Volume 7, Issue 9 (October 2010)
RIA Failure of High Burnup Fuel Rod Irradiated in the Leibstadt Reactor: Out-of-Pile Mechanical Simulation and Comparison with Pulse Reactor Tests
A high burnup boiling water reactor fuel rod was subjected to reactivity initiation accident (RIA) tests in a research reactor. Two ramp tests were carried out under almost identical irradiation conditions, resulting in cladding failure in a room temperature test, while no failure was observed in a high temperature test. An adjacent segment of the same rod was used for mechanical expansion-due-to-compression (EDC) testing simulating the pellet-cladding mechanical interaction loadings on the cladding during an in-reactor RIA. The EDC tests show the existence of a transition temperature where an abrupt increase in the specimen hoop strain at failure occurs. Additional tests revealed that the transition temperature depends on hydrogen concentration. A possible effect of the rapid heating, which is a specific condition for an in-reactor RIA compared to the static heating in the EDC tests, was verified in the rapid heating/loading tests on unirradiated hydrided Zircaloy, when both loading and heating are performed simultaneously within 50–80 ms. It was shown that strain to failure is dependent on the instantaneous material temperature and is not affected by the pre-heating history. The results show good consistency between the EDC and in-reactor pulse test data. It is concluded that the EDC test can provide valuable information to predict the in-reactor RIA fuel failure.