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[en] The present paper describes the influence of the secondary side Water Chemistry on the operating behaviour of KWU U-tube steam generators. This description includes the operating experience both with AVT (All Volatile Treatment) and PO₄-treatment of the U-tube steam generators. Various aspects of design and tube material and their effect on operational experience regarding flow distribution, corrosion product behaviour and the corrosion resistance in aqueous media have also been discussed. It has been concluded that at present time on the basis of the proved design, material and chemistry of KWU U-tube steam generators there is no need for a change in any of the given parameters. (orig.)

[en] There are currently 77 steam generators of Siemens design, containing a total of around 327,000 tubes in operation in 23 plants worldwide. Between them, these components have clocked up approximately 950 years of operation. Since the time when the first of these originally went into service 24 years ago, leaks have only occurred in 13 of the 327,000 tubes and less than 0.4% of all tubes have had to be plugged. The key to this success lies not only in the component design, selected materials, and water chemistry, but also in the service technologies applied for maintenance. This paper will describe three examples of such advanced technologies i.e. secondary side steam generator chemical cleaning and primary side mechanical and chemical decontamination. (author)

[en] In the area of primary coolant chemistry two parameters can be varied in a controlled manner. Those are the lithium (or potassium) and the hydrogen concentrations. Such variations are necessary to minimize the metal release rates of the structural materials and avoid any type of selective corrosion. Furthermore, variations in the lithium concentration can impact the transport of corrosion products including deposition on fuel cladding surfaces, subsequent activation, release and incorporation into corrosion films on out of core surfaces. The presence of hydrogen assures reducing coolant conditions and avoids the net decomposition of the coolant. The current operational practices regarding PWR primary water chemistry will be reviewed taking the above mentioned parameters into consideration. It will be shown that the operating pH-values (at 300deg C) range from 6.8 to 7.4 whereas the hydrogen concentration centers around 3 ppm H₂. (author)

[en] Water chemistry plays a major role in fuel cladding corrosion and hydriding. Although a full understanding of all mechanisms involved in cladding corrosion does not exist, controlling the water chemistry has achieved quite some progress in recent years. As an example, in PWRs the activity transport is controlled by operating the coolant under higher pH-values (i.e. the ''modified'' B/Li-Chemistry). On the other hand, the lithium concentration is limited to a maximum value of 2 ppm in order to avoid an acceleration of the fuel cladding corrosion. In BWR plants, for example, the industry has learned on how to limit the copper concentration in the feedwater in order to limit CILC (Copper Induced Localized Corrosion) on the fuel cladding. However, economic pressures are leading to more rigorous operating conditions in power reactors. Fuel burnups are to be increased, higher efficiencies are to be achieved, by running at higher temperatures, plant lifetimes are to be extended. In summary, this paper will describe the state of the art in controlling water chemistry in operating reactors and it will give an outlook on potential problems that will arise when going to more severe operating conditions. (author). 3 figs, 6 tabs

[en] A discussion is presented of the following available KWU methods: the two-step process, the one-step process, one-step process for total PHT systems. 5 refs

[en] The present paper describes the coolant chemistry and its consequences for 1300 MWsub(e) KWU PWR plants. Some selected systems, i.e. primary heat transport system, steam water cycle and cooling water arrangements, are chosen for this description. Various aspects of coolant chemistry regarding general corrosion, selective types of corrosion and deposits on heat transfer surfaces have been discussed. The water supply systems necessary to fulfill the requirements of the coolant chemistry are discussed as well. It has been concluded that a good operating performance can only be achieved when - beside other factors - the water chemistry has been given sufficient consideration. (orig./RW)

[en] The present paper describes the coolant chemistry and its consequences for 1300 MWsub(e) KWU PWR plants. Some selected systems, i.e. primary heat transport system, steam water cycle and cooling water arrangements, are chosen for this description. Various aspects of coolant chemistry regarding general corrosion, selective types of corrosion and deposits on heat transfer surface have been discussed. The water supply systems necessary to fulfill the requirements of the coolant chemistry are discussed as well. It has been concluded that a good operating performance can only be achieved when - beside other factors - the water chemistry has been given sufficient consideration. (orig.)

[en] The entry of corrosion products into steam generators, their deposition on tube plates and the consequential concentration of salts can be the cause of various corrosion mechanisms on the heating tubes. Mechanically operating techniques have been developed in order to remove the corrosion products deposited on the tube plates. However, a significantly higher effectiveness is attained today with the use of chemical techniques which operate with complex compounds and also remove the corrosion products which have been deposited on the heating tubes. The paper describes the mechanical and the chemical cleaning processes and evaluates the results which have been obtained in practice. (orig.)

[en] Almost 30 years of operating experience with PWR nuclear power plants have shown that corrosion and wear in the steam generator (SG) can have a considerable influence on the output and availability of the whole plant. At a very early stage, Siemens embarked on careful analysis of the damage mechanisms registered worldwide. The results of this evaluation have continuously been incorporated into the design and operation of steam generators and of the associated steam/water cycles. The KWU Group of Siemens now has 62 SG's in operation. The good performance of these SG's relies on harmonizing the design of the SG, the structural materials used and the operating water chemistry. The following describes the forms in which damage occurs and the Siemens concept for combatting the problem. (author)