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Iron transport, oxide deposition and pressure loss in once-through steam generators are all strongly influenced by the choice of feedwater chemistry. However, the choice of plant feedwater chemistry is also determined by the need to ensure integrity of the pressure boundary throughout the steam-rising circuit. This paper describes investigations of iron transport, oxide deposition and pressure loss in a full-scale model boiler, to determine the best method available to control increasing pressure loss in AGR helical boilers by modification of the feedwater chemistry, that does not risk unacceptable damage of the boiler tubing. The influence of both pH and changing REDOX conditions are presented. A plant trial of one of the options is also described.

Specific nuclear resonance reactions, 4He ion backscattering and ESCA have been used to investigate the depth distribution of oxygen, carbon, fluorine and magnesium in complex corrosion films formed on Magnox AL 80 after exposure to nuclear reactor coolant gas and to multi-component aqueous solutions. Results of experiments with water enriched in H218O have shown that magnesium hydroxide which is highly permeable to solution is formed at the metal/film interface. The oxide formed in hot CO2 contains carbon, carbonate and traces of carbide-like material. This oxide hydrates uniformly in solutions of pH ⩾ 11.5 but complete equilibration with solution is rather slow. In solutions containing fluoride ions which inhibit the corrosion reaction the product is a hydroxy-fluoride Mg(OH)2−x and fluoride also exchanges to an appreciable extent with pre-formed magnesium hydroxide.

Thin layer surface activation is a technique in which the surface layers of a material are made radioactive by high energy charged particle bombardment. The resulting activity distribution as a function of depth within the surface is well defined, and consequently measurement of the activity loss from the material provides a means of monitoring any surface loss which has occurred. The application of this technique to the measurement of erosion-corrosion losses from mild steel specimens under boiler feedwater conditions is described, and further possibilities for its application are discussed.

Ion backscattering at MeV energies, coupled with nuclear reaction analysis, has been used to determine quantitatively the composition of complex corrosion films produced by the exposure of 316 stainless−steel specimens to a variety of alkaline solutions. The oxygen content as a function of depth, up to about 2 μ, and the trace heavy metal content were determined by helium backscattering at 2.9 MeV. The lithium content was measured by means of the Li7 (p,α) reaction at Ep = 3 MeV, with a calibration achieved by comparison with LiNbO3. It is shown how much more valuable such ion−beam techniques become when combined with microscopic examination using SEM, EDAX, and optical methods. In this way, for example, the variation in composition with depth has been correlated with oxide thickness. The advantages of this form of analysis for other corrosion problems will be described.