Extending the intervals of safety-related Instrument Calibration Periodic Test can shorten the refueling outage period and improve unit economy. Based on the general requirements for extending the Safety-related Instrument Calibration Periodic Test Intervals and in consideration of the characteristics of CPR1000 Nuclear Power Unit with Digital Control System, an evaluation method is proposed and investigated, which consist of instrument drift analysis, protection channel analysis, channel uncertainty calculation, setpoint analysis and relevant channel tests evaluation. The research on the extension of pressurizer pressure transmitter calibration test interval is carried out in detail. The results show that the drift resulting from the interval extension will have no effect on the protection channel setpoint, the acceptance criteria for channel consistency test should be reduced and the acceptance criteria for channel function test should remain unchanged. The research of this paper has a reference value for unit economy improvement and outage optimization.

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