Copper Canisters Research Articles

Fe-oxide fracture fillings as a palæo-redox indicator: Structure, crystal form and Fe isotope composition

Penetration of oxygenated waters to the deeper sub-surface may occur in association with deglaciation events and significantly change the geochemical processes acting at depth. Such a scenario may compromise long-term storage of radioactive waste in underground repositories where copper canisters would corrode in the presence of oxygen. In this study, Fe-oxides from fractures in granite drill-cores and from drilling debris were investigated and a method developed to trace the low-temperature, oxidising conditions which may have been caused by prior deglaciations. X-ray diffraction and Mössbauer spectroscopy showed that all the examined fracture fillings contained Fe-oxides. Based on their structure and form, three genetic types of Fe-oxides were identified: (I) coarse-grained (∼ 100 nm) hydrothermal hematite; (II) very fine-grained (∼ 10 nm) amorphous Fe-oxides that precipitated during drilling; (III) Intermediate grain-size crystalline Fe-oxides, that are interpreted to have formed naturally at low-temperatures (∼ 10 °C). Fe isotope composition of the Fe-oxides was determined by multiple-collector inductively coupled plasma mass spectrometry using a 58Fe– 54Fe double-spike. δ 56Fe of the Fe-oxides ranges from − 0.8 to + 0.8‰ (relative to the IRMM-14 standard). Hydrothermal samples have intermediate δ 56Fe (− 0.3 to 0.0‰), whereas natural low-temperature samples may be isotopically lighter (− 0.8 to 0.0‰), and samples precipitated from drilling activity are isotopically heavier (− 0.2 to 0.8‰). Within the three genetic suites, δ 56Fe correlates with the relative proportion of Fe(III). For the hydrothermal samples, Fe isotope composition likely reflects input of partially dissolved chlorite. The Fe isotope composition and Fe redox state of the low-temperature and drill-induced samples is consistent with a conceptual model where Fe isotope fractionation occurs during dissolution and oxidation. In our study, the deepest sample showing evidence of natural low-temperature oxidation, putatively as a result of penetration of oxidising surface waters during deglaciation, is from a depth of ∼ 100 m.

Creep in phosphorus alloyed copper during power-law breakdown

During the first phase of storage, creep will take place in the copper canisters in the KBS-3 package for nuclear waste. The temperatures are below 100 °C, and the creep is well inside the power-law breakdown regime. Creep models for this situation have been developed. The analysed material is pure copper with about 50 ppm phosphorus. Constitutive equations for creep and other plastic deformation have been set up based on a generalised Norton expression and Kocks–Mecking’s model for the back stress. A model for the minimum creep rate based on fundamental principles for climb and glide has been derived. This model gives the correct order of magnitude for the creep rate in the temperature range from 400 to 20 °C without the use of fitted parameters. The creep exponent varies from 5 to 105 in this interval. The constitutive equations have also been formulated for multiaxial stress states.

Experimental studies of the interactions between anaerobically corroding iron and bentonite

In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters will be surrounded by bentonite buffer and placed in perforated steel containers in long horizontal boreholes in the crystalline bedrock, at a depth of ≈500 m. Under the chemical conditions in a deep repository, it is possible that the release of iron from the steel containers could influence the physico-chemical properties of the bentonite, for example, by exchange of the interlayer ions. In order to gain further insights into this process, an experimental study was undertaken, to investigate the mode of iron uptake into bentonite and the extent of changes induced in the basic physico-chemical properties of bentonite. The samples were taken from long-term anaerobic corrosion tests of carbon steel or cast iron in compacted bentonite (Na/Ca-bentonite: Volclay MX-80, ∼4% Fe 2O 3) in contact with a simple artificial groundwater at 30 °C or 50 °C. A range of analytical techniques was applied to samples of corrosion product on carbon steel and cast iron and to the bentonite surrounding the corroding specimens. Corrosion products and bentonite samples were analysed using scanning electron microscopy (SEM), electron microprobe analysis (EPMA), Raman spectroscopy, X-ray diffraction (XRD) and Mössbauer transmission spectroscopy. In addition, the bentonite samples were analysed using Fourier transform infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED), exchangeable cation analysis and cation exchange capacity (CEC) measurements. Hydraulic conductivity and swelling pressure were also measured. From visual observation, the corrosion product formed on the carbon steel in bentonite was less voluminous than that formed on steel in artificial porewaters with no bentonite, although previous work showed that the corrosion rates were slightly higher in the presence of bentonite. The Raman spectroscopy analysis showed that corrosion products on the surface of carbon steel and cast iron consisted of an inhomogeneous mixture of magnetite, hematite and goethite. The predominant species was magnetite. In the bentonite, the concentration of iron decreased with increasing distance away from the iron–bentonite interface, with local iron concentrations as high as 20 wt% in some experiments. The total iron content of the bentonite in contact with corroding carbon steel wires increased by several percentage points during the experiments and the cation exchange capacity of the bentonite was reduced. After contact with corroding steel wires the hydraulic conductivity of MX-80 increased substantially. The results of the analyses were consistent with ion exchange of Fe 2+ ions with Na + ions in the montmorillonite interlayer positions but the exact chemical location of all the additional Fe 2+ ions is currently uncertain. There was no evidence for the transformation of montmorillonite to an iron-rich clay mineral phase.

