Canisters corrosion

Conditioning of the near field geochemistry by the canister corrosion processes... 

Gases may also be produced from chemical and radiolytic interactions of high-level waste and the anticipated brine which may migrate to the waste canisters. Canister corrosion is expected to occur and can result in H2 and HCl generation. These reactions must be examined and quantified under the anticipated conditions of pressure, temperature and leachant chemistry to determine whether they can be accomodated or should be prevented in a full-scale HLW repository. 

Canister corrosion. The Steel canister will corrode slowly, initially consuming any trapped oxygen in a moist atmosphere and then anaerobically in the presence of liquid water after the bentonite saturates. Based on very pessimistic assumptions, it is calculated that canisters fail mechanically after 10 years (NWGCT 1984 Steag Motor Columbus 1985). More recent analyses indicate that both the corrosion rates considered (McKinley 1991) and the safety margins for the mechanical calculations (Attinger ... 

Due to chemical buffering by the canister corrosion products and bentonite minerals (particularly pyrite and siderite), it is not expected that the oxidizing conditions, which may form at the surface of spent fuel, will have a significant influence on the rest of the EBS (Smith Curti 1995). In this case, the solubility limits derived for the vitrified waste case can be directly applied - a redox front may exist within the canister corrosion products or bentonite but this will not influence releases from the nearfield to the geosphere. Extensive precipitation may occur at this redox front which may initially be in the form of colloids. The small pore size (average c. 2-lOnm, Pusch 1980 McKinley 1988) of the compacted bentonite should ensure that any colloids formed are immobile in this... 

Canister stress and stability analyses have shown that a canister suffering pitting corrosion to a depth of 50 mm will still survive the maximum external isostatic pressure of 30 MPa (Steag Motor Columbus 1985), indicating that the conservative assessment of 30 mm canister corrosion in 1000 years still leaves a high margin of safety in the design. 

Fig. 1. Redox scales for important components of groundwater and engineered barriers in the Swedish repository design concept. At left an arithmetic scale lists redox potentials from —0.6 V up to +1.0V. The scales are qualitative, but are based on unit activities of all reactants and products except protons (pH = 7) at 25°C. The centre scale lists some major redox couples that commonly occur in groundwater. The oxidized form of each element is listed on the left, and the reduced form on the right. Oxidized forms (the oxidants) can react with any reduced forms (reductants) that are lower on the scale. The scale at right lists important redox couples that correspond to important engineered barriers in the Swedish repository concept. The possibility of copper canister corrosion and spent fuel oxidation is of concern to repository performance.

In unalloyed steel containers formamide discolors slowly during shipment and storage. Both copper and brass are also subject to corrosion, particularly in the presence of water. Lead is less readily attacked. Aluminum and stainless steel are resistant to attack by formamide and should be used for shipping and storage containers where the color of the product is important or when metallic impurities must be minimized. Formamide attacks natural mbber but not neoprene. As a result of the solvent action of formamide, most protective paints and finishes are unsatisfactory when in contact with formamide. Therefore, formamide is best shipped in containers made of stainless steel or in dmms made of, or coated with, polyethylene. Formamide supphed by BASF is packed in Lupolen dmms (230 kg) or Lupolen canisters (60 kg) both in continental Europe and overseas. 

Health and Safety. Protective clothing that is compatible with the remover formula must be worn. Caustic soda baths should be ventilated to remove vapors from the work area. Most caustic removers are corrosive and cause severe bums with minimal contact to the skin. Canister respirators that are compatible with the remover should be worn. 

Storage stability Unstable polymerizes without stabilizer stable for less than 30 days in canister munitions will polymerize to form the solid cyanuric chloride which is corrosive and may explode. 

The transport process from the repository is schematically illustrated in Figure 3. Radionuclides and corrosion products would diffuse from the canister into the groundwater, and the migration will then be retarded first in the backfill barrier and after that in the bedrock. 

An example of such a product is ioBio , marketed by Baltimore Aircoil Co. (BAC). It is proposed for small cooling systems. This system is, in effect, an in-line dispenser of prilled elemental iodine (U), with replaceable iodine canisters available. The equipment is placed in the makeup waterline to the tower, and in-line options include filters, water meters, and back-flow prevention devices. Claims made are that the biocidal action of the elemental iodine is not affected by changes in temperature, system load, or water chemistry. Also, the system is compatible with virtually all scale and corrosion inhibitors and does not contribute to the corrosion of metal surfaces. 

Another underground disposal site project is in Finland at the Olkiluoto Nuclear Power Plant. The proposed waste site will store spent fuel rods in iron canisters sealed in copper shells to resist corrosion. The canisters will be placed in holes surrounded by clay far below ground. The project is slated for completion in 2020. 

Metered-Dose Inhalation Aerosols Quantity of delivered dose, total number of acceptable doses delivered, color, solvate formation with propellant, particle size distribution, weight loss of canister (i.e., loss of propellant), pressure, valve corrosion, and storage in both upright and inverted positions. 

The smoke thus produced is only one-half as dense as sulfur trioxide smokes, but is less corrosive and far more penetrant to the gas-mask canisters used during the w ar. For this last reason tin tetrachloride w as employed principally in mixtures w ith phosgene and chlorpicrin to increase the visibUity and penetrability of the gas cIoucaused other compounds to be substituted toward the end of the w ar. 

---