Monitoring system for preventing leakage of main steam pipeline in nuclear power plant

The invention provides a monitoring system for preventing leakage of a main steam pipeline in a nuclear power plant. The monitoring system provided by the invention is different from a reactor coolant loop and main steam pipeline leakage monitoring system in the conventional nuclear power plant; the external part of the main steam pipeline adopts a sleeve structure; annular sealed space is formed on the outer side of the main steam pipeline by using a sleeve; the pressure of the annular sealed space is lower than the pressure on the inner side of the main steam pipeline; the annular sealed space is used as a main steam pipeline leakage accommodating area; meanwhile, monitoring devices such as a pressure sensor and a hygrometer are arranged in the annular sealed space, so that leakage of the main steam pipeline can be monitored; besides, a leakage rate calculation module calculates out a leakage rate and gives an alarm, so that an operator is reminded of paying attention to the running status of a unit to make a correct judgment and take certain measures in necessity to provide support for safe running of the unit.