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

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A 1970 study initiated by the National Bureau of Standards (NBS), now known as the National Institute of Standards and Technology (NIST), buried over 6000 corrosion coupons or specimens of stainless steel Types 201, 202, 301, 304, 316, 409, 410, 430, and 434. The coupons were configured as sheet metal plates, coated plates, cross-welded plates, U-bend samples, sandwiched materials, and welded tubes. All coupons were of various heat-treatments and cold worked conditions and were buried at six distinctive soil-type sites throughout the United States. The NBS scientists dug five sets of two trenches at each of the six sites. In each pair of trenches, they buried duplicate sets of stainless steel coupons. The NBS study was designed to retrieve coupons after one year, two years, four years, eight years, and x years in the soil. During the first eight years of the study, four of five planned removals were completed. After the fourth retrieval, the NBS study was abandoned, and the fifth and final set of specimens remained undisturbed for over 33 years. In 2003, an interdisciplinary research team of industrial, university, and national laboratory investigators were funded under the United States Department of Energy's Environmental Management Science Program (EMSP; Project Number 86803) to extract part of the remaining set of coupons at one of the test sites, characterize the stainless steel underground corrosion rates, and examine the fate and transport of metal ions into the soil. Extraction of one trench at one of the test sites occurred in April 2004. This report details only the characterization of corrosion found on the 14 welded coupons-two cross welded plates, six U-bends, and six welded tubes-that were retrieved from Site D, located near Wildwood, NJ. The welded coupons included Type 301, 304, 316, and 409 stainless steels. After 33 years in the soil, corrosion on the coupons varied according to alloy. This report discusses the stress corrosion cracking and crevice corrosion cracking of the U-bend coupons; the minimal corrosion found on the cross-bead plates; and the general, pitting, and crevice corrosion found on the welded tubes. In general, the austenitic Type 301, 304 and 316 samples showed little if any corrosion after 33+-years in the soil, whereas the ferritic alloys-Type 409 and 434-showed a spectrum of corrosion.

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