Features of the Water-Chemical Mode of the I Circuit and Problems of Equipment Operation in the Reactor Units of Atomic Icebreakers

Analysis of the experience gained in operating atomic icebreakers, the specifics of operating equipment of the first circuit, and the organization of the water-chemical regime shows the relationship between the high content of gases in the coolant and the problems of ensuring reliable equipment operation. Spatial modeling of vapor-gas bubbles’ mass transfer in the SG-28 steam generator during damping confirmed the possibility of forming a gas cushion in the stagnant zone of the SG. The abrupt increase in the volumetric content of hydrogen during the transition from the liquid to the gas phase of the water coolant explains the anomalous hydrogenation in the area of weld no. 62 on the tubing of the AO SKBK design steam generators. The multiscale, multiphysical approach to conducting calculations was based on the adaptive use of different calculation codes in accordance with the required degree of analysis detail. Four computational models were developed—a common one based on the Relap5 code and three for the CFD code. An offline scheme of combining codes was used. Within its framework, a consistent decomposition of the general problem into computational domains was carried out; appropriate models for them were used, and organization of information exchange between models was based on the initial and boundary conditions. An analysis of the operating conditions and the nature of the mass transfer of vapor-gas bubbles, taking into account the patterns of their fragmentation, confirms the possibility of their entry into the active zone in transient conditions. The presence of oxygen in vapor-gas bubbles dramatically changes the corrosive environment and can cause the nodular corrosion of zirconium shells. To drastically reduce the content of noncondensable gases in the coolant of the first circuit, it was proposed to study the possibility of using a steam volume pressurizer instead of a gas pressurizer in promising projects of transport nuclear power plants (NPPs).