GSI-191问题喷射冲击影响区域的计算分析

在压水堆LOCA(Loss of Coolant Accident)事故之后,高能管道流体喷射冲击导致破口附近的保温层等材料破裂为碎片。这些碎片随流体在安全壳内传输并在地坑滤网沉积形成碎片床,阻碍应急堆芯冷却系统的正常运行。部分碎片可能旁通滤网进入反应堆压力容器,从而引起一系列的效应。该问题被称之为GSI-191(Generic Safety Issue-191)问题。为解决GSI-191问题,首先需要确定破口附近产生的碎片量。当前研究基于ANSI/ANS58.2-1988标准和等效体积球体模型,自主开发了喷射冲击影响区域计算工具JETZOI。采用该工具计算获得的NEI(Nuclear Energy Institute)算例的喷射轮廓和等压线与美国核管会(United States Nuclear Regulatory Commission,U.S NRC)的结果符合很好,从而实现了对NEI算例的成功复现。进一步进行了不同滞止工况的敏感性分析。分析结果表明,在相同的滞止压力下,流体温度的升高将导致影响区域破坏半径的减小和碎片量的减少。因此在开展喷射冲击试验获得影响区域的破坏半径时,应当保守选取冷段双端断裂作为极限工况以使喷射冲击产生的碎片量最大。

Calculation and analysis of jet-impact influence zone in GSI-191 issue

Background: In Loss of Coolant Accidents (LOCAs), jet impact of fluid from a high energy pipe could damage insulation materials,etc. near the break into debris, which would be transported along with fluid in containment and finally deposit on sump screen to form a debris bed, impeding normal operation of Emergency Core Cooling System (ECCS). A part of the debris may bypass the screen and flow into the reactor pressure vessel, resulting in a series of effects. The issue is referred as GSI-191 (Generic Safety Issue 191) problem.Purpose: In order to solve this issue, quantity of debris generated near the break should be determined firstly.Methods: One calculation tool for jet impact Zone of Influence (ZOI) was developed independently based on ANSI/ANS 58.2-1988 standard and equivalent volume sphere model.Results: The jet outline and isobar of the Nuclear Energy Institute (NEI) test case obtained by the tool agreed well with the results of U.S NRC (United States Nuclear Regulatory Commission) and thus the duplication of the NEI test case was realized successfully. Furthermore, sensitivity analysis under different stagnation conditions was performed. Analysis results showed that, under the same stagnation pressure, increase of fluid temperature will result in the decrease of the ZOI destruction radius and debris quantity.Conclusion: So when jet impact test is performed to obtain the ZOI destruction radius, double ended guillotine break of cold leg should be selected conservatively as the limiting condition to maximum the debris quantity generated during jet impact process.