| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 296841 | Nuclear Engineering and Design | 2013 | 9 Pages |
•Debris filtering efficiencies for two debris filter designs used in PWRs are provided.•Various debris used in the tests are selected to simulate actual debris found in PWRs.•Debris filter efficiency is explained by flow-hole size and grid strap height.•The effect of debris filters on flow blockage during LTC after a LOCA is described.
A cutting-edge debris-filter designs, Protective Grid (P-grid) and Guardian Grid (G-grid) attached to the upper part of bottom nozzle, have been employed for the PWRs in Korea since 2000s to protect the fuel from debris-induced fuel failures. The debris-filter efficiency of the P-grid and G-grid designs is improved by relatively smaller flow areas formed by the grid straps and dimples. The debris-filter efficiency of the P-grid design is further improved by the relatively smaller flow-hole bottom nozzle. The debris-filter flow tests employing eighteen debris types showed that the debris-filter efficiencies of the P-grid and G-grid designs are 91 and 96%, respectively, while that of the SYS80 fuel design having only the standard flow-hole bottom nozzle is 26%. The slightly better debris-filter efficiency of the G-grid design against the P-grid design may be explained by relatively smaller flow areas at the G-grid dimple region as well as by the relatively longer solid end plug and the higher G-grid strap. The P-grid design may capture circular shapes of debris larger than 3.44 mm in diameter at the flow holes formed by the P-grid dimples, whereas the G-grid design may capture circular shapes of debris larger than 2.54 mm in diameter at the flow holes formed by the G-grid dimples. The aforementioned difference in the debris-filter efficiency between the P-grid and G-grid designs may be predicted by the solid modeling technique generating three-dimensional flow paths. Using the minimum flow-hole areas generated by the P-grid and G-grid designs, on the other hand, the effect of debris injected from the containment sump into the reactor core on the long term cooling (LTC) capability after a loss of coolant accident (LOCA) was evaluated, which indicates that the debris-filter capability of the P-grid and G-grid designs may not have a detrimental effect on the LTC capability after a LOCA only if the sump mesh size is smaller than 2.54 mm in diameter.
