[en] Increasing pressure is being applied to reduce outages in an effort to improve plant efficiency. However, shorter outages must not come at the expense of regularly scheduled maintenance quality. The reduction of regularly scheduled maintenance may produce forced outages, thus further reducing efficiency and may increase the probability of extended maintenance shutdowns. Various programs have been implemented around the world to reduce the required time for preventative maintenance and to prolong the life of Steam Generators. This paper describes Framatome ANP's experience in servicing and implementing maintenance programs for various steam generators and the techniques used to reduce outage activities. These steam generators include Once Through Steam Generators (OTSGs), Recirculating Steam Generators (RSGs), CANDU, KWU, etc. (author)

[en] The 4th CNS International Steam Generator Conference took place in Toronto in May 2002. A conference theme of 'The Extended Service Challenge' was selected by the organizing committee to encourage discussion around all aspects of managing life attainment and life extension for operating steam generators, with perspectives varying from those of the research community, the designers, the operators and service providers to those of the regulators. The conference was successful in meeting that objective. There were more than 140 participants from North America, Europe and Asia and almost sixty presentations over seven sessions. These proceedings provide the reviewed papers on which presentations were based as well as a record of the discussion of the presentations at the conference. The value of the conference is seen to be its broad coverage of all major aspects of steam generator life management in a single-session format that allows specialists in each area to become aware of issues in other areas that may have an impact on their business or direction. Presenters were able to place their work in the broader context of the objective of extending steam generator life

[en] Steam generators are among the most important pieces of equipment in a nuclear power plant. They are required full time during the plant operation and obviously no redundancy exists. Past experience has shown that those utilities which implemented comprehensive steam generator inspection and maintenance programs and strict water chemistry controls, have had good steam generator performance that supports good overall plant performance. The purpose of this paper is to discuss a strategic Life Management and Operational-monitoring program for the Cernavoda steam generators. The program is first of all to develop a base of expertise for the management of the steam generator condition; and that is to be supported by a program of actions to be accomplished over time to assess their condition, to take measures to avoid degradation and to provide for inspections, cleaning and modifications as necessary. (author)

[en] In Dukovany's and Mochovce's steam generators (SG) identical system of feedwater distribution is used. Non-uniform feedwater distribution in these steam generators enables to optimize a secondary water chemistry of SG'. The aim of this optimization is the decrease of impurities concentration near the hot collectors, which are (thread holes) the crucial constructional part of VVER 440 steam generators. Measurements on Dukovany's SG's have shown, that after closing the SG blow-down cold line the concentration of impurities in SG considerably decrease. Because of different blow-down system in Dukovany' s and Mochovce's SG's, the set of measurements on Mochovce's NPP were performed during last two years to evaluate the influence of blow-down system on secondary water chemistry. (author)

[en] Excessive flow-induced vibration causing fretting-wear damage can seriously affect the performance of heat exchange components such as nuclear steam generators, heat exchangers and condensers. Fretting-wear damage generally takes place between vibrating tubes and their supports. It is related to a fretting-wear coefficient and a parameter called work-rate which formulates the dynamic interaction between tube and support. The work-rate is essentially the rate of mechanical energy dissipated at the support. On the other hand, the total available mechanical vibration energy in a tube is related to its mass, vibration frequency, mode shape, and vibration amplitude. This leads to the development of a simplified formulation based on energy considerations to relate tube vibration response and fretting-wear damage at the supports. The basic energy equations and the formulation of a simple energy relationship to predict fretting-wear damage are outlined in this paper. The relationship is verified against experimental data. The energy approach is also compared to time domain calculations using a non-linear finite element code. The results indicate that the simple energy approach may be very useful to estimate fretting-wear damage in practical situations. Finally, an example of a calculation for a typical steam generator tube configuration is given to illustrate the energy approach. (author)