Prototype repository: A full scale experiment at Äspö HRL

At Äspö Hard Rock Laboratory a full scale test of the Swedish concept for disposal of nuclear waste (KBS-3V) is in progress. The Prototype Repository project consists of two sections. The installation of the first section was made during summer and autumn 2001 and the second section during spring and summer 2003. Section 1 consists of four full-scale deposition holes, copper canisters equipped with electrical heaters, bentonite buffer consisting of blocks and pellets and a deposition tunnel backfilled with a mixture of bentonite and crushed rock, ending with a concrete plug. Section 2 consists of two full-scale deposition holes with a backfilled tunnel section and ends also with a concrete plug. Altogether 84 large bentonite blocks, with a total weight of about 130 tons, were installed and more than 2000 tons of backfill material were mixed and compacted in situ. Earlier developed techniques for both manufacturing and installing the buffer and the backfill were used in the project. Measurements and data from the installation allow calculations of the expected density in the buffer and in different parts of the backfill. The bentonite buffer in deposition holes 1, 3, 5 and 6, the backfill and the surrounding rock are instrumented with gauges for measuring temperature, water pressure, total pressure, relative humidity, resistivity, canister displacement and rock stresses. The instruments are connected to data acquisition systems by cables protected by tubes. These tubes are led through the rock in watertight lead-throughs to a nearby tunnel where the data acquisition systems are situated. More than 1100 transducers have been installed in the rock, buffer and the backfill. The technique for protecting the transducers from high water and swelling pressure was developed in this and preceding projects and furthermore different designs of transducers are used for the same type of measurement in order to compare their behaviour. The deposition holes have different water inflow rates (from 0.0007 to 0.08 l/min), resulting in different water uptake rates of the buffer. The water ratio as a function of time for different parts of the buffer can be estimated from measurement of the relative humidity in the pore system of the buffer. Deposition hole 1 with a relatively high water inflow (0.08 l/min), shows in some parts of the buffer very high degree of saturation while the drier holes 2, 3, 4, 5 and 6 (0.0007–0.003 l/min) show a very slow saturation rate in most parts of the buffer. The temperature in the buffer and on the surface of the canisters is carefully studied. The temperature measurements indicate a rather large drop in temperature (approx. 10 °C) over the 10 mm gap between the canister and the buffer. In deposition hole 1 the gap has vanished due to high degree of saturation, resulting in a lower temperature on the surface of the canister. The displacement of the canisters in deposition holes 3 and 6 has been measured continuously with six transducers in each deposition hole. The measurement allows calculation of the displacement of the canisters in all three directions. The maximum measured vertical displacement so far is about 8 mm upwards. The water uptake in the backfill is measured continuously with soil psychrometers. The results indicate a high degree of saturation close to the rock wall and on top of the buffer in the deposition holes, while the backfill in the more central part of tunnel shows slow increase in water ratio over the time. Transducers for measuring suction in the rock (soil psychrometers) have been installed very close to the surface of one of the deposition holes. The transducers are measuring rather high suctions close to the rock surface, indicating a not fully saturated pore system of the rock. The paper describes the following items: the test design, the installation phase, example of measurements made during the water uptake and some preliminary evaluations of water uptake of both the buffer and backfill up to November 1, 2004. The paper is mainly focused on the engineered barriers.

