A fuel performance analysis for an FCM fuel under LWR conditions - KF168

Fully ceramic micro-encapsulated (FCM) replacement fuel was conceived to replace conventional UO₂ fuel with accident-tolerant fuel in existing light water reactors (LWRs). In FCM fuel pellet, a large number of tri-isotropic coated fuel particles (TRISOs) are embedded in a silicon carbide (SiC) matrix. The TRISO consists of a uranium nitride kernel, a buffer, and three coating layers. As a preliminary scoping analysis for its feasibility, the following FCM fuel performance evaluations have been conducted: estimation of fuel burnup and depletion, analysis of gas pressure buildup in a TRISO, thermo-mechanical analysis of a TRISO, estimation of the failure of a batch of TRISOs, and fission product (FP) transport analysis. Fission gas pressures at various temperature conditions are maintained well below 4 MPa. The major gas species are xenon and krypton below 910 deg. C, but cesium becomes the major gas species above 910 deg. C. The tangential stress acting on the SiC layer of a nominal TRISO is mainly caused by the irradiation-induced dimensional change (IIDC) of the inner pyrolytic carbon (PyC). The contribution of the gas pressure to the SiC stress is negligible over the entire lifetime. The failure of the SiC layers does not occur during normal reactor operation. It is possible to prevent nearly all FP releases if the component parts of FCM fuel rods are intact and not contaminated with nuclear materials (authors)