Selection of Stainless Steels for Nuclear Applications

Transcription

1 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. **

2 Outokumpu Degerfors Sheffield Avesta Tornio Kemi Nyby New Castle Krefeld Calvert Wildwood Richburg Dillenburg Dahlerbrück Integrated melt shop, hot and cold rolling Other mills Mine San Luis Potosí Service center 11,000 people 2.4 million tonnes / annum

3 A Materials Challenge Coastal environment Complex chemical and radio-chemical situation Minimize maintenance requirement Very long term waste management expectation

4 Some Nuclear Applications of Stainless Steel Nuclear Island Turbine Island Balance of Plant (BOP) Primary containment Secondary support systems Mechanical Equipment - Pool liners - Heating & ventilation systems - Safety-Related Piping - Mechanical modules - Fire Protection systems - Cooling Water Piping & Handling Primary support systems Secondary Steam Cycle - Vertical Heat Exchangers - Heating & ventilation systems - Main Turbine - Horizontal Heat Exchangers - Fire Protection systems Reflective Metal Insulation - Tanks Reactor Coolant Systems - Main Condenser - Reactor Internals Condenser Tubing / Tubesheets - Control Rod Drives - Moisture Separator-Reheater Waste Storage - Tubesheets - Feedwater Heaters - MOX Fuel Transport baskets - Safety Injection Accumulator Tanks Mechanical Equipment - Waste canisters - Sodium Tanks - Class 1, 2, 3 Piping - Waste treatment vessels - Primary & secondary separators - Vertical Heat Exchangers - Wet Fuel Storage Racks Mechanical Equipment - Horizontal Heat Exchangers - Dry Storage Canister - 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)

5 Austentic R p0.2 [MPa] Duplex Materials Selection: Austenitic & Duplex Steels LDX 2101 EDX2304 LDX Hot rolled coil L 316L 317L 904L 254 SMO 150 Corrosion Resistance, CPT typical ASTM G150

6 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

7 Staining & pitting corrosion On-set of pitting corrosion, aesthetically undesirable Perforation from the inside

8 Ranking of corrosion resistance Pitting Resistance Equivalent (number) PRE PRE = %Cr + (3.3 %Mo) + (16 %N) PRE is a rough estimation of the resistance to localized corrosion Grade Structure PRE 304L/ Austenitic L/ L 254 SMO LDX 2101 Duplex 26 Laboratory measurements: pitting resistance through Critical Pitting Temperature Measurements (CPT) Real Life: Actual service experience valuable

9 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

10 Nuclear Power Plant Accumulator tanks Reactor type: PWR Plant (examples): o o Application: QinShan Phase II, China Olkiluoto 3, Finland Accumulator tanks o Grade: 304L Z2 CN19-10 Az (QC2) Cobalt 0.06% Olkiluoto 3. Construction site

11 Nuclear Power Plant Steam Separator Plates Basic requirement : o ASME/EN, 316L/ Plates, thickness: mm Special requirements: o Low Cobalt content o Grain size control Steam separator, Oskarshamn Nuclear Power Plant

12 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)

13 254 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, , 2507 o Compete with Titanium.

14 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 o o is radioactive; emits high energy, penetrating gamma radiation Is very harmful to human health (causes cancer) 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

15 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

16 Duplex Stainless Steels in Nuclear Applications

17 Austentic R p0.2 [MPa] Duplex Duplex steels vs Austenitic Steels LDX 2101 EDX2304 LDX Hot rolled coil L 316L 317L 904L 254 SMO 150 Corrosion Resistance, CPT typical ASTM G150

18 Why Duplex? Why Not Duplex? High Strength - use thinner material, save cost Good to excellent corrosion resistance Excellent resistance to Stress Corrosion Cracking Weldable in all section sizes, with appropriate procedure Lower nickel content, hence lower cobalt content (nuclear) More stable price over time Unsuitable for cryogenic use (below approx -50 C) Unsuitable for high temperature service above approx C Reduced Formability (cf 304, 316) High strength means more power required to bend (for given thickness) Less experience in fabricator community in forming and welding

19 Duplex Stainless Structural Engineering eg Bridges Storage Tanks Coastal Structures Pressure Vessels e.g. Un-vented Water Heater (Strength/SCC advantage)

20 Duplex LDX 2101 / EN Siemens Westinghouse AP1000 nuclear reactors Wall & Floor sandwich panel for Mechanical Equipment Modules ~150 Mechanical Modules per reactor LDX2101 / 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)

21 Sanmen Units 1 & 2

22 External structures Pile Fuel Cladding Silo - Doors Sellafield site Duplex Source: sellafieldsites.com

23 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

24 Austenitic Stainless Steel , 316 plus Alternative to standard 316L for general purpose and nuclear industry use

25 316 plus / Typical Composition & Minimum Mechanical Properties Name EN Carbon Nitrogen Cr Ni Mo PRE 316 plus L PRE = % Cr + (3.3 x % Mo) + (16 x % N ) Name EN Rp 0.2 MPa Rm MPa Elongation A80% 316 plus L (EN , hot rolled coil plate)

26 plus austenitic stainless steel Why Use plus? Why not use plus, stick with 316L? 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 Slightly higher bending forces needed Slightly reduced stretchforming and bending ability Not as widely stocked; Made to order Only recently introduced into international standards EN ASTM/ASME A240

27 / 316 plus application

28 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 o Specific requirement for critical nuclear areas of low cobalt content 316 plus / alternative steel with technical and cost advantages Duplex steels being specified for some New Build and Decommissioning uses

29 Contact Details Andrew Backhouse Technical Manager Outokumpu Stainless Ltd, Sheffield