Close-die forging of large Cu-lids by a method of low force requirement

This paper presents a FE-analysis and experimental results of a hot forging method for fabrication of large copper canister lids with a low forging load. The forging sequence is carried out in two parts, namely axisymmetric and cogging. The cogging tool is used to bite off small areas of the workpiece periphery surface at the same time as the outer material is forced into the deep die cavity of the bottom die. During this process, the bottom tool is rotated about 45° after each pressing before a new bite is taken. As a result the main part of the cavity is filled at the same time as a protrusion develops at the central part of the workpiece. The cogging tool works on it later. Due to the small contact surface between the upper tool and the workpiece, the forging load needed to complete die filling is small and does not exceed the maximum load of the press. The process was earlier optimised so that no flash was needed for complete die filling. Process parameters affecting the evolution of the microstructure are analysed. Material flow and forging load in different stages of the process are studied. Microstructures obtained in the final product are presented for different locations along the radius of a vertical symmetry plane of the circular lid. Grain size evaluations are roughly co-related to the accumulated effective strain distribution obtained during the different manufacturing operations and to the temperature distribution obtained at the end of the forming process. It is concluded from the simulations that a 4600-t press is sufficient to achieve complete die filling and from experiments that an acceptably small grain size is obtained throughout the lid. From the simulation results the whole volume of the lid has experienced high strains after the manufacturing steps. No regions of low strain were found which according to experience is coincidental with a coarse-grained microstructure.

Reliability evaluation of NDT techniques for Cu-welds for risk assessment of nuclear waste encapsulation

Abstract In order to handle the long living radioactive waste (spent nuclear fuel) SKB is planning to build a deep repository that requires no monitoring by future generations. The spent nuclear fuel will be encapsulated in copper canisters consisting of a graphite cast iron insert shielded by an outer 30–50 mm thick copper cylinder for corrosion protection. The most critical part of the encapsulation process is the sealing of the canister, which is done by welding the copper lid to the cylindrical part of the copper shell using friction stir welding and electron beam welding. The quality of the welding process and the reliability of the NDT system – radiographic and ultrasonic testing – must be satisfactorily determined and combined to derive assumptions regarding the frequency of undetected welding defects for a set of canisters as input for the risk assessment. This is done using the POD method according to the “Reliability Handbook MIL 1823” and its generalization.

Corrosion of Copper Canisters Through Microbially Mediated Sulphate Reduction

ABSTRACTA biogeochemical model was developed with an aim to illustrate the transport and reaction processes that may be involved in copper canister corrosion by sulphide in a deep repository for nuclear waste. Sulphide concentrations in the groundwaters in Sweden are relatively low and are generally considered to be of little importance for corrosion of the copper canisters. Sulphate, however, is present in relatively large amounts (50-700 mg/L) and may be reduced to sulphide by reaction with organic matter. Mediated by microbes, the reduction rate may be increased considerably compared to abiotic reduction. Microbially mediated sulphate reduction occurs in many natural environments, provided that reactive organic matter is available. Groundwater analyses indicate relatively high concentrations of dissolved methane (up to 16 mg/L) which thermodynamically is a suitable reducing agent. This processes could occur in fractures inthe bedrock provided that substrates are continuously supplied and that there is a sink for the reaction products. In the repository, the copper canisters may provide a sink for sulphide that yields a favourable environment for the microbe population. The model domain includes a canister with surrounding backfill material intersected by a hydraulically conductive fracture. Transport of substrates and reaction products in the fracture and backfillas well as microbially mediated reaction at the fracture opening is included in the model. Results indicate that microbially produced sulphide could potentially contribute to canister corrosion.

