INVESTIGATION OF COATED CLADDING BALLOONING BEHAVIOR USING BISON

摘要

Numerous fuel vendors throughout the world haveproposed new fuel rod designs that include a coating on theexterior surface of the clad for improved oxidationperformance. These designs are proposed as a potentialenhanced accident tolerant alternative to conventional fuelrods currently used in commercial light water reactors(LWRs). The current front runner in the majority of coatedclad designs is the use of chromium (Cr) for the coating.While the oxidation benefits have been widely studiedfrom both experimental and modeling point of views; amore recent speculation is that the inclusion of the coatingreduces the observed balloon size when compared touncoated clads during a loss of coolant accident (LOCA).In this paper, the Bison fuel performance code is used toqualitatively confirm the observation of reduced balloonsizes between Cr-coated and uncoated zirconium-basedclads. Bison is coupled to the Dakota software to performa parametric study that varies the coating thickness (0, 10,20, 50, and 100 ğœ‡m), the cladding substrate (Zr-4, M5®,and ZIRLOTM), the maximum cladding temperature (900,1000, 1100, and 1200 K), the internal pressure ramping rate(5, 10, and 20 kPa/s), and the fast neutron fluence (0, 2.5,and 5 × 10~(25) neutrons/m~2) to investigate these parametersinfluence the ballooning. Behavior. It is observed that thethermal expansion coefficient mismatch between thechromium and the Zircaloy substrate causes the coating toundergo permanent plastic deformation. This permanentdeformation reduces the balloon size observed in thecoated clads. Of the parameters varied in this study thepeak cladding temperature and pressure ramping rates hadthe largest impact on the balloon size whereas the fastneutron fluence and cladding substrate had limited to noinfluence. Further work is required to validate theseobservations once the experimental data becomes publiclyavailable.