At the power unit No 2 of Rostov NPP within the schedule preventive repair (SPR-2018) the specialists of the Centralized Repair Shop (CRS) under the management of the staff of Metal Non-Destructive Testing and Technical Control Department (ODMiTK) of Rostov NPP completed the works on unloading the witness samples from the reactor in order to control the changes of metal characteristics in the process of the operation.

The witness samples are the samples produced from the parent metal, weld metal, and heat-affected zone metal. The samples of the parent metal are made from the test ring of pipe shells and pipe shells of the pipe connectors in the reactor vessel area that are loaded in the reactor and are borne in the operation conditions. During the whole reactor unit’s life cycle the witness samples are occasionally unloaded and studied.

According to the head of the ODMiTK Evgeniy Salnik, in order to monitor the condition of the reactor vessel metal in the result of the temperature exposure, the container assembly was unloaded from the protective tube unit of the power unit No 2. In the near future, the unloaded witness samples will be sent to the Kurchatov Insitute for the further study.

“The elements of the reactor vessel are exposed to the increased temperature and neutron flux that leads to its properties’ change. Due to this a constant control over the condition of the reactor vessel metal is required. The studies with usage of witness samples are the only way the specialists can monitor the change of the mechanical properties and resistance characteristics to the brittle failure of the parent metal and welds of the reactor vessel during its lifespan”, the head of ODMiTK Evgeniy Salnik noted.

First of all, the safety of the reactor unit is defined by the safety of the barriers that retain the products of nuclear reactions from dissemination in the environment. One of the most important safety barriers is the reactor vessel. The main requirement presented to the reactor vessel is the preservation of its integrity under any operation conditions.

These studies that are occasionally carried out at all NPP’s power units are one of the conditions of reliable and safe operation of reactor and reactor unit in whole.

It is to be recalled that from 16 July the power unit No 2 of Rostov NPP in accordance with the Repair schedule of power units of NPPs of Russia in 2018 is put into the capital schedule preventive repair (SPR).