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628During the last decades, systematic and pro grammed works have been carried out in leading coun tries around the world for collecting and analyzing data on erosion-corrosion damages inflicted to the metal of equipment and pipelines at nuclear power stations (NPSs), studying the regularities pertinent to the mechanism of erosion-corrosion, developing software tools for estimating and predicting the ero sion-corrosion process, and optimizing measures for monitoring, revealing, and preventing erosion-corro sion thinning of the walls of power equipment and pipelines. In France, for example, works have been carried out for more than 15 years on revealing ele ments belonging to the risk group of intense wear and optimizing the operational monitoring (thickness measurements) of metal thinning in 58 power units at NPSs belonging to the EDF Company with the use of the BRT CICERO computation code [1]. The EDF database has been created using the results of these works, which included 99 534 elements, i.e., around 2000 elements per power unit as of April 2010. As the time for which NPPs have been in operation passed, cases involving inadmissible thinning and fail ures of the metal in welded connections are observed in more and more frequent occasions along with ero sion-corrosion failures of the main metal of pipeline and equipment elements. In 2002, the Electric Power Research Institute (the United States) published a report addressed to selective erosion-corrosion effect on welded connections. Since 2001, EDF has given the status of an individual problem to the wear of welded connections in a program on erosion-corro sion of the metal in NPS power units [1].Since 2007, the OAO Rosenergoatom Concern has been implementing a comprehensive program on the problem concerned with erosion-corrosion of the main metal of pipelines and equipment at Russian NPSs [2]. At present, sufficient grounds have ripen for drawing up a new version of this ongoing comprehen sive departmental program on the problem of damages inflicted to welded connections. The data on damage ability and the results from operational checks of metal that have been acquired and analyzed with due regard of the requirements specified in the above mentioned program made it possible to reveal numerous cases involving the occurrence of inadmissible thinning in welded connections and in near weld zones of NPS pipelines. Cases are also known in which loss of tight ness occurred in welded connections of NPS process loops as a result of their erosion-corrosion thinning.Such incident occurred in November 2004 in a power unit of the Balakovo NPS, at which a leak was found in the zone of welding the bypass pipeline bend (D nom = 108 × 6 mm) to a sleeve (D nom = 120 × 16 mm) of the feedwater pipeline (D nom = 426 × 24 mm). The working parameters of medium in the damaged part are 220°C and 8.0 MPa.Significant inadmissibly thinned places in welded connections of pipelines downstream of the feedwater control valves are observed in power units of Russian NPSs equipped with diffe...

The modern requirements for monitoring the state of reactor equipment during reactor operation are implemented by systems for on-line diagnostics, specifically, vibrational diagnostics system. Effective operation of this system is possible only after the auto-and cross-spectral characteristics of the registered signals have been interpreted. To this end, a noise experiment was performed on the first power-generating unit of the Kalinin nuclear power plant.Detectors. Three types of sensors recorded the noise signal with the aid of a 20-charmel system during the stationary operation of the reactor at 80% nominal power: three extracore ionization chambers (IC7, IC14, IC21), three pressure pulsation sensors (PPS) (Q4, $4, Q3), and 14 intracore direct-charge detectors (DCD) (two assemblies with each assembly containing seven DCDs) (Fig. 1). Experimental conditions were produced for switching the signals from the DCDs chosen by a specially developed method. Approximately 40 of the 20-charmel records permit investigating the following: reactivity and local effects caused by vibrations of the reactor vessel, intravessel apparatus, and specifically vibrations of fuel assemblies which have operated for different periods of time; distribution of the amplitude of different acoustic standing waves inside the reactor vessel; and, transfer functions whose parameters, characterizing the thermohydraulic state of the core, cannot be measured directly.Effects Masking the Vibrations of lntravessel Equipment. The most significant effects are the effects due to the transport of coolant nonuniformities, for example, temperature fluctuations, from the entrance into the core along the fuel channel. This is the so-called source 6Tin. The transport defect is also characteristic of the source 5G --fluctuations of the coolant flow rate. A detailed exposition of the thermohydraulic sources of neutron noise is given in [1]. Such wide-band effects (Fig. 2) cause a delay of one signal from DCD with respect to another by a time to; in spectral language, this is expressed as a linear frequency dependence of the phase of the cross-spectral power density. If the same frequency range contains the vibrational frequency of the intravessel devices, then the expected set of phases (most often in-or antiphaseness of signals from two neutron sensors) will not occur. To eliminate masking of this type, the phase characteristic must be corrected for the linear dependence. There are at least two such dependences. A direct calculation of the coolant velocity with respect to the parameter t o in the range 0-1 Hz is found to be a rough estimate. As shown in [1], the nonuniformity of the power-release field over the vertical coordinate in the core must be taken into account. Transport effects are also observed in the sensor pairs DCD-nearest IC (Fig. 3) and in the pairs DCD-DCD, placed in neighboring fuel assemblies. These effects have a high diagnostic value, but from the standpoint of vibrational diagnostics of intravessel equipment, they are sources of masking ...

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