系统分析程序预测MDNBR的保守性研究

Conservative Study of the System Analysis Code in the MDNBR Prediction

摘要: 为衡量压水堆偏离泡核沸腾的程度，已通过试验开发了专门的临界热流密度关系式来与堆芯实际热流密度测量后计算值进行比较，得到堆芯的最小偏离泡核沸腾比(MDNBR)，这些关系式或实验数据已被植入系统分析程序用于设计和瞬态分析。本文基于OECD压水堆燃料组件临界热流密度实验数据，采用不同建模方法研究了系统分析程序RELAP5计算MDNBR的保守性，并与子通道分析程序FLICAIII-F进行了比较。结果表明：系统分析建模方法影响结果的保守性，采用平均通道法并不一定保守，采用平均通道和热通道结合的方法可以较为全面反映出燃料组件平均通道特性和热通道特性且计算结果偏保守，采用多通道分析方法相对较为保守但受限于计算资源能力；在进行系统安全分析且需要确定堆芯MDNBR时，堆芯模拟应考虑采用平均通道和热通道相结合的分析方法来获取MDNBR，同时应以系统分析程序计算结果作为参考性输入条件，采用专用的子通道分析程序进行更为现实和准确的MDNBR计算。

Abstract: To judge the departure nucleate boiling degree in the PWR, special critical heat flux calculation relations based on the different experiments have been developed for comparing to the reactor real heat flux calculation. These correlations and experimental data have been written in the system code which is used to design and transient analysis. Based on the OECD PWR fuel assembly critical heat flux experimental data, different modeling methods are used with RELAP5 code to study the conservation of the calculated MDNBR. A calculation fruit from sub-channel analysis code FLICAIII-F is used to compare the RELAP5 results. The conclusion can be summarized as follows. The modeling method of the system analysis affects the final results conservation. The average channel method is not always conservative. The average channel and hot channel combined method can fully reflect the fuel assembly thermal characteristic both average channel and hot channel, and the result is most conservative. The fully channel method is relatively conservative but restricted by the computer resource capability. Therefore, to achieve the conservative MDNBR during the requiring core MDNBR of the system safety analysis process, the average channel and hot channel combined method of the core assembly modeling is strongly suggested. To obtain reality and accurate MDNBR value, a special sub-channel code calculation is required, which needs to extract the condition of MDNBR predicted by system code.