The National Academy of Sciences' Committee on Technical Bases for Yucca Mountain Standards recommended that standards for the disposal of high-level radioactive waste at Yucca Mountain should 1. set a limit on the risk of individuals, 2. use the critical group approach, as defined by the international Commission on Radiological Protection; 3. define the critical group using present knowledge and cautious, reasonable assumptions; 4. use a time period for conducting compliance assessment that includes the period of greatest risk; and 5. use a stylized calculation to assess whether the repository's performance would be substantially degraded as a consequence of a postulated intrusion.