Additional Research Needs to Support the GENII Biosphere Models

In the course of evaluating the current parameter needs for the GENII Version 2 code (Snyder et al. 2013), areas of possible improvement for both the data and the underlying models have been identified. As the data review was implemented, PNNL staff identified areas where the models can be improved both to accommodate the locally significant pathways identified and also to incorporate newer models. The areas are general data needs for the existing models and improved formulations for the pathway models. It is recommended that priorities be set by NRC staff to guide selection of the most useful improvements in a cost-effective manner. Suggestions are made based on relatively easy and inexpensive changes, and longer-term more costly studies. In the short term, there are several improved model formulations that could be applied to the GENII suite of codes to make them more generally useful. • Implementation of the separation of the translocation and weathering processes • Implementation of an improved model for carbon-14 from non-atmospheric sources • Implementation of radon exposure pathways models • Development of a KML processor for the output report generator module data that are calculated on a grid that could be superimposed upon digital maps for easier presentation and display • Implementation of marine mammal models (manatees, seals, walrus, whales, etc.). Data needs in the longer term require extensive (and potentially expensive) research. Before picking any one radionuclide or food type, NRC staff should perform an in-house review of current and anticipated environmental analyses to select “dominant” radionuclides of interest to allow setting of cost-effective priorities for radionuclide- and pathway-specific research. These include • soil-to-plant uptake studies for oranges and other citrus fruits, and • Development of models for evaluation of radionuclide concentration in highly-processed foods such as oils and sugars. Finally, renewed studies of radionuclide cleanup in various modern types of municipal water treatment facilities such as advanced filtration or reverse-osmosis processes may be performed without development of any new or costly experimental facilities

Recommended Parameter Values for GENII Modeling of Radionuclides in Routine Air and Water Releases

The GENII v2 code is used to estimate dose to individuals or populations from the release of radioactive materials into air or water. Numerous parameter values are required for input into this code. User-defined parameters cover the spectrum from chemical data, meteorological data, agricultural data, and behavioral data. This document is a summary of parameter values that reflect conditions in the United States. Reasonable regional and age-dependent data is summarized. Data availability and quality varies. The set of parameters described address scenarios for chronic air emissions or chronic releases to public waterways. Considerations for the special tritium and carbon-14 models are briefly addressed. GENIIv2.10.0 is the current software version that this document supports

Processing of the GALILEO

The availability of reliable tools and associated methodology able to accurately predict the LWR fuel behavior in all conditions is of great importance for safe and economic fuel usage. For that purpose, AREVA has developed its new global fuel rod performance code GALILEOTM along with its associated realistic thermal-mechanical analysis methodology. This realistic methodology is based on a Monte Carlo type random sampling of all relevant input variables. After having outlined the AREVA realistic methodology, this paper will be focused on the GALILEOTM code benchmarking process on its extended experimental database and the GALILEOTM model uncertainties assessment. The propagation of these model uncertainties through the AREVA realistic methodology is also presented. This GALILEOTM model uncertainties processing is of the utmost importance for accurate fuel design margin evaluation as illustrated on some application examples. With the submittal of Topical Report for GALILEOTM to the U.S. NRC in 2013, GALILEOTM and its methodology are on the way to be industrially used in a wide range of irradiation conditions

Multi-component gas transport in CANDU fuel rods during severe accidents.

The multi-component transport of steam, hydrogen and stable fission gas in the fuel-to-clad gap of defective CANDU fuel rods, during severe accident conditions, is investigated. Based on a general Stefan-Maxwell treatment this work considers how incoming steam will diffuse into a breached rod against a counter-current flow of non-condensable fission gases and out-flowing hydrogen that is produced from the internal reaction of steam with the Zircaloy cladding or urania. The ability of the oxidized clad to act as a physical barrier to either hydrogen or oxygen diffusion was further investigated in the current work with a molecular-dynamics approach, with the interactions between atoms represented by a Modified Embedded Atom Method. During the initial Zircaloy oxidation phase in the CRL experiments, the model was able to predict the reduced fission product release kinetics as well as the timing for the completion of the clad-oxidation process. In this simulation, the model (with an effective gap size of 20 {micro}m) was able to successfully predict whether singlesided or double-sided oxidation had occurred in accordance with the metallographic examination. However, in order to account for the observed release kinetics after the completion of clad oxidation, it was necessary to assume a greater atmospheric exchange due to possible cracking of the brittle oxide layer. With the assumption of cracking (by assuming a reduced path length for gas transport), the model was successfully able to reproduce the fission product release kinetics and the final fuel stoichiometry as determined from end-of-test weight gain measurements. This analysis particularly shows that local hydrogen production (from the internal fuel oxidation process) will result in a reduced local oxygen potential in the fuel-to-clad gap compared to that which occurs in the bulk coolant