At present, the power supply of domestic nuclear power plants is relatively rich and has a certain ability to provide defense in depth for nuclear safety. However, in the case of serious accidents, such as multiple power supply common mode failure, there is a lack of the ability to mitigate the accident at the end of the stage, so nuclear power plants have added additional mobile emergency diesel generator sets.
According to the experience of Fukushima Daiichi Nuclear Power Plant in Japan and the basic situation of the emergency power supply system of a domestic nuclear power plant, we should strengthen the power supply configuration, improve the defense-in-depth capability of the unit, set up special power supply equipment in the nuclear power plant, avoid the uncertainty of the accessibility of mobile power supply from outside in the case of serious accidents, and reduce the risk of "common mode failure".
(1) Add 380V mobile emergency diesel generator set.
According to the existing power supply strategy and the French Rules for the Design and Construction of 900MV Pressurized Water Reactor Nuclear Power Plant (RCC-P), in the case of power loss of the whole plant, the first step is to start the SBO diesel generator set. Then it is necessary to restore the ground supply as soon as possible and remove the fault. From the perspective of strengthening the power supply guarantee after the power loss of the whole plant, it should be considered to add a long-term standby power supply in the plant to supply power for the hydraulic test pump, part of the measurement, monitoring and control loads in the plant, so as to mitigate the accident. The total capacity of the power supply load required by the nuclear power plant is about 220kW, and the capacity of the mobile power generation unit is about 400kW, and the voltage level is 380V.
(2) Add 6.6kV mobile emergency diesel generator set.
The 6kV mobile diesel generator set has a high voltage level and can start some nuclear island medium-voltage equipment. However, due to the capacity limitation of mobile equipment, it can supply power to some equipment on the primary side or secondary side respectively to ensure the heat removal capacity. According to the accident analysis, it is mainly considered to supply power for one auxiliary feedwater pump or one low safety injection pump and one containment spray pump, and it can also supply power for one fire pump when necessary. According to the investigation of the mobile diesel generator set and the above power supply requirements, and the verification of the starting capacity of the whole large-capacity motor, the diesel generator set should be selected with a capacity of no less than 2000kW.
(3) Storage of mobile diesel generator set.
Full consideration must be given to the equipment safety and the accessibility to the site reception point in the case of extreme natural disasters. According to the actual situation of each plant site, an independent anti-seismic plant shall be built in the place far away from the nuclear island and more than 5m higher than the nuclear island for the storage of mobile power equipment.
(4) Safety analysis.
Under the condition of power loss of the whole plant, the access panel and cabinet of the new 380V mobile emergency diesel generator set will be disconnected from the system under normal operation, which will not affect the original panel and cabinet structure, and will enhance the reliability of power supply for the hydraulic test pump, important heating and ventilation loads and important instruments, and further improve the defense capability in depth.
The 6kV interface is set in a temporary access mode, which also does not change the original panel and cabinet structure, and can enhance the reliability of the unit to restore power supply.
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