Source IST 2.0 validation approach

SOURCE IST 2.0 is a code for calculating the release of fission products from the fuel pellets to the surrounding environment. For most accidents that environment is the Primary Heat Transport System. For other scenarios (such as End-Fitting Failures and Fuel Handling Accidents) it would be the containment atmosphere. The validation approach being used by the Canadian nuclear industry is founded on the use of: the Technical Basis Document (which describes controlling phenomena that apply in each phase of a postulated accident), discipline-specific Validation Matrices (which relate phenomena and ranges of conditions to experimental data sets), and code-specific Validation Plans (which list the data sets to be simulated and describe their coverage of controlling phenomena and accident conditions). The controlling phenomena for fission product release from fuel are modelled in the code. For some of these phenomena detailed physical models are employed, but for others assumptions or approximations that lead to limiting consequences are used. This combination of best-estimate and limit-consequence models poses interesting challenges in interpreting validation results. The nature of SOURCE IST 2.0 as an industry standard tool being developed for multiple platforms has imposed certain requirements on validation activities, e.g., portable test cases, reproducing tests on multiple platforms. This paper describes the approach adopted for SOURCE IST 2.0 in the context of the constraints imposed by the nature of the problem being solved, the nature of the solution methodology selected, and the multi-platform requirements. SOURCE IST 2.0 will be validated using Canadian and international separate effects and in-reactor experimental data sets. (author)