The construction duration of a nuclear power plant has been considered as a important factor to occupy the competitive edge. For the optimization process of APR1400 which is nuclear reactor newly developed in Korea, it has been suggested that the modularization of reactor vessel internals (RVI) was one of useful means to reduce the construction duration. In general, RVI consists of three components such as core support barrel (CSB), lower support structure/core shroud (LSS/CS) and upper guide structure (UGS). It is complicated and tedious to assemble the RVI by the conventional method which requires about 8∼10 months. In order to modularize the RVI, the gap between the CSB snubber lug and the reactor vessel (RV) stabilization lug must be measured by a remote measurement method. By using a remote measurement method, the welding of CSB and LSS/CS can be performed in advance of the reactor installation process to reduce the construction duration of a nuclear power plant. Compared with the conventional method, the duration of about 2 months required in the welding of CSB and LSS/CS is finally reduced. In this study, first of all we developed the remote measuring system that included the digital probes to measure the 72 points of gap at once. The system device consists of digital probe section, pneumatic supply and control section, electric power section, remote control computer and program. The selected digital probe of linear variable differential transformer (LVDT) type and the calibration device for the zero-point adjustment jig and the other devices have sufficient reliability and accuracy. And the digital probe connection jig has sufficient consistency. The network and system for remote measurement were very stable and no disturbance at electromagnetic interference environment. And we carried out the proof test of our remote measuring system to evaluate the application on the real plant conditions using the RV and RVI mock-up. The results of remote measurement were compared with existing manual measuring method and the reliability of the system was verified. Finally, we confirmed that our remote measuring system had the efficient reliability could be applied to measure the gap of RVI.

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