[en] The U.S. Department of Energy's Yucca Mountain Site Characterization Project is scheduled to submit a License Application in the year 2002. The License Application is to show compliance with the regulations promulgated by the U.S. Nuclear Regulatory Commission which implement standards promulgated by the U.S. Environmental Protection Agency. These standards are being revised, and it is not certain what their exact nature will be in term of either the performance measure(s) or the time frames that are to be addressed. This paper provides some insights pertaining to this regulatory history, an update on Yucca Mountain performance assessments, and a Yucca Mountain Site Characterization Project perspective on proper standards based on Project experience in performance assessment for its proposed Yucca Mountain Repository system. The Project's performance assessment based perspective on a proper standard applicable to Yucca Mountain may be summarized as follows: a proper standard should be straight forward and understandable; should be consistent with other standards and regulations; and should require a degree of proof that is scientifically supportable in a licensing setting. A proper standard should have several attributes: (1) propose a reasonable risk level as its basis, whatever the quantitative performance measure is chosen to be, (2) state a definite regulatory time frame for showing compliance with quantitative requirements, (3) explicitly recognize that the compliance calculations are not predictions of actual future risks, (4) define the biosphere to which risk needs to be calculated in such a way as to constrain potentially endless speculation about future societies and future human actions, and (5) have as its only quantitative requirement the risk limit (or surrogate performance measure keyed to risk) for the total system