50. Extended overpower transient testing of LMFBR oxide pins in EBR-II

As part of a joint effort between the Power Reactor and Nuclear Fuel Development Corporation of Japan and the US Department of Energy, a series of five extended slow overpower transient tests are being conducted in the Experimental Breeder Reactor-II (EBR-II) on preirradiated mixed oxide fuel and blanket pins. In the first two tests conducted in the series, fuel and blanket pins were subjected to a 0.1%/s power ramp to approx. 60% overpower before the transient termination. None of the test pins breached during the transient. A significant cladding breaching margin over the normal PPS trip setting of approx. 12 to 15% was thus demonstrated for the 0.1%/s ramp. The transient-induced pin cladding strains, caused principally by fuel-cladding mechanical interaction, were small but measurable.