BEPU分析方法在CNP600弹棒事故中的应用

最佳估算加不确定性（BEPU）事故分析方法同传统的保守性事故分析方法相比,可获取现实的分析结果和安全裕量,在保证核电厂安全性的前提下,提高核电厂的经济效益和运行灵活性。针对CNP600的设计特点,利用最佳估算程序RELAP5-3D建立热态满功率（HFP）和热态零功率（HZP）条件下的弹棒事故（REA）分析模型。通过弹棒事故现象识别分级表（PIRT）识别事故瞬态下重要的过程和现象,筛选出对关键安全参数有重要影响的输入参数。利用DAKOTA程序对重要不确定性输入参数进行拉丁超立方抽样（LHS）,通过非参数统计方法计算关键安全参数的单侧容忍上限。计算结果显示:两种弹棒条件下,REA瞬态过程中的最大芯块平均焓值、芯块峰值温度、包壳峰值温度、系统峰值压力均满足弹棒事故验收准则；利用非参数统计方法计算的核功率峰值单侧容忍上限结果合理,最大芯块平均焓值单侧容忍上限计算值同传统弹棒事故保守计算值相比具有可观的安全裕量。

Application of best estimate plus uncertainty analysis method for CNP600 rod ejection accident

Compared with conservative accident analysis method, best estimate plus uncertainty (BEPU) accident analysis method can gain realistic analysis results and safety margins, and improve the nuclear power plant economy and flexibility of operation with the reasonable security assurance. The rod ejection accident (REA) analysis models under the condition of hot full power (HFP) and hot zero power (HZP) were established by using the best estimate code RELAP5-3D according to the design features of CNP600. The dominant phenomena and processes were identified through REA phenomena identification and ranking table (PIRT), and the important input parameters which have significant impacts on the key safety parameters were selected. The DAKOTA code was used to generate the samples of the important uncertainty input parameters by taking the Latin hypercube sampling (LHS) approach and the one sided tolerance upper limits of the key safety parameters were calculated through non-parametric method. In both cases the results obtained show that the maximum average fuel pellet enthalpy, peak fuel pellet temperature, peak cladding temperature, peak system pressure during accident transient meet the REA acceptance criteria. In both cases the one sided tolerance upper limits of peak nuclear power obtained by the non-parametric method are reasonable, and the one sided tolerance upper limits of maximum average fuel enthalpy obtained have considerable safety margins compared with the traditional REA conservative analysis values.