Abstract:

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.

Key words: Jet impact, Debris, Zone of influence, LOCA