Contents Issue 2 (2000)

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Gernot Repphun and Andreas Hiltpold

Corrosion Potential and Contamination in BWR

The corrosion on steel surfaces in boiling water reactors (BWR) is an electrochemical process. For this reason, the electrochemical corrosion potential (ECP) influences the steel corrosion to a considerable extent. The electrochemical corrosion potential affects the protective layer form, growth, and susceptibility to stress corrosion cracking. The oxide layer structure has an effect on corrosion or erosion of materials and the contamination of steel surface with activated corrosion products. The increase of ECP contributes to a certain extent to oxide layer stabilization. In contrary, the ECP reduction might have a positive influence on the susceptibility to stress corrosion cracking. The coolant ECP is essentially fixed by the radiolytic-formed oxygen and amounts to 50 - 250 mV (SHE) at NWC conditions. The ECP can be decreased by the oxygen concentration reduction, e.g., by the hydrogen addition into the coolant (HWC).

The experimental results regarding the oxygen transport influence over the ECP at different flow conditions under BWR conditions are presented as well as the calculations with the mixed potential model. The results demonstrate that the oxygen transport on the phase boundary coolant/steel is of significant influence on the ECP. In addition, it is shown that a lower ECP results in an increased activity intake of the corrosion layers.

PowerPlant Chemistry 2000, 2(2)

Robert Svoboda, Harald Sandmann, and Frank Gabrielli

Steam/Water Cycle Chemistry: Current Developments and Challenges in the Future

Current developments in steam-water cycle chemistry comprise the requirements of combined cycle plants. An example is the optimization of cycle water treatment with drum-type heat recovery steam generators. Traditional techniques as All Volatile Treatment and Phosphate Treatment are applied. Experiences indicate the necessity for individual consideration of the different boiler stages, which introduces a complexity that will be one of the many challenges the chemist will meet in a combined cycle plant.

PowerPlant Chemistry 2000, 2(2)

Karol Daucik, Niels Henriksen, and Jørgen Peter Jensen

Supercritical Steam Oxidation of Steel Surfaces

Water and steam react readily with steel surfaces at elevated temperatures. The reaction results in an oxide protective layer on the steel surface. The reaction rate depends on a number of parameters among which the temperature and steel properties are the most important. Hydrogen is another product of the reaction between water/steam and steel. Hydrogen formation monitoring make the evaluation of the reaction rate possible.

Monitoring of hydrogen concentration in steam in four sampling points of an ultra supercritical boiler was performed. The data were related to the operational parameters. Good correlation was found between the hydrogen concentration and the exit steam temperature. However, the hydrogen concentration is an integral value expressing the sum of the formation in the superheater or reheater. Therefore, approximations are required for data evaluations. The evaluated results are compared with a model for growth of protective layer based on measurements of thickness of protective layer on tube samples. Reasonable agreement was found between the evaluated hydrogen concentrations and the model based on tube samples.

The pros and cons of the hydrogen monitoring in steam are discussed particularly concerning the indication of local high temperatures within superheaters and reheaters.

PowerPlant Chemistry 2000, 2(2)

VGB Conference "Chemistry in Power Plants 1999" - Extended Abstracts

The contribution compiles twenty-six extended abstracts of the papers presented in the course of the VBG Conference "Chemistry in Power Plants 1999" in Essen, Germany, last October.

A.G.L. Zeijseink and J.B.J. van den Bergen: A Method for Cost-benefit Analysis of Power Plant Chemistry; J. Bane et al.: Oxygen Treatment of a 300 MW Drum Boiler;

P. Necker et al.: Restructuring of the Water Supply and Disposal at the Power Station Site Altbach/Deizisau Following Construction and Operation of the Combined Heat and Power Plant HKW 2;

G. Kuhnle et al.: Investigations During the Chemical Cleaning and Commissioning of the Water/Steam Cycle at Combined Heat and Power Station 2, Altbach/Deizisau;

R. Ertelt and H. Prenzel: Lubricating Oil Management;

H. Winkler and U. Wasko: Selective Removal of Mercury from Sludge Originating in Flue Gas Desulphurisation Sewage Plants;

E.V. Maughan et al.: The VGB Guidelines for Organic Matter and Dissolved Carbon Dioxide in the Steam/Water Circuit of Power Plants - Crossing the Next Frontier in Power Plant Chemistry;

H.D. Pflug et al.: Theoretical and Practical Aspects for the Verification of Carbon Dioxide in the Water-Steam Cycle of Power Plant;

S. Huber: Behavior of Natural Organic Matter in Boiler Feedwater Production;

T. Wacker and M. Rziha: Method for the Determination of Traces of Short-chain Organic Acids in Water/Steam Cycles,

R.L. Cowan, et al.: Experience with Noble Metal Chemical Addition in BWRs;

V. Schneider et al.: Magnetit Depositions in the Plant Cycle of PWRs;

M. Meintker and G. Enkler: Reduction of Operating Costs by Application of Electro Membrane Process in the Coolant Treatment of Nuclear Power Plants with Pressurized-water Reactor;

A. Puthawala and N. Henzel: Hydrogenation of BWR with System-integrated Membrane Electrolyser;

J. Haag et al.: Activity and Dosage Capacity Development During Zinc Dosage in Power Plant Biblis;

R. Ruf et al.: Transport of Corrosion and Activated Products During Zinc Dosage in Nuclear Power Stations Biblis and Obrigheim: A Stock-taking;

M. Rosskamp and U. Staudt: Operating Experience with Brass Condensers in German BWR Plants;

G. Repphun and A. Hiltpold: Dependence of the Corrosion Potential on the Flow Regime under LWR Conditions,

S. Kiil et al.: Modeling of Limestone Dissolution in Wet Flue Gas Desulphurisation Systems: The Importance of an Accurate Particle Size Distribution;

N.O. Knudsen and F. Fogh: Measures by Aluminum-induced Limestone Inhibition at Gypsum-producing -Desulphurisation Plants;

B. Herbst: Comparison of Different Test Methods for the Determination of Reactivity of Limestone Products used for Flue Gas Desulphurisation;

M. Hein et al.: Corrosions in the Flue Gas Path - Results Achieved by the Working Group;

A. Glasner and K. Baernthaler: Optimization of a Limestone Scrubber by Means of CFD Models and 3D Simulation of the Absorption of SO2;

J. Wirling et al.: Adsorptive Waste Gas Cleaning During Sewage Sludge Co-combustion in an Industrial-scale Lignite-fired Power Plant;

M. Luckas and B. Heiting: Simulation of the Wet Limestone Flue Gas Scrubbing Process in Power Plants;

W. Hoffmann et al.: Efficiency Improvement in Flue Gas Desulphurisation systems - Use of Adipic Acid in the Frimmers-dorf Lignite-fired Power Plant of RWE Energie AG,

make this report more complete.