I、II类工况下堆芯预计发生DNB燃料棒数量的统计学计算方法
Statistical Calculation Methodology of the Expected Number of Fuel Rods Experiencing DNB in Core under Condition I and Condition II

偏离泡核沸腾(DNB, Departure from Nucleate Boiling)设计准则用于确保在I、II类工况下，极限燃料棒表面不发生DNB。然而DNB设计准则考虑了95/95原则，因此即使验证了堆芯在特定工况下满足DNB设计准则，堆芯发生DNB燃料棒数量的期望值仍然可能大于1根。为了验证满足DNB设计准则的I、II类工况下堆芯发生DNB燃料棒数量的期望值小于1根，一种全新的用于计算I、II类工况下堆芯发生DNB燃料棒数量的统计学方法被建立。CPR1000堆型的一种典型II类事故工况通过这种方法进行了分析。结果显示堆芯预计发生DNB燃料棒数量的期望值小于1，即从统计学角度认为在该工况下堆芯不会发生DNB。
Departure from nucleate boiling (DNB, Departure from Nucleate Boiling) design basis is used to ensure that DNB does not occur on fuel rods under condition I and condition II. However, 95/95 principle is used in DNB design basis, so that the expected number of fuel rods experiencing DNB may still be greater than 1, even if the core meets DNB design basis under a specific condition. In order to verify that the expected number of fuel rods experiencing DNB in core which meets DNB design basis under condition I and condition II is less than 1, a new statistical methodology for calculating the expected number of fuel rods experiencing DNB under condition I and condition II is established. And a typical condition II of CPR1000 unit is analyzed with this methodology. The result shows that the expected number of fuel rods experiencing DNB under this typical condition is less than 1, which means that DNB does not occur in core from a statistical point of view.