Further Studies of the Anaerobic Corrosion of Steel in Bentonite

ABSTRACTIn the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters with cast iron inserts will be surrounded by bentonite buffer and mounted in perforated carbon steel support structures in boreholes within the bedrock. The groundwater will be reducing, leading to anaerobic corrosion of the ferrous material. It is important to understand both the effect of bentonite on the corrosion behaviour of the steel and the effect of the corrosion products on the performance of the bentonite. Previous work on the corrosion of steel in bentonite was extended to investigate a wider range of conditions, including the possible effects of alkaline plumes released from concrete support structures and the effect of chloride concentration and temperature on the corrosion rate of steel in bentonite. Corrosion rates were measured by collecting hydrogen produced by the anaerobic corrosion of iron. In addition, a range of analytical techniques was applied to study the composition and morphology of the corrosion products and the distribution and chemical state of the iron released into the bentonite. Comparison was also made between corrosion in compacted bentonite and artificial bentonite porewater. In the presence of bentonite, the corrosion product layer was relatively thin compared to fully aqueous conditions, probably because the ferrous ions released by corrosion exchanged with the bentonite interlayer or attached to the surface of the bentonite grains, rather than forming a separate iron oxide phase.

Creep of the copper canister in the Swedish program

ABSTRACTThe Swedish programme for disposal of high level nuclear waste includes the development of a container which comprises a cast iron load bearing canister contained in a 50 mm thick copper corrosionshield.The temperature of the outside of the canister is likely be up to 100°C, and repository processes may lead to long term loads of up to 50MPa. Creep of the copper is therefore an issue. SKB (The Swedish Nuclear Fuel and Waste Management Co.) have been conducted tests on three materials, OF copper containing 10ppm sulphur (OF1), OF copper containing 6ppm sulphur (OF2) and OF copper containing 6ppm sulphur and 50ppm phosphorus (OFP). In order to improve confidence in extrapolation of test results to practical temperatures and stresses, it is desirable to support the extrapolation procedures with a physical model.Life predictions made using the Frost and Ashby model [5] together with a simplification of the Cocksand Ashby model [6] provide good agreement with published experimental data for OF2 and OFPmaterials. Extrapolation of this data using the model leads to life predictions of 12,000 years for the OF2material and 120,000 years for OFP material. The prediction for OFP depends on an assumption that an observed strengthening mechanism conferred by phosphorus at high stresses and temperatures, is equally as effective under repository conditions.OF1 material fails after a relatively short life and by a different mechanism to OF2 and OFP. The changein mechanism may be explained, using the model [6], for cases where segregating species reduce surface energy of grain boundary voids. It is suggested that in this case the segregating species is sulphur.

Impact of iron released from steel components on the performance of the bentonite buffer: a preliminary assessment within the framework of the KBS-3H disposal concept

ABSTRACTSteel components in the engineered barrier of HLW repositories have a potential to react with the clay buffer and induce adverse effects on its properties. These effects have been assessed within the KBS-3H disposal concept, which includes spent fuel in copper canisters surrounded by bentonite blocks and a steel supercontainer (SC), placed within tunnels in deep crystalline Olkiluoto-type host rock. Based on literature review and thermodynamic modeling, the SC is predicted to completely corrode within a minimum of a few thousand years. The resulting corrosion products are expected to be magnetite, and depending on groundwater compositions, also iron sulfide and perhaps siderite. Furthermore corrosion-derived Fe(II) may react with the clay to form non-swelling phyllosilicates, such as berthierine. From simple mass balance estimates and by applying a more realistic reactive transport model, it can be deduced, that the effect of iron from the SC on the integrity of the bentonite buffer is limited. However, large uncertainties in adequately quantifying this effect pertain due to limited process knowledge on Fe-bentonite interactions.

Development of a rapid screening test for SCC susceptibility of copper in disposal vault conditions

ABSTRACTStress corrosion cracking is a potential failure mechanism of the copper canister proposed to be the main corrosion barrier in the Scandinavian design of the final nuclear waste disposal vault. The main target in SCC-oriented research is to determine the limiting values for the critical concentration of harmful species, the potential range in which these species cause SCC and the threshold stress level required for SCC. The present paper attempts to redefine the criteria for SCC susceptibility of copper in acetate solutions through analysis of potentiodynamic curves using both rotating disc and thin plate electrodes insulated on one side. A potential range in which the current densities at a slow sweep rate are lower than those at a fast sweep rate exists for Cu in 0.001 M - 0.1 M acetate. However, the values of the current densities within this range are significantly smaller than those postulated for active anodic dissolution, implying dissolution mediated by a surface film. New criteria for the SCC susceptibility of pure copper in acetate solutions have been formulated through Stern-Geary analysis of the polarisation curves. Several electrochemical characteristics, such as the current density at the positive crossover potential, the ratio between the corrosion current densities determined from the slow and fast sweeps, as well as the anodic current density in a fast sweep show a clear jump for concentrations between 0.01 M and 0.05 M. This, however, cannot yet be considered as an indication of SCC susceptibility at higher acetate concentrations, as evidenced by complementary SSRT tests.

