonal mandrel was not a concern. It was noticed that

the hexagonal mandrel and the inlet chuck jaws were offset with respect

to each other. Therefore the inlet jaws were redesigned with a suitable

offset to match the orientation of the mandrel during feed and turn.

Inlet Jaws

Ingoing Tube

CIRC TO HEX HEX TO HEX HEX TO HEX

With Redesigned Jaws

Consistency Of Hardness(VHN) & Strength on Hex-can,

manufactured by Hexcan To Hexcan Pilgering Route

Position

(from corner

in mm)

FACE

1

FACE

2

FACE

3

FACE

4

FACE

5

FACE

6

AVERA

GE

0 255.9 259.1 256.4 268.2 259.1 251.0 255.9

2 255.5 250.1 257.8 247.9 258.7 251.0 249.6

3 240.7 250.1 238.7 251.9 261.0 231.8 241.7

4 238.7 234.6 232.6 244.5 250.6 225.7 236.6

5 222.0 227.2 233.4 251.9 247.5 230.7 238.5

6 233.4 232.6 240.3 251.9 255.5 235.4 242.6

7 235.0 247.5 232.2 242.0 244.1 261.5 245.6

8 242.0 237.4 239.9 250.1 260.5 254.6 248.2

9 248.8 243.7 245.8 247.5 254.6 253.7 246.7

10 252.8 252.3 239.9 238.2 248.4 234.6 246.9

11 257.3 240.3 258.7 245.8 251.4 243.2 250

12 264.3 250.6 255.5 246.6 250.1 236.2 246.2

13 259.6 230.3 235.4 238.2 255.5 232.6 245.3

14 252.3 228.0 256.8 244.5 265.3 245.4 245

15 263.8 224.6 247.9 224.9 242.0

Variation

across face42.3 22.7 26.5 13.7 42.3 35.8 34.9

500

550

600

650

700

750

800

16 17 18 19 20 21

Percentage Cold Work

Strength

(M

Pa)

UTS

YS

Variation of UTS and YS with cold work in hexcans of SS D9

Variation of micro hardness across the face of hexcan, manufactured by

hexcan to hexcan and circular to hexcan pilgering.

150

170

190

210

230

250

270

290

0 5 10 15 20 25 30

DIST FROM CORNER

MIC

RO

HA

RD

NE

SS

(V

HN

)FACE 1

FACE 2

FACE 3

FACE 4

FACE 5

FACE 6

AVERAGE

CIR TO HEX

PILGER MILL FOR PILGERING OF

HEXCANS

HEAT TREATMENT

• After each stage of cold working (except final coldworking) the material is subjected to solutionisingtreatment at 1020

0to 1080

0C in LPG Annealing

Furnace.

• The channels are passed slowly through the heatingzone to achieve the required time for soaking.

• After the heat treatment, the hexcans areimmediately quenched in water to avoid sensitization.

INSPECTION AND QUALITY CONTROL PROCEDURE

At each stage of manufacturing, process quality control measures areadequately taken to obtain consistent quality in the product.

– During extrusion process, important process parameters such asextrusion temperature, strain rate and lubrication conditions arecritically monitored

– The extruded hollows are thoroughly tested for their soundness byUltrasonic Examination with 5% wall thickness standard in additionto visual & dimensional checks.

– By proper control of process parameters during pilgering such astool design, lubrication, feed and speed etc., consistent quality ofproduct in terms of surface finish, dimensional tolerances areachieved.

– After each stage of pilgering, the dimensional accuracy and surface-finish are monitored.

MICROSTRUCTURAL STUDIES

MICROSTRUCTURE OF D9 HEXCAN

IN PILGERED CONDITION

MICROSTRUCTURE AFTER

SENSITISATION AT 6500 C FOR 1 HR,

SHOWING DUAL MICROSTRUCTURE

MICROSTRUCTURE AFTER

SENSITISATION AT 6500 C FOR

1 HR SHOWING DITCHED

MICROSTRUCTURE

ACCEPTABLE UNACCEPTABLE

Comparison of FBTR & PFBR Subassembly Design

Reactor FBTR- 13MWe PFBR- 500MWe

No. of Subassemblies

(SA) /core

65 (85+96=181)

Fuel PuC (70% ) + UC PuO2 (21.7 & 28.7%) + UO2

Clad SS316M D9

Wrapper SS316L D9

Structural

components

SS316L SS316LN

Pin design Fuel & Lower and Upper

blankets put in separate pins

Integrated design-all in same pin

No of pins/SA 61 217

Lower plenum Provided with a tube / disc-

supporting the fuel column

Fuel column supported on a

middle plug crimped in the clad

Overall Dimension 1.6m & 49.8mm (Hex. A/F) 4.5m & 131.6mm (Hex. A/F)

Weight 30kg 250kg

1st End Plug Welding Machine

2nd End Plug Welding Machine

Spacer Wire Wrapping &

Spot Welding Machine

• Precision current control to ±0.5Amps withfeedback system with smooth arc start and arcstability in Helium atmosphere.

• Automatic initial arc gap setting and arc gapcontrol.

• Automatic data acquisition and feedback controlsystem with recording facilities for criticalparameters like current, voltage, (arc distance),weld speed, vacuum level, Helium pressure,oxygen level (inert gas quality), etc.

• Precision special purpose fixtures for GTAW,Resistance welding techniques.

Special Features of the Equipment

Automatic Crimping Machine

Middle Plug

Clad Tube

Button Forming Machine

i. Lower Part

ii. Hexcan welded to Handling Head

iii. 217 Fuel Pins loaded in 2 Pin Magazines

Manufacture of Subassemblies

Automatic Hexcan

Welding Machine

� Automatic torch inclination with Torch

oscillation axis provided for keeping it

perpendicular to welding face in

synchronization with tube rotation.

� Software based automatic control with

feedback system for all critical parameters

with recording facilities.

� Electronic Arc Distance Control provided for

welding while rotating the hexcan

Thanks for your attention

Pre0038-Saibaba Nudurupati

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