[en] Degradation and failure of steam generators (SG) and other heat exchange components due to flow-induced vibration (FIV) and consequent fretting-wear must be addressed as a part of studies to assess the remaining life of in-service components. Atomic Energy of Canada Limited (AECL) has developed a methodology to assess tube wear damage within components and to predict the progression of damage during the component lifetime. The methodology incorporates the effects of the following parameters on the initiation and progression of tube damage: flow conditions, FIV mechanisms, tube-support geometry, tube wear properties. The assessment of a component includes the evaluation of existing tube damage from eddy-current (ET) inspections, and the prediction of the progression of damage through non-linear vibration analyses using FIV and fretting-wear computer codes. The evaluation of existing damage is used to verify that the progression of damage is within expectations. The remaining life of the component from a fretting-wear point-of-view is estimated by extrapolating the damage to a plugging criterion. (author)

[en] Successful life management of nuclear steam generators requires proactive planning to monitor and assess all potential degradation mechanisms. One such degradation mechanism is tube fretting as a result of flow induced vibration. Traditional flow induced vibration predictive methods are based on deterministic nonlinear structural analysis techniques and are routinely used for design purposes. The authors have proposed the application of probabilistic techniques to better understand and assess the risk associated with operating nuclear generating stations with aging re-circulating steam generators. These probabilistic methods are better suited to address the variability of the parameters in operating steam generators, e.g., flow regime, support clearances, manufacturing tolerances, tube to support interactions, and material properties. This paper describes an application of a Monte Carlo simulation to predict the propensity for fretting wear in an operating re-circulation steam generator. Tube wear damage is evaluated under steady-state conditions using two wear damage correlation models based on the tube-to-support impact force time histories and work rates obtained from nonlinear flow induced vibration analyses. (author)

[en] A systematic managed process for steam generators has been implemented at Ontario Power Generation (OPG) nuclear stations for the past several years. One of the key requirements of this managed process is to have in place long range Steam Generator Life Cycle Management (SG LCM) plans for each unit. The primary goal of these plans is to maximize the value of the nuclear facility through safe and reliable steam generator operation over the expected life of the units. The SG LCM plans integrate and schedule all steam generator actions such as inspection, operation, maintenance, modifications, repairs, assessments, R and D, performance monitoring and feedback. This paper discusses OPG steam generator life cycle management experience to date, including successes, failures and how lessons learned have been re-applied. The discussion includes relevant examples from each of the operating stations: Pickering B and Darlington. it also includes some of the experience and lessons learned from the activities carried out to refurbish the steam generators at Pickering A after several years in long term lay-up. The paper is structured along the various degradation modes that have been observed to date at these sites, including monitoring and mitigating actions taken and future plans. (author)

[en] An 'equivalent rectangular crack' approach was employed to predict rupture pressures and leak rates through laboratory generated stress corrosion cracks and steam generator tubes removed from the McGuire Nuclear Station. Specimen flaws were sized by post-test fractography in addition to a pre-test advanced eddy current technique. The predicted and observed test data on rupture and leak rate are compared. In general, the test failure pressures and leak rates are closer to those predicted on the basis of fractography than on nondestructive evaluation (NDE). However, the predictions based on NDE results are encouraging, particularly because they have the potential to determine a more detailed geometry of ligamented cracks, from which failure pressure and leak rate can be more accurately predicted. One test specimen displayed a time-dependent increase of leak rate under constant pressure. (author)

[en] Since the 3rd International Steam Generator and Heat Exchanger Conference in 1998, a number of steam generator chemical cleanings have been performed worldwide. The objective of these cleanings was to reduce the corrosive impact of steam generator secondary side deposits on the steam generator tubes and to improve the heat transfer performance of the steam generator. During the last four years, cleanings have been performed on Babcock and Wilcox, Westinghouse, Combustion Engineering, KWU, and CANDU steam generators. These cleanings have been performed using a variety of cleaning processes including high temperature plant heat processes, external heat crevice processes, and bulk processes. This paper describes the experiences and results from the three most recent steam generator chemical cleaning projects in the US. (author)