Nuclear Power Plant Shutdown Industrial Accidents And Their Disposal,

The general concern for the safety analysis of PWR power plant is mainly on the study of the transients and accidents at power operation, but the safety issue of plant at shutdown condition was seldom studied. In recent years, several accidents occurred when the PWR power plant was operated at shutdown conditions, and some of these accidents had the potential consequences to cause the core damage, and this has attracted people's attention.This thesis initiates a study focused on safety issues of nuclear power plant at shutdown conditions. And a deterministic methodology is used to perform a study on shutdown accident of Qinshan Nuclear Power Plant (QNPP). The details of this research include safety anaIysis about two accidents: Loss of Residual Heat Removal Accidents, and Inadvertent Boron Dilution Accidents.Selecting the Qinshan Nuclear Power plant as the reference plant, assuming that the pIant operates at cold shutdown and mid-loop operation mode, the thermal-hydraulic response of the plant after the RHR system failed has been evaluated with the thermal-hydraulic transient analysis code RELAP5/MOD2. The evaluating results show that the up part of the core will start to be uncovered at l7 minutes after lost of RHR, then at about 1 hr the temperature of the core will rise rapidly. If no measures have been taken to mitigate the accident, the core would be damaged. If safety injection into the cold loop is activated at l800 seconds following' the accident, the core water level can be restored, and the rapid rising of the core temperature would not occur, so the core damage can be avoided. This gives the plant operator about 30 minutes to take action to mitigate the accident.RELAP5/MOD2 code also has been used to simu1ate the inadvertent boron dilution accident at hot shutdown operation. The results show that the accident's process is very fast and. it's sequence is hazardous. If the low concentration boron water package has formed, the water package will go through the core after l0 seconds of the primary pump restart. This will make the core reactivity increase abruptly, and the core power will increase rapidly too. lf core reach criticism, it would have damages to the fuel elements. The critical volume of low concentration boron water package varies from 2 to 5 stere according to different boron concentration.The results and conclusions from this research can be applied to the accident management at shutdown mode for QNPP, and they are also of significance for the accident management at shutdown mode for other domestic NPPs.