Dr. Mahmut Cinbiz
Oak Ridge National Laboratory

Abstract

The beyond-design-basis accident at the Fukushima Daiichi nuclear power plant after Tohoku earthquake and aftermath tsunami boosted the advanced accident-tolerant fuel (ATF) technologies to replace the current nuclear fuel materials and core components in service. Several materials are being considered as ATF cladding which must enhance fuel performance during beyond design basis accidents by increasing the amount of coping time without active cooling during the severe accident. ATF fuel and cladding materials must also at least maintain the reactor performance and safety characteristics of the present uranium dioxide and zirconium-based alloy fuel systems during normal operation, operational transients, and postulated design-basis accidents such as a reactivity-initiated accident (RIA).

During an RIA, positive reactivity can be inserted as result of control rod removal from the reactor core. Because of the positive reactivity, the fission rate exponentially increases until the power pulse is turned around by fuel temperature feedback due to the Doppler broadening effect. The thermal energy deposition during RIA causes a rapid temperature increase in fuel pellets, which results in thermal expansion of the fuel. If the fuel-cladding gap has closed or closes during the event, the expansion of the fuel causes pellet-clad mechanical interaction (PCMI) and thus impose a strain on the cladding. The power pulse occurs on a time scale of tens of milliseconds and may cause cladding failure if the cladding is sufficiently strained.

This seminar aims to describe the continuing DIC-aided separate effects mechanical test development at Oak Ridge National Laboratory to reproduce the rapid PCMI-like mechanical loading of the cladding during postulated RIA or RIA-like transients for different ATF cladding candidates. The separate-effects tests also target to inform the future integral effects tests of ATF cladding candidates. The mechanical results will be described by the failure modes of distinct ATF candidate claddings and the evolution of the average hoop strain on the outer surface of the ATF cladding samples.

Biography 

M. Nedim Cinbiz has obtained his Ph.D. degree on the zirconium hydride formation in zirconium alloys and the influence of the stress state on the hydride reorientation at the Pennsylvania State University. He is currently conducting research on the mechanical behavior of accident tolerant fuel cladding during reactivity insertion transients of light-water reactors as a part of DOE’s Advanced Fuel Campaign and the hydriding effects on the zirconium based alloys at Oak Ridge National Laboratory.