Development of an equilibrium loading pattern and whole-core fuel performance assessment in the Advanced Boiling Water Reactor (ABWR) with UO_2 and U_3Si_2 fuels

摘要

The Advanced Boiling Water Reactor (ABWR) is an established evolutionary water reactor that has successfully achieved design certification in a number of countries. However, core design information is scarce in the open literature and this makes studying the suitability of new fuel types difficult and complicates comparisons with other reactor systems. This study therefore aimed to address important data gaps in the open literature relating to the latest generation of BWR core designs. Furthermore, this paper describes an assessment which has been carried out comparing the performance of U3Si2 and standard UO2 fuel deployed in the ABWR.An ABWR core design model has been created using the reactor physics software package CASMO-SIMULATE, with the method used to develop the model and the key set of parameters employed to determine the viability of the core design detailed. A major part of the optimisation process involves the application of simulated annealing to generate loading pattern candidates. Whilst simulated annealing has been employed routinely in loading pattern optimisation, one of the novel aspects in this study relates to each candidate adhering to a predetermined batch map to develop a viable equilibrium loading pattern.NNL's whole-core fuel performance framework NEXUS, which utilises ENIGMA as the fuel performance engine, was used in conjunction with the developed core model to investigate how standard UO2 fuel behaves in a modern BWR design and therefore highlight the most limiting fuel performance characteristics. The NEXUS results highlighted that, for the core designed here, the most limiting fuel performance characteristic for UO2 fuel was rod internal pressure.In addition, a first preliminary whole-core fuel performance assessment was carried out for the proposed enhanced Accident Tolerant Fuel candidate U3Si2 using the same power histories from the UO2 core design to enable a comparison of fuel behaviour independent of power history discrepancies. The assessments for U3Si2 have focused largely on temperature as, due to lack of U3Si2 in-pile experimental measurements, fuel performance parameters that are heavily dependent on swelling and fission gas release models currently have large uncertainties regarding their validity. Therefore, we begin to quantify the potential temperature characteristics associated with U3Si2 relative to UO2, in particular the peak homologous fuel temperature (that is the maximum fuel temperature throughout irradiation as a fraction of its melting point) for U3Si2, which was found to be 0.51 compared with 0.61 for UO2 fuel operating under the same conditions. As a further comparison between UO2 and U3Si2, simple single pin power-to-melt calculations were performed using ENIGMA. It was found that power-to-melt for UO2 is around 88 kW/m and the power-to-melt for U3Si2 is around 230 kW/m.