核电厂停堆工矿下事故及其处置研究

【作者】 杜春；

【导师】 李吉根；

【作者基本信息】 中国原子能科学研究院 ， 反应堆工程与安全， 2000， 硕士

【摘要】 在核电厂的安全研究中，通常着重研究功率运行下的瞬态和事故，而对停堆工况下的安全问题研究较少。近年来，核电厂停堆工况下发生了儿起典型事故，这些事故具有可能导致堆芯损坏的严重后果的特性，这引起了人们对此类事故的重视和研究。 本文主要围绕核电厂停堆工况下的安全问题开展研究，采用确定论的方法对我国秦山核电厂停堆工况下的事故及其处置进行了分析研究，并提出了事故处置措施。分析了两类事故：余热排出系统失效事故和意外硼稀释事故。 选定秦山核电厂为计算对象，假定电厂处于环路半充水的冷停堆工况，采用热工水力系统瞬态分析程序RELAPS/MOD2，对失去余热排出系统后电厂的热工水力响应进行模拟计算（主要是堆芯和一回路的响应）。计算结果表明，在丧失余热排出系统冷却后大约1040秒，堆芯上部即开始裸露，大约3380秒堆芯温度快速上升，如果没有缓解措施，将导致堆芯损坏；在执行缓解措施的情况下，假定在30分钟启动投入安注，此后堆芯水位能及时得到恢复，堆芯温度陡升的现象不再发生，从而可避免堆芯的损坏。即操纵员可以有30分钟的时间米采取措施缓解事故。 对于意外硼稀释事故，应用RELAPS/MOD2程序计算了热停堆工况下的快速硼稀释事故。计算结果表明，该事故进程非常迅速，事故后果也很严重。在低硼浓度水团己经形成的情况下，主泵再启动后大约10秒左右，该水团将穿过堆芯，使堆芯反应性迅速增加，如果堆芯达到临界，堆芯功率将快速增长，并可能造成燃料元件的损坏。根据不同的硼浓度，计算得到的临界水团体积从2m～3到5m～3不等。 对上述两种典型事故的分析结果及结论可实际应用于秦山核电厂停堆工况下事故管理中，同时对我国其他核电厂的停堆工况下事故管理也具有指导意义。更多还原

【Abstract】 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.更多还原