А study for measuring core barrel swelling in nuclear power plants caused by operating conditions

The policy of each NPP is to ensure safe production of electrical energy as well as security of supply. The metal of NPP equipment is influenced of aging mechanisms from the working environment – neutron and thermal brittleness, corrosion, erosion, fatigue and wear. Neutron flux causes the most damaging effect on the metal structure. After prolonged periods of exposure to high-energy neutrons (several decades), the metal of the reactor vessel becomes brittle and strengthened, and defects are expected to appear and develop in the structure, which further fragile the metal. Temperature and dose load gradients can cause swelling of the metal of the reactor internals. In this 'worst-case scenario', the distance between the core barrel and the fuel roads is expected to be reduced, to disturb the movement of the heat carrier and the heat balance, to obtain jamming and blocking of units of the reactor control and protection system. At the same time, neither the regulatory framework nor the technological regulations of nuclear power plants require regular measurement of the actual geometric dimensions of the reactor internals. This paper presents a study for measuring the geometric dimensions of the Core baffle. The method is new and has not yet been studied in depth. The aim of the article is to present a possible way to measure the geometric dimensions of the Core barrel due to expected swelling of the metal due to neutron and thermal effects. The mechanisms of degradation of mechanical properties of the metal are presented. From a practical point of view, this information can be used to carry out technical diagnostics of the equipment in NPPs.