Alternate approach to developing target levels Increasingly common ( NASA, NRC, USEPA )

1. Probabilistic Risk Assessment (PRA) • Alternate approach to developing target levels • Increasingly common (NASA, NRC, USEPA) • Statistical vs deterministic inputs (can be combined) • Addresses uncertainty • Site-specific vs default SCTL application • Requires ID of appropriate input distributions Draft Copy Subject To Change

2. Probabilistic vs Deterministic • Uses distributions vspoint estimates for inputs • Seeks to characterize degree of uncertainty by iterative calculations (e.g., 100,000 events) • Avoids unintentional cumulative conservatism • 376.30701(2), F.S. speaks to protection against risks under “actual circumstances of exposure” • Typically Tier 3 rather than Tier 1 exercise Draft Copy Subject To Change

3. Implementation • Option for PRA use in 62-780 • Previously used in 2008 62-302 Baseline analysis • Recently used in 2013 SW criteria establishment • Use for revamping 62-777 SCTLs would require consensus selection of applicable distributions Draft Copy Subject To Change

4. Summary • Commercial software options for PRA available • PRA can be combined w/deterministic elements • Will require review of various distributions • Applicable as a risk assessment option now • May be longer term exercise for default SCTLs • May not be appropriate for Tier 1 analysis Draft Copy Subject To Change