Coupled transport/reaction modelling of copper canister corrosion aided by microbial processes

Summary Copper canister corrosion is an important issue in the concept of a nuclear fuel repository. Previous studies indicate that the oxygen-free copper canister could hold its integrity for more than 100000 years in the repository environment. Microbial processes may reduce sulphate to sulphide and considerably increase the amount of sulphide available for corrosion. In this paper, a coupled transport/reaction model is developed to account for the transport of chemical species produced by microbial processes. The corroding agents like sulphide would come not only from the intruding groundwater, but also from the reduction of sulphate near the canister. The reaction of sulphate-reducing bacteria and the transport of sulphide in the bentonite buffer is included in the model. The local depth of copper canister corrosion is calculated by the model.

Creep testing of thick-wall copper electron beam and friction stir welds

Abstract:Thick section copper canisters are planned to be used as a corrosion protection of nuclear waste disposal containers for long term underground deposal in Sweden. The copper canisters will have the top and possibly the bottom lid welded to the canister walls using electron beam or friction stir welding. Due to the high external hydrostatic pressure and the relatively high temperature of the waste during the first one hundred years the copper will creep. The creep process will close the manufacturing gap between the cast iron container and the copper canister. The creep ductility must be sufficient to avoid cracking of the weld.Specimens cut from the friction stir welds and the electron beam welds have been creep tested at temperatures ranging from 75 to 175 °C. Cross-weld specimens were used for both friction stir and electron beam welds. Weld metal, heat affected zone and base metal were also studied for friction stir welds. The results for the electron beam welds show that the main creep deformation is concentrated to the weld metal where the failure takes place. Weld metal and most cross-weld tests of friction stir weld material show similar creep lives and ductility as base metal tests. Ductility at rupture was found to exceed 30% for friction stir weld specimens, and the Norton power law exponent was determined to be between 30 and 50.

Finite Element Modelling of Temperature Distribution in Friction Stir Welding Process and Its Influence on Distortion of Copper Canisters

AbstractIn an effort to enhance safety for long time disposal of waste nuclear fuel, friction stir welding has been developed as one alternative to seal copper canisters. To avoid the formation of voids and cracks during the welding process, an understanding of the heat and material flow andthereby the evolution of the microstructure, is of great importance. Finite element modelling has been used to simulate the heat and material flow as well as thermal expansion during the friction stir welding process. A model involving heat transfer, material flow, and continuum mechanics has been developed. The steady state solutions have been compared with experimental temperature observations as well as analytical solutions, showing good agreement. Temperature distribution is affected by the welding speed. For a given reference pointperpendicular to the welding direction, a lower welding speed corresponds to a higher peak temperature. The plunging position of welding tool influences the temperature distribution and therefore the displacement distribution of the weldment.

A Weld that Lasts for 100,000 Years: Friction Stir Welding of Copper Canisters

ABSTRACTFriction Stir Welding (FSW) is a novel solid-state joining process where the work pieces are joined together using a rotating non-consumable tool. The process has mainly been used for joining aluminium alloys, and has not yet been used in production for any other metal. However, the results from the development program confirm that FSW can consistently seal 50mm thick copper canisters without creating defects. A new machine is now installed at SKB's Canister Laboratory to further automate the process to production level.

Microstructure Development in Copper Welded by the FSW-Process

ABSTRACTTo ensure safe storage of nuclear fuel waste, copper canisters are proposed as corrosion barrier. One alternative for sealing the copper canisters is Friction Stir Welding (FSW). During the joining process friction heat and mechanical deformation appear between the rotating tool and the material being welded. Liquid metal will not form, since this is a solid state welding process. Three distinct microstructural zones are developed namely the nugget, the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ). The nugget is in the centre of the weld, where the pin is located and where severe plastic deformation occurs that leads to recrystallisation. Surrounding the nugget, the TMAZ is only partially recrystallised, due to lower temperature increase and deformation compared to the nugget. The third zone, HAZ, surrounds the TMAZ. The initial nugget can have a classic round aluminium nugget image, when the welding conditions are cold, but the steady state nugget, is wider near the shoulder and shorter in the weld root.

