Mechanical and Hydraulic Characterization Tests of a Mid Grid for X-Gen Fuel

The Korea Nuclear Fuel Co. requested the high frequency flow-induced vibration and pressure drop, and the high temperature and high pressure fretting wear tests of mid grid candidates of X-Gen fuel. The following results were obtained for each test. - High frequency flow-induced vibration and pressure drop test Maximum vibration amplitudes of the two candidates (Y-10, T-20) were 570 mil/s and 1260 mil/s at the flowrate of 18 ft/s and 19 ft/s, respectively. Those of the other types (PLUS7 and modified PLUS7) were 1360 mil/s and 410 mil/s at the flowrate of 14 ft/s and 18 ft/s, respectively. The frequency characteristics showed a uniform increase from 1500 to 4500 Hz following the increase of the flow velocity, and a jump of the peak frequency at a specific velocity. Variation of the vane angle did not affect the frequency characteristic during the flow velocity change (cf. Y-10, T-20), while the characteristic varied considerably when the strap height was varied (cf. PLUS7 and its modified version). Average relative errors of the pressure drop[DP1, DP2] with respect to the PLUS7 were [-2.29 %, -2.0 %], [3.62 %, 4.82 %], [-1.61 %, -2.64 %] for X-Gen no.1, X-Gen no.2 and modified PLUS7 in order. Relative difference in the pressure drop showed an irregular tendency. A sensitivity of the pressure drop due to the variation of the strap height and vane angle was verified. - High temperature and high pressure fretting wear test Canoe-Y10 spring showed the most severe wear. An impact/sliding wear mechanism as well as the circular trace of the fuel rod motion were attributed to this result. The impact/sliding wear mechanism was confirmed from the wear scar observation. An actual wearing process was investigated by analysing the displacement signal obtained from the lower displacement sensors at the contacts