During visual inspections of VVER type reactor vessels with STS-K-78P TV inspection system that took place during the period from 1996 to 2004 some defects at the early stage of their development were revealed. These defects were revealed at one NPP during summer outage.

    Until now the most difficult work was removal of defects revealed below the cold nozzle area.

Operations were complicated because of highradiation exposure to personnel in this area. A special-purpose robot manipulator was needed due to demanding requirements of repair operations (providing clear surface and specified geometry/shape).

     In 2004 DIAKONT designed System for Removal of Defects on Reactor Surface (SRDRS) that provides automated removal of defects, including defects located below the cold nozzle area.

SRDRS includes:

remote-controlled manipulator, which provides grinding of defect according to specified geometry/shape, precision and smoothness of surface;

2 radiation tolerant TV systems to monitor positioning of the manipulator and the process of grinding of defect;

control equipment that allows to control removal of defect from remote area.

      Requirements specification, technical project and design documentation for SRDRS were agreed upon with the main designer of reactor vessel OKB “Gidropress” and with the manufacturer of reactor vessel OAO “Izhorskie Zavody”. In 2004 SRDRS successfully passed the acceptance tests at mock-up reactor in which representatives of OKB “Gidropress” and OAO “Izhorskie Zavody” also took part.

      In summer of 2004 a visual inspection of VVER type reactor vessel revealed a grid of cracks covering an area more than 10 mm². This defect was grinded by SRDRS. Thanks to this automated system, repair work was successfully completed within two hours with minimum radiation exposure to NPP personnel.

      Introduction of the new automated SRDRS allows fast and high-precision removal of defects on internal surface of reactor vessel at the early stage of their development, providing high level of safety of NPP operation.

Examples of Defects, revealed by TV inspection
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