Sensitivity Study of Fiber Length Effect on Pressure Drops in the Mockup PLUS7 Fuel Assembly

There has been a concern that following a loss-of-coolant accident (LOCA), particulates, fibrous material and chemical precipitate could be ingested into the emergency core cooling system (ECCS) and flow into the reactor coolant system (RCS). This phenomenon could be harmful for a long term core cooling (LTCC) when the debris accumulates on the core inlets and blocks the flow of cooling water. The in-vessel downstream effect tests for the APR1400 have been performed to address this generic safety issue (GSI) 191. In this study, we performed sensitivity tests using a fiber grinder for 10 seconds and 8 seconds. When the fiber is gridded for shorter time, the fiber length is increased. In this study, sensitivity study of fiber length effect on pressure drops has been performed using a mockup PLUS7 FA. Particulate-to-fiber mass ratio of 1:1 was chosen, because the condition caused most limiting results. The fiber gridded for 8 seconds was used, and the result showed higher differential pressure than the condition of 10 seconds gridded. Because, both cases meet the fiber length distribution in the test protocol developed by the PWROG, the tests should be run using the fiber grinded for 8 seconds which gives more limiting results. However, all the test results meet the acceptance head loss (91.8 kPa) of the APR1400 with a sufficient margin