Microbial Sulphide Production in Compacted Bentonite at the Commencement of Long-Term Disposal of High-Level Radioactive Waste

ABSTRACTThe use of nuclear reactors produces electrical power but also high-level radioactive waste (HLW). In Sweden it has been decided that the HLW shall be disposed of in a deep geological repository 500 meters underground. The HLW will be encapsulated in copper canisters, surrounded by bentonite and then the access tunnel will be backfilled with a bentonite and crushed rock mixture.We have investigated activity of sulphate reducing bacteria (SRB) in compacted bentonite with densities of 1.5, 1.8 and 2.0 g·cm−3 using stainless steel oedometers with 35SO42- as the main sulphur source for the SRB. The investigations were performed under in situ conditions at a depth of 450 m at the Äspö Hard Rock Laboratory. Canister type copper plates were placed in the oedometers, with the top either in contact with the added groundwater or with 3–4 mm bentonite between the plate and the added groundwater. Radioactive hydrogen sulphide formed by the SRB reacted with the copper and formed radioactive copper sulphide, which was measured by electronic radiography using an Instant Image Micro autoradiography instrument (Packard). A similar set-up with filter-sterilized groundwater (0.2 μm) was used as control. A second experiment was set up as the first experiment but using only filtered groundwater and adding heat treatment of the bentonite in the control. Here, we show that SRB were active and produced hydrogen sulphide during the initial phase of bentonite swelling. The activity of the SRB was inversely correlated with the final density of the bentonite as the highest density had the lowest overall SRB activity. We also found that SRB were present in a dormant state in the commercial MX-80 bentonite. By addition of water, these dormant SRB became active and started to produce hydrogen sulphide.

The Impact of Cementitious Materials on the Corrosion of Copper Canisters

ABSTRACTCementitious materials could be used in an underground repository as seals, bulkheads, grouts, or to provide a smooth surface for vehicles in the rooms and tunnels during repository construction. There is a possibility that an alkaline plume could be released from the cementitious materials in the repository and impact the corrosion behaviour of the canisters. The available literature information on the corrosion and electrochemical behaviour of copper in alkaline environments has been reviewed. Alkaline conditions promote passivation of the canister, whereas the presence of chloride groundwaters supports general dissolution. Localized corrosion due to an alkaline plume is considered to be unlikely because the protectiveness of the passive film (as measured by the difference between the corrosion and pitting potentials) increases with increasing pH.

Analogues for the Corrosion-induced Expansion of Iron in HLW containers

ABSTRACTIn Sweden, spent nuclear fuel will be encapsulated in sealed cylindrical canisters, consisting of a cast iron insert and a copper outer container. The canisters will be placed in a deep geologic repository and surrounded by bentonite. If a breach of the outer copper container were to occur the cast iron insert would undergo anaerobic corrosion, forming a magnetite film whose volume would be greater than that of the base metal. In principle there is a possibility that accumulation of iron corrosion product could cause expansion of the copper canister. Anaerobic corrosion rates are very slow, so in the work described in this paper reference was made to analogous archaeological materials that had been corroding for long periods in natural anoxic aqueous environments. This paper describes a number of archaeological artefacts containing iron and copper corroding in constrained geometries in anoxic natural waters. No evidence has been obtained which would suggest that severe damage is likely to occur to waste canisters as a result of expansive corrosion of cast iron under repository conditions.

Atmospheric Corrosion of Copper 450 Metres Underground. Results From Three Years Exposure in the Äspö HRL

ABSTRACTResults from an atmospheric exposure of copper at the Äspö Hard Rock Laboratory (HRL) are reported. Corrosion test coupons were exposed under sheltered conditions at 450 meters depth. The exposure was performed in order to gain insight into the likely state of a copper canister surface at the time when water begins to fill a repository for nuclear waste. The conditions for the experiment were selected to be relevant for the conditions predicted for a repository during an initial dry phase. Visual observations show that copper exposed at ambient temperature remained bright and shiny whereas coupons exposed at elevated temperature had a dull greenish appearance.