General and Localized Corrosion of Austenitic and Borated Stainless Steels in Simulated Concentrated Ground Waters

Abstract

Boron containing stainless steels are used in the nuclear industry for applications such as spent fuel storage, control rods and shielding. It was of interest to compare the corrosion resistance of three borated stainless steels with standard austenitic alloy materials such as type 304 and 316 stainless steels. Tests were conducted in three simulated concentrated ground waters at 90°C. Results show that the borated stainless were less resistant to corrosion than the witness austenitic materials. An acidic concentrated ground water was more aggressive than an alkaline concentrated ground water.

Electrochemical Testing of Ni-Cr-Mo-Gd Alloys

“…It is possible that the corrosion rate of the secondary phase has a different corrosion rate dependence on environment than the base material. The corrosion rates obtained by LPR for Alloy 22 are about two orders of magnitude higher than the rates (slightly different environments) obtained by exposure testing for Alloy 22 (see Reference 19,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. One explanation for the discrepancies between the two measurement methods might be the higher rates for a material immediately following immersion.…”

“…9 However, the corrosion rates measured on the Neutronit material at the Long-term Corrosion Test Facility located at Lawrence Livermore National Laboratory were higher than expected. 10,11 The BSC materials staff then decided that the Ni-Cr-Mo-Gd alloy under development at INL was a promising replacement. An initial corrosion rate of 1 µm/year was recommended for Yucca Mountain Project (YMP) modeling purposes based on analysis of published corrosion data on the Ni-Cr-Mo-Gd alloy and Alloy C-4.…”

Electrochemical Corrosion Testing of Neutron Absorber Materials

“…The A978 specimens were refinished from coupons previously used for the YMP corrosion studies (culled for the least amount of damage) by Lawrence Livermore National Laboratory (LLNL) (Heats E084295 and N156129). 13 These specimens…”

“…This specimen was exposed at the water line to simulated cement modified water (SCMW) at 90°C for 2,134 days at the Long Term Corrosion Test Facility (LTCTF), formerly located at LLNL. 13,29 The specimens in the test program were affixed to an insulated and threaded rod through a central hole, as shown in Figure 28. 29 Note that part of the test specimen is cut away in the drawing for clarity.…”

“…19 Because there was not sufficient corrosion product from the testing of the Grade A materials, previously provided specimens from the longer-term corrosion tests performed at LLNL were used. 13 These samples were analyzed using scanning electron microscopy with energy-dispersive x-ray spectroscopy to determine the disposition of chromium/boride particles in the corrosion products. An additional corrosion product from one sample was analyzed with x-ray diffraction (XRD).…”