Long Term Corrosion/Degradation Test Six Year Results

Abstract

The Subsurface Disposal Area (SDA) of the Radioactive Waste Management Complex (RWMC) located at the Idaho National Engineering and Environmental Laboratory (INEEL) contains neutronactivated metals from non-fuel, nuclear reactor core components. The Long-Term Corrosion/Degradation (LTCD) Test is designed to obtain site-specific corrosion rates to support efforts to more accurately estimate the transfer of activated elements to the environment. The test is using two proven, industry-standard methods-direct corrosion testing using metal coupons, and monitored corrosion testing using electrical/resistance probes-to determine corrosion rates for various metal alloys generally representing the metals of interest buried at the SDA, including Type 304L stainless steel, Type 316L stainless steel, Inconel 718, Beryllium S200F, Aluminum 6061, Zircaloy-4, low-carbon steel, and Ferralium 255. In the direct testing, metal coupons are retrieved for corrosion evaluation after having been buried in SDA backfill soil and exposed to natural SDA environmental conditions for times ranging from one year to as many as 32 years, depending on research needs and funding availability. In the monitored testing, electrical/resistance probes buried in SDA backfill soil will provide corrosion data for the duration of the test or until the probes fail.This report provides an update describing the current status of the test and documents results to date. Data from the one-year and threeyear results are also included, for comparison and evaluation of trends.In the 6-year results, most metals being tested showed extremely low measurable rates of general corrosion. For Type 304L stainless steel, Type 316L stainless steel, Inconel 718, and Ferralium 255, corrosion rates fell in the range of "no reportable" to 0.0002 mils per year (MPY). Corrosion rates for Zircaloy-4 ranged from no measurable corrosion to 0.0001 MPY. These rates are two orders of magnitude lower than those specified in the performance assessment for the SDA.The corrosion on the carbon steel, beryllium, and aluminum were more evident with a clear difference in corrosion performance between the 4-ft and 10-ft levels. Notable surface corrosion products were evident as well as numerous pit initiation sites. Since the corrosion of the beryllium and aluminum is characterized by pitting, the geometrical character of the corrosion becomes more significant than the general corrosion rate. Both pitting factor and weight loss data should be used together. For 6-year exposure, the maximum carbon steel corrosion rate was 0.3643 MPY while the maximum beryllium corrosion rate was 0.3282 MPY and the maximum aluminum corrosion rate was 0.0030 MPY.ii (This page is intentionally left blank.)iii ACKNOWLEDGMENTS

Evaluation of Groundwater Impacts to Support the National Environmental Policy Act Environmental Assessment for the INL Remote-Handled Low-Level Waste Disposal Project

“…The 6-year average corrosion rates, assuming 0.535-cm surface area to volume ratios for their reported results, are given in Table 3. In all cases, the fractional release rate observed by Adler-Flitton et al (2004) is less than that derived from Nagata and Banaee (1996). Inconel and ferralium 1.0E-04 2.54E-7 1.36E-7…”

“…Combining the corrosion rate and geometry data provides a fractional release from stainless steel of 1.19E-05/year in the soil where the dust suppressant had been applied. The chloride in the dust suppressant increases the corrosion rate relative to what would occur under natural soil conditions as shown by Adler-Flitton et al (2004). Based on direct testing of coupons buried 1.22 m (4 ft) and 3.05 m (10 ft) at RWMC, corrosion rates for aluminum, carbon steel, ferralium, zircaloy-4, inconel, 304L and 316L stainless steel, and 316L welded stainless steel were obtained after 1 year, 3 years, and 6 years of burial.…”

Explanation of Significant Differences Between Models used to Assess Groundwater Impacts for the Disposal of Greater-Than-Class C Low-Level Radioactive Waste and Greater-Than-Class C-Like Waste Environmental Impact Statement (DOE/EIS-0375-D) and the

“…Combining the Nagata and Banaee (1996) corrosion rate (2.22E-05 cm/year) and the Oztunali and Roles (1986) geometry factor (0.535 cm -1 ) results in a fractional release rate from stainless steel of 1.19E-05/year. In comparison, fractional release rates using average 12-year corrosion rates from Adler-Flitton et al (2011) for different metal types (see Table 4), are lower by one to three orders of magnitude. For conservatism, a 1.19E-05/year fractional release rate was used in the groundwater impacts analysis for the INL RH-LLW disposal facility.…”

Comparison of LLW Disposal Facilities at Major Department of Energy Sites

“…However, sorption is assumed to occur only within the interbed layers, as the basalt layers contain enough fractures to allow for fast pathways of infiltrating moisture. This reduces the thickness of the vadose zone to 9 m, and K d s for target radionuclides were calculated for the interbed sections (Adler Flitton et al., ; DOE Idaho, ; Holdren & Broomfield, ). Perched water has also been found above the B‐C and C‐D interbeds.…”