[en] As with any repository program, predictions of the performance of a site over very long time frames may often meet with skepticism from the public and decision-makers, such as regulatory and governmental agencies. Experience at the WIPP and the YMP indicate that demonstrating the defensibility of data, conceptual models, computer codes, and numerical analyses is critical. Five overarching principles have been found to be the basis of a technically and publicly acceptable repository. The principles are traceability, transparency, reproducibility, retrievability, and reviews. - Traceability allows one to understand the source and justification of data and other input that generate conclusions. - Transparency allows one to follow the logic, calculations, and other operations that produce results. - Reproducibility allows one to reconstruct the results without recourse to the originator of the information. - Retrievability allows one to retrieve documentation that demonstrate these overarching principles. - Reviews ensure that the work is technically acceptable, complete, and accurate. This paper discusses how these principles are applied to the WIPP and the YMP. By setting up quality assurance and management controls (e.g., procedures, audits, peer reviews) these principles are implemented. Without successfully applying these principles the WIPP would not have gone from research to industrial maturity. The YMP is ensuring that these are implemented for activities that support licensing. Any repository program concerned with demonstrating defensibility to the public and regulators would do well by incorporating traceability, transparency, reproducibility, retrievability, and reviews into their program. (authors)