No abstract available

[en] Steam generators (SG) are the weak link of nuclear power plants, their service life is shorter than the service life of other NPP components. This paper is dedicated to a statistical analysis of SG damages and failures. Heat exchanging tubes (HET) are the most damaged elements in SG, there are on average 286 plugged or repaired tubes in each operating SG. The usually mechanisms of tube failure are the following: denting, corrosion at tube outside, pitting, fretting, and circular crack propagation. Most of damages are located in the transition zone above a tube plate. This study shows that the factors that are involved in the SG HET fault probability are: - design features of SG and secondary equipment elements (high pressure feed heaters (HPFH), low pressure feed heater (LPFH)), - water chemistry at different points of condensate feed pipe, composition and density of deposits on HET surface, efficiency of mechanical and chemical washing, - the physical and chemical properties of the materials that compose SG HET and secondary equipment (HPFH, LPFH,...), and - operation conditions of heat exchanging equipment. (A.C.)

No abstract available

[en] Flow accelerated corrosion is the most common mechanism of metal degradation. NPP equipment and pipelines manufactured from pearlitic steel are exposed to erosion-and-corrosion wear. Recently many problems related to life management of NPP equipment and pipelines exposed to erosion-and-corrosion wear have been solved. The present paper analyzes the development, certification in supervisory authorities, and adaptation of normative documentation on life management of secondary pipelines operation at NPPs. (authors)

[en] Low operational reliability of steam generators (SG) of NPPs with VVER type reactors is one of main factors affecting stability and quality of the output electric energy. Unscheduled unit stoppage when detecting heat exchange tubes (HET) and other steam generator components defects, caused by their repairing or replacement of whole SG, result in underproduction of electric energy and decreasing NPP capacity factor (CF). For these reasons the steam generator lifetime does not conform to the lifetime of NPP primary equipment. Therefore the enhancement of SG operational reliability attracts attention of experts from the countries operating PWR and VVER NPPs. (author)

[en] Full text of publication follows: The flow - accelerated corrosion (FAC) is a widespread source of damage in NPP piping. Last years many tasks concerning service life control of pipe line system which are exposed to FAC were solved. The tasks included development of computer codes (CC) for calculations of FAC rate, thinning degree of pipe walls and assessment of tolerance of wall thickness for sections with common and local thinning of the wall. The Russian NPPs began to organize the life control service for the pipe systems exposed to FAC, later than in other countries. Usage of foreign and domestic experience allowed reducing of time consumed for CC development for FAC calculation, for wall thickness tolerance and other information. In this report the experience of development, certification of control authorities and CC usage are analyzed on NPPs with WWER reactor systems. In accordance with rules and regulations for NPP in force in Russia the utilization of developed CC have to be certified by control authorities. Other worked out documentation demands approval of control organs, as well. The list of CCs in Russia (EKI-01, EKI-02, EKI-03 and EKI-04) is the same as the well known foreign CCs, namely CHECWORKS in USA and COMSY in Germany. In contrast to Russia, the foreign CCs are not calibrated by authorised organisations. As the Russian experience shows, the CC calibration accompanies the increasing of requirements for vindication of the calculation accuracy and a more precise definition of a factor range included in CC. Type of reactor and pipe lines system list have to be put in the verification reports. The report of CC development has to include results of FAC calculation of reactor pipe lines indicated in the verification documents. Verification necessity increases time required by the CC development. The certification of Russian control organisations is in conformity with a new developed (2000-2002) management directive. The computer codes EKI-01 and EKI-02 are dedicated to calculation of FAC pipe lines with single phase medium in the NPPs with WWER -1000 and WWER-440 reactors, respectively, the computer codes EKI-03 and EKI-04 are for FAC calculation of steam lines in NPPs with WWER-440 and WWER-1000, respectively. FAC calculating CC have to be applied to NPPs combined with other methodical and regulation documents. There are regulations of wall thickness tolerance, methods for determination of chemical composition of pipe line metal and other data. The secondary piping metal which is used on NPP with WWER contains chromium, copper and molybdenum as impurities. Presence of such impurities helps to reduce the FAC rate. Information about the metal concentration in pipe line systems, which is needed for the calculation of the FAC rate, is usually scarce and it is determined by direct measurements. In the report other issues which are connected to FAC are considered as for instance the influence of corrosion deposits on reliability of the operational control. Registered are also the thickness of non-attacked metal and corrosion deposits determined by the ultrasonic method. Data acquisition of factors which entered the CC, ensures the volume of the operational on-site control in the pipe lines exposed to FAC. The information about a series of significant factors can be missing. The volume of the operational control requires adjustment and further refining