Methods to Improve the Safety of Nuclear Power Units When Reactors Fail to Scram

Abstract

The invention discloses a method for improving security of a nuclear power unit during the failure of emergency shut-down of a reactor. The method comprises the following steps: generating an anticipated transient protection signal during the failure of emergency shut-down of the reactor, wherein the anticipated transient protection signal comprises first-kind signals and second-kind signals; and triggering first-kind protective action according to the first-kind signals and triggering shut-down of a main pump according to the second-kind signals. Compared with the prior art, the invention has the following advantages: the second-kind signals trigger shut-down of the main pump, and after shut-down of the main pump, the coolant flow of a primary coolant circuit drastically decreases and the temperature of the primary coolant circuit rises, so negative feedback characteristics (e.g., the negative temperature coefficient of a moderator) of the moderator with reactor core neutronics characteristics in the nuclear power unit of a pressurized water reactor are excited; the negative feedback characteristics are fully and ingeniously utilized, so the risk of overpressure of a primary coolant circuit system of the reactor in an anticipated transient moment when the nuclear power unit loses all the water supply and fails to carry out emergency shut-down is effectively eliminated, corresponding accident acceptance criteria are met, severe accidents are prevented, and security of the nuclear power unit is improved.

Description

technical field [0001] The invention relates to the technical field of reactor control and protection, in particular to a method for improving the safety of nuclear power units when the reactor fails to shut down in an emergency. Background technique [0002] Taking the CRP1000 nuclear power unit as an example, when the expected transient (ATWS) protection signal that the nuclear power unit fails to emergency shutdown is sent out, the ATWS mitigation system will be triggered to perform the following protection actions: [0003] (1) Steam turbine tripping: set the reactor power to the final power setting value, reduce the power by automatically adjusting the average temperature (R) rod group and power regulation (G) rod group, and prevent the steam generator from burning out; [0004] (2) Start the auxiliary water supply system: supply about 6% NF water to the steam generator to prevent the steam generator from drying out; [0005] (3) Block the third group of GCT discharge ...

AI Technical Summary

Problems solved by technology

[0007] However, the ATWS protection signal of the above-mentioned CPR1000 unit and its mitigation system, for the failure of the reactor regulation system (such as mechanical sticking, the unit is in manual mode, etc.) ) cannot be inserted into the core in a timely and effective manner, the accident mitigation capability is limited, and the risk of overpressure in the primary circuit system cannot be completely and effectively eliminated

Because during the transient state of ATWS, if the reactor regulator rod group cannot be inserted into the core, the reduction of the reactivity of the core will be restricted, resulting in a certain impact on the pressure drop of the primary circuit system, and the result is that the fuel cycle will last for the entire lifetime (especially It is the first cycle) when the loss of normal water supply-ATWS accident occurs, the peak pressure of the primary circuit is higher than the maximum allowable pressure, which cannot meet the accident acceptance criteria

[0008] Therefore, the current CPR1000 unit ATWS protection signal and its mitigation system are not enough to completely avoid the risk of overpressure in the reactor primary circuit system during ATWS, and cannot meet the corresponding accident acceptance criteria, which may lead to serious accidents

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