Vibration as a factor promoting cracking of cold PGV-1000 collectors

Abstract

In the present report, the results of generalizations and many investigations [1, 2] where it is acknowledged that the appearance of damage in cold collectors is a complicated and multifactor phenomenon are used. It is asserted that the operating temperature of cold collectors (280-290~ at which the effect of a corrosion medium is strongest, is important for explaining the reasons for the damage. It turns out that the fact that, on the one hand, cracking was previously acknowledged to be a more multifactor phenomenon and, on the other, the vibration, as a result of which cases of cracking of equipment metal are most often observed, remains inadequately analyzed, has been neglected.Each structural element possesses mass and elasticity and is potentially subjected to mechanical vibration, though under design conditions of normal operation all elements of the reactor and the first-loop system are regarded as being stationary or quasistationary (they can only move under temperature expansion).Initial data on high-frequency loading in accordance with the standard [3] are obtained after vibrations are discovered during operation and after analysis of the measurements performed on a corresponding element followed by the required calculation. In other words, during operation it is necessary to discover the vibration, collect initial data for calculations, perform the calculations, and then if necessary make a decision about continuing operations.Evidently, pumps and the moving cooling are a source of vibrations [4]. There is no doubt that vibrations of equipment and pipelines are initiated by the main circulation pump, turbulence, and standing waves of pressure in the coolant and steam in the main steam lines, as well as by boiling in the steam generator. It should be noted that in the year before cracking occurred in the cold PGV-1000 collectors --in 1985, a substantial vibration of the main steam lines, which was acknowledged to be caused by hydroacoustic pulsation of the pressure in the steam [5, 6], was discovered in the first power-generating unit of the Zaporozh'e nuclear power plant.Most likely, the situation preceding cracking of cold collectors can be represented as follows. When the reactor plant operates in transient and stationary states, as a result of pressure pulsations on the circulating and multifreqencies of the main circulation pump caused by formation of standing waves of pressure in the first loop and steam lines, the first-loop equipment, the main circulation pipe lines, and main steam lines were subjected to vibrations of different intensity. It appears that the cold collectors of steam generators in some power-generating units of nuclear power plants in Russia and the Ukraine are the weakest point. In other units with VVt~R-1000 reactors, either the quality of fabrication was higher or the assembly and unfastening of the equipment were better or both were present at the same time but vibration did not result in cracking of the collectors in any steam generator in the Roven, Khmel'nitsk, or Kali...

Possible Probabilistic Safety and Longevity Evaluations of the Metal in the Studs of the No. 2 Generating Set at the Sayano-Shushenskaya HPP

“…2 generating set at the Sayano-Shushenskaya HPP, and the metal of some components of other power equipment is staged or random, although based on deterministic design analysis, these components have been considered long-lived and reliable [7,8].…”