Pollution of the Heat Carrier and Its Influence on the Service Life of Power-Generating Units of Nuclear Power Plants

Abstract

We present the data of autoclave testing of 10GN2MFA and 08Kh18N10T steels for cyclic crack-growth resistance in reactor borated water at a temperature of 300°C. We tested standard 25-mm-thick specimens for two values of the load ratio equal to 0.2 and 0.7. The loading frequency of specimens in the autoclave did not exceed 0.0167 Hz. We propose a model and a procedure of numerical evaluation of the increments of crack length according to the mechanisms of corrosion-fatigue and static corrosion cracking under the conditions of their combined action based on the analysis of principal characteristics of structural materials. Unlike the method based on the use of the Paris equation proposed by foreign standards, the method developed in the present work is more general and informative. Moreover, it includes the method used in standard specifications as a special case and enables one to explain the premature fracture of collectors of steam generators at the South-Ukrainian Nuclear Power Plant and other elements of power-generating units of the nuclear power plants. It is shown that, in the absence of corrosion-fatigue cracking, power-generating units of nuclear power plants can operate without emergency shutdowns for the entire service life. In the case where the heat carrier is polluted to a level sufficient for the initiation of the mechanism of static corrosion cracking, the service life of units to the time where the crack attains its critical size sharply decreases. We propose to improve the systems of water supply and perform continuous monitoring of the controlled parameters of the heat carrier and, in particular, of the contents of admixtures promoting the static corrosion cracking of steels.