Two-unit alternative-discharging method of containment vessel filtering discharging system

The invention belongs to a reactor designing technology, and particularly relates to a two-unit alternative-discharging method of a containment vessel filtering discharging system. The two-unit alternative-discharging method comprises the steps of after an accident occurs, firstly, switching on a containment vessel isolating valve of a first unit so as to carry out filtering discharging on the first unit; when the pressure of a second unit is high, closing a discharging pipeline of the first unit, switching on an isolating valve of the second unit so as to carry out filtering discharging on the second unit; and when the pressure of the first unit raises, switching off the isolating valve of the second unit, switching on the isolating valve of the first unit so as to carry out filtering discharging on the first unit, and repeatedly executing the steps. By determining a time window in which each unit discharges in alternative operation, the pressure of a containment vessel of the two units is not enabled to exceed a safety limit value under the condition of reducing the switching frequency as soon as possible. According to the two-unit alternative-discharging method, hardware investment of a nuclear station does not need to be increased, the capacity of coping two-unit serious accidents by the nuclear station with two units is improved, and the probability of a large quantity of radiological release is reduced.