Fuels corrosivity

Finally, other tests to control jet fuel corrosivity towards certain metals (copper and silver) are used in aviation. The corrosion test known as the copper strip (NF M 07-015) is conducted by immersion in a thermostatic bath at 100°C, under 7 bar pressure for two hours. The coloration should not exceed level 1 (light yellow) on a scale of reference. There is also the silver strip corrosion test (IP 227) required by British specifications (e.g., Rolls Royce) in conjunction with the use of special materials. The value obtained should be less than 1 after immersion at 50°C for four hours. 

Corrosion by the fuel usually occurs in the hot section of the engine, either in the combustor or the turbine blading. Corrosion is related to the amounts of certain heavy metals in the fuel. Fuel corrosivity can be greatly reduced by specific treatments discussed later in this chapter. 

Hydrazine compounds are widely used as fuels, corrosion inhibitors, catalysts, and dyes. However, such compounds are recognized as toxic agents consequently, their detection and processing are of much concern. Only a few recent papers pertain to the catalytic oxidation of hydrazine [148-150], with special emphasis... 

The carryover of caustic into a finished fuel blend usually has minimal effect alone on the corrosion of ferrous metals. However, in fuel systems containing a conventional tall oil dimer-trimer fatty acid or partially esterifled corrosion inhibitor, caustic can react with and negate the effect of the corrosion inhibitor. As a calcium or sodium salt, these inhibitors will no longer function effectively as an oil-soluble, fuel corrosion inhibitor. 

During the refining and processing of fuel, corrosion inhibitors, antifoulants, filmers, neutralizers, and other organic compounds may carry over into a finished product. These polar organics may attract and interact with water to tightly bind it into the fuel as an emulsion. The result is usually a cloudy, hazy fuel. These emulsions are often quite difficult to break. If the water present contains caustic, organic salts, or corrosion products, the emulsion may be quite stable. 

Previous review articles on spent nuclear fuel and UO2 corrosion have dealt with the details of uraninite alteration (Finch Ewing 1992), spent fuel corrosion in oxidizing and reducing environments (Johnson Shoesmith 1988 Wronkiewicz Buck 1999 Shoesmith 2000), and the evolution of spent fuel microstructure (Poinssot et al. 2002). In this Chapter, the behaviour of three important radionuclides (237Np, 99Tc, and 239Pu) is examined with examples of studies from spent fuel corrosion tests to illustrate the potential geochemical behaviour of these radionuclides. 

The majority of radionuclides (>90%) generated during in-reactor burning are retained in the U oxide matrix hence, their release should be closely related to the corrosion rate of the matrix. The release of Cs and I are generally independent of the fuel corrosion rate, and the metallic elements (Mo, Ru, Tc, Rh, Pd), Xe-Kr gas bubbles, and perovskite phases ((Ba,Sr)Zr03) may only be partly controlled by the matrix corrosion rate. 

In SNF corrosion tests, there has been a tendency to use the release of more soluble species Tc, Cs, and Mo as markers for fuel corrosion (Finn et al. 2002). As none of these elements are present in the U02 matrix, this approach may not reveal the actual fuel matrix corrosion rate. Furthermore, short-term leaching tests may not expose possible diffusion-limited (tl/2) release of gap and grain boundary species and assume excessive rates of reaction based on initial fast release rates. The microstructure, radiation field, and composition will change over time, so that tests carried out on fuel today may not be relevant to fuel behaviour 300 to 1000 years from now, once the high p-,y-field has decayed. 

Indications from both microscopic analyses of metallic particles from corrosion tests and evidence from the Oklo natural reactors indicate that performance assessment calculations should not assume 99Tc is easily mobilized. It is entirely inappropriate to use "Tc release as a marker for fuel corrosion because Tc is not located in the fuel matrix. The TEM examinations of corroded e-particles have shown that Mo is preferentially leached from these phases, a behaviour that is similar to the one observed at Oklo. It is interesting to note that laboratory dissolution of billion-year old 4d-metallic particles for a chemical analysis required a corrosive mix of peroxide and acid (Hidaka Holliger 1998) similar to the experience at SNF reprocessing plants. It is doubtful that the oxidation potential at the surface of an aged fuel will be sufficient to move Tc(0) from the e-metal particles. 

Buck, E. C., Finch, R. J., Finn, P. A. Bates, J. K. 1998. Retention of neptunium in uranyl alteration phases formed during spent fuel corrosion. Materials Research Society Symposium Proceedings, 506, 87-94. 

Christensen, H. Sunder, S. 2000. Current state of knowledge of water radiolysis effects on spent nuclear fuel corrosion. Nuclear Technology, 131, 102-123. 

Shoesmith, D. W. 2000. Fuel corrosion processes under waste disposal conditions. Journal of Nuclear Materials, 282, 1-31. 

Figure 16 Illustration of the procedure used to evaluate fuel corrosion performance in a nuclear waste vault (A) fuel corrosion rate as a function of radiation dose rate [from (B) in Figure 15] (B) calculated radiation dose rate decay curve (C) fuel corrosion rates as a function of time in a waste vault. The dashed line indicates that there is a limit to the acceptable extrapolation of rates determined electrochemically.

The fuel corrosion potential, ECOrr, is computed from the relationship... 

Figure 21 Schematic illustrating the one-dimensional array of layers considered in the mixed potential model of nuclear fuel corrosion in a failed (flooded) nuclear waste container.

Fossil fuels Corrosion due to SO2 in coal-fired power plants Flue gas scrubber system eliminates S02... 

There is virtually no contact between the primary circuit medium and coolant in case of the first-type cracks. During operation only gaseous and volatile fission products could be released via such cracks to the primary circuit medium. The second-type cracks could cause fuel corrosion and washing out of soluble fission products (cesiiun, strontium) and fuel particles to the coolant circuit. 

Under the pseudo-dry storage one understands the presence of water in unsealed shrouds due to either insufficient unwatering of storage pools or atmospheric precipitations. In case of considerable deviations of the storing-medium quality from the established corrosive-admixture-concentration standards rather active fuel corrosion is possible. 

Some sulfur compounds can also have a corroding action on the various metals of the engine system, varying according to the chemical type of sulfur compound present. Fuel corrosivity is assessed by its action on copper and is controlled by the copper strip test (ASTM D-130, IP 154), which specifies that not more than a slight stain shall be observed when the polished strip is immersed in fuel heated for 2 h in a bomb at lOO C (212°F). This particular method is not always capable of reflecting fuel corrosivity toward other fuel system metals. For example, service experience with corrosion of silver components in certain engine fuel systems led to the development of a silver corrosion test (IP 227). The mercaptan sulfur content (ASTM D-1219, ASTM D-3227, IP 104, IP 342) of jet fuels is limited because of objectionable odor, adverse effect on certain fuel system elastomers, and... 

---