Expert express assessment of the impact of heat and mass transfer processes on the residual life of the WWER-1000 reactor vessel due to cyclic damage

Abstract

Ukraine remains a country dependent on nuclear energy for both heat supply and satellite supply. In cities close to nuclear power plants, electric heating from the electricity they produce is appropriate. On the other hand, Ukraine is the only country in the world where the worst accident at a nuclear power plant occurred at the Chernobyl NPP Unit 4 on the night of April 26, 1986. Another characteristic feature of Ukraine's nuclear energy is the significant number of power units with exhausted project resources - the so-called "old" power units. Their wear is associated with the influence of heat and mass transfer processes, which lead to periodic thermal deformation of the elements, which causes cyclic damage. An example of expert rapid assessment of the residual life of a specific reactor vessel WWER-1000 is given taking into account the combined action of non-stationary heat and mass transfer and mechanical processes. A detailed express calculation of cyclic (tired) damage to the metal of the WWER-1000 reactor vessel due to the dangerous emergency mode has been performed. The WWER-1000 reactor is the last most widespread and most powerful water-water nuclear reactor of the former USSR, operated on 13 of the 15 operating power units of Ukrainian nuclear power plants (NPPs) - Zaporizhia, Rivne, Khmelnytsky and South Ukraine (SUNPP). The reactor is the most important indispensable element of a nuclear power plant, which determines its safety and resource. Given the design resource and the dates of commissioning of Ukrainian NPP units, the issue of rapid expert assessment of the technical condition of WWER-1000 hulls is quite relevant. Of course, modern engineering has the full range of tools needed to perform such estimates, from powerful computers to advanced computing software. But the known and inevitable costs of modern engineering - complex and time-consuming modeling and calculations. Experience has shown that a certain "reasonable" combination of the use of relatively simplified "light" calculation methods allows us to assess the safety, strength and service life of WWER-1000 reactors very quickly and with the necessary accuracy acceptable for expert opinion. The publication considers as an example the real emergency situation of October 22, 1985 and the WWER-1000 reactor of SUNPP Unit 1. Since this emergency situation led to rapid cooling of this reactor, the calculation of the effect of cyclic damage of reactor steel on the strength and reliability of the reactor vessel is shown. This example and the consideration of the real emergency situation demonstrates the effectiveness and acceptability of the use of estimated expert rapid assessments to accurately determine the reliability and safety of such critical elements of nuclear power plants as nuclear reactor buildings.