Fuel-coolant interaction modeling supporting treat experimental analysis

In order to qualify Advanced Technology Fuels for Light Water Reactors, transient nuclear heating tests will be required. Current plans involve a series of experiments using capsules of a small fuel rod segment in a static water pool (MARCH-SERTTA) to investigate the response of new fuel materials to postulated reactivity insertion accident (RIA) scenarios. UW-FCI, a one-dimensional, non-equilibrium model used to predict the energetics associated with fuel-coolant interactions was shown to be able to reproduce the energetics associated with past RIA experiments. UW-FCI was then used to predict the energetics of a hypothetical RIA experiment in the MARCH-SERTTA capsule, where a bounding energy deposition of 2.26 x10⁶ J/kg-UO₂ (540 cal/g-UO₂) was assumed. Uncertainties associated with the conditions of the fuel and coolant at the time of fuel rod failure required conservative bounds to be placed on UW-FCI input parameters. Using these conservative estimates, UW-FCI predicted a peak pressure of 61 MPa and an impulse of 0.012 kN-s. To estimate the effect of clad oxidation on the fuel-coolant interaction energetics a steam diffusion rate-limited hydrogen generation model was implemented into UW-FCI. Modeling of hypothetical experiments in the MARCH-SERTTA capsule show that between 20-50% of the zirconium cladding present in the test capsule oxidizes, which increases the energetics of the FCI event given the additional thermal energy released from the exothermic oxidation.