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-NETNUC- SCC Properties and Oxidation Behaviour of Candidate Materials at SCW conditions . Sami Penttilä. NETNUC/GEN4FIN meeting 03.04.2009, VTT, Espoo. Content. Weight gain tests SCC susceptibility Status of oxidation studies using bellows system Summary. Weight gain tests.

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netnuc scc properties and oxidation behaviour of candidate materials at scw conditions

-NETNUC-SCC Properties and Oxidation Behaviour of Candidate Materials at SCW conditions

Sami Penttilä

NETNUC/GEN4FIN meeting

03.04.2009, VTT, Espoo

content
Content
  • Weight gain tests
  • SCC susceptibility
  • Status of oxidation studies using bellows system
  • Summary
chemical compositions of the studied alloys wt

Weight gain tests

  • Sixteen materials from the four different alloy groups for screening stage:
Chemical compositions of the studied alloys (wt-%)
slide4

Weight gains at different temperatures for selected alloysafter ~600 h exposure to SCW conditions (25 MPa)

weight gain test
Weight gain test

Weight gains of 316L pipe with different surface treatments

T = 650°C, t = 1000 h, p = 25 MPa and D02 = 125 ppb

slide6

316L pipe samples with different surface finishes after 1000 h exposure to SCW at 650°C

machined

as received

grit #600

grit #1200

optical images of the 316l pipe samples after 1000 h exposure to scw at 650 c
Optical images of the 316L pipe samples after 1000 h exposure to SCW at 650°C

grit #1200 surface finish

machined surface

oxide thickness ~ 40 – 50 µm

oxide thickness ~ 2 µm

slide8

Improving corrosion and oxidation behavior of materials at SCW conditions

  • Chemical composition, Cr content > 18%
  • GB modification → thermomechanical processing
  • Application of surface treatment, e.g. CW
  • Effect of CW
  • An enhanced Cr diffusivity
    • increased defect density
  • Results to a more compact and continuous (uniform diffusivity) Cr-oxide layer
  • Dense Cr-oxide layer decrease the outward/inward transport of Fe and O

Babcock-Hitachi Europe Gmbh, Advanced materials for AD700 boilers, Milano, Italy, 2005

scc susceptibility ssrt
SCC susceptibility - SSRT
  • T = 500°C and 650°C, p = 25 MPa and DO2 = 125 ppb
  • Strain rate of 3x10-7 s-1
  • Materials
    • 316NG
    • 347H
    • 1.4970
    • BGA4
    • PM2000
stress strain curves for the studied alloys under scw conditions at 500 c and 650 c
Stress-strain curves for the studied alloys under SCW conditions at 500°C and 650°C

500°C

650°C

status of db system
Status of DB-system
  • Problems with pressure tube material (316L)
  • Problems with welding
  • New miniature DB-system has been designed by P. Moilanen
    • Purpose is to perform mechanical loading (3-PB etc.) tests for selected materials at SCW conditions
  • Oxidation kinetic studies using CER/CEI methods
    • CEI and CER analysis have showed that most of the commercial materials behave like semiconductors under SCW conditions
summary
Summary
  • The oxidation rate of F/M steels is too high for SCWR core components even at the temperatures below 500°C
  • Austenitic stainless steels, which have a good enough oxidation resistance up to 500 – 550°C have been selected as a candidate materials for most HPLWR core components
  • 20% Cr ODS steel was selected for the fuel rod cladding material because of its excellent oxidation resistance even up to 650°C, its SCC resistance and its good creep specifications
  • However, the SSRT results in this work are not in line with the creep strength specifications
    • More studies are needed in the behaviour of high Cr F/M ODS steels in supercritical water
  • Other problems with the ODS materials are the difficulties in welding and high prices
    • Therefore these materials are recommended to applications where high strength and oxidation resistance are needed, but only little additional joining is required
  • A possible road for the fuel cladding development may be coating of austenitic stainless steels or F/M steels
    • Processes that have been studied are diffusion coatings (i.e. slurry application, CVD) and overlay coatings (thermal spray, PVD, electroless coatings)