Selection of Stainless
Steels for Nuclear
Applications
Andrew Backhouse
Technical Manager
Outokumpu Stainless
** Technical advice and assistance is provided without charge and
in good faith without any undertaking, representation or warranty
and Outokumpu will obtain no liability - neither compensatory nor
consequential - for advice or assistance given. **
Outokumpu
Avesta
Tornio
Kemi
Degerfors
Nyby
Sheffield
New Castle
Krefeld
Calvert
Wildwood
Dillenburg
Richburg
Dahlerbrück
San Luis Potosí
Integrated melt shop,
hot and cold rolling
Other mills
Mine
Service center
11,000 people
2.4 million tonnes / annum
A Materials Challenge
Coastal environment
Complex chemical and
radio-chemical situation
Minimize maintenance
requirement
Very long term waste
management expectation
Some Nuclear Applications of Stainless Steel
Nuclear Island
Turbine Island
Balance of Plant (BOP)
Primary containment
Secondary support systems
Mechanical Equipment
-
-
-
Pool liners
Mechanical modules
Heating & ventilation systems
Fire Protection systems
Primary support systems
Secondary Steam Cycle
- Heating & ventilation systems
- Fire Protection systems
Reactor Coolant Systems
- Reactor Internals
-
Main Turbine
° Reflective Metal Insulation
Main Condenser
° Condenser Tubing / Tubesheets
- Control Rod Drives
- Moisture Separator-Reheater
- Tubesheets
- Feedwater Heaters
- Safety Injection Accumulator Tanks
Mechanical Equipment
- Sodium Tanks
- Class 1, 2, 3 Piping
- Primary & secondary separators
- Vertical Heat Exchangers
Mechanical Equipment
- Horizontal Heat Exchangers
- Class 1, 2, 3 Piping
- Tanks
- Other Tanks
° PRESSURIZED RELIEF TANK (X2 CR Ni 19-11)
° VOLUME CONTROL TANK (304L)
° REACTOR COOLANT DRAIN TANK (X2 CR Ni Mo 17-12)
Safety-Related Piping
Cooling Water Piping & Handling
Vertical Heat Exchangers
Horizontal Heat Exchangers
Tanks
Waste Storage
-
MOX Fuel Transport baskets
Waste canisters
Waste treatment vessels
Wet Fuel Storage Racks
Dry Storage Canister
Materials Selection: Austenitic & Duplex Steels
Hot rolled coil
600
LDX2404
550
Duplex
400
EDX2304
2205
2304
4565
350
300
250
200
150
Austentic
Rp0.2 [MPa]
500
450
2507
LDX
2101®
304L
316L
317L
904L
Corrosion Resistance, CPT typical ASTM G150
254
SMO
Pitting Corrosion & Crevice Corrosion
• Most commonly a result of prolonged contact with chloride
• Sodium Chloride (Salt) - aggressive
towards many metals
• Food ingredients, particularly processed
foods
• Hypochlorite bleach disinfectant
• Salt water / Sea water / “Tap” Water
• Coastal Environments
• Nuclear plants often located near the
sea, and utilise sea water cooling
Staining & pitting corrosion
On-set of pitting corrosion,
aesthetically undesirable
Perforation from the inside
Ranking of corrosion resistance
Grade
Structure
PRE
304L/1.4307
Austenitic
18
Pitting Resistance Equivalent (number) PRE
PRE = %Cr + (3.3 × %Mo) + (16×%N)
PRE is a rough estimation of the
resistance to localized corrosion
316L/1.4404
24
904L
34
LDX 2101®
Laboratory measurements: pitting resistance
through Critical Pitting Temperature
Measurements (CPT)
Real Life: Actual service experience valuable
43
254 SMO®
Duplex
26
2205
35
2507
43
Nuclear Waste Storage
• Nuclear storage facilities often near the sea (eg Sellafield)
• In waste storage containers, integrity needed for a very long time
– often between 50 and 150 years - sometimes longer
• Wide use of 304L & 316L austenitic stainless steels,
o
but increasing use of 2205 duplex
Source: Sellafieldsites.com
Nuclear Power Plant
Accumulator tanks
•
Reactor type: PWR
•
Plant (examples):
o QinShan Phase II, China
o Olkiluoto 3, Finland
•
Application:
Accumulator tanks
o Grade:
• 304L
• Z2 CN19-10 Az (QC2)
• Cobalt  0.06%
Olkiluoto 3. Construction site
Nuclear Power Plant
Steam Separator Plates
•
Basic requirement :
o
ASME/EN, 316L/ 1.4435
•
Plates, thickness: 35 – 85 mm
•
Special requirements:
o Low Cobalt content
o Grain size control
Steam separator, Oskarshamn Nuclear Power Plant
Spent Fuel Storage – Pool Liners
•
Low cobalt containing 304L
stainless steel
•
Pool Liners for storage of
spent nuclear fuel, prior to
reprocessing (or long term
dry storage)
254 SMO seawater cooling condensers
• Application:
o Condenser tubes & tube sheets
o Filters
• Grades
o Seawater cooling requires highalloyed grades.
o “Super-austenitic”or “super-duplex”
grades for seawater handling: eg
o 254 SMO, 1.4529, 2507
o Compete with Titanium
.
Low Cobalt Stainless Steels
•
Naturally occurring cobalt metal (Co-59) is not
radioactive
•
Absorption of a neutron by cobalt during nuclear
fission converts Co-59 to Co-60
•
Co-60 :
o is radioactive; emits high energy, penetrating
gamma radiation
o Is very harmful to human health (causes cancer)
o Has a half-life of 5.3 years
•
Why to be concerned about this with stainless steels?
•
Cobalt often occurs in nature alongside nickel ore
o nickel-containing stainless steels,
will therefore also contain traces of cobalt
Low Cobalt Stainless Steels
Need to restrict cobalt level for nuclear island
equipment
Typically 0.2% max Cobalt, or tighter
Consequence for supply chain :
Steelmaker has to restrict use of recycled
scrap in the steelmaking process, & use
“virgin” low – Cobalt ores
Steel often made to order specifically for the
project
15
Duplex Stainless Steels
in Nuclear Applications
Duplex steels vs Austenitic Steels
Hot rolled coil
600
LDX2404
550
Duplex
400
EDX2304
2205
2304
4565
350
300
250
200
150
Austentic
Rp0.2 [MPa]
500
450
2507
LDX
2101®
304L
316L
317L
904L
Corrosion Resistance, CPT typical ASTM G150
254
SMO
Why Duplex?
Why Not Duplex ?
High Strength - use thinner
material, save cost
Unsuitable for cryogenic use
(below approx -50° C)
Good to excellent corrosion
resistance
Unsuitable for high temperature
service above approx 250-300°C
Excellent resistance to Stress
Corrosion Cracking
Reduced Formability (cf 304, 316)
Weldable in all section sizes,
with appropriate procedure
Lower nickel content, hence
lower cobalt content (nuclear)
More stable price over time
High strength means more power
required to bend (for given
thickness)
Less experience in fabricator
community in forming and
welding
Duplex Stainless
Structural Engineering eg Bridges
Storage Tanks
Coastal Structures
Pressure Vessels
e.g. Un-vented
Water Heater
(Strength/SCC
advantage)
Duplex LDX 2101 / EN1.4162
Siemens Westinghouse AP1000 nuclear reactors
•
Wall & Floor sandwich panel for “Mechanical Equipment Modules”
•
~150 Mechanical Modules per reactor
•
LDX2101 / 1.4162 duplex inner wall membrane (13 m x 3m plates):
– Corrosion-resistant water tight inner layer
– Carbon steel outer plate
– Concrete sandwich infill
•
Sanmen 1 & 2; Haiyang 1 & 2; Vogtle 3 & 4 (China, USA)
Sanmen Units 1 & 2
External structures
Pile Fuel Cladding Silo - Doors
•
Sellafield site
•
Duplex - 2205
Source: sellafieldsites.com
Duplex Stainless Steel Waste Containers
• Why 2205 Duplex?
• More corrosion resistant than 316L
• Higher strength material; thinner wall
construction for equivalent duty
• Fabrication & Welding :
o Increased power requirement, cf
304L, 316L
o Specific duplex weld procedures
3 cubic-metre box
Austenitic Stainless
Steel
1.4420, 316plus
Alternative to standard 316L
for general purpose and
nuclear industry use
316plus /1.4420
Typical Composition & Minimum Mechanical
Properties
Name
EN
Carbon
Nitrogen
Cr
Ni
Mo
PRE
316plus
1.4420
0.02
0.2
20.3
8.6
0.7
26
316L
1.4404
0.02
-
17.1
10.1
2.1
24
PRE = % Cr + (3.3 x % Mo) + (16 x % N )
Name
EN
Rp 0.2
MPa
Rm
MPa
Elongation
A80%
316plus
1.4420
350
650 – 850
35
316L
1.4404
220
530 - 680
40
(EN10028-7, hot rolled coil plate)
1.4420 316plus austenitic stainless steel
Why Use 1.4420 316plus ?
Lower cost than 316L
Weldability good at all
thicknesses, similar to 316L
Slightly higher strength –
possibility to reduce thickness
Similar or slightly better
corrosion resistance to 316L
Example applications:
- Most current general uses
of 316L
- Lower cobalt from standard
production for nuclear use
Why not use 1.4420 316plus, stick with 316L ?
Slightly higher bending forces
needed
Slightly reduced
stretchforming and bending
ability
Not as widely stocked; “Made
to order”
Only recently introduced into
international standards
EN10028-7 ASTM/ASME A240
1.4420 / 316plus application
Summary – Material Selection in Nuclear
applications
•
Corrosion resistance and strength primary technical drivers
•
Standard 304L & 316L widely used, partly due to long standing experience
•
o
Specific requirement for critical nuclear areas of low cobalt content
o
316plus / 1.4420 alternative steel with technical and cost advantages
Duplex steels being specified for some New Build and Decommissioning uses
Contact Details
Andrew Backhouse
Technical Manager
Outokumpu Stainless Ltd, Sheffield
0114 2613879
[email protected]